Free and total (after basic hydrolysis) polyphenols in nine types of raw and roasted nuts and two types of peanut butter (54 commercial samples) were analyzed after methanol extraction by a single step Folin-Ciocalteu reagent using catechin as standard. Walnuts had the highest free and total polyphenols in both the combined raw and roasted samples. Total polyphenols in the nuts were significantly higher than free polyphenols. Roasting had little effect on either free or total polyphenols in nuts. Raw and roasted walnuts had the highest total polyphenols. The efficacy of raw and roasted nut antioxidants was assessed by measuring the ability of the free polyphenol nut extracts to inhibit the oxidation of lower density lipoproteins (LDL + VLDL). A nut polyphenol, catechin, was measured after binding of three nut extracts to lower density lipoproteins. Walnut polyphenols had the best efficacy among the nuts and also the highest lipoprotein-bound antioxidant activity. Based on USDA availability data, the per capita total polyphenols was 162 mg from nuts per day in 2008. This corresponds to 19% of the total polyphenols from fruits and vegetables, nuts, grains, oils and spices in the US diet. Nuts provided 158 mg of polyphenols per day to the European Union diet. Nuts are high in polyphenol antioxidants which by binding to lipoproteins would inhibit oxidative processes that lead to atherosclerosis in vivo. In human supplementation studies nuts have been shown to improve the lipid profile, increase endothelial function and reduce inflammation, all without causing weight gain. These qualities make nuts a nutritious healthy snack and food additive.
Paper funded by The International Tree Nut Council Nutrition Research & Education Foundation of which the California Walnut Commission is a member and provides financial support.