Improving rice fermentation flavor: Screening and evaluation of two endogenous flavor-producing strains

Abstract

Fermentation critically shapes flavor profiles in rice-based foods. However, flavor-friendly bacteria contributing to the natural fermentation of indica rice have been rarely reported. In this study, 18 strains were isolated from the natural fermentation liquid of indica rice. Two strains were selected based on sensory evaluation, hemolytic test, enzyme-producing ability, bacterial inhibition capacity, and acid tolerance. These strains were identified as Limosilactobacillus fermentum FR-21 and Acetobacter orientalis AO-21 using morphological characteristics and genetic sequencing. During the fermentation, both strains exhibited stable growth patterns and effective acid-producing capabilities, resulting in pH values of 3.8 and 4.2, respectively. After 48 h of fermentation, L. fermentum FR-21 promoted the production of sweet and umami amino acids, while A. orientalis AO-21 significantly enhanced the formation of bitter amino acids. In addition, 43 volatile flavor compounds (VFCs) were identified in rice fermented with L. fermentum FR-21. These compounds were primarily aldehydes and alcohols contributing to a fermented and light fragrance. In contrast, 31 VFCs were detected in rice fermented with A. orientalis AO-21, dominated by acids that provided an acidic aroma. This study successfully isolated two bacterial strains that contribute distinct fermented and acidic aromas, offering potential applications in the development of fermented rice-based foods.