Formation of glutathione patulin conjugates associated with yeast fermentation contributes to patulin reduction

Abstract

Patulin (PAT) is a fungal secondary metabolite which is mainly detected in rotten apples, and possesses serious risks to human health. Saccharomyces cerevisiae has become a promising biological control candidate due to its ability to degrade PAT. However, the degradation mechanism remains elusive. In this study, the degradation system and potential other metabolisms of PAT by S. cerevisiae were investigated. After a 96 h fermentation, 5.0 mg/L of PAT was completely metabolized by S. cerevisiae. Among the mixture of metabolites, ascladiol was identified but only accounted for 3.3% of the initial PAT. Yeast cell lysates, attained from a 96 h culture, altered 10 mg/L of PAT within 8 h. As this activity was reduced by heat treatment, it indicated that soluble intracellular enzymes were key components in PAT transformation. In addition, these effective intracellular enzymes were obtained in PAT-treated yeast cells instead of the untreated cells, indicating the activity was induced by PAT. LC-MS/MS revealed a drastic decrease of glutathione (GSH) in cell lysate upon addition of PAT. Several glutathione-patulin (GSH-PAT) conjugates (mainly c-GSH-PAT and l-GSH-PAT) were later identified. The conjugation of GSH and PAT plays an important role in PAT reduction by yeast cell lysate, even after enzymes in the lysate have been heat inactivated. Therefore, the PAT reduction by S. cerevisiae was a consequence of PAT-induced intracellular enzymes and GSH-mediated conjugation.