壳聚糖金属配合物对冬枣保鲜作用及降解有机磷农药

为了降低由于冬枣腐烂造成的经济损失及提高冬枣食用安全性，该文研究了室温贮藏条件下壳聚糖锌(Ⅱ)、铈(Ⅳ)配合物对冬枣的保鲜作用，并探讨了其对冬枣表面有机磷农药的降解效果和机理。结果表明，在冬枣贮藏期间，壳聚糖金属配合物涂膜组处理的冬枣的质量损失率、呼吸强度和多酚氧化酶的活性均显著低于对照组，可溶性固形物、维生素C和多酚的质量分数均显著高于对照组，对有机磷农药毒死蜱的降解率显著高于对照组；总有机碳质量分数(TOC)、气相色谱-质谱联用(GC-MS)分析表明，壳聚糖金属配合物降解毒死蜱的中间产物主要为O,O-二乙基(3,5,6-三氯-2-吡啶基)、3,5,6-三氯-2-吡啶醇，最终降解产物为PO43-、NO3- 和Cl-，降解途径主要为氧化和水解作用，不会引起中间产物积累而导致二次污染。研究结果为冬枣的采后保鲜和壳聚糖金属配合物降解有机磷农药的实际应用提供理论依据。

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.