The pathways by which hexoses are metabolised divides lactic acid bacteria into two groups, homofer mentative and heterofermentative (Fig. 1). For a detailed description of these pathways the reader is referred to Axelsson (1998). Briefly, homofermenters such as Pediococcus, Streptococcus, Lactococcus and some lactobacilli produce lactic acid as the major or sole end-product of glucose fermentation. However, under altered growth conditions and when the
initial substrate is a pentose this may change (London, 1990; Kandler, 1983). Homofermenters use the Embden–Meyerhof–Parnas pathway to generate two moles of lactate per mole of glucose and derive approximately twice as much energy per mole of glucose as heterofermenters. Heterofermenters such as Weisella and Leuconostoc and some lactobacilli produce equimolar amounts of lactate, CO and ethanol from glucose via the hexose monophosphate or pentose pathway.