Divergent Volatile Metabolomes and Flavor Attributes in Rice Fermented by Aspergillus oryzae and Aspergillus flavus

Abstract

The generally recognized as safe (GRAS) fungus Aspergillus oryzae has been used for millennia in the production of traditional Asian fermented foods and beverages. This prolonged domestication has led to phenotypic adaptations that distinguish A. oryzae from its wild relative, Aspergillus flavus. While genomic and phenotypic differences between these species have been partially characterized, their comparative production of volatile compounds during food fermentation remains poorly understood. Here, we evaluated alpha-amylase activity, aflatoxin production, taste attributes (via electronic tongue), and volatile profiles (via dynamic headspace gas chromatography-mass spectrometry) of the food-grade strain A. oryzae RIB40 and two wild A. flavus strains, NPK13tox and AflaGuard. A. oryzae RIB40 exhibited significantly higher alpha-amylase activity during rice fermentation, and only A. flavus NPK13tox produced aflatoxin. Sensory analysis revealed that rice fermented by A. oryzae RIB40 exhibited more favorable taste attributes, including significantly lower astringency, aftertaste, and bitterness, as well as significantly higher richness (defined as umami aftertaste). Additionally, A. oryzae RIB40 produced a greater number and higher concentrations of volatile compounds, with 20 compounds significantly elevated compared to rice fermented by A. flavus. 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 previously been linked to A. oryzae-fermented foods. These findings suggest that the volatilome of A. oryzae RIB40 has been shaped by domestication to produce a more desirable sensory profile, enriched in alcohols, aldehydes, ketones, and heterocyclic compounds contributing fruity, umami, and malty notes.