Bioactive constituents of pecans [Carya illinoinensis (Wangenh.) K. Koch]

Abstract

Epidemiological studies have shown an inverse relationship between nut consumption and chronic diseases of humans. For this reason, commercially-viable U.S. cultivars were assessed for their antioxidant and anti-inflammatory constituents. Acetonic extracts of defatted pecans possessed marked in vitro antioxidant capacities as determined by a number of assays including total phenolics content (TPC), ferric reducing antioxidant potential (FRAP),hydrophilic-oxygen radical absorbance capacity (H-ORACFL), and total procyanidins content (DMAC). Depending on the cultivar, H-ORACFL values ranged from 13.5 ± 3.5 to 25.5 ± 3.0 mmol Trolox eq/100 g. The procyanidins content of crude extracts (420 ± 20 to 655 ± 43 mgprocyanidin B2 eq/100 g) correlated better with H-ORACFL data than TPC values. The impact of roasting on the antioxidant activity and phenolics content was investigated. Pecans were roasted in an impingement oven at 175°C for 8.2 min. No significant differences were observed in FRAP quantities and only one cultivar showed a significant decrease in H-ORACFL. Significant decreases were observed for both TP (~10%) and PAC (~25%) contents. Fractionation of the crude acetonic extracts by Sephadex LH-20 column chromatography into low-molecular-weight (LMW) and tannin-rich phenolic compounds (HMW) was achieved. Results indicated that the tannin-rich fraction, comprised of proanthocyanidins, possessed substantially more antioxidant activity than the LMW phenolic fraction. Phenolic acids identified in the crude acetonic extract and LMW phenolic fraction by RP-18 HPLC included gallic, ellagic, protocatachuic, and p-hydroxybenzoic acids as well as the proanthocyanidin monomers, catechin; these were tentatively identified, confirmed using ESI-LC-MS and quantified (both in their free, esterified, and bound forms) by HPLC. Normal phase-HPLC revealed that the tannin rich fraction, which accounted for most of the antioxidant activity, comprised both hydrolyzable and condensed tannins. Degrees of polymerization for the tannin-rich samples were determined to contain monomers-pentamers with dimers representing the largest fraction (56.7%). Anti-inflammatory properties of the crude and acetonic extracts (both LMW and HMW fractions) were evaluated using lipopolysachharide-stimulated RAW 264.7 macrophage cells. Nitric oxide, an index of inflammation, was measured using the GRIESS assay. The LMW fraction proved to be most effective and showed a dose-dependent effect.