Correlation Between Protein Hydrolysates and Color During Fermentation of Mucor-Type Douchi

The correlations between the color of douchi and different protein hydrolysates from the post-fermentation period were analyzed. The results showed that peptides had the highest correlation with the color change, while free amino acids were second, which indicated that peptides and free amino acids were more involved in the Maillard reaction. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the 7S component may be more involved in the Maillard reaction during the pre-fermentation of douchi, and that 11S subunits may be more involved in the formation of melanin in the initial stage of post-fermentation. The water-soluble extracts of two douchi samples in the most rapid formation stage of melanin were analyzed by reversed phase-high performance liquid chromatography. The results showed that the hydrophilicity of hydrolysates decreased depending on color. Meanwhile, the amino acid analyses demonstrated that the four amino acids with the maximum loss ratios were all hydrophilic in this stage, which indicated a loss in the hydrophilic components due to their involvement in the Maillard reaction.