Dairy Chemistry And Biochemistry

CHEMISTRY AND BIOCHEMISTRY OF CHEESE AND FERMENTED MILKS^407

Soluble CaPOJlactate

Concentration Gradient

5

.- (Lower) (Higher)

pH gradient

I

Ammonium ion (Higher)

concentration gradient

i

Cross-sectional view

* Lactate metabolized

ca3(po4)'2

precipitated

* 'Ammonia

produced

Cheese

exterior with

surface microflora

Figure 10.17 Schematic representation of the gradients of calcium, phosphate, lactic acid, pH

and ammonia in ripening of Camembert cheese.

In surface smear-ripened cheeses, e.g. Munster, Limburger, Tilsit, Trapist,

the surface of the cheese is colonized first by yeasts which catabolize lactic

acid, causing the pH to increase, and then by Breuibucterium linens, the

characteristic micro-organism of the surface smear but which does not grow

below pH 5.8, and various other micro-organisms, including Micrococcus,

Arthrobacter and coryneform bacteria.

Lipolysis. Some lipolysis occurs in all cheeses; the resulting fatty acids
contribute to cheese flavour. In most varieties, lipolysis is rather limited
(Table 10.5) and is caused mainly by the limited lipolytic activity of the
starter and non-starter lactic acid bacteria, perhaps with a contribution from
indigenous milk lipase, especially in cheese made from raw milk.
Extensive lipolysis occurs in two families of cheese in which fatty acids
and/or their degradation products are major contributors to flavour, i.e.
certain Italian varieties (e.g. Romano and Provolone) and the Blue cheeses.
Rennet paste, which contains pre-gastric esterase (PGE) rather than rennet
extract, is used in the manufacture of these Italian cheeses. PGE is highly
specific for the fatty acids on the sn-3 position of glycerol, which, in the case
of milk lipids, are predominantly highly flavoured short-chain fatty acids
(butanoic to decanoic). These acids are principally responsible for the
characteristic piquant flavour of these Italian cheeses.