Abstract
Two common extraction solvent systems, namely acidified aqueous methanol and acidified aqueous acetone, were used to extract blackberry phenolics, and the antioxidant properties of the recovered extracts were compared. The crude extracts were fractionated into low- and high-molecular-weight phenolics by Sephadex LH-20 column chromatography. The hydrophilic-oxygen radical absorbance capacity (H-ORACFL), ferric reducing antioxidant power (FRAP), and the cellular antioxidant activity (CAA) assays were employed as indices to assess antioxidant capacity of the extracts and their respective fractions. The methanolic solvent system displayed a greater efficiency at extracting anthocyanin and flavonol constituents from the blackberries, while the acetonic solvent system was better at extracting flavan-3-ols and tannins. Anthocyanins were the dominant phenolic class found in the blackberries with 138.7 ± 9.8 mg C3G eq./100 g f.w. when using methanol as the extractant and 114.6 ± 3.4 mg C3G eq./100 g f.w. when using acetone. In terms of overall antioxidant capacity of blackberry phenolics, the acetonic solvent system was superior. Though present only as a small percentage of the total phenolics in each crude extract, the flavan-3-ols (42.37 ± 2.44 and 51.44 ± 3.15 mg/100 g f.w. in MLF and ALF, respectively) and ellagitannins (5.15 ± 0.78 and 9.31 ± 0.63 mg/100 g f.w. in MHF and AHF, respectively) appear to account for the differences in the observed antioxidant activity between the two solvent systems.
Highlights
Worldwide, blackberries (Rubus spp.) are cultivated commercially and are a prominent source of polyphenols with purported antioxidant benefits
Total Phenolics Content (TPC) and Antioxidant Capacities of the Phenolic Extracts Prepared from the Two Different Solvent Systems
It is obvious that solubilization of phenolics is a complicated process, and its efficiency is governed by a complex interplay of parameters
Summary
Blackberries (Rubus spp.) are cultivated commercially and are a prominent source of polyphenols with purported antioxidant benefits. Two dominant classes of phenolics in blackberries are anthocyanins and hydrolyzable tannins [1,2]. Anthocyanins are colorful O-glycosidic pigments with a flavylium cation that have been long recognized for their health-promoting potential. Hydrolyzable tannins, notably ellagitannins, can be depolymerized to yield smaller phenolic compounds such as ellagic acid or hexahydroxydiphenoyl (HHDP) moieties, which were originally connected to a central glucose molecule via ester linkages, thereby contributing to the diversity in the extent of polymerization [5,6]. The dominant unit in blackberries is bis-HHDP-glucopyranose and its galloylated form, namely galloyl-bis-HHDP glucopyranose; the latter can be considered as the basic polymeric unit in many high-molecular-weight ellagitannins like lambertianin C [5]
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