To investigate the pattern of quality formation and its correlation with microbial community succession during the spontaneous fermentation of chili pepper, this study combined targeted metabolomics and high-throughput sequencing to analyze the changes in key quality indicators and microbial community structure in chili pepper after 0, 3, 10, 20, and 30 days of fermentation. The results showed that as fermentation progressed, pH decreased significantly, total acid content increased, and nitrite content initially increased and subsequently decreased, which remained within the safety range throughout the process. The 10-day fermented sample had the highest sensory score, exhibiting optimal aroma complexity and taste harmony. The content of total organic acids increased, with lactic acid gradually becoming the dominant organic acid. Aspartic acid was found to be the free amino acid that contributed most to the overall flavor. A total of 19 key aroma-active compounds (odor activity value > 1) were identified, the main ones being alcohols, esters, and aldehydes. Significant microbial community succession occurred, with Weissella being the dominant bacterial genus. In the early fermentation stage, the fungal community was dominated by Debaryomyces and Hanseniaspora, which were subsequently replaced by Pichia in the mid-to-late stages. Redundancy analysis (RDA) revealed that pH and total acid were key factors driving microbial community succession, and correlation analysis showed a significant positive association between Weissella and nerol synthesis. This study reveals the intrinsic relationship between microbial community succession and quality formation in spontaneously fermented chili pepper, providing a theoretical basis for the screening of dominant fermentation strains (such as Weissella) and the precision regulation of the fermentation process.

The polysaccharide purified from Undaria pinnatifida Suringar was phosphorylated using phosphate as a crosslinking agent. The structure of the phosphorylated polysaccharide was characterized by ultraviolet (UV) absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), periodate oxidation and Smith degradation, Congo red test, β-elimination reaction, and iodine-potassium iodide test, and the free radical scavenging capacity and hypoglycemic activity of the raw and modified polysaccharide were evaluated. The results showed that the substitution degree of phosphate was 9.26, and the characteristic absorption peaks of P=O and P–O–C appeared at 1216 and 886 cm^-1, indicating that the phosphorylation modification was successful. The maximum relative molecular mass of the phosphorylated polysaccharide was 94.4 × 10³. It had a triple-stranded helical structure and was composed of glucopyranose unis linked together by β-glycosidic bonds. The polysaccharide and amino acids were linked together mainly by –O– glycopeptide bonds. The main linkages between monosaccharides were 1→3, 1→2,1→4 and 1→6 glycosidic bonds, the molar ratio was 0.494:0.504:0.002, and the sugar chain had a branched structure. The scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical, superoxide anion radical (O₂^-·) and hydroxyl radical (·OH) and the α-glucosidase inhibitory activity of the polysaccharide were significantly increased by 34.76%, 12.30%, 76.05% and 3.70% after the phosphorylation modification (P < 0.05), indicating that phosphorylation modification enhanced the free radical scavenging capacity and hypoglycemic activity of the polysaccharide from Undaria pinnatifida Suringar.