PHOTOCHEM® for Determination of Antioxidant Capacity of Plant Extracts

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 (R) 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 (R) 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 (R) device as a tool for measuring antioxidative capacity is discussed.