CheeseScience.net

Publication- Food Chem

2011-11-21T15:48:00.001Z

Parente, E., H. Patel, V. Caldeo, P. Piraino and P.L.H. McSweeney (2012). RP-HPLC peptide profiling of cheese extracts: a study of sources of variation, repeatability and reproducibility. Food Chemistry 131, 1552-1560.

Publication- Int Dairy J

2011-11-15T16:46:00.001Z

Costa, N.E., M.J. Mateo, D.J. O’Callaghan, V. Chaurin, M. Castillo, J.A. Hannon, P.L.H. McSweeney and T.P. Beresford (2012). Influence of an exopolysaccharide produced by a starter on milk coagulation and curd syneresis.. International Dairy Journal 22, 48-57.

Cheese fun

2011-10-14T11:49:00.002+01:00

Click here for a little bit of fun... Nice website too.

Lactose-6 Production of lactose

2011-07-05T12:00:00.000+01:00

Compared to sucrose, relatively small quantities of lactose are produced worldwide. Lactose is produced by concentrating whey (a by-product of casein and cheese manufacture) or ultrafiltration permeate by vacuum concentration followed by crystallization of lactose from the concentrate, and recovery and drying of the crystals. An alternative method for lactose preparation is the Steffen process (precipitation with Ca(OH)₂).

Applications of lactose in the food industry include in the manufacture of infant formulae (human milk contains more lactose than cows’ milk and hence cows’ milk-based infant formulae must be supplemented with lactose). Lactose has a low sweetness compared with other sugars. However, if properly crystallized, it has a low hygroscopicity which makes it suitable for certain uses in icing on confectionary products. Lactose is also used in the pharmaceutical industry as a diluent for tableting drugs (i.e., the small amount of active ingredient is “diluted” with lactose to make a sufficiently large tablet) and as a flavour adsorbent.

Course: October 2011

2011-06-03T09:27:00.003+01:00

Course Programme

Milk Quality

• Seasonal variations in milk composition
• Somatic cell count and quality
Principles of Cheese manufacture
• Rennet gelation and curd formation
• Control of cheese composition
• Cheese Ripening
Cheese making Efficiency
• Definition, measurement and prediction
• Influence of key factors
• Milk standardisation/composition
• Milk Processing treatments
• Manufacturing parameters
Cheese composition and Quality consistency
• Prominent Quality Defects
• Bitterness, flavour defects
• Mottling, colour defects
• Cracks/Slits/Openings
• Crystalline deposits
Quality Assurance in Cheese Manufacture
Whey processing
•

Milk fat and fines recoveries from whey streams
• Manufacture of whey-based products

Publications- Encyclopedia of Dairy Sciences

2011-05-03T10:14:00.005+01:00

McSweeney, P.L.H. (2011) Biochemistry of cheese ripening. In: Fuquay JW, Fox PF and McSweeney PLH (eds.) Encyclopedia of Dairy Sciences, Second Edition, vol. 1, pp. 667-674. San Diego: Academic Press.

McSweeney, P.L.H. (2011) Catalase, glucose oxidase, glucose isomerase and hexose oxidase. In: Fuquay JW, Fox PF and McSweeney PLH (eds.) Encyclopedia of Dairy Sciences, Second Edition, vol. 2, pp. 301-303. San Diego: Academic Press.

Cheese science course

2011-04-26T14:51:00.002+01:00

Cheese course in Tomas Bata University, Zlin, Czech Republic. See here for details.

Dairygold Co-Op...

2011-04-21T09:55:00.003+01:00

It is nice to see some good business news out of Ireland; Dairygold, the country's largest farmer-owned business, reported 60% increase in profits last year. And they are not alone; Kerry and Glanbia are doing very well also.

Publication- Encyclopedia of Dairy Sciences

2011-04-14T16:09:00.002+01:00

Fuquay, J., P.F. Fox and P.L.H. McSweeney (eds). (2011). Encyclopedia of Dairy Sciences, 4 vols., 2nd ed., Elsevier, Oxford.

An alphabetical list of articles and abstracts is available here.

Lactose-5 Destabilisation of milk on freezing

2011-03-22T17:03:00.001Z

Destabilization of casein micelles can occur on freezing. Crystallization of lactose as a-monohydrate binds up some unfrozen water. Hence, the amount of unfrozen water decreases and thus the Ca²⁺ concentration increases leading to destabilization of casein micelles. Also, since milk is supersaturated with respect to calcium phosphate, some precipitates on freezing:

3Ca²⁺ + 2H₂PO₄^- → Ca₃(PO₄)₂ + H⁺

Production of H⁺ leads to a drop in the pH of the unfrozen part from 6.7 to ~5.8, leading to further destabilization.

Destabilization can be avoided by:

· Reducing the rate of lactose crystallization (by using very low temperatures or increasing the viscosity of the product),

· Rapid freezing and agitation (this gives faster crystallization and less destabilization)

· Reduce lactose content (e.g., by ultrafiltration or lactose hydrolysis).

8th Cheese Symposium

2011-01-21T14:21:00.002Z

8th Cheese Symposium, September 28 & 29, 2011, Moorepark, Fermoy, Co. Cork. For further details, click here.

Cheese Problems Solved- Russian Translation

2011-01-13T22:11:00.002Z

Cheese Problems Solved has been translated into Russian (St Petersburg, 2010).

Lactose-4

2011-01-05T09:13:00.000Z

When a-lactose is added in excess to water at 20°C, about 7 g per 100 g dissolves immediately (this is the true solubility of a-lactose). Some a-lactose then mutarotates to b-lactose until an equilibrium of 62.7b:37.3a is achieved. The solution is now unsaturated with respect to a-lactose and since the solubility of b-lactose is higher than that of a-, as b-lactose is produced by mutarotation, more lactose goes into solution until, at equilibrium, the final solubility is 18.2 g lactose per 100 g water (7 g a-lactose plus 11.2 g b-lactose).

If excess b-lactose is added to water, its initial solubility is ~50 g per 100 g. Some b-lactose then mutarotates to a-lactose to establish an equilibrium of 62.7b:37.3a. However, at this ratio and starting with 50 g b-lactose, the solution would contain 30.8 g b- and 19.2 g a-lactose, and thus would be supersaturated with respect to a-lactose. Some a-Lactose then crystallizes out of solution, upsetting the equilibrium and leading to further mutarotation from b- to a-lactose. These two events, i.e., crystallization and mutarotation continue until two criteria are met: 7 g a-lactose per 100 g in solution and a ratio of 62.7b:37.3a. The final solubility is the same, 18.2 g lactose (a + b), whether one starts with a- or b-lactose. However, since b-lactose is more soluble than a-lactose and mutarotation is slow, it is possible to form more highly saturated solutions by dissolving b- rather than a-lactose. However, the final equilibrium concentration and ratio is the same.

Lactose-3

2010-12-09T17:01:00.002Z

Lactose exists in two anomeric forms and can mutarotate from the a- to the b- form and vice versa by changing the configuration around the anomeric carbon. If either a- or b-lactose is dissolved in water, there is a gradual change from one form to the other until an equilibrium is established. In water at 20°C, the equilibrium mixture is composed of 62.7% b- and 37.3% a-lactose. The proportion of a-lactose increases with increasing temperature. The final proportions of a- and b-lactose in the mixture are not influenced by pH, but the rate at which the mixture reaches equilibrium is slowest at pH 5.0. The a- and b- forms of lactose differ with respect to:

· Solubility

· Crystal size and shape

· Hydration of crystal form (and hence hygroscopicity)

· Specific rotation

· Sweetness.

Publication- Dairy Sci Technol

2010-12-04T15:59:00.002Z

Bansal, N., P.F. Fox and P.L.H. McSweeney (2010). Inhibition of rennet activity in cheese using equine blood serum. Dairy Science and Technology 90, 673-685.

Publication- Aust J dairy Technol

2010-12-03T09:33:00.001Z

McSweeney, P.L.H., V. Caldeo, A. Topcu and D.R. Cooke (2010). Ripening of cheese: oxidation-reduction potential and calcium phosphate. Australian Journal of Dairy Technology 65, 178-184.

Japan

2010-11-19T09:28:00.001Z

Visit to the Yotusba Dairy Company, Hokkaido, Japan.

Cheese science course

2010-10-22T14:21:00.002+01:00

Participants at the cheese science course held recently in UCC.

Cheese science course

2010-09-28T15:19:00.002+01:00

For further details click here. Detailed course timetable is now available here. Registrations are still being accepted.

Lactose-2

2010-09-09T10:50:00.001+01:00

Mammals synthesise lactose as a ready source of energy. Fat and lactose are the principal sources of energy in milk (in cows’ milk, ~50%, ~30%, ~20% of energy comes from fat, lactose and protein, respectively). Lactose is synthesized in mammary epithelial cells within the udder by a two-component enzyme, lactose synthase. Component A is a non-specific galactosyl transferase which transfers galactose from UDP-galactose to a number of acceptors. Component B is the whey protein a-lactalbumin which acts as an enzyme-modifier and makes the transferase highly specific for glucose. The reason for this modification appears to be to enable the precise control of the production of lactose and thus the osmotic strength of milk. There is an approximate inverse relationship between protein and lactose contents of milks from different species.

Milk is isotonic with blood and ~50% of the osmotic pressure of milk is due to lactose. The osmotic pressure of blood is fixed, hence the osmotic pressure of milk is also fixed. On an equal weight basis, monosaccharides have twice the osmotic pressure of disaccharides, hence there is an advantage in having a disaccharide as the principal sugar in milk.

Lactose is the principal carbohydrate in milk. There are numerous other sugars in milk present in very low concentrations, particularly in colostrums. Human milk contains more non-lactose carbohydrates than bovine milk, usually as oligosaccharides. Carbohydrates are present in milk also as parts of glycoproteins and glycolipids.

Publication- Int J Dairy Technol

2010-09-07T12:40:00.003+01:00

Bansal, N., P.F. Fox and P.L.H. McSweeney (2010). Inhibition of rennets by blood serum. International Journal of Dairy Technology 63, 381-386.

Publication- J Dairy Sci

2010-08-23T16:01:00.002+01:00

Costa, N.E., J.A. Hannon, T.P. Guinee, P.L.H. McSweeney and T.P. Beresford (2010). Effect of exopolysaccharide produced by isogenic strains of Lactococcus lactis on half-fat Cheddar cheese. Journal of Dairy Science 93, 3469-3486.

Lactose-1

2010-08-17T16:19:00.004+01:00

Lactose is the principal carbohydrate found in milk and, after water, is the component of milk present in the greatest amount. Milk contains only trace amounts of other carbohydrates. Bovine milk contains ca. 4.6 % lactose but levels are affected by breed of cow, udder infection (mastitis) and stage of lactation. Unlike protein and fat, the levels of which decrease with advancing lactation, levels of lactose increase with stage of lactation. Lactose levels in the milks of other mammals varies widely.

Lactose in milk is important as

· It is essential for the production of fermented dairy products (cheese and yogurt) as it acts as a growth substrate for lactic acid bacteria.

· It contributes to the nutritive value of milk (although some people cannot metabolise lactose, a condition called lactose intolerance, see below).

· It influences the texture of frozen dairy foods (especially ice cream).

· It can become involved in the Maillard reaction leading to browning and the production of flavour compounds. (Browning of dairy products is often a defect.)

Lactose is a disaccharide of galactose and glucose linked by a b1-4 glycosidic bond. Its systematic name is b-O-D-galactopyranosyl-(1-4)-a-D-glucopyranose (a-latcose) or b-O-D-galactopyranosyl-(1-4)-b-D-glucopyranose (b-latcose). Lactose is a reducing sugar and may exist in two anomeric forms (a- or b-lactose).

Seriously strong Cheddar...

2010-08-09T12:00:00.001+01:00

I couldn't resist this! Be sure to wait until the end of the clip. No mice were hurt during the making of this commercial (I hope!)...

Microbial changes in Camembert

2010-07-02T12:17:00.002+01:00

In Camembert and related surface mould-ripened cheeses, the mesophilic starter reaches perhaps 10^9 cfu/g at the end of manufacture. Spores of Penicillium camemberti may be added to the milk or sprayed on the surface of the cheese after moulding. Initially, the surface microflora is composed of adventitious acid-tolerant yeasts and Geotrichum candidum. P. camemberti appears after about 6 days and dominates the ripening of Camemert and Brie-type cheeses. Eventually, towards the end of ripening, a Gram-positive bacterial microflora begins to develop. These organisms, that are often pigmented, are adventitious and similar to those found of the surface of smear-ripened cheeses.

Picture credit.

Cheese science course

2010-06-17T15:59:00.002+01:00

UCC/Teagasc Strategic Alliance

2010-05-29T08:35:00.003+01:00

Agriculture minister Brendan Smith TD yesterday officially launched the UCC/Teagasc Strategic Alliance in Food Research and Innovation. Overall, an excellent idea that will strengthen the already strong links between the two institutions.

Fate of the starter in Cheddar

2010-05-21T09:31:00.003+01:00

The starter grows during Cheddar cheese manufacture from ~10^7 to 10^8-10^9 cfu/g and reduces the pH from that of milk (~6.7) to ~5.4 at the point of milling. Since Cheddar is a dry-salted variety, and unlike many other cheeses, acidification must be close to complete at the end of manufacture and before salt addition. Salt-in-moisture levels increase rapidly in Cheddar due to the large surface area of the curd chips.

During the early stages of ripening, viable starter counts decrease rapidly at a strain-dependent rate. This decline is due to the unfavourable conditions in cheese for the growth and survival of lactococci: low pH, high concentration of NaCl and lack of fermentable carbohydrate. The salt-in-moisture level largely determines the rate of utilisation of residual lactose in the cheese which is of significance to cheese quality.

After death, the lactococci lyse at a rate that is strain dependent and contribute many important enzymes to cheese ripening (particularly its battery of peptidases but also esterases). There is evidence emerging that starter cells may be metabolically active but non-culturable during ripening and that they may contribute to amino acid catabolism in that state.

NSLAB

2010-05-14T15:17:00.002+01:00

Non-starter lactic acid bacteria (NSLAB) are a common component of the microflora of many cheeses and nearly all hard ripened varieties. In a cheese such as Cheddar, they are perhaps the only aspect of the cheese that remains largely uncontrolled.

NSLAB in Cheddar are usually wild strains of Lactobacillus paracasei/Lb. casei that probably gain access to the cheese from the raw milk by surviving pasteurization or from the cheesemaking environment. These organisms grow from very low numbers and typically reach about 10^7-10^8 cfu/g within 2-3 months. They have enzyme systems generally similar to those of Lactococcus and probably contribute to ripening or indeed to the development of off-flavours (research in New Zealand has suggested many flavour defects in Cheddar made under best practice are due to NSLAB). NSLAB are the dominant viable microflora of mature Cheddar cheese. Ripening temperature and, significantly, the rate of cooling of Cheddar blocks after manufacture are major factors which control the growth rate of NSLAB.

Techniques in the literature used to study the contribution of NSLAB to ripening include comparison of raw and pasteurised milk cheeses, microfiltration, use of antibiotics, aseptic cheesemaking and low ripening temperatures.

Further information:

Fox, P.F., P.L.H. McSweeney and C.M. Lynch (1998). Significance of non-starter lactic acid bacteria in Cheddar cheese. Australian Journal of Dairy Technology 53, 83-89.

Ayran

2010-04-28T10:26:00.002+01:00

On a very enjoyable trip to Cyprus recently, I was introduced to Ayran. This dairy product is essentially a savoury drinking yogurt; it contains about 0.5% NaCl and so has a distinctly salty taste which was nicely refreshing in the warm Mediterranean climate during our visit.

The photo above shows a half-finished glass of Ayran in front of me and also Prof Pat Fox and Dr Adnan Hayaloglu of Inonu University, Malatya, Turkey (who introduced me to Ayran).

Enzyme assay kits

2010-04-27T13:42:00.003+01:00

Enzyme assay kits are convenient ways to measure certain constitutents of cheese (e.g., lactose, D/L-lactate or citrate). The the example shown below, D-lactate is determined by using D-lactate dehydrogenase which catalyses the conversion of D-lactate to pyruvate and NAD+ to NADH. This reaction does not naturally go to completion so a second enzyme, glutamate-pyruvate transaminase, which reacts pyruvate and glutamate, is used to pull the first reaction to completion. The conversion of NAD+ to NADH is measured spectrophotometrically as the oxidized and reduced form of this co-factor absorb differently at 340 nm.

Enzyme assay kits are quick and convenient as all reagents necessary come with the kit. However, their use can be expensive for large number of samples and the kits cannot be stored for long periods of time without loss of enzyme activity.

Cheese in Space...!

2010-04-12T12:47:00.004+01:00

At our weekly journal club this morning, an interesting paper cropped up...

Grenon and Lake (2010). Generalised Swiss-cheese cosmologies: mass scales. Physical Review D, 81, a/n 023501.

The authors generalised Swiss cheese cosmologies and included reference to non-zero momenta of associated boundary surfaces and concluded that final effective gravitational mass and size of evolving inhomogeneities depended on their linear momenta.

I think I'll steer clear of theoretical physics and stick to the stuff made from milk! Much tastier! Jokes aside, I would welcome a physicist explaining this aspect of cosmology to me in words of one syllable...

Picture credit.

Cheese and honey...

2010-03-18T15:08:00.003Z

A new spread that combines honey and cream cheese created by UCC students was the winner of the UCC New Food Product Development Showcase. This Showcase is an annual exhibition of new food products developed by students from the BSc Food Science and BSc Food Business degree programmes at UCC as part of their final-year research projects. For more information, please click here.

Actually, the flavours of hard cheese and honey complement each other surprisingly well; if you don't believe me, give it a try!

RELAY Report

2010-03-12T15:19:00.002Z

During the course of this project the research team developed significant expertise and novel technologies that can benefit Irish Cheddar cheese manufactures. Specifically, they have developed methods to enhance the flavour and accelerate the ripening of Cheddar cheese using milk pre-treatments as well as enzymology and mircofluidisation technologies. Companies interested in exploiting the expertise or technologies are invited to contact directly Professor Paul McSweeney in UCC or Dr Kieran Kilcawley in Teagasc.

To download this document, please click here Expertise and technology to improve cheese flavour and ripening

For more information on this project and related projects log onto http://www.relayresearch.ie/

Publication- Dairy Sci Technol

2010-02-08T13:57:00.001Z

Hayaloglu, A.A., K.C. Deegan and P.L.H. McSweeney (2010). Effect of milk pasteurization and curd scalding temperature on proteolysis in Malatya, a Halloumi-type cheese. Dairy Science and Technology DOI: 10.1051/dst/2009052

alpha-Keto acids. 3

2010-02-05T12:00:00.005Z

Although it is not fully clear, the rate-limiting step in amino acid catabolism appears to be the action of aminotransferases on amino acids. Hence, there has been attention paid to accelerating this step by increasing in cheese the concentration of the co-substrate for aminotransferase action, alpha-ketoglutarate.

alpha-Ketoglutarate may be produced from glutamic acid by the action of glutamate dehydrogenase (essentially a reversal of aminotransferase action) or, in citrate-positive lactococci, by the citrate-oxalate pathway. Another possible pathway involving citrate metabolism, the citrate-isocitrate pathway, does not appear to be operational in lactic acid bacteria.

A number of authors (e.g., Yvon et al., 1998; Banks et al., 2001; Shakeel-Ur-Rehman and Fox, 2002) have added alpha-ketoglutarate to cheese and seen its effect on the products of amino acid catabolism. For example, Banks et al. (2001) added alpha-ketoglutarate to Cheddar curd at salting and saw a statistically significant increase in the concentration of some volatile flavour compounds derived from amino acid catabolism (see table).

Another strategy (e.g., Rijnen et al., 2000) involves cloning the gene for glutamate dehydrogenase into a strain of Lactococcus; likewise, these authors also found an effect on the production of volatile flavour compounds in model cheeses.

Further reading

Banks, J.M., Yvon, M., Gripon, J.C., de la Fuente, M.A., Brechany, E.Y., Williams, A.G. and Muir, D.D. (2001). Enhancement of amino acid catabolism in Cheddar cheese using a-ketoglutarate: amino acid degradation in relation to volatile compounds and aroma character. Int. Dairy J. 11, 215-243

Curtin, Á.C. and P.L.H. McSweeney (2004). Catabolism of amino acids in cheese during ripening. In Cheese: Chemistry, Physics and Microbiology, Volume 1, General Aspects, 3^rd edition, P.F. Fox, P.L.H. McSweeney, T.M. Cogan and T.P. Guinee (eds), Elsevier Applied Science, Amsterdam. pp. 436-454.

Rijnen, L., Courtin, P., Gripon, J-C. and Yvon, M. (2000). Expression of a heterologous glutamate dehydrogenase gene in Lactococcus lactis highly improves the conversion of amino acids to aroma compounds. Appl. Environ. Microbiol. 66, 1354-1359

Shakeel Ur-Rehman and Fox, P.F. (2002). Effect of added a-ketoglutaratic acid, pyruvic acid or pyridoxal phosphate on proteolysis and quality of Cheddar cheese. Food Chem. 76, 21-26.

Public lecture

2010-01-25T14:40:00.003Z

Public lecture: From Molecules to Milk, Wednesday January 27, 8 pm Boole 4, UCC. For more information, click here...

Cheddar Cheese Research - Yield, Quality and Consistency

2010-01-19T15:59:00.003Z

A RELAY workshop entitled "Cheddar cheese research- yield, quality and consistency will be held in Moorepark on Thursday, February 18 2010. For further information, click here.

Picture credit

DIAA Cheese Science conference, Auckland

2010-01-07T14:03:00.002Z

FIRM Research

2010-01-04T14:06:00.005Z

The Food Institutional Research Measure (FIRM) is administered by the Department of Agriculture and Food under the National Development Plan with the aim of supporting research, development and innovation in the Irish food industry. FIRM provides a strategic framework for institutional research in generic technologies aimed at supporting innovation and product development in the Irish food industry. It provides funding for "public good" research that is neither commissioned nor carried out in-house by individual firms. The results of the research are widely disseminated for the benefit of the food industry by the individual research teams and by RELAY, the national dissemination service charged with communicating the results of publicly funded food research to the Irish food industry. The following project is supported under the FIRM programme:

Novel strategies for optimization of the Cheddar cheese manufacturing process

Despite considerable research, it is still not possible to guarantee premium quality Cheddar cheese. In Ireland, 139,000 tonnes of cheese is made per annum, mostly Cheddar, from a pool of milk drawn from a small geographical area using starters and coagulants obtained from a limited number of commercial sources and often with identical technology. However, intra- and inter-factory variations in quality beset cheesemakers and have defied their best attempts to produce consistently premium-grade Cheddar. While cheesemakers pay close attention to pH, composition, ionic strength (NaCl) and temperature; it is possible that equally close attention to physicochemical and biochemical parameters which have to date received little attention, including oxidation-reduction potential, micro-scale distribution of enzymes, water activity, levels of residual lactose/lactate, and galactose (in cheeses made with starter systems containing Streptococcus thermophilus), may allow much more precise control of cheese quality and avoid specific defects. The parameters studied in this project could easily be measured and/or implemented in industry and could form part of future strategies for optimization of the Cheddar cheesemaking process and reducing variation in quality. Routine determination of some of these parameters will lead to the generation of new sets of quality parameters giving a competitive advantage to the Irish Cheddar cheese industry.

Existing research on Cheddar cheese quality has concentrated on a very limited number of attributes and industrial quality strategies typically focus on pH, moisture, fat-in-dry-matter salt-in-moisture and moisture-in-non-fat-substances, the importance of which were established by research in New Zealand up to nearly four decades ago. This project will focus on other area of cheese including its oxidation-reduction (redox) potential, the fate of galactose liberated by Gal- components of the starter, water activity and its influence on microbial growth and physiology and activity of ripening and strategies for greater control and standardization of lactose (and hence lactic acid)-to-buffering, and galactose/lactate content of Cheddar.

The partners in this FIRM-funded project are University College Cork (Prof PLH McSweeney, coordinator), Teagasc, Moorepark (Dr T Beresford, Dr TP Guinee) and University of Limerick (Dr MG Wilkinson).

Christmas greetings...

2009-12-17T16:32:00.003Z

Since it is once again that time of year, I would like to thank all the readers of this little website and wish a most Merry Christmas and a Prosperous New Year to those who celebrate these festivals at this time of the year and, to those who do not, please accept my good wishes for your special days.

Stilton and port wine is one of the few Christmas traditions associated with cheese and so it is appropriate to make reference to the King of (English) Cheeses. Stilton is a traditional Blue cheese with PDO status made in the English counties of Derbyshire, Nottinghamshire and Leicestershire. Like all Blue cheeses, the ripening of Stilton is dominated by the metabolism of the blue mould, Penicillium roqueforti which leads to high levels of lipolysis and further metabolism of free fatty acids to alkan-2-ones which dominate the flavour of Blue cheese. The Stilton Cheesemakers Association have a nice website including a good video of how this traditional cheese is made.

Picture credit

Dairy Technology Expertise in Ireland

2009-11-23T12:36:00.002Z

The third technology and expertise alert has been prepared for the dairy sector by Relay. This highlights the technology and expertise as well as the facilities, equipment, services and key contacts at Irish institutes and universities. It is hoped that this document will help researchers quickly identify who can help with R&D/technical challenges and where the relevant expertise and equipment is available.

The Department of Agriculture, Fisheries and Food through the FIRM programme has funded 104 projects directly aimed at supporting the dairy industry and this research has contributed in a significant way to the expertise at the institutes and universities.

To download this document, please click here: Dairy Technology and Expertise in Ireland.

(Picture credit)

alpha-Keto acids. 2

2009-11-20T11:27:00.003Z

In addition to conversion to hydroxyacids by the action of 2-hydroxyacid dehydrogenases, alpha-keto acids can be decarboxylated to the corresponding aldehyde. In the example of the degradation of tryosine, its alpha-keto acid (p-hydroxy phenylpyruvate) is converted to phydroxy phenylethanal, which in turn can be oxidised to the corresponding alcohol (p-hydroxy phenylethanol) or reduced to the corresponding carboxylic acid (p-hydroxy phenylethanoic acid). alpha-Keto acids can also undergo a series of chemical degradations leading, in the example of tyrosine to products such as p-hydroxy benzaldehyde.

Publication- Dairy Sci Technol

2009-11-18T14:15:00.002Z

Daly, D.F.M., P.L.H. McSweeney and J.J. Sheehan (2009). Split defect and secondary fermentation in Swiss-type cheese. Dairy Science and Technology (DOI: 10.1051/dst/2009036).

This article is one of Dairy Science and Technology's "highlight papers" and is available free from the publisher's website.

Now for something different...

2009-11-13T20:47:00.002Z

Publication- Int J Dairy Technol

2009-11-10T14:03:00.001Z

Brickley, C.A., J.A. Lucey and P.L.H. McSweeney (2009). Effect of the addition of trisodium citrate and calcium chloride during salting on the rheological and textural properties of Cheddar-style cheese during ripening. International Journal of Dairy Technology 62, 527-534.

alpha-Keto acids. 1

2009-10-30T12:04:00.005Z

The alpha-keto acids produced by aminotransferase activity are relatively unstable and do not accumulate in cheese but are rather degraded via a range of pathways. Taking tyrosine as an example, its alpha-keto acid (p-hydroxy phenylpyruvate) can be degraded by 2-hydroxyacid dehydrogenases to the corresponding hydroxy acid (p-hydroxy phenyl lactate). Other pathways of degradation of alpha-keto acids include decarboxylations and chemical degradations forming other volatile flavour compounds, which will be discussed in future posts.

Aminotransferases

2009-10-22T14:02:00.004+01:00

The catabolism of amino acids to a wide range of volatile flavour compounds is amongst the most important series of reactions in the development of cheese flavour. The key enzymes in the degradation of free amino acids appear to be aminotransferases (ATases) from lactic acid bacteria. ATases are intracellular enzymes whose physiological role is in the interconversion of amino acids. These enzymes require pyridoxal-5'-phosphate (PLP) as a co-factor and catalyse the transfer of the amino group of a donor amino acid (leucine in the example below) to an acceptor molecule, usually alpha-ketoglutarate, forming a product alpha-keto acid corresponding to the donor amino acid (alpha-ketoisocaproate in this example) and glutamic acid. The catalytic mechanism of ATases involves two steps: firstly, the amino group of the donor amino acid is transferred to PLP to yield the product alpha-keto acid and enzyme-bound pyridoxamine-5'-phosphate. Secondly, the amino group is transferred from pyridoxamine-5'-phosphate to the acceptor alpha-keto acid, thus regenerating PLP. The alpha-keto acids formed by ATase action are unstable and degrade to a wide range of compounds via enzymatic and/or chemical pathways.

Syneresis- V

2009-10-16T16:03:00.003+01:00

Stirring the curds-whey mixture facilitates heat transfer during cooking, prevents the curd pieces from fusing and promotes syneresis by encouraging collisions with other curd pieces and the vat wall. It is important to stir gently after cutting to avoid curd shattering (and thus yield losses); indeed, some cheesemakers leave a 5-10 min "healing time" after cutting before starting to stir.

In Cheddar-type cheeses, the curds-whey mixture is stirred and cooked to a desired pH (e.g., 6.1-6.2) but in many varieties (e.g., Emmental), the whey is drained at a target temperature. In a few varieties (e.g., stirred-curd Cheddar or Colby cheese), it is normal to stir the curd pieces after drainage ("dry stirring") which also promotes syneresis.

Note: Figure shows the effect of stirring (solid curves) and no stirring (lower broken line) on percentage syneresis as a function of time afer cutting.

Syneresis- IV

2009-10-02T16:12:00.004+01:00

Cooking temperature is a major factor that determines the rate of syneresis. Cooking temperature varies from ~31C (Camembert) to 52-55C (Emmental or Parmigiano-Reggiano) and temperature must match the starter. Acid production by lactococci is slowed ~35C and many strains are killed >40C (which is very close to the Cheddar cooking temperature of ~38.5C). Thermophilic starters, while surviving high temperatures do not gro >~52C so syneresis in Swiss cheese (cooked 54-55C) is mainly due to heat; starter grows as curd cools.

Cooking is normally achieved using a jacketed vat although "curd washing" (removal of perhaps 30-40% of the whey and replacement with hot water) is used in Dutch-type cheeses. In addition to increasing the temperature, curd washing reduces the lactose levels and helps to control the final pH of the cheese.

The rate of cooking is important. If it is too fast in the early stages, case hardening can result.

America's dairyland...

2009-09-17T12:44:00.004+01:00

The mid-western US state of Wisconsin prides itself on being "America's Dairyland", produces more milk than any state other than California and is the leading US producer of cheese. Is the Wisconsin State Quarter the only coin in the world featuring a cheese (by the looks of it, a wheel of Gouda)...?

Conference- Health aspects of cheese

2009-09-11T09:25:00.003+01:00

Health aspects of cheese, 6th - 8th of October 2009

How low does the fat content of cheese really needs to be in order to be healthy? This question will be discussed during the 5 sessions of this symposium:

Session A: Probiotic microorganisms in cheese
Session B: Bioactive compounds in cheese
Session C: Reduced component cheese (Low fat and low salt)
Session D: Too low fat cheese for health?
Session E: Maturation of cheese varieties of the Nordic Countries

The symposium will be located on the island Oscarsborg outside of the small city Drøbak 30 km south of Oslo in Norway. The Symposum will be held at Oscarsborg Hotel & Spa which is a former fortress. For more information on the programme, click here.

Graduations

2009-09-07T22:22:00.001+01:00

We had our graduations today and my new gown got its first outing...

Conference- Avellino (Italy)

2009-09-04T18:52:00.003+01:00

Methods and Issues in Cheese Authenticity Studies

Avellino 3-5 September 2009

Publication- J Dairy Res

2009-08-26T13:52:00.002+01:00

Bansal, N., P.F. Fox and P.L.H. McSweeney (2009). Comparison of levels of residual coagulant activity in different cheese varieties. Journal of Dairy Research 76, 290-293

2009-08-22T17:27:00.003+01:00

The Irish Examiner this morning carried an interested story of how makers of Parmigiano Reggiano cheese use their ripening cheese as collateral for loans to keep their business financially sound. Parmigiano Reggiano is an extra-hard internal bacterially ripened variety from northern Italy with controlled designation of origin and one of the longest ripening times (>2 years) of any common cheese. This long ripening time would impose unacceptably high inventory costs on a factory were it not for a system such as this. If only we could use our unripe housing stock similarly to kick-start the Irish economy...

Picture credit

Publication- Milchwissenschaft

2009-08-12T11:45:00.002+01:00

Sheehan, A., G. O’Cuinn, R.J. Fitzgerald, P.L.H. McSweeney and M.G. Wilkinson (2009). Characterization of Cheddar cheese juice is a useful index of starter strain related proteolysis during ripening. Milchwissenschaft 64, 272-276

Syneresis- III

2009-08-04T10:46:00.004+01:00

Processing variables that influence syneresis include the size of the curd particles. The smaller the pieces, the greater the greater the surface area for whey expulsion hence the greater the syneresis. Indeed, curd for high moisture cheeses not cut but scooped into mould.

Acidification also has a major influence on syneresis. The lower the pH, the greater is syneresis.

Other processing variables that influence syneresis will be discussed in future posts.

Publication- Int Dairy J

2009-07-23T14:44:00.001+01:00

Sheehan, J.J., A.D. Patel, M.A. Drake and P.L.H. McSweeney (2009). Effect of partial or total substitution of bovine for caprine milk on the compositional, volatile, non-volatile and sensory characteristics of semi-hard cheeses. International Dairy Journal 19, 498-509.

Course in cheese science- February 2010

2009-07-16T09:01:00.002+01:00

For further details, click here.

Syneresis- II

2009-07-14T09:54:00.002+01:00

Factors affecting syneresis are associated with the milk or with the processing operations. Factors that affect syneresis associated with the milk include:

% Fat. Increasing fat decreases syneresis as fat globules inhibit the movement of moisture to the surface of the curd piece. Increasing the fat content of milk increases cheese yield (Ya, actual yield) by 1.2 x mass of added fat due to increased retention of moisture.

% Casein. Casein is the structural element in the reticulum of the curd and so increasing casein content of milk results in better syneresis.

pH of milk. Reducing the pH of milk improves syneresis which is optimal at the isoelectric point of the caseins (pH 4.6). As pH moves towards 4.6 the net charge on the casein is reduced facilitating their interaction.

Ca2+ generally improves syneresis.

NaCl added to milk. At low levels, salt added to the milk improves syneresis but at higher levels it reduces syneresis. Addition of salt to milk is a practice used only in the manufacture of a very small number of varieties (e.g., Egyptian Domiati).

However, in general processing operations have a greater effect on syneresis than milk composition and will be discussed in future posts.

Portuguese cheeses

2009-06-25T12:11:00.002+01:00

Southern European countries generally have a rich tradition of cheesemaking and Portugal is no exception. A book on Portuguese cheeses QUEIJOS PORTUGUESES e um olhar gastronómico sobre famosos queijos europeus (Portuguese Cheeses and a Gastronomic Look over Famous European Cheeses) written by Dr Manuela Barbosa, retired from INETI, Lisbon, and M. de L. Modesto is available which discusses this rich tradition. This book received the Award of Gastronomic Literature, 2007, given by the Portuguese Academy of Gastronomy.

Syneresis- I

2009-06-19T11:12:00.004+01:00

Rennet-induced milk gels are relatively stable if left undisturbed. However, if the gel is cut, broken or exposed to pressure, the para-casein matrix contracts on itself expressing its aqueous phase (as whey) in a process known as syneresis. Controlling syneresis is the key to cheesemaking as it allows the cheesemaker to control moisture which, in turn, largely determines the quality, ripening and stability of the cheese. After the gel has formed, it is subjected to various treatments (cutting, cooking, stirring, acidification, pressing...) to encourage the expulsion of whey.

In hard cheeses such as Swiss and Cheddar syneresis occurs mainly in the vat while the gel for soft (high moisture) varieties such as Camembert may be scooped directly into moulds where whey expulsion is driven mainly by the decrease in pH.

Perhaps surprisingly for such an important parameter, methodology for measuring synersis is relatively poor. Approaches used have included measuring the volume of whey produced or the volume, moisture content or conductivity of the curd. Tracer/marker methods have also been used and some authors mimic the cheesemaking protocol (e.g., addition of starter, cooking) when measuring syneresis. However, all methods have inherent drawbacks.

Just a thought...

2009-06-19T10:19:00.003+01:00

It struck me recently that many animals love cheese. Leaving aside Homo sapiens, dogs, cats, mice and even fish (it can be used as bait) love the flavour of cheese. The incorrigible mutt in the photo above, Pirate, goes mad whenever I open some cheese in the kitchen; a piece of Cheddar is his ultimate treat. Is the reason known why cheese, and indeed other dairy products, have such cross-genus appeal? I would be very grateful to hear from anyone who might know the reason (but please from a strictly scientific perspective) why cheese and dairy products are liked by so many different species...

Publication- Int Dairy J

2009-06-08T15:00:00.001+01:00

Bansal, N., M.A. Drake, P. Piraino, M.L. Broe, M. Harboe, P.F. Fox, P.L.H. McSweeney (2009). Suitability of recombinant camel (Camelus dromedarius) chymosin as a coagulant for Cheddar cheese. International Dairy Journal 19, 510-517.

Publication- Handbook of Dairy Foods Analysis

2009-06-02T16:18:00.003+01:00

Bansal, N., P. Piraino and P.L.H. McSweeney (2009). Methods for the determination of proteolysis in cheese during ripening. In, Handbook of Dairy Foods Analysis, L. Nollet and F Toldra (eds), CRC Press, Boca Raton, FL, pp. 409-430.

Course in Cheese Science- Preliminary Announcement

2009-05-26T15:22:00.003+01:00

A two-day graduate-level course on the science of cheese manufacture and ripening will be held in University College Cork on February 24 and 25, 2010. This course will be given by Prof PLH McSweeney and Dr TP Guinee (Teagasc, Moorepark, Fermoy, Co. Cork). This course will cover the science of the manufacture of rennet-coagulated, acid-curd and processed cheese and will concentrate on the biochemistry of cheese ripening (proteolysis, lipolysis, metabolism of lactose, lactate, citrate, fatty acids and amino acids) and rheological and functional properties of cheese.

This course would be particularly suitable for graduates from outside the food science area who now find themselves working with cheese and indeed for food science graduates who wish to increase their knowledge of current trends in cheese science.

For registration and further details, please contact:

Ms Mary McCarthy-Buckley

Food Industry Training

University College Cork, Ireland

Tel: 353 21 4903178

m.mccarthybuckley@ucc.ie

And for more information, please visit www.ucc.ie/fitu

Facebook

2009-05-15T16:27:00.004+01:00

We have recently formed a Facebook group for current and (in particular) former members of UCC's Lab 232 (the home of cheese research on campus). I thought it would be a nice way to keep in contact with people who have now left the lab and moved on to the real world of cheese. If you would like to join, please go to Lab 232..Cheese Lab,UCC!!! on Facebook. We will not discriminate so even if you were based down the hall in Labs 227 or 230 (or even elsewhere in UCC), please feel free to join!

Paper- Milchwissenschaft

2009-05-06T12:18:00.002+01:00

O’Mahony, J.A., P.L.H. McSweeney and J.A. Lucey (2009). Rheological properties of rennet-induced skim milk gels made from milk protein concentrate solutions with different ratios of as-:b-casein. Milchwissenschaft 64, 135-138.

Cheese books- Website

2009-05-06T11:30:00.001+01:00

I came across a useful website recently which lists all books on cheese currently in print.

Processed cheese

2009-05-01T11:52:00.004+01:00

Processed cheese (or process cheese) is produced by comminuting, blending and melting one or more natural cheeses, and sometimes optional ingredients, into a smooth homogeneous blend with the aid of heat, mechanical shear and emulsifying salts (often sodium salts of citric or phosphoric acids). Processed cheese is sometimes moulded into blocks or the molten mass of cheese may be cooled on the surface of a large drum, cut into ribbons, interleaved with packaging at cut into slices.

A significant quantity of processed cheese is made worldwide and the product has some advantages over natural cheese including:

Great variety in flavour, consistency, functionality (e.g., sliceability, consistency, flowability) and consumer appeal.

Providing an outlet for lower grade natural cheese. This, together with the use of cheap non-cheese ingredients, reduces their cost compared to natural cheese.
Adaptability to the fast-food trade (e.g., use in cheeseburgers).

Relatively long shelf-life. Processed cheese is relatively stable due to the high temperatures used in processing which inactivate many microorganisms and enzymes.

However, typically processed cheese has a bland flavour.

Health aspects of cheese- Symposium October 2009

2009-04-24T15:24:00.003+01:00

The seminar will focus on health aspects of cheese with a special attention paid to Northern European cheese varieties. Four main sessions will be held, each introduced by a major review paper. Poster presentations allowing direct communication with the authors will complement the oral programme.

Keynote speakers:

1. Session: Probiotic microorganisms in cheese
Key note speaker: Vesa Joutsjoki, MTT, Finland

2. Session: Bioactive compounds in cheese
Key note speaker from Agroscope Liebefeld-Posieux
Research Station (ALP), Switzerland

3. Session: Reduced component cheese (low-fat and low-salt)
Key note speakers:
– Paul McSweeney, University College Cork, Ireland
– Siv Skeie, Norwegian University of Life Sciences and
& Ylva Ardö, University of Copenhagen

4. Session: Too low fat cheese for health?
Key note speaker: Tine Tholstrup, University of Copenhagen, Denmark

Oral & Poster presentations
Participants are encouraged to submit their recent research results for an oral or a poster presentation. Please submit an extended abstract (1-2 pages) of your oral or poster presentation before 30.06.2009 according to the guidelines given at www.umb.no/nordost/symposium Posters should have the maximum size of 90 x 120 cm

The seminar will be held in Drøbak (Norway) at the Oscarsborg Hotel & Spa.

Formal registration with subm. of abstracts: 30.06.2009
Final registration without pres. normal fee: 10.08.2009
Final registration without pres. higher fee: 18.09.2009

Seminar: 6-8.10.2009
Pre-registration and information:
siv.skeie@umb.no Phone +47 6496 5844
www.umb.no/nordost/symposium

National Dairy Council

2009-04-17T12:52:00.003+01:00

The National Dairy Council (founded in 1964) is Ireland’s principal source of information on milk and dairy products for consumers, parents, health professionals and those working in the dairy and food industries. The NDC regularly commissions independent research on consumer perceptions of milk and dairy products and assembles leading edge, science-based information on the issues of personal nutrition and the contribution of dairy foods well-being of society. Its core activities include advocacy and communications, the school milk programme, marketing and promotion and nutritional awareness.

The NDC recently revamped their website which is certainly worth a visit and contains much user-friendly information on milk and dairy products in addition to information about the organization and its activities.

Short course

2009-04-07T12:16:00.002+01:00

The Department of Food and Nutritional Sciences is delighted to host a (free) two-day course:

An introduction to dynamic model building in food science, microbiology and biochemistry

May 11-12, 2009

Lecturer: Prof. E. Parente
Dipartimento di Biologia, Difesa e Biotecnologie Agro-Forestali – Università degli Studi della Basilicata, Potenza, Italy
(http://www2.unibas.it/parente/HomeEP.html

This course is intended for MSc/PhD students (and research staff) in Biology, Microbiology, Biochemistry and Chemistry and provides an introduction to dynamic model building in biology and biochemistry. Most of the examples focus on Microbiology, Fermentation and Biochemistry, but can be easily extended to other fields

At the end of the course students

will know the principles of the development of a dynamic model for a simple biological system
will be able to use software tools for dynamic model building
will be able to develop a simple dynamic model for a biological or chemical system.

Course content
Lectures: Introduction. Static, comparative static and dynamic models. Principles of modelling. Model components: stocks, constants, converters, flows, etc. Ordinary differential equations, difference equations, discrete elements; integration methods. Model validation. Examples of dynamic models in microbiology, bioihemistry, biology, ecology.
Workshop: An introduction to the use of Berkeley Madonna.

Suggested reading
Hannon B., Ruth M. 1997. Modeling dynamic biological systems. Springer
Macey R., Oster G., Zahnley. 2000. Berkeley Madonna User’s Guide. UC Berkeley.

Interested students and staff please contact Prof Paul McSweeney (p.mcsweeney@ucc.ie) for further details.

Advanced Dairy Chemistry Volume 3

2009-04-02T12:50:00.002+01:00

The Advanced Dairy Chemistry series was first published in four volumes in the 1980s (under the title Developments in Dairy Chemistry) and revised in three volumes in the 1990s. The third edition of this series commenced with the publication of Volume 1 (Proteins) in 2003 and Volume 2 (Lipids) in 2006. With a total of 2,949 pages and 66 chapters in its three volumes written by well in excess of one hundred scientists from 15 countries, the third edition of the Advanced Dairy Chemistry series is by far the most comprehensive treatise on the chemistry of milk and dairy products ever published.

This series has become the leading reference source on dairy chemistry, providing in-depth coverage of milk proteins, lipids, lactose, water and minor constituents for research institutes, academics and postgraduate students in universities, milk processing companies, and regulatory agencies worldwide.

The final volume in the third edition of the series, Advanced Dairy Chemistry Volume 3: Lactose, Water, Salts, and Minor Constituents, edited by PLH McSweeney and PF Fox, has just been published by Springer (New York) and reviews the extensive literature on lactose and its significance in milk products. This volume also reviews the literature on milk salts, vitamins, milk flavours and off-flavours and the behaviour of water in dairy products.

Advanced Dairy Chemistry Volume 3: Lactose, Water, Salts and Minor Constituents, 3rd ed., 2009,
PLH McSweeney and PF Fox (Eds.)
Springer, New York.
Hardcover
ISBN: 978-0-387-84864-8
€139.95

Methods and issues in cheese authenticity studies: a workshop

2009-04-01T13:10:00.002+01:00

Methods and issues in cheese authenticity studies: a workshop.

4/9/2009 – 5/9/2009
Sala Convegni, Banca della Campania
Collina Liguorini, Avellino (Italia)
http://www.isa.cnr.it/ micheeses@isa.cnr.it

Authenticity and traceability are key issues for the protection of traditional food products, and EU and member states have developed quality branding schemes and specific regulation to this end. Recent scandals connected to frauds related to origin, authenticity, safety, labelling of some PDO and non-PDO cheeses have weakened consumers’ confidence in quality branding schemes and caused severe economical damage to producers. The objective of this meeting, organized by the Food Science Institute of the National Research Council of Italy, is to present to researchers, public quality control agencies, cheesemakers organizations, an overview of analytical, economic and technical issues on cheese authenticity and traceability.

Preliminary programme.

Session 1. Invited speakers. 4/9/2009 9.00-18.30
1. Welcome addresses: Prof. R. Coppola, Director, ISA-CNR, Prof. E. Parente, Dip. Biologia, Università degli Studi della Basilicata, Italy
2. Factors that affect the quality of cheese - Prof. P. F. Fox, University College Cork, Cork, Ireland
3. Classification schemes for cheese - Prof. P. McSweeney, Dept. of Food and Nutritional Sciences, University College Cork, Cork, Ireland
4. Protein and peptide composition analysed by CE, HPLC and LC-MS - Prof. Y. Ardö, Dept. of Food Science, University of Copenhagen, Denmark
5. Evaluation of dairy products authenticity by spectroscopic methods - Dr. D. Andueza and Dr. B. Martin, Herbivore Research Unit, INRA Clermont-Ferrand Theix, France.
6. Microbial fingerprinting and authenticity of cheese - Dr. D. Ercolini, Dip. Scienza degli Alimenti, Università degli Studi “Federico II”, Napoli, Italy.
7. Immunochemical methods for cheese authenticity studies – Dr. R. Pizzano – ISA-CNR, Avellino, Italy.
8. Small molecules for the evaluation of cheese authenticity - Dr. M. C. Messia, DISTAAM, Università degli Studi del Molise, Italy
9. Statistical methods for cheese authenticity studies – Prof. E. Parente, Dip. Biologia, Università degli Studi della Basilicata, Potenza, Italy
10. The Role of the Italian Central Inspectorate for Food Quality in the protection of food authenticity - Dr. F. Fuselli, Ispettorato Centrale per il Controllo della Qualità dei Prodotti Agroalimentari, Rome, Italy

Session 2. 5/9/2009 9.00-13.30
Oral communications (max 10, 10 min each). Poster session
Round table: cheese authenticity and traceability, technical, economical, sociological and legislative aspects.

Language.
The official languages of the workshop are English and Italian. Simultaneous translation will be available on request.

Poster and oral communications.
Instructions for submission of abstracts for posters and oral communications will be published in the second circular.

Fees.
The registration fee (200 €) must be paid before July 31st, 2009. We anticipate that registration will be open from April 15th, 2009

Scientific Committee.
Prof. Raffaele Coppola, Direttore ISA-CNR, Avellino, Italy; Prof. Eugenio Parente, Università degli Studi della Basilicata, Potenza, Italy; Prof. Gianfranco Panfili, Università degli Studi del Molise, Campobasso, Italy
Technical secretariat. ISA-CNR Avellino, Dott.ssa Manuela Oliva , Dott. Luigi Cipriano, Sig. Antonio Ottombrino, Rag. Gennaro Russo, Dott. Patrizio Tremonte

Registration information.
If you are interested in receiving the second circular, please complete the form below for your data, copy and paste in the body of an E-mail to micheeses@isa.cnr.it
Title, Name and Middle Initial, Surname
Institution
Street address, ZIP/Postal code, Town, Country
Phone number
Fax number
E-mail
I plan / do not plan to submit an abstract. The tentative title is…..

Lost indigenous cheeses of Ireland

2009-03-16T20:59:00.005Z

As it is St Patrick’s Day, I thought it would be nice to say a few words about the lost world of indigenous Irish cheeses. Unlike perhaps all other European countries and for the reasons outlined below, Ireland has no extant traditional indigenous cheese but rather makes variants of cheeses that originated elsewhere.

Cheese and other dairy products were consumed in ancient Ireland and apparently constituted a substantial portion of the diet. References to cheese are relatively common in the Gaelic literature but, unfortunately, only rarely is information available other than the name of the cheese and have extant no detailed description of any indigenous Irish cheese variety.

The modern Irish word for cheese, cáis, is derived via Norman French from the Latin caseus. When used without qualification, cáis appears to refer in the Gaelic literature to a pressed cheese. Tanag (and the similar Grus) is thought to have been a hard cheese, perhaps made from skim or semi-skimmed milk. There is an account of how the mythical Maeve, Queen of Connacht, was killed by her nephew who fired a piece of Tanag from a slingshot. Faisce Grotha (literally “compression of curds”) appears to refer to a relatively small curd-cheese which was moulded and probably consumed fresh. A story is told that an attempt was made on the life of St Patrick by giving him a piece of this cheese that had been poisoned. A number of names of unpressed cheeses also survive including Gruth, That, Millsen, Maothal, Mulchan and Gruthnuis.

None of the ancient indigenous cheeses of this island have survived into modern times. The feudal system, with its self-contained agricultural communities, which flourished on mainland Europe and developed many cheeses, did not become established in Ireland. Unlike their continental counterparts, Irish monasteries developed and declined earlier and were more scholastic and missionary in their outlook and thus contributed little to agricultural development. However, the major reason for the loss of the indigenous Irish varieties was the economic and social decline following the English conquest of the country in the 16th and 17th centuries. Cheesemaking in Ireland declined further during the 17th and 18th centuries as a result of political instability and the imposition of the Cattle Acts (1663, 1669), which imposed tariffs on the export of cattle from Ireland to Britain and had the effect of encouraging the production of butter and pigs. Although buttermaking flourished, cheese manufacture in Ireland remained negligible until the early 20th century. Cheese production was substantial for a short period during the First World War but declined thereafter until about 1950 after which production began a steady increase. Ireland now produces in large centralised factories approximately 120,000 tonnes of cheese per annum and this figure is projected to increase substantially in the coming years due to abolition of milk quotas.

The drawing above is a famous depiction of a mediaeval banquet entitled “McSweeney Dines as the Bard Recites” and depicts a chieftain of the McSweeney (Mac Suibhne) clan, seated centre, being entertained by his bard. Perhaps one of the cheeses mentioned above was on the menu?

Further reading:

Ó Sé, M. (1948). Old Irish cheeses and other milk products. J. Cork Hist. Archeol. Soc. 53, 82.

McCarthy, J. (1992). History of the development of the Irish cheese industry. Proc 3rd Cheese Symp., Teagasc, Moorepark, Fermoy, Co. Cork, p. 1.

Publication- Food Res. Int.

2009-03-03T12:22:00.001Z

Pino, A., F. Prados, E. Galán, P.L.H. McSweeney and J. Fernandez-Salguero (2009). Proteolysis during the ripening of goats’ milk cheese made with plant coagulant or calf rennet. Food Research International 42, 324-330.

Finishing operations-I

2009-02-26T15:21:00.003Z

Cheese curds may be moulded either after acidification (e.g., Cheddar) or directly after cooking (e.g., Emmental). Curds of high moisture varieties mat together under their own weight but curds of low moisture cheeses must be pressed to form a homogeneous mass. The moulds used give cheese the size and shape characteristic of the variety. Curds (particularly those of low moisture cheeses) should be warm to ensure that they mat together, avoiding mechanical openings which are a defect in most varieties.

Salting-VI. Attainment of equilibrium

2009-02-19T14:00:00.003Z

Salt absorption is a relatively rapid event taking perhaps 15-30 min for curd chips of Cheddar cheese, ~7.5 h for Camembert and perhaps 15 d for Parmigiano-Reggiano. After NaCl is absorbed into cheese curd, there then must be established a salt equilibrium across the cheese mass.

In dry-salted cheeses, true equilibrium is rarely is ever fully achieved and substantial intra- and inter-block variation in NaCl distribution are common for Cheddar. NaCl equilibrium is established quickly within each curd chip but there is poor transfer of NaCl across the chip boundary. In brine-salted cheeses, however, there is initially a very large NaCl gradient from the outer portion of the cheese towards its centre; attainment of equilibrium is very slow indeed, taking up to 10 months for a large wheel of Parmigiano-Reggiano.

Further reading:

Guinee, T.P. and Fox, P.F. (2004). Salt in cheese: physical, chemical and biological aspects, in Cheese: Chemistry, Physics and Microbiology, Vol. 1 General Aspects, 3rd edition, P.F. Fox, P.L.H. McSweeney, T.M. Cogan and T.P. Guinee (eds), Elsevier, Amsterdam, pp. 207-259.

(Picture credit)

Salting-V. Brine salting

2009-02-06T08:58:00.003Z

In brine salted cheeses, the difference in osmotic pressure between the (often saturated) brine and the cheese aqueous phase is the driving force for NaCl migration. Diffusion of brine into cheese is an impeded diffusion process (Na+ and Cl- ions must migrate around fat globules and the hydrated casein matrix of cheese).

Factors that affect NaCl uptake in brine-salted cheeses include:

Concentration gradient. Uptake increases as brine concentration increases from 5-25% (w/w) NaCl.

Salting time. Uptake increases but at a diminishing rate with salting time.

Brine temperature. Uptake increases as brine temperature increases from 5 to 20 C. There is a minimum temperature for uptake at ~32C as fat exudes at the cheese surface (above this temperature fat is more liquid and is lost more easily).

Surface area:volume ratio of the cheeses. Salt uptake increases with increasing surface area:volume ratio.

Shape of cheese. Assuming an equal surface area:volume ratio, rectangular cheeses brine more quickly than cylindrical cheeses, which in turn brine more quickly that spherical cheeses. (Faster brining is caused in this case by the presence of corners in the cheese which allow brine diffusion from two or more directions.)

Moisture content of the curd. Rate of NaCl uptake increases as curd moisture increases.

Fat content of the curd. Increasing fat tends to impede diffusion.

Curd pH. Uptake decreases as pH increases from 4.7 to 5.7. This effect is caused by increased charge on the caseins as one moves away from their isoelectric point causing greater hydration of the protein and thus tending to impede diffusion.

Further reading:

Guinee, T.P. and Fox, P.F. (2004). Salt in cheese: physical, chemical and biological aspects, in Cheese: Chemistry, Physics and Microbiology, Vol. 1 General Aspects, 3rd edition, P.F. Fox, P.L.H. McSweeney, T.M. Cogan and T.P. Guinee (eds), Elsevier, Amsterdam, pp. 207-259.

Guinee, T.P. (2007). What factors affect salt uptake in cheese curd? In Cheese Problems Solved, P.L.H. McSweeney (ed), Woodhead, Cambridge, pp. 87-89.

Photo shows an industrial brine bath used to brine Mozzarella-type cheeses moulded into fist-sized pieces.

Salting-IV. Dry salting

2009-01-28T19:07:00.004Z

Relatively few cheese varieties are dry salted but a high percentage of the world's cheese production is dry salted! This discrepancy can be explained by the fact that Cheddar, the variety produced in the largest quantity, is a dry-salted cheese. In dry salting, the curd is milled (cut) into small pieces at the end of acidification and dry NaCl is sprinkled on the surface of the curd chips.

NaCl dissolves in whey on the surface of curd chips and diffuses inwards (in effect, each individual curd chips is "brined" in its own salty whey) and each curd chip acts as a "mini-cheese". The milled curd chips have a very large surface area: volume ratio which leads to very rapid uptake of salt in Cheddar and related varieties. As high salt-in-moisture inhibits the growth of starter organisms, it is important that the curd has achieved close to its final pH before dry salting.

Factors affecting salt uptake in dry-salted cheese include:

Quantity of salt added to milled curd: Salt uptake increases as salting level increases)
Mellowing time: Salt uptake increases as mixing time increases from 20 s to 6 min.
Holding time between salt addition/mixing and pressing: Uptake increases as holding time increases.
Curd temperature: Uptake decreases as curd temperature increases from 24 to 41C (this effect is largely due to increased liquefaction of milkfat at the surface of the curd chips which inhibits NaCl uptake).
Surface area: volume ratio of curd chip: NaCl uptake increases as surface area is increased (i.e., by reducing chip size).
Curd moisture: NaCl uptake decreases as curd moisture increases. As moisture increases, there is more syneresis of press whey which removes more NaCl from the chip.
Curd acidity: Salt uptake decreases as acidity decreases (i.e., lower uptake at higher pH).

Further reading:

Guinee, T.P. (2007). What factors affect salt uptake in cheese curd? In Cheese Problems Solved, P.L.H. McSweeney (ed), Woodhead, Cambridge, pp. 87-89.

Research update

2009-01-19T14:10:00.004Z

Relay has just published a short update on our FIRM-funded project Understanding the biochemistry and enzymology of cheese ripening and development of novel strategies to enhance the biogenesis of cheese flavour (with partners in University College Cor, University of Limerick and Moorepark Food Research Centre). Please visit http://www.relayresearch.ie/ for further details.

Casu Marzu

2009-01-16T15:32:00.006Z

Perhaps the most unpalatable cheese in the world is the Sardinian "variety", Casu Marzu ("rotten cheese", also known as casu modde, casu cundhídu, or formaggio marcio), an Italian ewes' milk cheese but one which is riddled with live insect larvae. After manufacture, the cheese fly (Piophila casei; see below) is encouraged to lay its eggs on the cheese and the insect larvae cause dramatic changes to the cheese flavour (or so say those foolhardy enough to taste it!) and texture. This cheese is available only on the black market as it has been outlawed for obvious food safety reasons, not least of which is enteric myiasis caused my living larvae in the intestines! Certainly one cheese to be avoided... For those with strong stomachs, an interesting video clip about Casu Marzu is availble on YouTube.

Salting-III. How is cheese salted?

2009-01-08T18:25:00.004Z

There are three basic methods by which cheese is salted. The large majority of cheese varieties worldwide are brine salted. This simply means placing the cheese after forming into a concentrated (and often saturated) NaCl solution which diffuses into the cheese. Cheddar and related varieties are dry salted. After acidification, the curd is milled (cut) into small pieces and dry salt is added and mixed with the curd; the salted curd is then pressed. Some Blue cheese varieties can be salted differently by the repeated surface application of dry salt. After forming, dry NaCl is patted onto the surface of the cheese and this process is repeated as necessary to give the desired salt concentration in the cheese. Different methods of salting have very different effects in cheese as will be discussed later.

The photo above shows milled Cheddar curd being dry salted by students a few years ago in the UCC Pilot Plant dairy. The photo below is of an industrial brine bath taken in a Mozzarella factory in northern Italy.

Salting-II. Salt and bitterness

2009-01-06T16:59:00.004Z

Chymosin cleaves beta-casein mainly towards its hydrophobic C-terminus. After the Phe-Met bond of kappa-casein, the Leu192-Tyr193 bond of beta-casein is the bond in the casein system most susceptible to chymosin action. Cleavage of this bond produces a large polypeptide, beta-CN (f1-192) and a short peptide (f193-209) which is hydrophobic and extremely bitter.

The rate of cleavage of the Leu192-Tyr193 bond is very dependent on the ionic strength of the cheese aqueous phase. Increasing ionic strength by increasing NaCl concentration results in increased hydrophobic interaction between the hydrophobic C-terminal regions of beta-casein thus tending to block the action of chymosin and reducing the production of beta-CN (f193-209) and related peptides and thus bitterness.

Hence (and strangely), the first question to ask if a cheese is bitter, is what is its salt content!

Note: "beta" and "kappa" above are usually written as Greek letters but I cannot seem to use them on this site. The photo above shows the amino acid sequence of the C-terminal region of bovine beta-casein with arrows indicating some cleavage sites of chymosin on this protein.

Salting- I. Functions of NaCl

2009-01-05T14:36:00.004Z

Nearly all varieties of cheeses are salted to some extent. NaCl has a number of functions in cheese:

Controls microbial growth. In particular, starter growth is inhibited. Likewise, Propionibacterium freudenreichii, essential for eye development in Swiss-type cheese, is very sensitive to NaCl. Hence, Swiss-type cheeses have the lowest salt contents of any ripened cheese variety.

Influences enzyme activity. In particular, NaCl promotes hydrophobic interactions of C-terminal region of beta-casein, inhibiting chymosin action (and the development of bitter peptides)

Regulates the water activity of cheese

Affects composition. In general, about 2 kg moisture lost per kg NaCl absorbed.

Affects flavour, through its direct salty flavour, by controling activity of enzymes, and of microorganisms. In particular, by promoting hydrophobic interaction between molecules of beta-casein and this reducing the action of chymosin, it controls the development of bitterness.

Affects texture by dehydration, effects on composition and proteolysis.

Merry Christmas

2008-12-20T19:16:00.011Z

The figure above shows the locations of the last couple of dozen hits to www.cheesescience.net. As can be seen, the world of cheese is very diverse, but hereabouts it is shortly going to be Christmas, a time for goodwill and thanks. Hence, I would like to thank the people behind the 4,129 hits to www.cheesescience.net since about last March. It is very gratifying to see that this little site receives so many hits and I hope the miscellany of snippets about cheese science and technology have been of some interest and use to you.

It was a busy year for me travel-wise: conferences in Berne, Buenos Aires and Mexico City, teaching courses in Ankara and a university in Bolu (a city half-way between Ankara and Istanbul) and visiting students in parts of north Cork as far-flung as Kanturk! Holidays this year were tied mainly onto work trips. I had a couple of fascinating days revelling in museums and the Byzantine remains of Istanbul and finally got to explore a bit of Argentina properly with a few days in Buenos Aires (and yes, I did see the tango in its native habitat!) with a short trip right up north to Salta in the foothills of the Andes (wonderful scenery). As for publishing, with great relief to me and Prof Fox, the manuscript for the third and final volume of the third edition of Advanced Dairy Chemistry (covering lactose, water, vitamins and minor constituents of milk) left my desk for the publishers during the summer with publication due for early 2009. Our main publishing project now is the revised edition of the four volume Encyclopedia of Dairy Sciences which will be published by Elsevier in 2011.

I wish a most Merry Christmas and a Prosperous New Year to those who celebrate these festivals at this time of the year and, to those who do not, please accept my good wishes for your special days. There are not many Christmas traditions related to cheese, but I do suggest you try the combination of Port wine and Stilton (or the Blue variety of your choice). The full bodied intensity of Port perfectly complements the strong methyl ketone flavour of Blue cheese.

I leave you with my best wishes and a photo of the Christmas tree in chez McSweeney.

Cheese... but not as we know it

2008-12-18T21:22:00.011Z

A present (photo) from a visiting student from Norway reacquainted me with a distinctive group of Norwegian unripened "cheese" varieties which are made by thermal evaporation, concentration and crystallisation of whey to which may be added skim milk or cream. These cheeses (collectively referred to as Brunost, meaning brown cheese, and including Geitost, Mesost/Myseost [popular in Sweden and Denmark, respectively], and Gudbrandsdalsost) are characterised by a smooth, creamy body and a sweet, caramel-like taste. Unusually for dairy products, the Maillard reaction is encouraged (the only other example that immediately springs to mind where extensive non-enzymatic browning is desirable in dairy products is the Argentinean dessert confection, Dulche de Leche). It is arguable whether Norwegian whey cheeses should be called "cheese" as they are really fat/protein-enriched by-products of concentrated heated whey. The vast majority of cheeses involve dehydration of milk by controlled syneresis of rennet- or acid-induced casein gels. In the case of these products, dehydration is achieved quite differently (by thermal evaporation) and their manufacture involves extensive lactose crystallisation. Still, to paraphrase the Bard, in this case, a cheese by any other name would taste as sweet!

Further reading:

Fox, PF, TP Guinee, TM Cogan and PLH McSweeney (2000). Fundamentals of Cheese Science. Aspen Publ., Gaithersburg, MD.

Kosikowski, FV and VV Mistry (1997). Cheese and Fermented Milk Foods (3rd edn, 2 vols), FV Kosikowski LLC, Westport, CT.

Production of succinate from citrate by Lb. plantarum

2008-12-16T13:54:00.002Z

Succinic acid has an acidic, salty/bitter, taste and contributes to savoury flavour of cheese; Emmental cheese contains approximately 0.8-1.4 g succinate/kg. Succinate may be produced from citrate by Lactobacillus plantarum via a reductive tricarboxylic acid pathway (see below). Lb. plantarum is a component of the non-starter lactic acid bacterial (NSLAB) flora of many cheeses.

However, succinate is not usually found in Cheddar at concentrations above its taste threshold (~37 ppm). This may be because (i) strains of Lb. plantarum in NSLAB may not be able to use pathway, (ii) not enough organisms and/or (iii) other citrate-positive microorganisms outcompete Lb. plantarum.

Further reading:

Dudley, EG and Steele, JL (2005). Succinate production and citrate catabolism by Cheddar cheese nonstarter lactobacilli. J. Appl. Microbiol. 98, 14-23.

Christmas is a coming...!

2008-12-16T09:45:00.004Z

Christmas must be around the corner since the cheese researchers of Lab 232 had their annual lunch last Friday! From left to right, Diletta, Shirinda, Veronica, Paul, Anna, Kim and Himanshu. This year we had four different nationalities around the table (Ireland, Italy, Norway and India). As usual, we went to Cafe Paradiso, a prize-winning vegetarian restaurant on Lancaster Quay near UCC. I strongly recommend Cafe P should anyone be visiting Cork; the food is superb.

Last week also saw the winter conferrings at which our 2007-08 MSc (Applied Science) in Food Science graduated.

Lactose metabolism in lactic acid bacteria

2008-12-06T23:48:00.002Z

Since cheese is a fermented dairy product, lactose metabolism by lactic acid bacteria has been thoroughly studied and is now well understood. Lactococcus lactis transports lactose into the cell using the phosphoenolpyruvate phosphotransferase system which phosphorylates lactose to lactose-6-phosphate. Lactococci possess a phospho-beta-galactosidase which hydrolyses lactose-6-phosphate to glucose and galactose-6-phosphate. The latter is converted, via the tagatose pathway, to dihydroxyacetone-phosphate which is isomerised to glyceraldehyde-3-phosphate and thus into the glycolytic pathway. The glucose moiety of lactose is metabolised to lactic acid by glycolysis. Lactococci produce 4 mol L-lactate per mol lactose.

Most other lactic acid bacteria transport lactose into the cell as lactose using a permease. These organisms hydrolyse lactose to glucose and galactose using a beta-galactosidase; galactose is converted to glucose-6-phosphate by the Leloir pathway and thus into the glycolytic pathway. Streptococcus thermophilus metabolises 1 mol lactose to 2 mol L-lactate since they metabolise only the glucose moiety of the disaccharide. Certain species of lactobacilli produce D- or DL-lactate, depending on the type of lactate dehydrogenase they possess. Leuconostoc sp. use a different sequence of biochemical events for lactose metabolism; the end products of phosphoketolase pathway are quite different (1 mol lactose is converted to 2 mol D-lactate, 1 mol ethanol and 2 mol CO2) to those of glycolysis.

Further reading:

Fox, P.F., T.P. Guinee, T.M. Cogan and P.L.H. McSweeney (2000). Fundamentals of Cheese Science. Aspen Publishers, Gaithersburg, MD. 587 pp

Predicting cheese yield

2008-12-06T15:26:00.015Z

The manufacture of many cheeses involves an approximate 10-fold concentration of the solids in milk. Thus, a very rough rule-of-thumb suggests that one should obtain about 1 kg cheese from 10 L milk. Various formulae have been developed down through the years to estimate more accurately the yield of cheese of specific varieties. A widely used formula is the Van Slyke yield formula:

Where Ya is actual cheese yield (kg per 100 kg milk), F and C are the fat and casein contents of the cheesemilk (with added starter culture), respectively, %FR is fat recovery (%FR/100 is often 0.93 for Cheddar cheese), a is a coefficient to account for casein loss (often 0.1 for Cheddar) and b is a coefficient to account for cheese solids non-fat, non-protein (often 1.09 for Cheddar). This formula often underestimates yield of high moisture cheeses. Also, 93% recovery of fat may not be achieved. Factors must be varied for other cheese varieties and can also vary between factories and application of a generic yield formula may not accurately predict yield in all plants. If pronounced seasonal variation, theoretical formulae give less accuracy, mainly due to errors in estimating casein concentration.

Plant specific formulae are developed by analysing historical data on cheese yield in relation to milk composition, milk quality, fat and protein recovery and cheese salt and moisture contents. These must be updated regularly but give very accurate predictions for a particular plant. However, they are not applicable to other plants and are dependent on accuracy of historical data. Also, it is important to remember that accurate prediction does not mean that a plant is operating at maximum efficiency!

Further reading:

Banks, J.M. (2007). How can cheese yield be predicted? In Cheese Problems Solved, P.L.H. McSweeney (ed.), Woodhead, Cambridge, pp. 105-6.

Lipoprotein lipase

2008-11-27T16:07:00.005Z

Milk contains quite high levels of an indigenous lipase, lipoprotein lipase (LPL). Like many enzymes in milk, LPL enters milk from the cow's blood. The physiological role of LPL is in the metabolism of plasma triglycerides. Milk contains sufficient LPL activity to cause perceptible rancidity very quickly under optimal conditions. The reason milk does not become rancid is ude to compartmentalisation of enzyme and substrate. Most (>80%) LPL is associated with the casein micelles while its substrate, triacylglycerols, is protected by the milk fat globule membrane (MFGM). If this compartmentalisation is compromised (as, for example, would occur if the MFGM of raw milk is damaged by excessive pumping or homogenisation), then enzyme and substrate come together and high levels of free fatty acids are liberated.

LPL is relatively non-specific for fatty acid type but specific for fatty acids esterified at the sn-1 and sn-3 positions of triacylglycerols. Since, in bovine milkfat, short chain fatty acids are preferentially esterified at the sn-3 position, LPL appears to release them preferentially.

Much LPL activity is lost on pasteurization of milk but 78C x 15 s is required for complete inactivation. However, residual LPL activity in pasteurized milk is usually not of significance. LPL is of most importance during the ripening of cheeses made from raw milk. Levels of lipolysis in cheeses made from raw milk are usually higher than cheeses of the same variety made from pasteurized milk.

Further reading:

Olivecrona, T., Vilaro, S. and Olivecrona, G. (2003). Lipases in milk. In Advanced Dairy Chemistry-1 Proteins, Part A, 3rd edition, P.F. Fox and P.L.H. McSweeney (eds), Kluwer Academic Publ., New York, pp. 473-494.

A hard case!

2008-11-18T17:47:00.005Z

Case hardening is caused by too rapid increase in cooking temperature, particularly early on in the cooking process; it is better to increase the temperature of the curds/whey mixture slowly soon after cutting. If the initial rate of increase in temperature is excessive, it can lead to increased syneresis at the outside of the curd piece which causes a dehydrated protein layer inhibiting further movement of moisture out of the curd piece and thus acts to reduce whey loss. Thus (and paradoxically), excessive cooking can lead to poor overall syneresis and high moisture in the cheese! Case hardening can be avoided by reducing the rate of increase in temperature during the early stages of cooking and/or by introducing (or extending) a healing time between cutting and the start of cooking.

Further reading:

McSweeney, P.L.H. (ed.) (2007). Cheese Problems Solved. Woodhead Publ., Cambridge.

Enzyme-modified cheese

2008-11-07T12:53:00.003Z

Enzyme-modified cheese (EMC) is cheese curd which has been treated with enzymes to produce a concentrated cheese flavour ingredient.

Manufacturing protocols for EMC are very variable and are usually closely guarded secrets. The first step generally involves blending freshly made cheese curd, and perhaps other ingredients such as other sources of fat and protein, with water and emulsifying salts to form a paste which is then pasteurized (to inactivate microorganisms and enzymes) and may be homogenized. A blend of enzymes (e.g., proteinases, peptidases and lipases) is then added sometimes together with starter organisms and the paste is incubated for a few days before being heat-treated to inactivate the added enzymes and to stabilize the product. EMCs are available as pastes or dried to form powders. EMCs, which may have approximately 15-30 times the flavour intensity of natural cheese, are used to give a cheese flavour note to products such as processed/analogue cheese, cheese powders, soups, sauces, dips, crackers, salad dressings and in coatings for snack foods.

Further reading:

Guinee, T.P and Kilcawley, K.N. (2004). Cheese as an ingredient. In Cheese: Chemistry, Physics and Microbiology Vol. 2 Major Cheese Groups 3rd ed. P.F. Fox, P.L.H. McSweeney, T.M. Cogan and T.P. Guinee (eds) Elsevier Academic Press, Amsterdam. pp. 395-428.

Kilcawley, K.N., Wilkinson, M.G. and Fox, P.F. (1998). Enzyme-modified cheese. Int. Dairy J. 8, 1-10.

Hail to the cheese...

2008-11-04T16:58:00.004Z

Considering the day that is at hand, I thought it would be interesting to note the dairy angle to the US presidential election. The Huffington Post records a press interview by Senator McCain courting the dairy vote in front of the cheese counter of a supermarket...

Lest I be accused of any bias, one should also note that Senator Obama now has a cheese named in his honour!

n-Methyl ketones and Blue cheese flavour

2008-10-29T09:55:00.005Z

Like that of certain other food products, the flavour of Blue cheese is often an acquired taste. Some people initially find the pugnent, almost peppery, flavour of varieties such as Roquefort, Stilton (shown above), Gorgonzola, Danish Blue and similar cheeses to be overly strong. However, when one becomes used to the flavour, it is quite delicious. The flavour of Blue cheese is dominated by a class of compounds known as n-methyl ketones (alkan-2-ones).

Spores of the blue mould, Penicillium roqueforti, germinate within mechanical openings in the cheese mass to form the blue veins characteristic of these varieties. P. roqueforti produces two potent extracellular lipases which dominate lipolysis in these cheeses which have the highest levels of free fatty acids of all cheese families. However, liberation of fatty acids from triacylglycerols is only the start of the process of producing Blue cheese flavour. P. roqueforti converts fatty acids to n-methyl ketones by a four-step pathway corrersponding to the early stages of beta-oxidation. Heptan-2-one and nonan-2-one (below) are the predominant n-methyl ketones in Blue cheese and contribute greatly to its pungent flavour.

Futher reading:

Collins, Y.F., P.L.H. McSweeney and M.G. Wilkinson (2003). Lipolysis and free fatty acid catabolism in cheese: A review of current knowledge. International Dairy Journal 13, 841-866.

Rennet hysteresis

2008-10-17T16:09:00.003+01:00

Heating milk increases its rennet coagulation time (RCT) to a lesser or greater extent depending on the severity of heating. However, if milk is held in the cold for extended periods after heat treatment (e.g., after pasteurisation), its RCT increases significantly and the lower the storage temperature and longer the storage time, the greater the effect. This increase in RCT on storage of heat-treated milk is known as rennet hysteresis.

Adverse effects of heating on RCT is caused mainly by denaturation of the whey protein, beta-lactoglobulin which interacts with kappa-casein at the micelle surface. However, this adverse effect is offset to some extent by beneficial effect of lower pH caused by heating (heating milk causes precipitation of calcium phosphate from soluble to colloidal states with the production of hydrogen ions, thus reducing the pH which favours rennet action). However, heat-induced changes to milk salts equilibria are partly reversible on cooling, so full adverse effects of protein-protein interaction on RCT then become apparent.

Residual rennet

2008-10-01T15:42:00.002+01:00

The principal role of chymosin or other enzymes in rennets is to destabilize the casein micelle and thus cause the gelation of milk, but a small amount of coagulant is retained in the cheese curds and contributes to the ripening of many cheese varieties. The level of coagulant retained in cheese curd depends on several factors related to the milk or the procedure of cheese manufacture, e.g., concentration of the caseins in milk, ratio of different caseins, casein micelle size, ionic strength of milk, heat treatment of milk, extent of acidification of milk prior to addition of rennet, pH at whey drainage, cooking temperature, level of moisture and cheese age. The quantity of rennet retained in cheese curd also varies with the type and ratio of enzymes in the rennet, their stability to pH and temperature during cheesemaking and the influence of pH on their ability to bind to the caseins.

Because of these factors, the amount of residual rennet activity in cheese differs between varieties (expressed in the graph above as peak area units/mg dry matter/h and determined by HPLC on a synthetic substrate). Low levels of residual chymosin are found in cheeses which are cooked to high temperatures (e.g., Parmesan and Emmental) and in pasta-filata cheeses, the curds for which are heated and stretched after acidification. Camembert contains relatively high amounts of residual rennet activity as it has a high moisture content, little or no cooking and, significantly, syneresis is driven by acidification which means that much whey drains at low pH values encouraging retention of rennet. It is interesting to compare levels of residual rennet in Feta and Cast Feta; the latter cheese is made from milk pre-concentrated by ultrafiltration and so there is little or no whey drainage during manufacture and thus little or no loss of rennet.

Further reading:

Bansal, N., P.F. Fox and P.L.H. McSweeney (2007). Factors that affect the retention of rennet in cheese curd. Journal of Agricultural and Food Chemistry 55, 9219-9225.

Upadhyay, V.K., P.L.H. McSweeney, A.A.A. Magboul and P.F. Fox (2004). Proteolysis in cheese during ripening. In Cheese: Chemistry, Physics and Microbiology, Volume 1, General Aspects, 3rd edition, P.F. Fox, P.L.H. McSweeney, T.M. Cogan and T.P. Guinee (eds), Elsevier Applied Science, Amsterdam. pp. 392-433.