The effect of pH on cell growth, sugar consumption and -
carotene production was first investigated in 500-ml shake flasks
with different initial pHs ranging from 4.0 to 7.0 (Table 1). The
results showed that the initial high pH was favorable for cell growth
and sugar consumption as indicated by the increased biomass and
glucose consumption rate with elevated pH. However, the specific
-carotene content increased alone with the decrease of initial
medium pH, indicating that a relatively low pH is beneficial for -
carotene formation. The highest specific content (3.15 mg/g DCW)
was achieved at a pH of 5.0, which was 37.6%, 25.5% and 56.7%
higher than those of pH 4.0, 6.0 and 7.0, respectively. Similarly, the
highest -carotene production (22.36 mg/l) was obtained at a pH
of 5. These results suggested that the optimal pH conditions for cell
growth and -carotene production by recombinant yeast were different.
The relatively high pH was favorable to cell growth, while a
low pH was suitable for -carotene synthesis.