Characterization of kokumi γ-glutamyl peptides and volatile aroma compounds in alternative grain miso fermentations

The term kokumi is used to describe sensory attributes of mouthfulness, lingeringness, and thickness. It is caused by γ-glutamyl di- and tri-peptides, and is especially prevalent in fermented food products. This study explores the influence of substrate, microbial strain and fermentation time on the development of kokumi peptides in barley and sorghum misos, both grain-based fermentations produced by Aspergillus oryzae. Unlike other reports, kokumi peptide evolution is considered in the context of the fermentation process overall, including the volatile aroma compounds and physico-chemical parameters. We show that fermentation time and microbial strain play important roles for the γ-glutamyl profile. We also show that peptides γ-EL, γ-EF, γ-EV, and γ-EVG are present throughout the fermentation process for all misos, and that the evolution of certain kokumi peptides can be predicted from redox, pH, and color. In addition, there is significant correlation between γ-glutamyl peptides and several dozen volatile compounds including esters, alcohols, aldehydes, acids, ketones, and hydrocarbons, overall contributing a comprehensive view of the flavor space of kokumi. The correlation to many ester compounds suggests a connection between kokumi and fruity/sweet/waxy aromas. Our results can inform flavor and texture parameters in plant-based food innovation.