Antioxidant Activity of Phenolic Fractions

The antioxidant activity of the FP, AKP, and AP fractions and their identified released monomeric PP were evaluated by three methods. The radical scavenging activities based on DPPH (515 nm) and ferric reducing antioxidant power (FRAP; 630 nm) assays were determined using a spectrophotometer FLUOstar™ OMEGA (BMG LABTECH; Chicago, IL, USA) according to the procedures described by Palafox-Carlos, Yahia, Islas-Osuna, Gutierrez-Martinez, Robles-Sánchez, and González-Aguilar [57 (link)] and Benzie and Strain [64 (link)], respectively, but with minor modifications in reaction volumes as suggested by Palafox-Carlos, Yahia, Islas-Osuna, Gutierrez-Martinez, Robles-Sánchez, and González-Aguilar [57 (link)]. The percentage of inhibition of DPPH radical vs sample concentration (0–200 µg/mL) was plotted, and the effective concentration to reach 50% radical inhibition (EC50) was then calculated and expressed as µmoles of antioxidant/mL for individual PP assayed, and µg of extract/mL for FP, AKP, or AP fractions. FRAP values of individual PP were expressed as µmoles of trolox equivalents (TE)/moles of antioxidant, whereas values of extract’s fractions were expressed in µmoles TE/g of extract (µmoles/g). The ORAC assay was performed according to Ou, et al. [65 (link)], and the results for individual PP were expressed as millimoles TE/moles of antioxidant, and as µmoles/g of dried extract for FP, AKP, and AP extract’s fractions. All assays were carried out according to the conditions recently reported by our group [66 (link)].