Dynamics changes of nutrients, flavor compounds, and beneficial microorganisms during Jianshui stinky tofu fermentation

Introduction Traditional stinky tofu is predominantly produced via open fermentation, which is highly susceptible to environmental fluctuations. This leads to inconsistent product quality and severely restricts its industrial development and market promotion. This study aimed to systematically investigate the dynamic changes in basic physicochemical parameters, free amino acids, and volatile flavor compounds during the solid-state fermentation of Jianshui stinky tofu, to provide a scientific basis for its production quality control. Methods We monitored the fermentation process of Jianshui stinky tofu and analyzed key quality indicators including titratable acidity, protein content, amino acid nitrogen, total polyphenols, and total flavonoids. Free amino acid profiles were determined using high-performance liquid chromatography (HPLC), and volatile flavor components were identified via headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). Dominant microbial strains were isolated and identified through morphological observation and molecular biological methods. Results During fermentation, titratable acidity increased to 0.80 g/100 g, while crude protein content decreased by 15.04%, and total amino acid nitrogen increased 4-fold due to continuous microbial metabolism. The bioactive components were significantly enhanced: total polyphenol and total flavonoid contents increased by 29.84% and 162.02%, respectively. Total free amino acids reached 402.07 mg/100 g, with essential amino acid content increasing 6-fold, indicating that fermented stinky tofu had significantly improved nutritional value and was more easily digestible. A total of 53 volatile flavor components were identified, with both the number and concentration of volatile compounds increasing markedly after fermentation. Ketones and heterocyclic compounds were the main contributors to the characteristic flavor of stinky tofu. Notably, phenol content was significantly higher than in other fermented soybean products, which was identified as the key substance forming its unique aroma. A high-protease-producing strain was isolated and identified as Mucor circinelloides . Discussion This study systematically revealed the dynamic changes in quality and flavor formation during Jianshui stinky tofu fermentation. The findings provide a theoretical foundation for precise fermentation process control and the development of novel stinky tofu products.