Effect of chitosan coating with different molecular weights and concentrations on oxidation activity in the pistachio nut

Iran is one of the largest pistachio producer and exporter in the world. Under unfavorable conditions during storage, pistachio quality will be reduced due to undesirable reactions. This study was conducted to evaluate the influence of chitosan coating with different molecular weights and concentrations on oxidation activity in the Akbary variety of pistachio nuts. Therefore, using acetic acid as 1% (v/v), chitosan with low molecular weight (LMC) and medium molecular weights (MMC) at concentrations of 0.5%, 1% and 1.5% V/W were prepared and pistachios were coated by them. In order to prepare control group, coating was performed with water and acetic acid as 1% V/V. Coated pistachios were packed in polyethylene bags and kept at room temperature and relative humidity (25-27 °C and 35-45%) for six months. Samples were examined every two weeks for peroxide and thiobarbituric acid value during storage. The results showed that during storage, chitosan coating reduced the rate of oxidation significantly (P <0.05). The LMC exhibited higher anti- oxidant activity than MMC and increased concentration correlated with higher antioxidant activity. The thiobarbituric acid value of pistachios was always zero due to non-formation of secondary compounds of oxidation reactions. In this research, LMC was found appropriate edible coating material for pistachio nuts.