Study of the effect of sodium alginate coating containing pomegranate peel extract on chemical, sensory and microbial quality of walnut kernel

Background: Due to the adverse effects of artificial preservatives on food and its harmful effects on human health, researchers have been considering replacing these materials with natural substances. In this study, the effect of pomegranate peel extract (PPE) on the stability and antifungal activity of the walnut kernel was studied. Methods: The pomegranate peel was extracted by the solvent and water-solvent method. The extracted sap was evaluated using the antioxidant assay by 2,2-diphenylpicrylhydrazyl (DPPH) assay. The results showed that the extracted sap had 40.11 mg/g dry phenol and 47.27% free radicals scavenging. Four concentrations (0%, 2%, 6%, and 10%) of pomegranate liquid extract were prepared and studied for 90 days for the walnut kernel coating. Walnut kernels were coated on days 1, 15, 30, 60, and 90, and examined for moisture, acidity, peroxide, conjugated diene, and anisidine tests. Data were analyzed using SPSS version 21. Results: By increasing the extract concentration from 2 to 10%, the stability of the walnut kernel during storage was increased. Acidity in the samples with 10% PPE coating, decreased from 0.18 to 0.11 on the first day until the 15th day, and increased to 0.48 from day 15 to 90. The results showed that the moisture content and acidity increased with increasing the extract concentration. By increasing the extract concentration up to 10%, the sustainability indices, including peroxide, anisidine, and conjugated diene were significantly decreased. At 90 days, by increasing the concentration of pomegranate extract from 2% to 10%, the count of molds and yeasts was reduced from 3.59 to 2.29 CFU/g. The count of molds and yeasts in the uncoated samples was 5.81 CFU/g. Conclusion: According to the results, PPE can increase the stability and antifungal activity of walnut, therefore, the health quality of the product increases.