Paenibacillus brasilensis YS-1: A Potential Biocontrol Agent to Retard Xinyu Tangerine Senescence

The Xinyu tangerine ( Citrus reticulata Blanco) is a non-climacteric fruit that is widely cultivated and consumed in China but highly susceptible to fungal infections. Antagonistic microorganisms can control postharvest diseases and extend the storage life of citrus fruits. However, little work has been done to investigate the effects of applying Paenibacillus brasilensis YS-1 by immersion to enhance the cold storability of Xinyu tangerines. Fruits were soaked with P. brasilensis YS-1 fermented filtrates for 10 min and in sterile water as the control. The decay incidence, weight loss, nutrient content, respiration rate, malondialdehyde (MDA) content, and defensive enzymes activities in citrus fruit were measured during cold storage at 5 ± 0.5 °C. The results showed that P. brasilensis YS-1 treatment significantly reduced postharvest decay and effectively maintained the nutritional quality compared to the control under cold storage. The weight loss, respiration rate, and MDA content were lower in P. brasilensis YS-1-treated fruits than the control fruits, indicating that P. brasilensis YS-1 treatment increased the activities of superoxide dismutase (SOD), peroxidase (POD), polyphenol oxidase (PPO), and phenylalnine ammonia-lyase (PAL). According to the results, a postharvest application of P. brasilensis YS-1 can control the postharvest decay and maintain fruit quality, as well as increase the defensive enzyme activity, so as to achieve the purpose of retarding postharvest senescence in citrus fruit.