Importance of carbon source feeding and pH control strategies for maximum kojic acid production from sago starch by Aspergillus flavus

Abstract

To maximize kojic acid production by Aspergillus flavus Link 44-1 using gelatinized sago starch as a carbon source, the performance of different fermentation modes (batch and fed-batch with different feeding modes) was investigated in an 8- l stirred tank fermentor. The addition of a large volume of concentrated sago starch (140 g/ l) 2 d after the start with an initial starch concentration of 60 g/ l produced the maximum concentration of kojic acid (16.43 g/ l), which was about 4 times higher than that for batch fermentation of 100 g/ l sago starch. Further improvement of kojic acid production was obtained by adding small amounts of concentrated starch (140 g/ l) intermittently at 2-d intervals to the culture. Using this technique of fermentation, the dissolved oxygen tension (DOT) can be controlled at high levels (40–50% saturation) during the active growth phase, which is required for the enhanced secretion of α-amylase used for saccharification of starch and also for the production of mycelia with higher ability in synthesizing kojic acid. Maintaining the culture pH at 3 throughout the intermittent fed-batch fermentation reduced kojic acid production (7.26 g/ l) significantly. Very little kojic acid (0.93 g/ l) was produced when the pH was kept at 4 during the growth phase and then lowered to 3 during the production phase. A high level of kojic acid production (31.00 g/ l) was achieved in fermentation where the pH was not controlled throughout the cultivation or not controlled during the growth phase but kept at 3 during the production phase. This result indicates that the pH control strategy is important; with the variation in culture pH during the growth phase being most significant and critical to kojic acid production.