Effect of sourdough lactic acid bacteria fermentation on phenolic acid release and antifungal activity in pitaya fruit substrate

Natural preservation of bakery fruit fillings is less studied. In this study, 12 lactic acid bacteria (LAB) strains were screened for antifungal activity against 3 fungal strains; and used as starters in natural preservation of pitaya fruit substrate. Antifungal activity and antifungal phenolic acid (PA) metabolites released during fermentation were determined and quantified. Eight of twelve LABs with strong antifungal activity were selected. Higher antifungal activity observed in cell-free supernatant of L. plantarum and P. pentosaceus than L. pentosus after 3 and 5 days. Aspergillus niger and Cladosporium sphaerospermum were most sensitive, and Penicillium chrysogenum most resistant. Fermented fruit substrate model, fermentation conditions: F1 (30 °C, 24 h) and F2 (31.04 °C, 19.5 h) were used. LABs adapted to substrate as confirmed by low pH (3.37–3.74), TTA (6.2–9.9 mL) and microbial counts (2.65 × 107–9.8 × 108). Compared to control, phenolic content (0.98–1.87 μg/mL, GAE) was higher (p < 0.05); except BT 1–5 (P. pentosaceus) samples, all fermented samples had higher antifungal activity (higher value in F1 samples fermented by same LAB). RP-HPLC results showed presence of diverse antifungal PAs in fermented samples; only ferulic and p-hydroxybenzoic acid found in control. LAB fermentation of fruit substrate released antifungal PA from their precursors which acted independently or synergistically to inhibit fungal growth.