Physically crosslinked polyphenol-chitosan edible coating for the application of walnut kernels during roasting

This study developed an edible chitosan-based coating incorporating the main polyphenols from walnut kernel seed coats (gallic acid, ferulic acid, and ellagic acid) to enhance the oxidative stability and sensory quality of fresh walnut kernels during roasting. SEM and AFM analysis revealed that gallic acid-loaded chitosan films exhibited a uniform yet rough morphology, while zeta potential measurements (36-41 mV) confirmed improved film stability. The gallic acid-loaded film demonstrated superior wettability (contact angle: 21.45°) and low water vapor permeability (2.87 × 10^-3 g/(mm∙h∙kPa)), ensuring strong adhesion. FTIR and UV-Vis analyses confirmed hydrogen-bonded crosslinking between polyphenols and chitosan. Thermal stability increased, with DSC and TGA peaks at 181.97 °C and 343 °C for the gallic acid-loaded film. Coated kernels exhibited significantly lower oxidation, with peroxide and acid values (0.04 g/100 g, 0.5 mg/g) outperforming uncoated samples. These findings suggested that gallic acid-loaded chitosan coatings effectively improve walnut kernel quality during roasting.