A significant by-product of the industrial processing of pistachios: shell skin – RP-HPLC analysis, and antioxidant and enzyme inhibitory activities of the methanol extracts of Pistacia vera L. shell skins cultivated in Gaziantep, Turkey

Abstract

The aim of this study is to evaluate the antioxidant and enzyme inhibitory activities of the methanol extracts of immature and mature shell skins of Pistacia vera L. As well as biological activity tests, phytochemical compositions of the extracts were also investigated. The total phenolic and flavonoid content was determined in addition to the amounts of gallic acid, protocatechuic acid, (+)-catechin, p-hydroxybenzoic acid, caffeic acid, (−)-epicatechin, syringic acid, p-coumaric acid, hesperidin, quercetin, kaempferol, and apigenin. The immature shell skin was found to be rich in both phenolic and flavonoid compounds (52.29 mg of gallic acid equivalent (GAE) per g of extract and 16.78 mg of rutin equivalent (RE) per g of extract). In immature shell skins, the amounts of protocatechuic acid (4335 μg per g of extract), p-hydroxybenzoic acid (12 925 μg per g of extract), p-coumaric acid (120 μg per g of extract), quercetin (620 μg per g of extract), and apigenin (190 μg per g of extract) were higher than those of the mature one. In parallel to these findings, immature shell skins exhibited a higher antioxidant activity in all test systems than that of the mature one. The samples did not show any inhibitory activity on butyrylcholinesterase and α-glucosidase. Mature shell skins exhibited considerable inhibitory activity on acetylcholinesterase (2.15 mg of galantamine equivalent (GALAE) per g of extract). The tyrosinase inhibitory activity of the mature shell skin was also found as 3.14 mg kojic acid equivalent (KAE) per g of extract. The immature shell skin remained inactive on this enzyme. The samples also showed remarkable inhibitory activity of α-amylase.