Dual Lactiplantibacillus plantarum-Derived Postbiotics Reduce Pathogens and Preserve the Quality of Goldenberry (Physalis peruviana L.) During Storage

Microbial contamination of fresh fruits remains a major food safety concern due to the ability of pathogenic bacteria to persist on fruit surfaces during storage. This study evaluated the antimicrobial efficacy of ExAF-E1, a postbiotic formulation derived from Lactiplantibacillus plantarum strains UTNGt28L and UTNGt2, against multidrug-resistant Escherichia coli L1PEag1 and Staphylococcus epidermidis L4MStp5 on goldenberry (Physalis peruviana L.). Fruits were artificially contaminated, treated, and stored for 7 days at room temperature (RT) and refrigerated (4 °C), with analyses conducted in quadruplicate. At RT, ExAF-E1 significantly reduced total aerobic counts (TAC) and pathogen loads (p < 0.05), achieving early reductions of ~0.4–0.5 log CFU/g in TAC and ~1.0–1.5 log CFU/g in pathogens, with inhibition maintained through day 7. In contrast, the commercial disinfectant (CD) showed transient reductions, with microbial levels not significantly different from the control at later stages (p > 0.05). Under refrigeration, ExAF-E1 produced greater and persistent reductions, reaching ~1.0–1.2 log CFU/g in TAC and ~1.5–2.5 log CFU/g in pathogens by day 7 (p < 0.05), whereas CD exhibited strong initial reductions followed by partial regrowth. Fruit quality parameters (pH, TA, TSS, TPC, AOX, AAC) were not significantly affected by treatments (p > 0.05). Ultrastructural analyses using transmission and scanning electron microscopy revealed disruption of bacterial cell envelope integrity, including membrane damage, cytoplasmic leakage, and morphological deformation. These findings demonstrate that ExAF-E1 provides rapid and sustained antimicrobial activity under both storage conditions while preserving fruit quality, supporting its application as a postharvest strategy for improving the microbial safety of fresh produce.