Aspergillus flavus NPK13tox whole-genome sequencing

Aspergillus oryzae has been used for thousands of years in the production of traditional Asian fermented foods and beverages. This long-term usage of A. oryzae in food substrates has led to phenotypic adaptations distinct from its wild relative Aspergillus flavus. While previous studies have characterized some of the genomic and phenotypic differences between A. oryzae and A. flavus, very little is known about the differences in volatile compounds produced during food fermentation. Here, we compared alpha-amylase activity, aflatoxin production, taste attributes (via electronic-tongue) and volatile compound production (via Dynamic Headspace Gas Chromatography Mass Spectrometry) of the food grade strain A. oryzae RIB40 (type strain), and the wild A. flavus strains NPK13tox and AflaGuard. We found that A. oryzae RIB40 had significantly greater alpha-amylase activity during rice fermentation, and that only A. flavus NPK13tox produced aflatoxin. Additionally, when comparing electronic tongue results, rice fermented by A. oryzae RIB40 produced fewer compounds associated with astringency and bitterness, while producing more compounds involved in umami, compared to the rice fermented by A. flavus. Finally, A. oryzae RIB40 produced more volatile compounds during rice fermentation and 20 of these compounds were found at significantly higher levels in A. oryzae RIB 40 compared to the rice fermented by the A. flavus starter cultures. Many of these compounds (including 2-methyl-3-buten-2-ol, 3-octen-2-one, 2-methyl-butanal and 3-methyl-butanal) have aromas with positive sensory attributes, some of which have been previously associated with foods fermented by A. oryzae. Taken together, our analyses suggest the A. oryzae RIB40 volatilome has been shaped by domestication to produce more favorable volatile and sensory profile, characterized by higher levels of alcohols, aldehydes, ketones, and heterocyclic compounds associated with fruity, umami, and malty notes.