UV-A Light and Heat-Activated Poly(Lactic Acid) Composite with Chitosan: Effect on Bacterial Reduction and Vitamin C Preservation

This study investigates the effectiveness of biodegradable composites of poly(lactic acid)-chitosan (PLA-CHI) combined with UV-A light or mild heat (50 °C) treatments for controlling microbial contamination while maintaining nutrient quality in apple juice. PLA-CHI significantly decreased the microbial load of the bacterium Listeria innocua, achieving reductions of up to 99.9974% (4.59 log reduction) under mild heat and 99.9968% (4.49 log reduction) under UV-A irradiation. Kinetics revealed faster bacterial inactivation when PLA-CHI was present, suggesting an enhanced effect with the other treatments. Scanning electron microscopy showed severe cellular damage, including membrane disruption, cell shrinkage, and leakage of intracellular material, confirming the effectiveness of combined treatments. Surface analyses showed PLA-CHI maintained its structural integrity when exposed to the treatments, though topographical changes increased hydrophilicity and amine group exposure, possibly contributing to greater bactericidal effects. Vitamin C analyses indicated significant photodegradation (~ 33%) following UV-A light exposure, with PLA-CHI slightly accelerating initial degradation but not significantly contributing to overall reduction. Vitamin C was better preserved with mild heat treatments (~ 85% retention), with additional degradation from PLA-CHI being marginal. The integration of PLA-CHI with UV-A or mild heat offers effective antimicrobial activity while preserving nutritional quality. Given its biodegradability, structural stability, antimicrobial effectiveness, and minimal impact on nutrient quality, PLA-CHI presents a feasible and sustainable option for food-packaging applications.