Abstract
Kojic acid is an industrially important compound due to its powerful skin whitening effect, metal chelating ability, and antioxidant capacity. In addition, the gamma-pyrone, which is polyfunctional for synthesizing chemicals, in kojic acid makes it become a crucial precursor of various drugs and food additives such as Aspirin and maltol. Traditionally, kojic acid is produced by the submerged culture of Aspergillus oryzae in the manner of batch fermentation. Considering the high cost of batch replacements, reinoculations in long term fermentation as well as the poor mass transfer in free suspension culture, immobilization fermentation becomes one of the most potent replacements. Plastic composite supports (PCS), which is an extruding product composed of polypropylene and agricultural wastes, could be used as the immobilization scaffolds for kojic acid production. Previous studies show that applying PCS immobilization system increased the production and decreased the cost of some value-added products including bioethanol and pullulan. In the present research, the efficiency of immobilized culture for production of kojic acid, and the effect of changed morphology of A. oryzae on production were evaluated. Before evaluation, the optimal pH and PCS was selected. The optimal pH was verified as pH 3. Based on the kojic acid production, SFYBR, the PCS with the most complex ingredients, was chosen among 5 PCS with different compositions (SFY, SFB, SFR, SFYB, and SFYBR) and two control ( PP sticks and luffa) as the scaffold in following experiments. However, the production in immobilization system was one fifth of traditional free suspension culture (35.02 g/L). By using different degrees of nitrogen deprived medium and kojic acid added medium, the production in immobilization system increased to 26.34 g/L. Moreover, with the immobilization system, repeated-batch fermentation without loss of mycelia could be conducted for several cycles with productivity of 2.395 g/L/d, which is higher than free suspension culture in batch fermentation. It is an economical way in industry. To sum up, PCS immobilized fermentation system, which decrease the inconvenience and cost of batch submerged fermentation, is a potential tool in industrial production of kojic acid.
Published Version
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