High-cell-density culture enhances the antimicrobial and freshness effects of Bacillus subtilis S1702 on table grapes (Vitis vinifera cv. Kyoho)

•High cell density culture (HC) improves antimicrobial activity of B. subtilis.•HC’s supernatant suppresses fungal growth on grapes and maintains grape quality.•HC of B. subtilis enhances the secretion of antifungal cyclic lipopeptides.•HC enriches iturins and surfactins rather than fengycins. This study investigated the effects of Bacillus subtilis grown in high-cell-density culture (HC) on mold growth suppression and postharvest quality improvement in Kyoho grapes. The HC supernatant (HS) of B. subtilis was more potent than the conventional B. subtilis culture supernatant (CS) in suppressing fungal growth on grapes. Specifically, HS was more effective than CS in maintaining the cosmetic qualities (colour, firmness and abscission rate) and physiological indices (respiration, weight loss, pectinases, antioxidant enzymes and titratable acidity). Chemical analyses showed that HC enhanced the secretion of lipopeptides in B. subtilis culture, and high-pressure liquid chromatography further demonstrated that iturin A and surfactin were increased by 1.78- and 1.23-fold in HS compared with CS, respectively. However, LC-MS/MS analysis revealed that HC only upregulated iturins and surfactins, but not fengycins. Therefore, HC may provide an effective method to enrich antifungal lipopeptides from B. subtilis for preservation of fruits and vegetables.