Structural reconfiguration of fig pectin by microbial fermentation: Dual modulation of pulp rheological behavior and...

Pectin serves as the primary polysaccharide in fig pulp, with its structural characteristics significantly influencing the pulp's rheological and functional properties. This study compared two fermentation strategies: mixed fermentation with Torulaspora delbrueckii (0.3 g/L) and Lactiplantibacillus plantarum 90 (1% v/v) at 30 °C, and pure fermentation using only T. delbrueckii at the same inoculum level at 20 °C. Both treatments were conducted for 72 h, with uninoculated pasteurized fig pulp as the control. After fermentation, water-soluble pectin (WSP), chelate-soluble pectin (CSP), and sodium carbonate-soluble pectin (NSP) were sequentially extracted from the pulp. In unfermented pulp, the degrees of esterification of WSP and CSP were 62.39 ± 0.96% and 60.62 ± 1.31% (n = 3), respectively, classifying both as high methoxyl pectin. The WSP content was the highest, reaching 427.98 ± 9.61 mg/100 mL (n = 3). Fermentation significantly enhanced pectin methylesterase activity, which promoted pectin depolymerization and conversion. These changes in pectin structure influenced fig pulp quality through distinct pathways. Pure fermentation markedly reduced the pulp viscosity by decreasing the viscosity of WSP. In contrast, mixed fermentation improved the antioxidant activity of pectin by increasing rhamnose and arabinose content and raising the proportion of the RG-I region, while simultaneously reducing xylose content and the HG region ratio. These structural modifications ultimately enhanced DPPH (IC₅₀: 11.62 ± 0.69 mg/mL, n = 3) and hydroxyl radical (IC₅₀: 6.24 ± 0.26 mg/mL, n = 3) scavenging activities and FRAP (2.75 ± 0.29 mmol TE/L, n = 3) of fig pulp.