Effect of combination of UV-A light and chitosan-gallic acid coating on microbial safety and quality of fresh strawberries

Strawberries can be contaminated by foodborne pathogens or mold on farm or during postharvest handling. Photo-irradiation of edible chitosan coating containing gallic acid can be an innovative antimicrobial intervention to improve the safety and shelf-life of strawberries. This study investigated antimicrobial activity of chitosan-gallic acid coating under 360 nm UV-A light. The thin layer of coating material allowed 80% of UV-A light transmission while blocking the majority of UV-C (200-280 nm) light. The formation of the coating layer was visualized by light and confocal microscopes. After 180 min exposure to UV-A, a 2.3 +/- 0.4 log reduction of E. coli O157:H7 on chitosan-gallic acid (CH-GA) coated strawberries was achieved, which were significantly (P < 0.05) higher than CH, GA, and CH-GA without UV-A (average 0.3-1.0 log reductions) and UV-A. This level of inactivation was also significantly (P < 0.05) higher than GA + UV-A treatment (1.2 +/- 0.4 log reductions), but not significantly different from (P > 0.05) CH + UV-A (1.8 +/- 1.0 log reductions) treatment. The photo-irradiated coating did not significantly (P > 0.05) alter the mold decay incidence (%) in strawberries. Additionally, the redness and yellowness values of CH-GA + UV-A treated berries (35.4 +/- 0.9, 22.0 +/- 1.0) were initially lower (P < 0.05) than the control (40.5 +/- 0.3, 26.1 +/- 2.6), and became comparable (P > 0.05) after 14 days of storage. Comparatively, their firmness values did not show differences (P > 0.05) throughout the storage. Findings demonstrated the potential for using photo-irradiated coatings to reduce food safety risk in strawberries.

Automated summary

This study investigated the antimicrobial activity of a photo-irradiated chitosan-gallic acid coating on strawberries. The coating was found to effectively reduce the presence of E. coli O157:H7 when exposed to UV-A light. Additionally, the coating did not significantly impact mold decay incidence but did slightly reduce the redness and yellowness of the strawberries, which returned to normal after storage.