Rancidity cheese ripening

Parmesan or Grana, as it is known in Italy, is a group of very hard bacteria-ripened, granular-textured cheeses made from partially skimmed cow s milk. They originated in Parma, near Emilia, Italy, hence the name. Special lipolytic enzymes derived from animals are used, in addition to rennet, to produce the characteristic rancid flavor. 

In some mold-ripened cheeses, a very high FFA content (up to 25% of total fatty acids Gripon, 1987) is acceptable [e.g., >66 000 mg/kg for Blue cheese (Horwood et al., 1981) compared to <4000 mg/kg for good quality Cheddar (Bills and Day, 1964)]. High levels of butyric acid characterise Italian hard cheeses and certain pickled cheeses (Fox and Guinee, 1987), [e.g., up to 520 mg/kg for Greek Feta (Horwood et al., 1981) and >3000 mg/ kg for Romano (Woo and Lindsay, 1984)]. An imbalance in flavor constituents can, nevertheless, lead to undesirably rancid or goaty (C4 o-C8 0) or soapy (Cio o-Ci2 o) flavors in these cheeses (Woo and Lindsay, 1984). 

When there is a need, someone will solve it. A patent was issued in 1987 (22) describing a new and novel lipase produced by a mutant strain of Aspergillus that has an accelerating effect on cheese flavor development without lypolytic enzyme associated rancidity. The patent claims that this new lipase will be useful as a ripening accelerator in the production of mild flavored cheeses such as cheddar. 

Milk lipases may give undesirable rancidity when fresh milk is used for cheese making. The heat sensitivity of these lipases restricts them playing a major role in ripening of cheese made from pasteurized milk. Lipases play a very important role in flavour formation especially in mould cheeses such as Roquefort and Gorgonzola. 

Psychrotrophs, which can dominant the microflora of refrigerated milk, are a potentially important source of potent lipases in cheese. Cousins et al. (1977) considered that active lipase would be present in cheese if psychrotroph numbers exceed 10 CFU ml K Many psychrotroph lipases are heat stable and thus may cause rancidity in cheese over the course of a long ripening period. The subject of psychrotroph enzymes in cheese was discussed by Mottar (1989). Unlike psychrotroph proteinases, which are largely water-soluble and are lost in the whey, psychrotroph lipases adsorb onto the fat globules and are therefore concentrated in the cheese. 

The odor threshold values for methyl ketones are substantially higher than those for aldehydes (cf. Tables 3.32 and 3.47). Nevertheless, they act as aroma constituents, particularly in flavors of mold-ripened cheese (cf. 10.2.8.3). However, methyl ketones in coconut or palm oil or in milk fat provide an undesirable, unpleasant odor denoted as perfume rancidity . 

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