Microbial Succession and Functional Metabolite Formation During SCOBY Fermentation of Pomelo Peel Substrates

This study investigated the fermentation kinetics, microbial community succession, and potential functional metabolite formation in Symbiotic culture of bacteria and yeast (SCOBY)-mediated fermentation using pomelo peel substrates. Pomelo peel substrates were prepared using 1% and 6% (w/w) SCOBY combined with 10 g and 25 g pomelo peel and fermented at 30 °C for 25 days. The results showed that higher SCOBY inoculum significantly accelerated acid production, resulting in a rapid decrease in pH and an increase in titratable acidity. Total soluble solids continuously decreased due to microbial utilization of sugars. The highest lactic acid bacteria count (6.04 log CFU/mL) and total viable count (7.23 log CFU/mL) were observed in S6-P25 at day 25. Bioactive compound analysis revealed that total flavonoid content reached its maximum in S6-P25 at day 20 (15.34 ± 0.70 mg RE/g dry weight, DW), while the highest total phenolic content was found in S1-P25 (151.5 ± 1.29 mg GAE/g DW), suggesting that a lower SCOBY level may favor polyphenol production. Antioxidant activity (DPPH and TEAC) increased with fermentation time and was highest in S6-P25. Microbiome analysis demonstrated that Firmicutes was the dominant phylum, with Apilactobacillus ozensis accounting for 99% of the relative abundance, indicating strong microbial selection and its potential role in acid production and fermentation ability. This microbial structure was consistent with the improved fermentation performance and enhanced bioactive properties observed in the pomelo peel substrates. These findings highlight SCOBY fermentation as a promising biotechnological strategy for converting citrus processing by-products into fermented ingredients for food applications.