Decoding the role of Bacillus: Unraveling the transformation of bioactive compounds during the aging of Pericarpium Citri Reticulatae.

Bacillus are dominant bacteria in the aging process of Pericarpium Citri Reticulatae (PCR), yet their role in the modulation of PCR metabolites is rarely reported in the current literature. Therefore, this study employed both untargeted and targeted omics technologies to investigate the dynamic changes in metabolites during the liquid fermentation of PCR infusion (PCRI) by Bacillus strains isolated from PCR. The results demonstrated that, after three days of fermentation with Bacillus subtilis CP01, the total phenol and total flavonoid contents in PCRI increased by 11.90 % and 38.36 % (p < 0.05), respectively, accompanied by a significant enhancement in antioxidant and antilipidemic effects. Notably, fermentation induced significant alterations in 108 volatile compounds, predominantly terpenes, esters, and ketones, contributing to the enhanced fruity, fermented fruit, and herbal characteristics in the PCRI. Furthermore, untargeted metabolomics revealed that fermentation led to significant changes in 1176 non-volatile metabolites, with the majority enriched in the biosynthesis pathway of isoflavonoids. Intriguingly, 2'-hydroxydaidzein underwent significant changes after fermentation with Bacillus subtilis CP01, which is an isoflavone with anti-inflammatory activity. Additionally, Targeted quantification showed a marked decrease in flavonoid glycosides and a notable increase in aglycones during fermentation, with aglycones, which have stronger physiological activity and higher bioavailability, increasing while glycosides such as rutin decreased. In conclusion, these findings provide direct evidence that probiotics accelerated the accumulation of bioactive compounds in PCR through complex mechanisms, offering new insights for the industrial production of PCR.