longer than usual. Commercial starter cultures are also available usually
consisting of strains ofOenococcus oeni, formerlyLeuconostoc oenos.
Until recently it was unclear how LAB derive any benefit from
performing this reaction. Substrate-level phosphorylation does not occur
(it is not therefore, strictly speaking, correct to call it a fermentaion) and
the free energy of the decarboxylation reaction is low. It now seems that
the reaction conserves energy through a proton motive force generated
across the cell membrane by the transport of malate, lactate and protons.
9.5 Fermented Milks
9.5.1 Yoghurt
Fermentation to extend the useful life of milk is probably as old as
dairying itself. The first animals to be domesticated are thought to have
been goats and sheep in the Near East in about 9000 BC. In the warm
prevailing climate it is likely that their milks furnished the first fermented
milks and only some time later, between 6100 and 5800 BC in Turkey or
Macedonia, was the cow first domesticated.
Fermented milks which include yoghurt, buttermilk, sour cream, and
kefir differ from cheese in that rennet is not used and the thickening
produced is the result of acidification by lactic acid bacteria. Yoghurt
whose name comes from the Turkish word ‘Jugurt’ is the most widely
available fermented milk in the Western world today where its popularity
derives more from its flavour and versatility than from its keeping
properties.
It is made from milk, skimmed milk or fortified milk usually from
cows but sometimes from other animals such as goats or sheep. The
production process most commonly applied commercially is outlined in
Figure 9.4.
The first prerequisite of any milk to be used in a fermentation process
is that it should be free from antimicrobials. These could be antibiotic
residues secreted in the milk as a result of mastitis chemotherapy or
Figure 9.3 The malo-lactic fermentation
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