flavour is the result of diacetyl production by so-called flavour bacteria
such as strains of Lactococcus lactis subsp. lactis and Leuconostoc
mesenteroidessubsp.cremoris.
Most bacteria produce diacetyl and acetoin from carbohydratevia
pyruvate. However, because of the key role pyruvate plays as an electron
acceptor in LAB, it cannot usually be spared for this purpose unless an
additional source other than carbohydrate or an alternative electron
acceptor is available. Citrate metabolism can provide this extra pyruvate
and lead to the accumulation of diacetyl as indicated in Figure 9.6. Fresh
milk contains citrate but levels decline during storage so that, for the
Figure 9.6 Citrate fermentation. TPP,thiamine pyrophosphate
Chapter 9 329