The optimal pH for cell growth and -carotene production in a
synthetic grape juice medium by recombinant S. cerevisiae strain
T73-63 was different. A relatively high pH (7.0) is favorable for cell
growth, whereas a low pH (5.0) is suitable for -carotene synthesis.
A pH-shift controlled fermentation process was successfully developed
to increase -carotene production and formation rate. The
specific activities of SOD and CAT were simultaneously increased
by shifting the pH from 7.0 to 5.0, while pre-treatment with ascorbic
acid as an antioxidative agent reversed the enhancement of
-carotene production. Because oxidative stress is correlated to
increased -carotene production, it can be concluded that the
improvement in -carotene production by the low-pH stress strategy
resulted in an increased oxidative stress level in cells