Characterization of Aspergillus strains as novel starter cultures selected for surface-ripened koji cheese

Abstract

Koji cheese, a novel surface-ripened cheese using koji molds (KC43 and KC41), and its chemical composition have been clarified previously (Tomita et al., Food Res. int., 2022). In the present study, cheeses ripened with five candidate strains of Aspergillus oryzae were newly tested to expand the variety as koji cheese. Water-soluble and volatile metabolite profiling revealed that free amino acids responsible for umami taste markedly increased in all the samples whereas substantial differences in free fatty acids, methyl ketones, secondary alcohols, and 1-octen-3-ol levels were shown among the strains tested. It was also found that several strains characterized their cheeses by accumulations of specific metabolites such as fatty acid ethyl esters responsible for fruity odor and 3-hydroxy-3-methylglutaric acid, an antilipemic compound. The physical property (hardness) differed among the samples and the ripening by specific strains resulted in softer curd than that by KC43 and KC41. These strains might provide novel sensory, textural, and functional characteristics to koji cheese.