Effect of metal complex with chitosan on preservation quality and degradation of organophosphorus pesticides in Chinese jujube (zizyphus jujuba Mill. cv. Dongzao)

Abstract: The effects of a novel complex of zinc (II) and cerium (IV) with chitosan film-forming material on the preservation quality of Chinese jujube fruits (Zizyphus jujuba Mill. cv. Dongzao) and degradation of organophosphorus pesticides in the fruits during room temperature storage were investigated. The research was aimed at prolonging the shelf life of Chinese jujube fruits, reducing the economic losses due to jujube rotting caused by its physiological properties and characteristics of high respiratory intensity and high water content, and improving the edible security of Chinese jujube fruits. The results showed that the quality of Chinese jujube fruits treated with chitosan film-forming material bonding with zinc (II) and cerium (IV) were better than the control and chitosan film-forming material during the storage time. After 18 days of storage, the weight loss, respiratory intensity, and polyphenol oxidase (PPO) activity of fruits treated with the metal complex were 11.69%, 31.29%, and 7.07% lower than the control, which were 6.17%, 13.27%, and 6.57% lower than the chitosan film-forming material, respectively (p<0.05). Furthermore, total soluble solids, ascorbic acid, and polyphenol contents were 10.45%, 12.35%, and 16.1% higher than the control, which were 8.94%, 9.48%, and 19.70% higher than the chitosan film-forming material, respectively (p<0.05). The degradation rates of chlorpyrifos were increased to 97.31% for the complex treatment, which were 30.18% and 17.26% higher than the control and the chitosan film-forming material, respectively (p<0.05). The relatively regular crystal structure of chitosan had very important effects on the film-forming materials' ventilation property and using performance for chitosan and the complex with zinc (II) and cerium (IV). The complex with zinc (II) and cerium (IV) showed better performance than chitosan. The reasons were as follows: first, the structure of the chitosan coordinated with zinc (II) and cerium (IV) was changed, so the complex had more superiority in inhibiting the respiration intensity, lowering the metabolic rate, maintaining a relatively stable acidic internal environment and higher soluble solids content, reducing the degradation rate of vitamin C and the quick consumption of respiratory substrate, the suitable micro-controlled atmosphere environment passivated polyphenol oxidase activity, and reduced the loss of polyphenol contents in jujube fruits; second, zinc (II) and cerium (IV) has the function of scavenging harmful free-radicals in fruits, protecting vitamin C from oxidational losses; this is probably another reason for the better performance of the complex. TOC and GC-MS analysis showed that 3,5,6-trichloro-2-pyridinyl and 3,5,6-trichloro-2-pyridyl alcohol were the main intermediate products, and PO43-, NO3-and Cl- were the main ultimate products in the degradation of Chlorpyrifos by the metal complex, which would not lead to the accumulation effect of the toxic intermediate product by the degradation pathway of oxidation and hydrolysis effect. This article could provide a theoretical basis for the post-harvest preservation technique of Chinese jujube fruits, and for the practical application of metal complex with chitosan in the degradation of organophosphorus pesticides.