Impact of fermentation degree on phenolic compositions and bioactivities during the fermentation of guava leaves with Monascus anka and Bacillus sp.

Guava leaves (GLs) were processed by solid-state co-fermentation with Monascus anka and Bacillus sp., and the impact of the fermentation degree on the phenolic composition and their bioactivities was investigated. Three representative HPLC fingerprints of phenolic compositions from GLs can be clearly distinguished for the different fermentation degrees. Four characteristic compounds, including gallic acid, quercetin-3-O-α-L-arabinopyranoside, quercetin, and kaempferol, that significantly responded to the changes of bioactivity in the fermented GLs were identified as the marker components by principal component analysis. High levels of the four marker components in the HPLC fingerprints are an indication that the fermented GLs are mature. In addition, the correlation analysis confirmed that the total phenolic, total flavonoid, and the quercetin and kaempferol contents strongly correlated with its bioactivities. These results can provide a theoretical basis to quickly evaluate and control the mature degree of fermented products, which will help to obtain high bioactive fermented products.