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

Citation

Zhong, L., Carere, J., Mats, L., Lu, Z., Lu, F., Zhou, T. (2021). Formation of glutathione patulin conjugates associated with yeast fermentation contributes to patulin reduction. Food Control, [online] 123 http://dx.doi.org/10.1016/j.foodcont.2020.107334

Plain language summary

Patulin (PAT) is a fungal toxin mainly detected in rotten apples, possessing serious risks to human health. A strain of the bread yeast (Saccharomyces cerevisiae) has become a promising biological control agent to degrade the fungal toxin. However, the mechanisms of the patulin degradation by this yeast is not really clear. In this research, it was found that PAT was completely metabolized by the yeast after a 96 h fermentation. Among resulting metabolites, ascladiol was identified but only accounted for 3.3% of the initial PAT. Soluble intracellular enzymes were found to be responsible for the transformation of PAT to ascladiol. These intracellular enzymes were obtained in PAT-treated yeast cells but not the untreated cells, suggesting the activity was induced by PAT. In addition, the level of glutathione (GSH) in cell lysate decreased dramatically upon addition of PAT. Several glutathione-patulin (GSH-PAT) conjugates (mainly c-GSH-PAT and l-GSH-PAT) were later identified, indicating that the conjugation of GSH and PAT plays an important role in PAT reduction by yeast cell lysate. Therefore, the PAT reduction by S. cerevisiae was a consequence of PAT-induced intracellular enzymes and GSH-mediated conjugation.

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.

Publication date

2021-05-01