Antioxidant constituents of almond [Prunus dulcis (Mill.) D.A. Webb] hulls.
Almond hulls (Nonpareil variety) were extracted with methanol and analyzed by reversed phase HPLC with diode array detection. The extract contained 5-O-caffeoylquinic acid (chlorogenic acid), 4-O-caffeoylquinic acid (cryptochlorogenic acid), and 3-O-caffeoylquinic acid (neochlorogenic acid) in the ratio 79.5:14.8:5.7. The chlorogenic acid concentration of almond hulls was 42.52 +/- 4.50 mg/100 g of 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 microg/1 g of methyl linoleate) almond hull extracts had higher antioxidant activity than alpha-tocopherol. At higher concentrations (50 microg/1 g of methyl linoleate) almond hull extracts showed increased antioxidant activity that was similar to chlorogenic acid and morin [2-(2,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-1-benzopyran-4-one] standards (at the same concentrations). These data indicate that almond hulls are a potential source of these dietary antioxidants. The sterols (3beta,22E)-stigmasta-5,22-dien-3-ol (stigmasterol) and (3beta)-stigmast-5-en-3-ol (beta-sitosterol) (18.9 mg and 16.0 mg/100 g of almond hull, respectively) were identified by GC-MS of the silylated almond hull extract.
Takeoka
Gary R
GR
Western Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, 800 Buchanan Street, Albany, CA 94710, USA. grt@pw.usda.gov
Dao
Lan T
LT
D000975:Antioxidants / Q000032:analysis*; D002726:Chlorogenic Acid / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D062385:Hydroxybenzoates / Q000032:analysis; D010936:Plant Extracts / Q000737:chemistry; D027861:Prunus / Q000737:chemistry*; D012639:Seeds / Q000737:chemistry*
D000975:Antioxidants; D062385:Hydroxybenzoates; D010936:Plant Extracts; D002726:Chlorogenic Acid; C017616:phenolic acid