Temperature-induced metabolic changes of apples infected with Penicillium expansum characterized by non-targeted high-resolution mass spectrometry

Blue mold caused by Penicillium expansum is a prevalent postharvest disease that affects quality of apples during storage and transportation and is responsible for considerable, economic losses to the apple industry. Patulin (PAT), a secondary metabolite of P. expansum, is toxic and widely found in apples and their products, which is hazardous to human health. In this study, Fuji apples were inoculated with P. expansum then subjected to both room-temperature storage and cold storage. Measurements of the lesion diameter and PAT content revealed that the growth rate of P. expansum was lower during cold storage but the PAT content was higher, even in samples with the same lesion diameter. Non-targeted high-resolution mass spectrometry was employed to examine the metabolic changes in the infected tissues for a fixed lesion diameter (after 24 d of cold storage and 7 d of room-temperature storage). Clear differences were observed in the contents of organic acids, lipids, flavonoids, sugars, and other metabolites. Compared with the apples stored at room temperature, downregulation of metabolic pathways related to disease resistance and upregulation of those related to PAT synthesis at cold storage. The obtained results further elucidate the effects of temperature on P.expansum infection and apple resistance, thus providing a theoretical basis for the prevention and control of this problematic plant pathogen.