Effect of sodium alginate coatings enriched with α-tocopherol on quality of fresh walnut kernels

Abstract

Lipid oxidation of unsaturated fatty acids is the main cause of quality reduction in nuts. To protect the quality of walnut kernels, edible coatings play an important role. Fresh kernels were coated with sodium alginate added with α-tocopherol at concentrations 0.25, 0.5 and 0.75% (w/v) and assessed for moisture content, weight loss percentage, firmness, oxidative stability, nutraceutical potential, color and microbial stability. The results showed that coatings significantly reduced weight loss percentage (20.17 to 11.88 %), peroxide value (2.5 to 1.84 meq o2 /kg), free fatty acid content (1.4 to 0.9 % oleic acid) and microbial count (3.2 to 1.9 log cfu/g) compared to control. In addition, coatings effectively retained total phenolic content (0.88 to 1.07 GAE g−1), DPPH radical scavenging activity (60.13 to 75.12%) and maintained firmness (1.8 to 2.5 N). Alginate enriched emulsion coatings preserved the kernel pellicle color (L* and b*) value and presented high overall acceptable score than the control. Therefore, it is determined that sodium alginate enriched with antioxidants coating could be used as a natural preservative coating material to maintain the postharvest quality of fresh walnut kernels.

Keywords

• Walnut kernels
• Coatings
• Tocopherol
• Peroxide value
• Firmness
• Shelf life