Abstract:

Eight Lactobacillus acidophilus strains were cultivated in batch, and the activities of 10 enzymes involved in lactic acid fermentation pathway were measured, and the metabolic fluxes of lactic acid were analyzed at the logarithmic growth phase. Path analysis was used to investigate the direct and indirect influence of enzyme activity on lactic acid metabolic flux, followed by the establishment of a determination coefficient (R2(i)) which quantified the control effect similar to metabolic control coefficient. Results showed that pyruvate kinase(R2(PK) = 0.3705), hexokinase(R2(HK) = 0.3053), triosephosphate isomerase(R2(TPI) = 0.2733) and lactate dehydrogenase (R2(LDH) = 0.2601) exhibited higher determination coefficients, which suggested that they played a dominant role in control of lactic acid production. However, the determination coefficient of gylceraldehyde-3-phosphate dehydrogenase was negative (R2(GAPDH) = 0.1320), which suggested that GAPDH had a negative effect on lactic acid production.

Key words: enzyme activity , lactic acid flux , path analysis , metabolic regulation