Abstract:

In order to ascertain the effect of co-fermentation with Kluyveromyces marxianus on the biosynthesis pathway of
lactic acid by anaerobic metabolism of lactose, the contents of main lactose metabolites in fermented milks with lactic acid
bacteria alone and in combination with Kluyveromyces marxianus were analyzed and compared by HPLC, accompanied by
comparative measurement of related key enzymes activities. The results showed that lactose was degraded at a markedly
accelerated rate during co-fermentation with Kluyveromyces marxianus and lactic acid bacteria (P < 0.05). Kluyveromyces
marxianus could utilize the produced galactose during subsequent storage. Moreover, the presence of the yeast resulted
in significantly enhanced activities of β-galactosidase, lactate dehydrogenase, pyruvate kinase and hexokinase during
the fermentation process (P < 0.05). As a result, hexokinase and pyruvate kinase, the key rate-limiting enzymes in the
Embden-Meyerhof-Parnas (EMP) pathway, were significantly activated (P < 0.05). pH declined faster (P < 0.05) during
co-fermentation with Kluyveromyces marxianus than fermentation with single starter culture, which was associated with
significantly enhanced production of lactic acid (P < 0.05). However, no significant difference in pyruvic acid content was
found between the two fermented milks (P > 0.05). This study reveals that Kluyveromyces marxianus plays an important role
in promoting lactose glycolysis.

Key words: lactose metabolism, Kluyveromyces marxianus, fermented milk, enzymatic activity, metabolites