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

Area of Science:

• Food Science
• Materials Science
• Agricultural Chemistry

Background:

• Walnut kernels are susceptible to oxidation during roasting, impacting quality.
• Walnut seed coats contain beneficial polyphenols like gallic acid.
• Chitosan is a biocompatible polymer suitable for edible coatings.

Purpose of the Study:

• To develop an edible chitosan-based coating incorporating walnut polyphenols.
• To enhance the oxidative stability and sensory quality of fresh walnut kernels during roasting.
• To evaluate the efficacy of gallic acid-loaded chitosan films.

Main Methods:

• Coating formulation using chitosan and walnut polyphenols (gallic acid, ferulic acid, ellagic acid).
• Characterization of film properties using SEM, AFM, zeta potential, contact angle, and water vapor permeability.
• Analysis of chemical interactions using FTIR and UV-Vis spectroscopy.
• Assessment of thermal stability via DSC and TGA.
• Evaluation of oxidative stability by measuring peroxide and acid values in coated and uncoated walnuts.

Main Results:

• Gallic acid-loaded chitosan films showed uniform, rough morphology with improved stability (36-41 mV).
• Films exhibited superior wettability (21.45°) and low water vapor permeability (2.87 × 10⁻³ g/(mm∙h∙kPa)).
• Coated walnuts demonstrated significantly reduced oxidation (peroxide value: 0.04 g/100 g; acid value: 0.5 mg/g).

Conclusions:

• Edible chitosan coatings incorporating walnut polyphenols effectively improve walnut kernel quality during roasting.
• Gallic acid-loaded chitosan coatings provide enhanced oxidative stability and adhesion.
• This approach offers a natural strategy for preserving walnut quality.