Effect of low-temperature fermentation on flavonoid biotransformation and in vitro colonic fermentation potential in a controlled dried citrus peel-gochujang matrix

Abstract

Dried citrus peel is rich in flavanone glycosides and polymethoxyflavones, yet their transformation in high-salt fermented sauce matrices remains insufficiently characterized. This study evaluated the effects of low-temperature fermentation on flavonoid biotransformation and in vitro colonic fermentation potential in a controlled dried citrus peel-gochujang matrix. A sterilized gochujang-based matrix containing dried citrus peel was divided into low-temperature fermentation (LT F; 10 degrees C), room-temperature fermentation (RT F; 25 degrees C), corresponding sterile controls, and an unfermented baseline. Fermentation dynamics, targeted flavonoid quantification, untargeted metabolomics, in vitro digestion, short-chain fatty acid (SCFA) production, and metabolite-function correlations were analyzed. Time-dependent changes in pH, acidity, reducing sugars, and viable counts confirmed active fermentation, with stronger acidification at 25 degrees C. At the endpoint, LT F retained more hesperidin than RT F (+ 34.73%, p = 0.0072), whereas hesperetin (− 32.56%, p = 0.000052), naringenin (− 31.55%, p = 0.0011), and ferulic acid (− 22.60%, p = 0.00075) were lower. Untargeted principal component analysis (PCA) showed only limited global separation among fermentation groups, and recomputed LT F versus RT F feature testing found no false discovery rate (FDR)-significant individual feature, supporting cautious interpretation. In vitro assays showed bioaccessibility and SCFA responses that differed between compounds and endpoints, with propionate lower in LT F than RT F. Overall, low-temperature fermentation reshaped flavonoid profiles in a controlled citrus peel-gochujang matrix without uniformly enhancing aglycone formation or colonic fermentation endpoints.