Solid-state fermentation of corn gluten meal with Aspergillus oryzae 6002 enhances amino acid and dipeptide...

Corn gluten meal (CGM) is a protein-rich by-product of corn starch production that is primarily used as animal feed. In this study, we aimed to enhance the value of CGM while retaining its high-protein characteristics through solid-state fermentation (SSF) with Aspergillus oryzae 6002 to produce CGM koji. During Aspergillus-mediated SSF, the total amino acid content increased markedly, reaching 247.76 ± 0.60 μmol/g dry koji at 72 h. Notably, substantial increases in the free Asp and Glu were observed, although these amino acid residues are scarcely present in zeins, the major storage proteins of CGM. Additionally, γ-aminobutyric acid (GABA) accumulated to 18.38 ± 0.13 μmol/g dry koji at 48 h. These results indicate that SSF promotes protein biotransformation and metabolic conversion, leading to the generation of functional compounds, particularly GABA, whose level was comparable to that reported for GABA-rich plant-based products, as well as taste-active compounds such as umami-related Glu and Asp. Seventy-eight dipeptides accumulated during fermentation, with the total dipeptide content peaking at 49.3 μmol Ala-Ala equivalent/g dry koji at 24 h. Several of these dipeptides have been reported to possess bioactive properties. Although protein hydrolysis occurred during SSF, approximately 65 % of the initial protein content remained, indicating that CGM koji retained its protein-rich characteristics. Collectively, these findings demonstrate that the SSF of CGM with A. oryzae 6002 produces a novel material that retains a high protein content and accumulates functional amino acids and dipeptides, highlighting its potential as a value-added functional material.