Bioaccessibility, safety, and antidiabetic effect of phenolic-rich extract from fermented Psidium guajava Linn. leaves

Fermentation results in the release and biotransformation of phenolic compounds in guava leaves. This study aimed to evaluate the bioaccessibility, safety and antidiabetic effect of phenolic-rich extract from fermented guava leaves (PE-fgl) using Monascus anka and Bacillus sp. BS2. The total phenolics and flavonoids were 51.18% and 16.60% bioaccessible after gastrointestinal digestion, respectively. High bioaccessibility was observed, particularly for ellagic acid, isoquercitrin, quercetin-3-O-β-D-xylopyranoside, quercetin-3-O-α-L-arabinofuranoside and avicularin, resulted in high recovery of α-glucosidase inhibition activity and antioxidant capacity. Moreover, PE-fgl was practically nontoxic with a median lethal dose (LD50) greater than 5000 mg/kg and was without evidence of toxicity following subchronic administration up to the dose limit of 2000 mg/kg. Furthermore, PE-fgl significantly improved serum glucose and lipid levels as well as antioxidant capacity in diabetic mice. Liver, kidney and pancreas damage was also significantly alleviated. These results suggested that PE-fgl could be a nontoxic candidate for diabetes treatment.