"Food is the most important thing for the people, and safety is the most important thing for food". Fresh keeping of fruits and vegetables is an important link to ensure food safety, and has always been concerned by the public. By modifying chitosan and gellan gum, the dry land new materials research room of South Subtropical Crops Research Institute of Chinese Academy of Tropical Agricultural Sciences constructed amphiphilic chitosan/carboxymethyl gellan gum/mustard essential oil composite, studied the barrier properties, mechanical properties and antibacterial properties of the composite, and applied the composite coating solution to mango preservation, solving the problems of poor mechanical properties and insufficient antibacterial properties of single chitosan polymer coating film. The results showed that the coating treatment of amphiphilic chitosan/carboxymethyl gellan gum composite could prolong the peak respiration period of mango and the shelf life of mango for 10 days. In addition, the study found that the amphiphilic chitosan/carboxymethyl gellan gum composite added with mustard essential oil could delay fruit decay and senescence, and prevent significant changes in fruit nutrients.
Schematic diagram of preservation of mango by chitosan/gellan gum/mustard essential oil composite coating
At present, there are many methods for fruit storage and fresh-keeping, mainly including low temperature storage, controlled atmosphere storage, heat treatment and sterilization, irradiation storage, ozone treatment and chemical preservative treatment, but these storage methods have problems such as high cost, complex technology, difficult to control or toxic substance residues. The real green and healthy preservation method has become the expectation of the whole industry. Therefore, based on the principle of high efficiency, safety, environmental protection, low cost and easy operation, coating preservation came into being. Coating fresh-keeping is one of the new fresh-keeping methods emerging in recent years. It uses the coating solution to form a thin polymer film on the fruit surface to inhibit the gas and water vapor exchange of fruits and vegetables and the metabolism of fruits and vegetables, thereby reducing the respiratory intensity of postharvest fruits, reducing water evaporation, and achieving the purpose of extending the fresh-keeping period of fruits.
Green and efficient coating material is the key to develop coating preservative. Chitosan is one of the most abundant polysaccharides in nature. It has good biocompatibility, degradability, film-forming, barrier and antibacterial properties, and is considered to be one of the ideal materials for edible coating preservation. However, chitosan membrane has some problems, such as poor mechanical properties and insufficient bacteriostatic properties. Gelan gum is a natural microbial polysaccharide, which has high transparency, wide acid resistance, strong stability, gel property, flavor release, high temperature resistance and other properties. It has been widely used in food, daily necessities, medicine and other fields. The introduction of Gelan gum can effectively improve the mechanical properties of chitosan film. Plant essential oil is a kind of secondary metabolite of plant origin. It has broad-spectrum and efficient antibacterial activity. It is recognized as a pollution-free natural preservative. It can not only effectively improve the antiseptic and bacteriostatic effects of coating materials, but also improve the mechanical properties of the coating and produce synergistic effects. In this study, chitosan was modified with carboxymethyl group and then joined with cholic acid group to form amphiphilic chitosan derivative (CMCS-g-CA), which has good water solubility and better compatibility with hydrophobic materials. Then, it was compounded with water-soluble carboxymethyl gellan gum (CMGG) to construct polymer coating fresh-keeping materials. In this work, in order to obtain the composite membrane with the best mechanical and barrier properties, the appropriate weight ratio of CMCS-g-CA/CMGG was determined to be 5:2 through the water permeability, air permeability and mechanical properties of the composite membrane. At the same time, CMCS-g-CA/CMGG/MEO composite membrane added with mustard essential oil (MEO) has good antibacterial performance against Escherichia coli, Staphylococcus aureus and Bacillus anthracis, and the antibacterial activity gradually increases with the increase of MEO dosage. At room temperature, the shelf life of mango coated with CMCS-g-CA/CMGG/MEO was 10 days longer than that of non coated mango samples. This study shows that chitosan/gellan gum/plant essential oil composite can be used to develop food fresh-keeping packaging materials with high antibacterial activity, providing a new strategy for the development of green multifunctional fruit fresh-keeping materials.
Effect of Different Proportion of CMCS-g-CA/CMGG on Mechanical Properties (a) and Physical Properties (b) of Composite Membranes
Effect of different concentration of essential oil on antibacterial property (a) and fresh-keeping effect (b) of composite film
This research achievement was published in the international top journal Carbohydrate Polymers as "American chitosan/carboxymethyl gem composite films enriched with mustard essential oil for mango preservation". Yang Ziming, associate researcher of the South Subtropical Crops Research Institute of Chinese Academy of Tropical Agricultural Sciences, and Guan Chen, a joint graduate student of Huazhong Agricultural University, are the co first authors of the paper, and Li Puwang and Zhou Chuang, associate researchers, are the co corresponding authors of the paper. This work has been supported by the key research and development plan project of Hainan Province (ZDYF2021XDNY145), the expert workstation project of Yunnan Province (202005AF150007) and the basic research business cost project of the central public welfare research institutes (163006202006, 163006202022023).
