Effects of Aspergillus flavus inhibition by using UV-C ultraviolet radiation on dried red pepper quality

Aspergillus flavus pollution has posed the serious obstacle on the storage of dried red pepper (Capsicum annum L.). Particularly, the aflatoxins produced by A. flavus are the toxins with the strong carcinogenicity. It is a high demand to solve the aflatoxins contamination in the dried red peppers. Fortunately, a low-cost and safe sterilization, UV irradiation has been approved for use in food by the FAO/WHO. However, there is little research on the effect of ultraviolet irradiation on the inhibition of A. flavus and the quality of dried red pepper. Therefore, this article aims to explore whether the UV-C ultraviolet radiation was an effective tool to control A. flavus and aflatoxin B1 (AFB1) contamination on dried red pepper. The effects of ultraviolet irradiation on the growth and aflatoxins production of A. flavus on the dried red pepper were investigated through in vitro antibacterial experiments, in vitro experiments, and determination of AFB1 production. A comparison was made on the color brightness value (L), red-green value (a), yellow-blue value (b), extractable color (ASTA), total content of natural coloring substance and capsaicin content of dried red pepper before and after ultraviolet irradiation. A systematic investigation was implemented to explore the effect of ultraviolet irradiation on the quality of dried red pepper. The intracellular substance leakage, malondialdehyde (MDA) content, superoxide dismutase (SOD) and peroxidase (GSH) activities of A. flavus were measured to further determine the inhibitory mechanism of UV irradiation on A. flavus. The results showed that the UV-C method was used to effectively control the growth and AFB1 production of A. flavus in vitro (on PDA and PDB media), indicating the full kill the non-germinating A. flavus spores. The inhibition rate of A. flavus reached 40% in the already-grown colonies. The irradiation time and distance were controlled after UV-C treatment. The radiation dose was dominated in the inhibitory effects of ultraviolet on A. flavus on the dried red pepper. UV-C method showed the similar inhibitory effects on the growth and AFB1 production of A. flavus on dried red pepper with and without A. flavus colonies. The total number of colonies decreased by two orders of magnitude after 2.5 h UV treatment. In addition, there was no colony of A. flavus on the dried red pepper during the first four days of culture, indicating the very significant inhibitory effect. Once the UV irradiation time and distance were 2.5 h and 15 cm, respectively, the inhibition rate of AFB1 production on the dried red pepper was 59.74%. Moreover, the moisture content of dried red pepper decreased under UV irradiation, which was beneficial to the decreasing proliferation of microorganisms in the dried red pepper. Once the UV irradiation time was less than 2 h, UV irradiation was only reduced the red-green value in the color of dried red pepper, indicating no significant effect on the rest qualities. Further research has found that the damage mechanism of UV-C ultraviolet radiation to A. flavus was broken the integrity of the cell membrane, leading to the leakage of cell contents, damage to the intracellular antioxidant, cellular lipid peroxidation, and irreparable oxidative damage within the cell, thereby inhibiting the growth and AFB1 production of A. flavus on the dried red pepper. Therefore, the UV-C ultraviolet can be expected to serve as the potentially effective tool for the prevention of A. flavus and aflatoxins contamination in the dried red pepper. The finding can also provide the safety way to extend the storage period of dried red pepper.