Divergent volatile metabolomes and flavor attributes in rice fermented by Aspergillus oryzae and Aspergillus flavus.

Abstract

Introduction: The generally recognized as safe (GRAS) fungus Aspergillus oryzae has been used for millennia in the production of traditional Asian fermented foods and beverages. Domestication has led to genomic and phenotypic adaptations that distinguish A. oryzae from its wild relative, Aspergillus flavus. While differences between these species have been partially characterized, their comparative production of volatile compounds during food fermentation remains poorly understood.

Methods: We evaluated alpha-amylase activity, aflatoxin production, taste attributes using an electronic tongue, and volatile profiles using dynamic headspace gas chromatography-mass spectrometry. Analyses were conducted during rice fermentation using the food-grade strain A. oryzae RIB40 and two wild A. flavus strains, NPK13tox and AflaGuard.

Results: A. oryzae RIB40 exhibited significantly higher alpha-amylase activity during rice fermentation, and aflatoxin production was detected only in A. flavus NPK13tox. Sensory analysis revealed that rice fermented by A. oryzae RIB40 had significantly lower astringency, aftertaste, and bitterness, along with significantly higher richness (defined as umami aftertaste). Volatile profiling showed that A. oryzae RIB40 produced a greater number and higher concentrations of volatile compounds relative to rice fermented by A. flavus strains. Many of these volatiles, including 2-methyl-3-buten-2-ol, 3-octen-2-one, 2-methyl-butanal, and 3-methyl-butanal, are associated with pleasant sensory attributes and have been previously linked to A. oryzae-fermented foods.

Discussion: These findings suggest that the volatilome of A. oryzae RIB40 has been shaped by domestication to produce a more desirable sensory profile. This profile is enriched in alcohols, aldehydes, ketones, and heterocyclic compounds that contribute fruity, umami, and malty notes, highlighting the role of domestication in optimizing sensory outcomes during food fermentation.