Preventing microbe colonization on avocado ( var. ) through metabiotic treatment, a promising postharvest safety improvement.

INTRODUCTION

Lactic acid bacteria (LAB) produce various metabolites (i.e. metabiotics) with inhibitory capacity towards harmful foodborne pathogens.

METHODS

This study aimed to design several antimicrobial formulations based on metabiotics obtained from different native LAB species ( UTNGt5, UTNGt28, and UTNGt21O) and to detect the possible mode of action towards two multidrug resistant spp. strains isolated from avocado ( var. ) fruits. Additionally, the formulation with the highest inhibitory activity was tested on avocados at the immature (firm) ripeness stage to evaluate their effect on microorganisms' growth and fruit quality attributes post-harvest.

RESULTS AND DISCUSSION

Out of the top five formulations showing the highest bactericidal effect at their minimum inhibitory concentration (1 x MIC) on both spp. targets one candidate annotated P11 (consisting of UTNGt21O and UTNGt28; 1:3, v/v) was selected. Co-cultivation of strains with P11 formulation results in cell viability reduction by 98%, by impairing the integrity of the cell membrane inducing cytoplasm molecule content leakage, protein profile changes, and finally bacterial death. Even though the total coliforms, spp., r spp., molds, and yeasts counts were not fully eliminated by day 13 of storage, a statistically significant reduction ( < 0.05) in viable cell counts were observed by day 8 upon the P11 treatment compared with non-treated control (C) and treated with a commercial disinfectant (T1) samples, suggesting that P11 formulation inhibited microbial colonization during storage. Likewise, no visible dark spots were observed on the mesocarp (pulp) upon the treatment with P11, whereas T1 and C fruits showed greater dark spots on the pulp as indicative of damage. The quality attributes, such as pH, total soluble solids, total titratable acidity, antioxidant capacity, and total polyphenol content, were not affected by the treatment. Principal Component Analysis (PCA) conducted on these five variables showed a clear separation of samples according to the maturity stage regardless of the treatment.

CONCLUSION

These results suggest that the active metabolites from LAB strains might create a barrier between the exocarp and mesocarp, inhibiting the microorganisms colonization, reducing fruit damage, and lengthening the fruit quality and safety after harvest.