Currently, there are many methods to prevent fungal diseases and preserve mangoes after harvest, such as using hot steam (physical method), chemical substances, plant compounds. However, the above methods have many disadvantages, such as ineffective antifungal, short storage time, unsafe for human health. Therefore, the trend of using preservatives of natural origin, high preservation efficiency, and non-toxicity to users is being researched and applied in the domestic an foreign country.

Chitosan is a non-toxic natural polymer with many important biological properties, such as antibacterial, antifungal, etc., which has been studied and applied in many fields. However, chitosan usually has a large molecular weight and poor solubility (only soluble in acidic medium). In addition, when dissolved, it creates a solution with high viscosity, so the applicability of chitosan is limited.

The biological properties of chitosan depend mainly on its molecular weight (Mw). Chitosan with low Mw has good water solubility due to its short molecular chain, so it is often applied in the field of food preservation and post-harvest agricultural products, such as antimicrobial resistance, growth stimulation, and etc.

There are many methods to degrade chitosan with large Mw to form with lower Mw such as acid hydrolysis, enzyme cleavage, etc. However, these methods are not effective because of their complexity and can change the structure and properties of the end product. Facing that fact, the research team of the Center for Biotechnology in Ho Chi Minh City has carried out the project "Research to produce low-molecular-weight chitosan by means of irradiation combined with H2O2 treatment (synergistic effect), application to preserve fresh mangoes." This is a safe, highly efficient circuit cutting method that does not change the circuit structure and has the potential to be applied on a large scale.

According to research, chitosan is soaked in H2O2 (Hydro peroxide), also known as hydrogen peroxide 1, 2, 3%, to form a mixture of 5% (w/v). Then, irradiation was carried out with radiation doses of 5, 10, 15, 20 kGy on gamma Co-60 radiation source at Da Lat Nuclear Research Institute. Samples after irradiation were dried and ground into fine powder to form low Mw chitosan products.

The chitosan product with low Mw was investigated for its ability to resist some fungi L. pseudotheobromae, P. longicolla, C. gloeosporioides causing diseases on mango. At the same time, the ability to preserve mango fruit with low Mw chitosan film was tested.

Research results also show that the optimal concentration to create a film to preserve sand mango at normal temperature (30°C) is 3% and at 4°C is 2%.