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Microbial Decontamination of Onion by Corona Discharge Air Plasma during Cold Storage 时间:2018-11-15 11:59 来源:未知作者:admin 点击: 次 Abstract:Corona discharge air plasma (CDAP) is a nonthermal decontamination technology which is generating antimicrobial agents such as photons, electrons, positively and negatively charged ions, atoms, and free radicals. We investigated the effect of a corona discharge under atmospheric pressure on the sterilization of postharvest fungal pathogens on onion. The main antimicrobial reactive substance generated by CDAP was O3. The active species such as nitric oxide (NO) and nitric dioxide (NO2) were nearly detected in this experiment. CDAP treatment revealed different isolation frequencies depending on postharvest pathogens from diseased onions, showing less isolation frequency of Fusarium spp. and Alternaria sp. than that of Botrytis spp. when compared with untreatment onions during 10-month cold storage. CDAP treatment at 2∼2.6 ppm of O3 slightly stimulated the mycelial growth of Alternaria sp., while the treatment at 20∼24 ppm of O3 gradually inhibited mycelial growth by treatment time. However, Botrytis sp. showed different patterns of mycelial growth with CDAP treatment. Less than 4 hours’ treatment of CDAP slightly inhibited the mycelial growth of Botrytis sp., while 8 hours’ treatment of CDAP slightly stimulated the mycelial growth of Botrytis sp. not depending on the concentration of O3. The inhibitory effect of CDAP on the conidial germination of Alternaria sp. and Botrytis sp. was examined with treatment time and intensity of CDAP. The conidial germination of Alternaria sp. treated with CDAP at the concentration of 13.7∼14.4 ppm of O3 was strongly inhibited by time, showing y = 2.66x2 − 85.139x + 4.88 and R2 = 0.98. When the conidia of Alternaria sp. were exposed for 2 hours with varying plasma O3 concentration, the conidial germination was strongly inhibited as the concentration of O3 increases, showing y = −0.09x2 + 6.905x − 0.764 and R2 = 0.95. The conidia of Botrytis sp. also showed similar patterns to CDAP. The inhibitory effect of CDAP on the germination of postharvest pathogens depends on treatment time and O3 concentration.
1. Introduction
Onion, one of the widely consumed vegetables, is well known for various biological activities including antioxidant and antibacterial effects mediated by sulfur and phenolic compounds [1, 2]. Onion is commonly used as a spice in Korea. Onion is usually stored for several months in a cold, dry condition after curing process to cover the seasonal demands of market in Korea. Despite the cold storage to keep marketable quality, the onion losses are substantially occurred during the storage. The major losses are caused by plant pathogens without appropriate management of postharvest diseases [3]. Botrytis sp., Fusarium oxysporum, Penicillium sp., Aspergillus awamori, Rhizopus oryzae, and Alternaria sp. are well known to cause decay during onion storage in Korea [4, 5]. However, the application of agrochemical fungicides is limited because of public concerns over the human health and environmental risks over the agrochemical residues. Therefore, eco-friendly alternative measures should be considered to control the postharvest pathogens contaminated on onions bulbs.
Plasma is known as the state of ionized gas which contains energetic reactive species, such as electrons, photons, ions, free radicals, excited molecules, and atoms, and is considered as an emerging technology for the management of postharvest diseases. There are several methods to generate plasma, including gas discharge, photoionization, heat radiation, and radio frequencies. Among the methods, the common way to produce nonthermal plasma is gas discharge [6]. Corona discharge air plasma (CDAP) and dielectric barrier discharge are the most common approaches for nonthermal plasmas’ generation under atmospheric pressure. They are known to produce chemically active species, oxygen ions, and charged species such as NO+, NO−, hydroxyl and hydroperoxyl radicals, hydrogen peroxide, nitrogen oxide species (NO, NO2, etc.), atomic oxygen, and ozone [7]. The gases widely used to create plasma are air, pure Ar, mixture of He/O2 and Ar/O2, and pure N2 [8]. These active species act as very strong oxidizers and are considered to contribute to the antimicrobial effects of gas plasma [9]. There are many reports that state that low-temperature atmospheric plasma can kill various kinds of microorganisms, such as fungi, bacteria, and yeast [10, 11]. The mechanisms of nonthermal plasma for the inactivation of microorganisms are suggested as surface erosion and oxidation of microbial cell .........