Co-fermentation of okara with Kluyveromyces marxianus and Lactobacillus plantarum and its application in Chinese steamed bread

In this study, okara was fermented by Lactobacillus plantarum and Kluyveromyces marxianus with single and mixed strains, and the changes in main nutrients and free amino acids before and after fermentation were investigated. Gas-phase ion mobility spectrometry (GC-IMS) was used to examine volatile compound alterations in fermented okara. The impact of fermented okara on Chinese steamed bread (CSB) quality was then assessed. Results showed a rise in soluble dietary fiber in co-fermented okara from 4.2 % to 7.8 %. GC-IMS identified 65 volatile compounds in four fermented okara sourdough samples, with 46 compounds qualitatively confirmed. Aldehyde levels like hexanal and valeraldehyde significantly decreased post-fermentation. CSB formulations substituting wheat flour with 5 %, 10 %, and 15 % okara exhibited decreased specific volume, increased hardness and chewiness, and slight changes in cohesiveness and springiness. Sensory evaluation results indicated that the flavor, appearance, color, internal structure, and texture of CSB made with fermented okara were superior to those of the unfermented group. Co-fermented okara sourdough improved the quality and sensory attributes of okara CSB. Therefore, this study proposes a method for the redevelopment and utilization of okara. • Co-fermentation raises soluble dietary fiber and free amino acid content of okara. • GC-IMS result showed that fermentation reduces aldehydes, improving okara's scent. • Co-fermented okara sourdough shows promise in Chinese steamed bread production. • Optimal addition to maintain steamed bread quality is 10 % d.b. of fermented okara.