Increase of walnuts' shelf life using a walnut flour protein-based edible coating

Abstract

The present study aimed to improve walnut quality during storage. An edible coating was developed from defatted walnut flour and applied to the surface of walnut kernels, which were subsequently stored at 40 °C for 84 days along with walnuts coated with methylcellulose and uncoated kernels. On day 84, the walnuts coated with the walnut flour coating presented the lowest oxidized (13.33) and cardboard (34.73) flavors, the highest walnut flavor (72.27), the highest carotenoid (2.01 mg/kg) and γ-tocopherol contents (306.78 mg/kg) and the least deterioration of oleic/linoleic fatty acids ratio. Furthermore, the kernels covered in this coating displayed higher overall consumers' acceptance than those covered with methylcellulose (5.31). The methylcellulose and walnut flour coatings also prevented against polyunsaturated fatty acids’ deterioration, while walnuts coated with methylcellulose displayed a better behavior for peroxide value. Both coatings protected walnuts against the deterioration processes. Walnut flour coating could be used as a natural alternative to prolong the shelf life of walnut kernels, without the introduction of allergens nor synthetic compounds in this food product.