Probiotic Lactiplantibacillus plantarum strains showing anti-Botrytis activity: A food-grade approach to improve the overall quality of strawberry in post-harvest

Strawberry is a highly perishable soft fruit susceptible to microbial contaminations, with Botrytis cinerea among the main spoilers in post-harvest. Lactic Acid Bacteria (LAB) are well-known food-grade bacteria, usually employed in food fermentation for their protechnological and probiotic properties. Moreover, LAB strains are also used as biocontrol agents for their ability to synthesise antimicrobial metabolites. However, applications of selected LAB to improve the overall quality in the fruit sector are still underexplored. In this study probiotic Lactiplantibacillus plantarum strains showing anti-Botrytis activity were grown in strawberry juice (SJ). Probiotics were transferred to strawberries through dipping in fermented SJ, and the impact of the carrier matrix on their survival was evaluated in a simulated oro-gastrointestinal model. The best candidates were selected to investigate the postharvest quality of strawberries at different levels including functional (i.e., viability of probiotics at the end of the shelf life); safety (i.e., ability to control the growth of foodborne pathogenic bacteria); shelf life (i.e., biocontrol of B. cinerea); nutritional and sensory. The probiotic survival under simulated gastrointestinal conditions was up to 2.5 Log higher when strawberry was used as carrier. In co-inoculation assays on strawberries, L. plantarum 11 A and CB56 were able to reduce the growth of Listeria monocytogenes and Escherichia coli of about 1 Log after 7 days of cold storage. Moreover, live L. plantarum were able to control the growth of B. cinerea of about ten and five folds for strain 11 A and CB56, respectively, and a lower bioprotective effect was detected on strawberries dipped in the cell-free SJ fermented by L. plantarum 11 A. No significant effect was observed in terms of the main nutritional compounds, while improved descriptors related to the appearance of the fruit were observed. Therefore, this study allows us to elucidate the potential of selected LAB strains to improve the overall post-harvest quality of strawberries by using a thorough food-grade approach.