Microbicidal effect of negative air ion against Penicillium citrinum and quality control of Chinese bayberry

Chinese bayberry is susceptible to decay caused by Penicillium citrinum infection, which will cause food safety problems. Negative air ion (NAI) is a novel type of non-thermal microbicidal technology. This study presented NAI treatment's inhibitory effect and antimicrobial mechanism on P. citrinum isolated from Chinese bayberry fruit. The results indicated that NAI treatment had the optimal inhibitory effect on P. citrinum. P. citrinum cell membrane appeared to have visible wrinkles and damage after NAI treatment, which was observed by scanning electron microscopy (SEM) and transmission electron microscope (TEM). The contents of malondialdehyde (MDA), relative conductivity, soluble protein, soluble carbohydrate, nucleic acid leakage, and lactate dehydrogenase (LDH) in the culture medium increased obviously, which indicated that the membrane permeability of P. citrinum increased. With the laser confocal assay, NAI increased reactive oxygen species (ROS) accumulation and caused oxidative damage to membrane lipids. The membrane lipidomics of P. citrinum hyphae was determined by LC-MS. The results revealed that NAI treatment can hydrolyze the glycerophospholipid into phosphatidic acid (PA) and lysophosphatidylinositol (LPI). Besides, the results of energy metabolism illustrated that NAI treatment reduced the mitochondrial membrane potential (MMP) and energy charge of P. citrinum hyphae. Overall, the microbicidal effect of NAI consisted of two pathways: 1) NAI induced the accumulation of ROS and damaged the membrane structures; 2) NAI reduced mitochondrial membrane potential and caused energy metabolism disorders. In addition, the storage experiment proved that NAI could maintain the quality of Chinese bayberry by inhibiting microbial growth and delaying fruit decay. Hence, NAI hold promises as a potential low-temperature sterilization method for fruit and vegetable storage.