Glycolysis and related reactions during cheese manufacture and ripening

TLDR: Cheese contains a low level of citrate, metabolism of which by Streptococcus diacetylactis leads to the production of di acetyl, which contributes to the flavor and is responsible for the limited eye formation characteristic of such cheeses.

Abstract: Fermentation of lactose to lactic acid by lactic acid bacteria is an essential primary reaction in the manufacture of all cheese varieties. The reduced pH of cheese curd, which reaches 4.5 to 5.2, depending on the variety, affects at least the following characteristics of curd and cheese: syneresis (and hence cheese composition), retention of calcium (which affects cheese texture), retention and activity of coagulant (which influences the extent and type of proteolysis during ripening), the growth of contaminating bacteria. Most (98%) of the lactose in milk is removed in the whey during cheesemaking, either as lactose or lactic acid. The residual lactose in cheese curd is metabolized during the early stages of ripening. During ripening lactic acid is also altered, mainly through the action of nonstarter bacteria. The principal changes are (1) conversion of L‐lactate to D‐lactate such that a racemic mixture exists in most cheeses at the end of ripening; (2) in Swiss‐type cheeses, L‐lactate is meta...