Seriously strong Cheddar...

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

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

UCC/Teagasc Strategic Alliance

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

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

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

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

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...!

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...

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!