OPTIMIZATION OF CULTURE CONDITIONS FOR KOJIC ACID PRODUCTION IN SURFACE FERMENTATION BY ASPERGILLUS ORYZAE ISOLATED FROM WHEAT GRAINS

Abstract

Kojic acid is a natural organic acid synthesized during aerobic fermentation of carbohydrates as a secondary metabolite by some species of Aspergillus and has been used commercially in several industrial applications. The current investigation aims to optimize the culture conditions for kojic acid production from starch as a carbon source by the novel isolate Aspergillus oryzae 1034. Seventy-five isolates representing 11 species of Aspergillus were isolated from stored wheat grains and screened for kojic acid biosynthesis. Amongst, A. oryzae 1034 was selected as the most potent kojic acid producer from starch. This strain was subjected to different fermentation conditions to maximize the kojic acid production from starch versus glucose. The results concluded that glucose and starch substrates in concentrations 60 and 80 g/l, respectively were the optima for kojic acid production. The optimum phosphorus concentration was 0.5 and 2.0 g/l KH2PO4 in glucose and starch media, respectively. The maximum kojic acid yield was attained at 28oC for 11 days of incubation in both glucose and starch media with pH 4.5 and 5.0, respectively. Supplementation of Pb+2 to glucose medium and Zn+2 to starch medium stimulated the biosynthesis of kojic acid to 79.3 and 68.8 g/l, respectively. Alternatively, kojic acid biosynthesis was decreased by supplementation of amino acids in the fermentation medium. These findings suggest the possibility of using A. oryzae 1034 as a promising.