The interplay between (−)-epigallocatechin-3-gallate (EGCG) and Aspergillus niger RAF106, an EGCG-biotransforming fungus derived from Pu-erh tea

Although (−)-epigallocatechin-3-gallate (EGCG) exhibits various bioactivities, its low bioavailability and toxicity at high concentrations limit its application. Microbial biotransformation of EGCG could improve its bioavailability and bioactivities, but the interplay between EGCG and EGCG-transforming microbes was little known. Here, 50 g/L or less of EGCG was completely degraded at 48 h when co-incubated with Aspergillus niger RAF106 in potato dextrose broth. The degradation was accompanied by an unchanged radical-scavenging activity and increase in the production of (−)-epigallocatechin and gallic acid, which were degraded as the fermentation time increased. According to the compound structure, (−)-epicatechin and (−)-catechin were discovered after 120 h. When co-incubated with EGCG, RAF106 formed dispersed mycelia and grew faster. The inhibition of conidial agglomeration and changes in the ultrastructure of hyphal wall coincided with the inhibition of pellet formation. Additionally, the addition of EGCG increased the cellulase and pectinase activities and altered the transcripts of 1394 genes, including those associated with carbohydrate metabolism and fungal growth and development. Conclusively, co-incubation of EGCG and RAF106 resulted in EGCG conversion into smaller molecules, inhibition of fungal pellet formation, increased fungal growth and production of cellulases and pectinases, and significant changes in hyphal morphology and transcripts of several phenotype-related genes.