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The study aimed to improve polysaccharide-based packaging to extend the shelf life of fresh produce; a composite film with antimicrobial function was developed and tested. The packaging film is a blend of agar, a film-forming substrate; carrageenan, as a reinforcing agent; glycerol, as a plasticizer; and Nisin, an antimicrobial agent. The film was evaluated for its antibacterial, mechanical, and barrier properties at different humidity levels, using fresh-cut watermelon as the test food material. The film effectively inhibited the growth of Staphylococcus aureus and Listeria monocytogenes. Under relative humidity of 20%, 50%, and 90%, the tensile strength of the antibacterial film containing 0.28% Nisin was 23.08 ± 0.65, 16.09 ± 1.73, and 6.52 ± 0.56 MPa, respectively, and the film also had excellent barrier and heat-sealing properties. The packaging test using fresh-cut watermelon sealed in the antibacterial film containing 0.28% Nisin, under controlled atmosphere storage at either 4 °C or 20 °C, effectively inhibited microbial colonization in the melon and slowed the deterioration of the fruit, as indicated by measures of hardness, weight loss, and soluble solids. This method can extend the shelf life of fresh-cut fruit and provide a reference for further research on polysaccharide-based protective film for fresh produce.

In order to explore the distribution and transfer of lead elements in soil and rice in the five regions of Chahayang, Wuchang, Fangzheng, Xiangshui and Jiansanjiang in Heilongjiang Province, and analyze the impact of rice intake on human health, the samples were tested by ICP-MS. Modeling the lead-element transfer in the soil-rice system, using the Nemero comprehensive pollution index method and the health risk assessment model to evaluate the lead pollution status of rice in the study area and its health risks to adults and children. The results showed that the average content of lead in rice in the study area was Chahayang 0.02 mg/kg, Wuchang 0.03 mg/kg, Fangzheng 0.017 mg/kg, Xiangshui 0.023 mg/kg and Jiansanjiang. 0.024 mg/kg did not exceed the lead content limit specified by China's National Food Hygiene Standard (0.2 mg/kg); Based on the prediction model of heavy metal lead content, pH value, and organic matter in the soil, the transfer of lead elements in the soil-rice system of Chahayang, Fangzheng, Xiangshui, and Jiansanjiang rice fields can be significantly described, with R 2 values ranging from 0.224 to 0.419; Both the pollution index and the comprehensive pollution index in the study area were less than 1, which belong to the non-pollution category. The health risk index of heavy metal lead for adults and children in all five regions is lower than the maximum acceptable risk level recommended by USEPA, and there is no risk of causing cancer.

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