Effects of Temperature, pH and Relative Humidity on Penicillium expansum OM1 Growth and Patulin Production on Apple Puree Agar Medium (APAM)

Abstract

Apples are eaten all over the world, both as fresh fruit and apple products. Fungal infection of apples reduces their quality. Penicillium expansum (P. expansum), a postharvest pathogen of apples and a causative agent of soft rot, could endanger the apple industry by productin of patulin, a toxic secondary metabolite and commonly found in damaged apples. Frequent consumption of patulin-contaminated foods poses a serious threat to human health. In this study, mycobiota and patulin contamination in damaged apples were investigated. Fungi were isolated from the damaged apples, and P. expansum was the most predominant fungi. In addition, the effects of storage temperature (5℃, 10℃, 15℃, 20℃, 25℃ and 30℃), pH (3.5, 4 and 6), and relative humidity (RH) (98% and 95%) on growth of P. expansum and patulin production on Apple Puree Agar Medium (APAM) were examined. The fungal growth decreased as the medium's temperature (5℃-25℃) and RH decreased, After 6 days, the colonies grew slowly at 30℃. The relationship between fungal biomass and temperature, pH, and RH was similar to that of colony diameter, with the highest mycelial dry weight at 25°C and 98% RH. Patulin concentration was highest at 15℃, followed by 20℃, 25℃, 10℃ and 30℃. Refrigerated storage at 5℃ reduced patulin production as well as fungal growth rate. Colony growth and patulin production were optimal at pH 4 and they were highest at 98% RH. Compared with other culture media, APAM culture media showed a higher patulin production capacity, demonstrating its good patulin production capability.