Application of glucose to prepare Aspergillus oryzae koji as an adjunct to prevent rancidity in cheese products

Abstract

Koji made using Aspergillus oryzae shows potential for application as a cheese adjunct; however, flavor defects resulting from volatile free fatty acid (FFA) accumulation should be avoided. Hence, a modified glucose-containing whey solid medium was used to culture A. oryzae AHU 7139, and the triacylglycerol (TG) lipase activity and lipase gene (tglA and mdlB) expression were compared with those of a culture using a conventional whey solid medium. The results showed that TG lipase activity and the expression of both lipase genes were reduced in the modified medium. Moreover, the expression level of farA, a positive transcription factor of the lipase genes, was also reduced. The cheese adjunct prepared by culturing the AHU 7139 strain in the modified medium lowered the FFA content in the cheese products, resulting in comparable FFA levels with those in the adjunct-free cheese. Thus, adding glucose is recommended to prepare the koji adjunct for cheesemaking.