The continued exploration of the diversity of lactic acid bacteria in little-studied ecological niches represents a fundamental activity to understand the diffusion and biotechnological significance of this heterogeneous class of prokaryotes. In this study, Lactiplantibacillus plantarum (Lpb. plantarum) strains have been isolated from Tunisian vegetable sources, including fermented olive, fermented pepper and from dead locust intestines, subsequently evaluated for their antimicrobial activity against foodborne pathogenic bacteria, including Escherichia coli O157:H7 CECT 4267 and Listeria monocytogenes CECT 4031, as well as against some fungi, including Penicillium expansum, Aspergilus niger and Botrytis cinerea. In addition, their resistance to the oro-gastro-intestinal transit, aggregation capabilities, biofilm production capacity, adhesion to human enterocyte-like cells and cytotoxicity to colorectal adenocarcinoma cell line were determined. Further, the adhesion to tomatoes and the biocontrol potential on this model food matrix were analyzed. It has been found that all the strains were able to inhibit the indicator growth, mostly through organic acids production. Besides, these strains showed promising probiotic traits, including in vitro tolerance to oro-gastrointestinal conditions, adhesion to abiotic surface and to Caco-2 cells. Moreover, all tested Lpb. plantarum strains were able to adhere to tomatoes with similar rate (4.0-6.0 LogCFU/g tomato). The co-culture of LAB strains with pathogens on tomatoes showed that Lpb. plantarum could be a good candidate to control pathogen growth. Nonetheless, further studies are needed to guarantee their use as probiotic strains for biocontrol on food matrices.

The use of Lactic Acid Bacteria (LAB) for probiotic enrichment of minimally processed fruit is a well-established practice in literature. In addition, several LAB demonstrated a strain-specific ability to control harmful microorganisms and decay agents, improving shelf-life, maintaining quality and promoting the safety of fruits and vegetables. Edible coatings can help modulate phenomena of gas exchange and water loss by fruits, representing protection from physical damage and spoilage phenomena linked to oxidation and the development of undesired microorganisms. At the same time, the coating can represent an innovative delivery matrix for the LAB strains of potential interest to improve safety and quality in the postharvest management of fruits. In this work, five Lactiplantibacillus plantarum strains, previously characterized for their probiotic and antifungal activity, have been incorporated into a sodium alginate coating to develop edible probiotic coatings with antifungal properties for table grapes cv. Italia. The transfer of probiotics and their survival were evaluated by comparing coated and uncoated table grapes during 14 days of cold storage at 4 °C. The alginate edible coating increased the number of probiotics transferred to the surface of the berries from about 5 to more than 7 Log CFU/g, with a crucial impact on the potential functional attributes of the final product. The ability of the functionalised coatings to counteract the decay development was evaluated on table grapes berries artificially contaminated with Aspergillus niger CECT 2805. A significant reduction of lesion diameter was observed in alginate coating with L. plantarum 11-A. The lesion diameter reduction was also accompanied by the reduction of the symptoms of infection, such as browning around the wound. These results suggest the application of selected strains of L. plantarum as promising bio-resources to enhance the overall value of ready-to-eat fruits and vegetables, particularly in combination with edible coating as a carrier matrix. While a strain-dependent effect was not detected with respect to the improvement of the number of cells in the edible coating, a variability depending on the biotype used was detected for the properties linked to biocontrol, suggesting that the inclusion in edible packaging may represent an innovative criterion in the selection of lactobacilli to be applied postharvest.