Effect of culture conditions and medium compositions on kojic acid production by Aspergillus oryzae ATCC 10124

Abstract

Kojic acid is a secondary metabolite produced by some strains of Aspergillus spp and has been exploited commercially in food and cosmetic products. The objective of this work was to optimize the cultivation conditions of Aspergillus oryzae ATCC 10124 prior to triggering the fermentation process using organic broken rice noodles (OBRN) as a carbon source. Trials with various carbon and nitrogen sources show that 10% glucose and 0.05% yeast extract with ammonium sulfate was favorable for A. oryzae to produce kojic acid (1.58 g/L at day 4 of cultivation). Initial pH and agitation rate significantly affected the kojic acid formation. The maximum quantities of kojic acid were obtained when the pH of the medium was at 2.5, and shaking was at 200 rpm, at 1.60 g/L and 1.65 g/L, respectively. When the carbon source was changed to OBRN, the substrate was saccharified by alpha-amylase and glucoamylase, and 100% of the hydrolysate was used to replace glucose for the kojic acid fermentation. Kojic acid content increased when using OBRN, at 1.52 g/L, and was comparable to that yielded from the fermentation with glucose (1.58 g/L).