Improvement of Phenolic Contents and Antioxidant Activities of Longan (Dimocarpus longan) Peel Extracts by Enzymatic Treatment

This study demonstrated increases in the recovery of phenolic compounds from industrial waste, longan peel, after treatment with plant matrix degrading enzymes. Pretreatment of longan peel with cellulase, α-amylase, protease, or β-glucosidase enhanced total phenolic content in the extracts, leading to increases of DPPH scavenging activity, oxygen radical absorbance capacity, antioxidant in β-carotene/linoleate system, and ferrous ion chelating activity. In detail, cellulase increased the release of free phenolics e.g. o-coumaric acid, corilagin, and quercetin as well as the release of esterified phenolics e.g. ellagic acid, and gallic acid, while β-glucosidase increased the release of free phenolics e.g. ellagic acid. Among all enzymatic pretreatments, protease provided the highest proportion of phenolics’ recovery in the extract, while only cellulase and β-glucosidase significantly improved extraction yields by 31 and 17%, respectively. These results indicated enhancement of valorization of longan peel as a resource material for functional ingredients recovery.