Improvement of polyphenol and antioxidant extraction process from Miang for functional food ingredient development

Abstract

Miang is fermented tea leaves that contains many beneficial bioactive compounds, specifically polyphenols and catechins. However, the polyphenol and catechin contents of Miang are lower than those in other well-known tea beverages such as green, black, and oolong teas. To develop and utilize Miang as the source of bioactive substances for obesity prevention, an appropriate extraction method of polyphenols and catechins and enhancement of antioxidant activity of Miang have gained this research interest. The aims of this research were to optimize conditions for the ultrasonic-assisted enzymatic extraction of polyphenols under Miang and to optimize tannase treatment conditions for the improvement of antioxidant activity of Miang extracts via response surface methodology. Miang extracts treated with and without tannase were investigated for their inhibitory effects on digestive enzymes. The optimal conditions for ultrasonic-assisted enzymatic extraction of the highest total polyphenol (TP) (136.91 mg GAE/g dw) and total flavonoid (TF) (5.38 mg QE/g dw) contents were as follows: 1 U/g cellulase, 1 U/g xylanase, 1 U/g pectinase, extraction temperature of 74ºC, and extraction time of 45 min. The antioxidant activity of this extract was enhanced by the addition of tannase obtained from Sporidiobolus ruineniae A45.2 undergoing ultrasonic treatment and under optimal conditions (360 mU/g dw, 51ºC for 25 min). Surprisingly, the ultrasonic-assisted enzymatic extraction selectively promoted the extraction of gallated catechins from Miang. Tannase treatment improved the ABTS and DPPH radical scavenging activities of untreated Miang extracts by 1.3 times. The treated Miang extracts possessed higher IC50 values for porcine pancreatic α-amylase inhibitory activity than those that were untreated. However, it expressed approximately 3 times lower IC50 values for porcine pancreatic lipase (PPL) inhibitory activity indicating a marked improvement in inhibitory activity after the tannase treatment. The molecular docking results support the contention that epigallocatechin, epicatechin, and catechin obtained via the biotransformation of the Miang extracts played a crucial role in the inhibitory activity of PPL. Overall, the tannase treated Miang extract could serve as a functional food and beneficial ingredient in medicinal products developed for obesity prevention.