초록
Although phenolic compounds linked to proteins or polysaccharides in the cell wall from herbal plant through β-glycoside bonds are difficult to extract in aqueous solution, microorganisms that produce some key enzymes may be useful for enhancing the release of phenolic compounds. Solid-state fermentation with a combination of different microorganisms was used to promote the bioactivities of the polyphenol component in GL. The results showed that co-fermentation of GL with Monascus anka GIM 3.592 and Saccharomyces cerevisiae GIM 2.139 led to a significant increase in contents of quercetin and total polyphenols. Including gallic acid, chlorogenic acid, rutin, isoquercitrin, avicularin, quercitrin, kaempferol, and quercetin, all polyphenols extracted from fermented guava leaves (FGL) were quantitatively identified by high-performance liquid chromatography time-of-flight electrospray ionization mass spectrometry (HPLC-TOF-ESI/MS). Quercetin, which presented the highest bioactivity, was significantly increased after microbial conversion. Total polyphenols extracted from FGL showed higher bioactivities in scavenging 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and 2,2-Azino-bis 3-ethylbenzothiazoline-6-sulfonic acid diammonium salt (ABTS) caption radicals, anti-bacterial activity, and α-glucosidase inhibitory activity than those from GL. The activities of total polyphenols extracted from FGL by methanol were determined by calculating the IC<SUB>50</SUB>, with the highest values found to be 30.57μg/mL, 24.53μg/mL, and 0.09mg/mL for the scavenging of DPPH and ABTS<SUP>+</SUP> radicals and inhibition of α-glucosidase, respectively. Methanol was more effective for extracting components with high α-glucosidase inhibitory activities than acetone. The methanol extract (0.20mg/mL) efficiently inhibited 92.05% of α-glucosidase activity, which was significantly higher than that obtained using acarbose solution at an equal concentration. This microbial co-fermentation method can be used to upgrade the nutritional or medicinal values of herb leaves efficiently.