Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/7/2002
Publication Date: 12/2/2002
Citation: Takeoka, G.R., Dao, L.T. 2002. Antioxidant constituents of almond (prunus dulcis(mill.) d.a. webb) hulls. Journal of Agricultural and Food Chemistry. Vol 51, p. 496-501 Interpretive Summary: Almonds are a major California commodity, generating $852 million in gross sales in 2000. The annual production of almond hulls is currently in excess of 600,000 tons (1.2 billion pounds) with this production mainly used as livestock feed. In our continuing search for novel phytonutrients in agricultural products, we investigated the composition of almond hulls and identified chlorogenic acid, cryptochlorogenic acid and neochlorogenic acid. These compounds exhibit antioxidant and anticarcinogenic properties. We also identified the sterols, stigmasterol and beta-sitosterol (18.9 mg and 16.0 mg per 100 g almond hull, respectively). These dietary plant sterols have been demonstrated to reduce serum cholesterol levels and also may inhibit colon cancer development. This study found that the three chlorogenic acid isomers together comprised about 53.5 mg/100 g fresh weight of the hulls thus revealing that almond hulls are a good source of these dietary antioxidants.
Technical Abstract: Almond hulls (Nonpareil variety) were extracted with methanol and analyzed by reversed phase HPLC with diode array detection. Phenolic constituents of extracts were comprised of 70% 5-O-caffeoylquinic acid (chlorogenic acid), 13% 4-O-caffeoylquinic acid (cryptochlorogenic acid) and 5% 3-O-caffeoylquinic acid (neochlorogenic acid). The chlorogenic acid concentration of almond hulls was 42.52 ± 4.50 mg/100 g fresh weight (n = 4; moisture content = 11.39%). Extracts were tested for their ability to inhibit the oxidation of methyl linoleate at 40 degrees C. At an equivalent concentration (10 ug/1 g methyl linoleate) almond hull extracts had higher antioxidant activity than alpha-tocopherol. At higher concentrations (50 ug/1 g methyl linoleate) almond hull extracts showed increased antioxidant activity that was similar to chlorogenic acid and morin standards (at the same concentrations). These data indicate that almond hulls are a good source of these dietary antioxidants. The sterols, stigmasterol and beta-sitosterol (18.9 mg and 16.0 mg per 100 g almond hull, respectively), were identified by GC-MS of silylated almond hull extract.