Improving the Shelf Life of Peeled Fresh Almond Kernels by Edible Coating with Mastic Gum

Abstract

Coating, as a process in which fruits, vegetables, kernels, and nuts are covered with an edible layer, is an environmentally friendly alternative to plastic wrapping, which has been considered the most effective way to preserve them over the long term. On the other hand, prolonging the shelf life results in a reduction of spoilage and therefore achieving a goal that is very important nowadays—the reduction of food waste. The quality of preserved almonds kernels depends on factors such as grain moisture, storage temperature, relative humidity, oxygen level, packaging, and the shape of the stored nuts (along with being peeled, unpeeled, roasted, etc.). The commercial importance of the almond fruit is related to its kernel. Almonds that are peeled (without the thin brown skin) and stored have a shorter shelf life than unpeeled almonds since the reddish-brown skin, rich in antioxidants, may protect the kernels against oxidation. In this study, a bioactive edible coating has been tested, which may provide an effective barrier against oxygen permeation and moisture, thus preserving the quality of peeled fresh almonds by extending their shelf life. Mastic gum, as a natural coating agent, was used to coat the peeled fresh almond kernels in four different concentrations (0.5%, 1.0%, 1.5%, and 2.0% w/v). The effect of mastic gum coating on the quality parameters of the peeled fresh almonds (moisture uptake, oil oxidation, total yeast and mold growth, and Aspergillus species development) was studied during four months of storage. The results showed that mastic gum, as a coating agent, significantly (p < 0.05) reduced moisture absorption, peroxide and thiobarbituric acid indices, total yeast and mold growth, and Aspergillus species development in the peeled and coated fresh almonds, compared to the control, i.e., uncoated fresh almonds, during 4 months of storage, packed at room temperature (25–27 °C) inside a cabinet at 90% humidity. Therefore, mastic gum can be used as a great natural preservative coating candidate with antioxidant and antimicrobial effects.