PHOTOCHEM® for Determination of Antioxidant Capacity of Plant Extracts

Abstract

The antioxidative capacities of water- (ACW) and lipid-soluble (ACL) compounds in selected plant extracts were investigated by a facile chemiluminescence assay using a PHOTOCHEM® device. Prepared extracts contained various classes of polyphenolics and included Cyclone canola hulls (i.e., phenolic acids and condensed tannins), arugula greens (i.e., quercetin and other flavonoids), bearberry-leaf (i.e., arbutin, condensed and hydrolyzable tannins), as well as the leaf material (i.e., a mixture of phenolics including condensed tannins) of east-coast Canadian wild blueberries. All extracts examined had demonstrated a capability to retard lipid oxidation in other model system studies, albeit to varying degrees. Using the PHOTOCHEM® device, the ethanolic extract from blueberry leaves exhibited the strongest antioxidative capacity at inhibiting the photo-induced chemiluminescence (PCL) of luminol; that is, 5.93 mmol ascorbic acid eq/g extract and 10.4 mmol Trolox eq/g extract for the ACW and ACL assays, respectively, while extracts from arugula greens were weakest with ACW data ranging from 0.06 to 0.16 mmol ascorbic acid eq/g extract. The crude bearberry-leaf extract also showed strong antioxidant activity; moreover, individual results for the ACW and ACL experiments correlated strongly to one another (r=0.955). The crude bearberry-leaf extract was fractionated on a Sephadex LH-20 column using 95% (v/v) ethanol and 50% (v/v) acetone as mobile phases. The ethanol fraction demonstrated a reduced antioxidative capacity at retarding PCL of luminol whereas the acetone fraction, which contained more tannin constituents, exhibited an enhanced capacity (ACW: 0.94 and 7.70 mmol ascorbic acid eq/g extract, respectively; ACL: 5.80 and 36.3 mmol Trolox eq/g extract, respectively). The simplicity and effectiveness of the PHOTOCHEM® device as a tool for measuring antioxidative capacity is discussed.