Use of Rice Bran for Preparation of GABA (γ-aminobutyric acid)-rich Sourdough

Abstract

Preparation of GABA (γ-aminobutyric acid)-rich sourdough using rice bran and raisin was investigated. Preparation of sourdough began with pre-fermented raisin liquid, which is a widely used source of wild yeast and lactic acid bacteria. The number of naturally occurring cells in the liquid was 3.5×10⁷ CFU/mL for yeast cells and 3.4×10⁷ CFU/mL for lactic acid bacteria. The liquid was added to rice bran and then used to make sourdough via a three-stage fermentation process for 42 hours. The numbers of yeast (2.1×10⁸ CFU/g) and lactic acid bacteria (1.3×10⁸ CFU/g) in sourdough increased gradually with repeated fermentation. We also confirmed that the GABA and polyphenol contents of sourdough significantly increased during fermentation. Thus, sourdough enriched with GABA could be rapidly and easily obtained through a three-stage natural fermentation process using rice bran and raisin. These findings also provide useful information for the effective use of milling rice by-products.