Effect of film-forming solution pH on the mechanical, barrier, and biological characteristics of chitosan/Piper betel L. leaf extract coating film for mango preservation.

The present work aimed to investigate the effect of film-forming solution pH on characteristics of chitosan (CH) - Piper betel L. leaf extract (PBe) coating films and their potential applications in mango preservation. The coating films were fabricated from CH-PBe solutions in the pH range of 3-5 using a solvent evaporation technique. The analysis results (DSC and FTIR) demonstrate higher miscibility, better compatibility, and tighter intermolecular interactions between CH and active compounds in the film matrix prepared at low pH. The mechanical and barrier properties of the CH-PBe film significantly decreased with increasing pH value. Varying the film-forming pH insignificantly affected the antioxidant activity and antibacterial inhibition against Staphylococcus aureus (Gram-positive) of the resultant films. However, Escherichia coli (Gram-negative) was less vulnerable to the blend film prepared at the higher pH medium. The coating solution at pH 4 proved suitable for preserving 'Tu Quy' mangoes, according to the observation of color changes, accumulated decay rate, respiration rate, ripening index, and other related factors. The findings of this work reveal the importance of pH control in producing CH-PBe coating films for mango preservation and provide more insights into pH-affected interactions between CH matrix and polyphenols in PBe.