Research noteInhibitory effect of soy protein coating formulations on walnut (Juglans regia L.) kernels against lipid oxidation

The aim of this study was to improve the fat stability in walnut (Juglans regia L.) kernels using an edible coating treatment. Coating solutions were composed of soy protein isolate (SPI), carboxymethylcellulose (CMC) and catechin (CT). Walnuts were dipped in coating solution, dried and stored under abuse temperature condition (35 °C) for 21 days. Lipid oxidation was evaluated by peroxide and thiobarbituric acid reactive substance (TBARS) measurements. Results showed a slight decrease in peroxide values (POV) and a significant reduction of TBARS by coating treatment. The SPI-CT and SPI/CMC-CT coatings were the most effective and decreased the POV by 27 and 31%, respectively, as compared to uncoated walnut after 21 days. The SPI-CT and SPI/CMC-CT coatings also decreased the TBARS value by 16 and 26%, respectively. The incorporation of CT in SPI-based coatings resulted in a synergistic effect on the lipid oxidation preservation. The results of this study show that soy protein-based coating could be a good carrier for antioxidant molecules, and an effective preservative method for extending shelf life and improving the quality stability of oxidation-sensitive kernels.

► Soy protein-based edible coating treatment decreases lipid oxidation of walnut kernels. ► Catechin in soy protein coating formulation shows a synergistic effect on lipid oxidation of walnuts. ► Soy protein-based coating will be a good carrier for antioxidant molecules. ► Proposed coating formulation will be an effective preservative method for improving the quality stability of walnuts.