# Probiotic fermentation of soybeans and use of fermented soy in cookies

## TL;DR

This study explores using probiotic fermentation of soybeans to boost GABA content, which may help with mental health, and shows that fermented soy can be used in cookies without compromising texture.

## Contribution

The study demonstrates that Lactococcus lactis fermentation enhances GABA content and preserves cookie quality better than unfermented soy.

## Key findings

- Co-fermentation with Lactococcus lactis and Lactiplantibacillus plantarum significantly reduced phytic acid levels.
- Cookies with Lactococcus lactis-fermented soybean flour had higher GABA content and better hardness than those with unfermented soy.
- Fermentation with Lactococcus lactis preserved cookie texture comparable to 100% wheat flour cookies.

## Abstract

With increasing prevalence of mental health issues such as insomnia and anxiety, γ‐aminobutyric acid (GABA) has gained attention for its neurological benefits. The development of GABA‐rich functional foods has emerged as a promising research direction. Soybeans, rich in glutamate, are excellent substrates for GABA biosynthesis using microbial fermentation. In this study, Lactococcus lactis (LL) and Lactiplantibacillus plantarum (LP) were used to ferment soybeans, aiming to enhance GABA production. The effects of fermentation on pH value, yield, colony‐forming unit, phytic acid content, total phenol content, and ABTS+ free radical scavenging activity were investigated. Additionally, soybean flour fermented by LL was incorporated into cookie formulations to evaluate its effects on cookie spread factor and hardness. The GABA content of the cookies was also analyzed.

Co‐fermentation with LL and LP significantly reduced phytic acid levels. Mono‐fermentation with LL showed higher probiotic viability, better retention of total phenolics and antioxidant capacity, and superior GABA accumulation. Cookies supplemented with LL‐fermented soybean flour better maintained the hardness and exhibited a higher GABA content compared to those prepared with unfermented soybean flour (P < 0.05).

Fermentation with LL effectively enhanced GABA content (P < 0.05) and preserved cookie texture comparable to that of 100% wheat flour cookies. These results can support the potential of LL fermentation in developing GABA‐enriched plant‐based functional foods. © 2025 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.