Changes in Proteins during Nyufu Production

The aging rate of fungi-inoculated tofu was found to be 34.5% and that of 1-month-old and 3-month-old nyufu fermented milk 56.2% and 71.4%, respectively. The quantity of free amino acids in nyufu increased to approximately 10 times the level in fungi-inoculated tofu. Because solubilization of protein was shown to be associated with the duration of nyufu aging, changes in the molecular weight of the water soluble nitrogen fraction were assessed using HPLC gel filtration chromatography. Almost no peptides with a molecular weight over 5000 were found in the 3-month-old nyufu; approximately 57% had a molecular weight of 1800, and 38% existed at peaks below a molecular weight of 255, indicating a decreased molecular size and a noticeable difference in molecular weight distribution. Water soluble peptides were separated into acidic, basic, and neutral fractions. The neutral fraction had the highest score of sensory evaluation. The concentration of glutamic acid and aspartic acid was high in neutral and acidic fractions, reflecting the palatability. Approximately 50 of the peptide chromatograms were detected in peaks 2 and 3 of the neutral fraction, which was high in the sensory evaluation. This agreement between the sensory evaluation results and chromatographic analysis indicates that peptides influence the taste of nyufu.