Pistachio is one of the most popular nuts globally (Wu & Xu, 2020) grown in different countries such as Iran, the USA, Turkey, Syria, Italy, and Greece (Catalán et al., 2017). It contains high amounts of phenolic compounds with unique efficiency and high antioxidant potential (Wu et al., 2018). However, this valuable product is very susceptible to rancidity and molds' contamination (Holakouie Naieni et al., 2020).Contamination by storage pests is a significant problem faced with this product. Mold contamination in crops leads to the formation of critical secondary metabolites named mycotoxins, which are secondary metabolites of different fungus including Aspergillus flavus, Aspergillus parasiticus, Aspergillus tamarri, Aspergillus bombycitts, and Aspergillus nomius. These funguses produce different aflatoxins including B1, B2, G1, and G2. The metabolites mentioned above increase the risks of cancer and mutation in humans and animals (Ortega-Beltran et al., 2019).

Pistachio is a nut with high consumption that can be affected by aflatoxin contamination. Regarding influence of this fungus on global trade, broad studies in this area seem to be necessary. In this research, pistachio nuts were coated with methyl cellulose at different concentrations of 0.1%, 0.5%, 1%, and 2% by immersion method. Samples were stored in an incubator (25°C) for 4 months. Imaging was performed by electron microscope using SEM method and chemical changes (moisture, iodine, peroxide, and acidic value) were investigated during storage periods. Results showed that variations in storage time and methyl cellulose concentration had significant effect on moisture content and peroxide value (P < 0.05). Also, in case of acidic value, a significant difference was observed between treatments so that pistachio at concentration of 2% showed the highest acidic value. The highest iodine value loss was related to a concentration of 0.1% and the lowest value was observed in the control sample.