Application of emulated plasma technology incorporated with coating substance and ethylene inhibitor for reducing decay and extending the storage life of mangosteen under export stimulation

Mangosteen is a popular tropical fruit and being the demand of international market. It is called as the princes of fruit. At the present, Thailand is the major produce and export mangosteen in the world. In 2019-2020 the export volume was 291,950 – 409,027 tons that was as 15,020 – 16,703 million baht. The major customers are China, Hong-Hong, South Korea, Taiwan, and Japan. By the way, the exporting mangosteen is facing with various problems i.e. pericarp hardening, wilt of calyx due to high respiration and ethylene production leading to water loss and fruit deterioration rapidly. High respiration is a main cause of pericarp hardening and wilt of calyx during storage and transportation. Moreover, the physical damages during harvesting and transportation (such pressing, falling, compression, etc) can be the cause of pericarp hardening. Postharvest disease is also the serious problem of mangosteen exporting especially fruit rot disease caused by various fungal pathogens; C. gloeosporioides, Lasiodiplodia theobromae, Pestalotiopsis sp. and Phomopsis sp. Among of them Lasiodiplodia theobromae can grow very fast and the mycelium grow cover the fruit with 3 days, the mycelium penetrates through the pulp and then the pulp changes to be black color. Fungicide treatment is commonly applied but its residue is harm to the consumer health. This becomes a trade barrier for exporting Thai mangosteen. Thus, postharvest technologies with safety such a green technology to the consumer and environment should be integrated for minimizing the pericarp hardening, wilt of calyx, and fruit rot diseases.

          Plasma technology is a modern technique for disinfection of fungi and bacteria in air and water of the several industries. There are 2 types; non-thermal atmospheric plasma (NTAP)  and plasma activated water (PAW). Air or water under plasma condition, the reactive oxygen species (ROS), charged ions, UV ray, and ozone are generated, and they will oxidized the cell wall and genetic material (DNA, RNA) of microorganisms resulting to cell death. Plasma technology has been reported for extending the shelf life of postharvest fruit and vegetables. Go et al. (2019) used NTAP for controlling Fusarium oxysporum infection of harvested paprika.

Thirumdas et al. (2018) reported that mycelium and spore of Cladosporium sphaerospermum and Aspergillus oryzae was destroyed by NTAP treatment. PAW can be generated by using plasma jets, then ROS (superoxide anion radical (O₂^-), hydroxyl radicals (OH^•), peroxyl radical (ROO^•), singlet oxygen (¹O₂), hydrogen peroxide (H₂O₂)), reactive nitrogen species (RNS), UV photons, and free radicals will be created in PAW (Go et al., 2019; Zhang et al., 2016) which can be detected by measuring the increase of oxidation-reduction potential (ORP), electrical conductivity (EC) and the decrease of pH of water. At this condition, the cell wall of microorganism is destroyed and death. However, the adding of oxidizing chemicals such as NaCl, phosphate saline or N-Acetylcysteine (NAC) in water before treating with plasma jet results to increase the EC and ORP values higher than using PAW alone. The increase of EC and ORP value leads to increase the efficiency of microbial disinfection PAW (Thirumdas et al., 2018; Shintani et al., 2010). Using the chemical solution instead of water in plasma jet system is called plasma activated solution (PAS). There are harmful chemicals i.e. hydrogen peroxide (H₂O₂), nitrite (NO₂^-) and nitrate (NO₃^-) generated under PAS condition (Ercan et al., 2016). PAS application can help to minimize the time and heat that generates in solution during treatment (Shintani et al., 2010). PAW and PAS treatment are required the plasma jet which is expensive. Therefore, KMUTT researcher team has been developed the emulate plasma activated water (EPAW) and emulated plasma activated solution-H₂O₂ (EPAS-H₂O₂) that is no needed to use plasma jet. In vitro test, it was found that EPAW and EPAS-H₂O₂ could inhibit the mycelium and spore germination of Colletrotrichum gloeosporioides, a causal agent of anthracnose disease of chili seeds for 100% inhibition.  EPAS-H₂O₂ provided the antifungal activity better than PAW. Electron microscope observation showed that the structure of mycelium and spore was damaged. In vivo test, EPAS-H₂O₂ could inhibit the percentage of disease infection and enhance the seed quality (high percentage of seed germination and inducing the seedling growth) (Ahmad et al., 2022). Thus EPAS-H₂O₂ technology can be used to apply for controlling fruit rot disease of mangosteen.

          The problems of pericarp hardening and wilt of calyx can be solved by minimizing the water loss caused by high respiration and ethylene production such as coating substance and 1-Methylcyclopropene (1-MCP) respectively. Our research found that 1-MCP sachet (EthylBlocTM) helped to reduce the respiration and ethylene production of mangosteen fruit kept in LDPE bag, and also maintained the freshness of calyx, firmness, and freshness during storage at 13C for 30 days (Vo et al., 2016). Furthermore, 1-MCP in cooperating with ethanolic shellac-modified coconut oil (ES-MCO) provided more effectiveness to reduce fruit rot disease and maintain the fruit quality in compared with single treatment. The reduction of fruit rot disease is caused by antimicrobial effect of monoluaric acid that is contained in MCO. Sripong et al. (2014) found that ES-MCO completely killed the spore of C. gloeosporioides, a cause of anthracnose disease in mango.

          Thus, the objective of this research is to using EPAS-H₂O₂ in cooperating with ES-MCO and 1-MCP for reducing fruit rot disease, pericarp hardening, wilt of calyx and extending the shelf life of mangosteen fruit under shipment stimulation.