Analysis of Umami Peptides Flavor Characteristics in Watermelon Soybean Paste Based on STC-1 Cell Taste Perception Model

Watermelon soybean paste, a local special food, is a traditional fermented soybean product in Henan, Anhui, and Shandong provinces. The fermentation process of watermelon soybean paste makes it an excellent source for umami peptide research due to the hydrolysis of proteins by microbial proteases, which generated abundant umami amino acids and peptides. In this study, three novel umami peptides (AKEKFD, LAELK, and LTFVER) purified from watermelon soybean paste were selected as research subjects to evaluate their taste characteristics. The mouse enteroendocrine STC-1 cell line was employed as a taste perception model to assess the effects of these peptides on intracellular calcium fluorescence signals, while quantitative real-time PCR was used to measure the mRNA expression levels of the umami receptor T1R1 and T1R3. The results showed that all three peptides elicited calcium ion fluorescence signal responses in STC-1 cells, with each response lasting approximately 1 min. Among them, 1.0 mmol/L LAELK induced the highest peak response. However, the umami-enhancing effects did not increase with the increase of peptide concentrations. Further investigation revealed that these peptides activated the umami receptors T1R1 and T1R3 and up-regulated their mRNA expression. Specifically, AKEKFD and LAELK significantly enhanced the mRNA expression of both T1R1 and T1R3, whereas LTFVER primarily increased the expression of T1R1. This study aimed to provide a theoretical foundation for understanding the umami mechanism of peptides, supporting their functional application and promoting the utilization of watermelon soybean paste.