Gardenia fruit, a medicinal and edible resource rich in bioactive compounds, faces several limitations, including low extraction efficiency, poor stability, and intense bitterness. In this study, gardenia fruit powder at varying concentrations (2.5%, 5.0%, 7.5%, 10.0%, and 12.5%) was mixed with a kombucha inoculum and fermented for 8 days to develop functional beverages. The results demonstrated that fermentation with gardenia fruit powder effectively supported SCOBY growth. The 5.0% addition of gardenia fruit (G5Fer) produced thicker bacterial cellulose, higher total titratable acidity (10.43 g/L), and increased total polyphenols (37.12 mg GAE/100 mL) after 8 days of fermentation. G5Fer also achieved the highest sensory scores, especially in aroma, flavor, and overall acceptance. Higher doses of gardenia fruit (≥7.5%) caused turbidity, dark color, and strong sourness, leading to lower sensory scores. Non-targeted metabolomics revealed that kombucha fermentation reshaped the metabolic profile, enriching phenolic acids (e.g., gallic acid and caffeic acid) and flavonol glycosides (e.g., kaempferol-3-O-rutinoside) via the biosynthesis of phenylpropanoid pathways while antioxidant activity (DPPH and ABTS⁺ scavenging rate) was well maintained. Overall, G5Fer achieved the best balance among acidity, bioactive compounds, and consumer preference. In conclusion, gardenia fruit represents a promising substrate for developing a functional, palatable kombucha-like beverage, aligning with the growing demand for value-added fermented products.

Freeze-thaw (FT) cycles cause structural deterioration of maize starch (MS), accelerating starch digestibility and glycemic responses. This study investigated whether crimson snapper fish scale peptides (FSP) could modulate MS structure to reduce digestibility during FT cycles. FSP inhibited ice recrystallization and preserved bound water while suppressing free water increase. After three FT cycles, amylose content in MS-8FSP remained at 24.17% while 28.17% in MS, while Mw was unchanged. Hydrophobic interactions dominated FSP-starch binding, though hydrogen bonds weakened during freezing. SEM, XRD and DSC showed that MS-8FSP formed compact lamellar networks, with relative crystallinity increasing to 5.29% and Peak II enthalpy recovered after three FT cycles. Consequently, FSP reduced rapidly digestible starch and estimated glycemic index (MS-8FSP: 69.22; MS: 92.06). Pearson correlation analysis revealed that FSP binding and non-covalent bonds were negatively correlated with rapidly digestible starch and estimated glycemic index, whereas water permeability was positively correlated with both. In vivo, MS-8FSP significantly attenuated postprandial glucose responses in mice, with lower AUC than MS across all FT cycles. These findings suggest that FSP enhances starch FT stability and reduces digestibility, offering a promising ingredient for frozen starch-based foods with reduced glycemic potential.