View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Biblioteca Digital do IPB 7698 J. Agric. Food Chem. 2003, 51, 7698−7702 Determination of Sterol and Fatty Acid Compositions, Oxidative Stability, and Nutritional Value of Six Walnut (Juglans regia L.) Cultivars Grown in Portugal JOANA S. AMARAL,†,# SUSANA CASAL,‡ JOSEÄ A. PEREIRA,§ ROSA M. SEABRA,*,† AND BEATRIZ P. P. OLIVEIRA‡ REQUIMTE, Servic¸os de Farmacognosia and Bromatologia, Faculdade de Farma´cia, Universidade do Porto, R. Anı´bal Cunha 164, 4050-047 Porto, Portugal, and Escola Superior de Tecnologia e de Gesta˜o and Escola Superior Agra´ria, Instituto Polite´cnico de Braganc¸a, Quinta de Sta. Apolo´nia, Apartado 134, 5301-857 Braganc¸a, Portugal Six cultivars (Franquette, Marbot, Mayette, Mellanaise, Lara, and Parisienne) of walnuts (Juglans regia L.) were collected during the 2001 crop, from Braganc¸a, Portugal. Chemical composition, including moisture, total oil content, crude protein, ash, carbohydrates, and nutritional value, was evaluated. Fat was the predominant component, ranging from 62.3 to 66.5%. Total oil was extracted and analyzed for fatty acids, sterols, oxidative stability, and peroxide value. Fatty acids and sterols were determined by gas-liquid chromatography coupled to a flame ionization detector. Eighteen fatty acids were quantified. Polyunsaturated fatty acids and, in particular, linoleic acid were predominant. â-Sitosterol, ∆5-avenasterol, and campesterol were the major sterols found. Differences were observed among the studied cultivars, especially in peroxide values and in the sterol profile. KEYWORDS: Juglans regia L.; walnut; chemical composition; fatty acid composition; sterol composition; nutritional value INTRODUCTION in omega-6 and omega-3 polyunsaturated fatty acids (PUFA), which are essential dietary fatty acids. Epidemiological and Nuts are important components of the Mediterranean diet, clinical trials suggest that omega-3 PUFA might have a which is thought to be a healthy one and has been considered significant role in the prevention of CHD. Several mechanisms as one of the best in coronary heart disease (CHD) prevention were suggested for that action, including antiarrhythmic, hy- (1). From preagriculture times to the present day, nuts have been polipidemic, and antithrombotic roles (3, 4). Several epidemio- eaten as part of the human diet, providing macronutrients and logical studies to evaluate the effect of nuts on CHD have been micronutrients, as well as other bioactive constituents. A recent conducted during the past decade (5-8). They showed that the decline in the consumption of nuts was probably due to concerns inclusion of whole food nut consumption in the diet had a about ingesting fatty foods. Walnuts, for example, are ∼60% significant protective benefit with respect to fatal and nonfatal fat (fresh weight). Although total fat intake is certainly related CHD events. Studies were also conducted specifically on to health risks, there is now general agreement that the more walnuts, finding that frequent consumption of moderate quanti- important issue, where health is concerned, is the type of fat or ties of walnuts favorably modified the lipoprotein profile and fatty acids that are consumed. In fact, fatty acid composition decreased serum levels of total cholesterol (9, 10). can influence various physiological and biochemical processes, including blood pressure regulation, glucose metabolism, lipidic Nuts are also rich in phytosterols, which, due to their metabolism, platelet aggregation, and erythrocyte deformability structural similarity with cholesterol, inhibit its intestinal absorp- (2). tion, thereby lowering total plasma cholesterol and low-density Walnut fat is mostly unsaturated, and unsaturated fatty acids lipoprotein (LDL) levels (11, 12). Epidemiologic and experi- have been associated with beneficial effects on serum lipids. mental studies have been made suggesting that dietary phy- Compared with most other nuts, which contain mostly mono- tosterols may offer protection from cancers such as colon, breast, unsaturated fatty acids (MUFA), walnuts are highly enriched and prostate cancers (13, 14). Assessment of the identity and quality of vegetable oils * Corresponding author (telephone 351.222078934; fax 351.222003977; obtained from different sources is a challenge to the food e-mail [email protected]). industry in their efforts to meet consumer expectations. Gener- † Servic¸o de Farmacognosia. ally this involves many tests, including analysis of fatty acid # Present adress: Escola Superior de Tecnologia e de Gesta˜o. ‡ Servic¸o de Bromatologia. and sterol compositions because these are probably the most § Escola Superior Agra´ria. important major and minor components, respectively (15). 10.1021/jf030451d CCC: $25.00 © 2003 American Chemical Society Published on Web 11/19/2003 Sterol and Fatty Acid Compositions and Oxidative Stability of Walnuts J. Agric. Food Chem., Vol. 51, No. 26, 2003 7699 Tabulated data on food composition generally include only mean Table 1. Systematic and Abbreviated Names of Fatty Acids Used as values on fat composition, but there are several factors such as Standards the cultivar, geographical origin, and agricultural practices that can affect compositional values (16, 17). series IUPAC abbrev More detailed research focusing on the nutritional quality and saturated butanoate C4:0 health-promoting components of walnuts will enhance our hexanoate C6:0 octanoate C8:0 knowledge and encourage walnut consumption. Although there decanoate C10:0 have been some data published on the subject (15, 18-24), they undecanoate C11:0 include mean values, and there is no information concerning dodecanoate C12:0 the cultivars grown in Portugal. In this investigation, six cultivars tridecanoate C13:0 of walnuts growing in the same experimental orchard and tetradecanoate C14:0 pentadecanoate C15:0 subjected to the same agricultural practices were analyzed for hexadecanoate C16:0 total fat, moisture, crude protein, ash, carbohydrates, oxidative heptadecanoate C17:0 stability, and peroxide value. The chemical study was extended octadecanoate C18:0 to 18 fatty acids and 8 phytosterols to determine any differences eicosanoate C20:0 heneicosanoate C21:0 in the compositional profiles of the analyzed cultivars. docosanoate C22:0 tricosanoate C23:0 MATERIALS AND METHODS tetracosanoate C24:0 Samples. Six walnut (J. regia L.) cultivars, Franquette, Marbot, monounsaturated cis-9-tetradecenoate C14:1 Mayette, Mellanaise, Lara, and Parisienne, were studied. The trees were cis-10-pentadecenoate C15:1 cis-9-hexadecenoate C16:1 identified and carefully marked. The walnut fruits were gathered by ¸ cis-10-heptadecenoate C17:1 hand in “Quinta de Santa Apolo´nia”, an orchard in Braganca, in the trans-9-octadecenoate C18:1ω9t northeastern region of Portugal (6° 46′ W, 41° 49′ N, 670 m elevation). cis-9-octadecenoate C18:1ω9 The orchard has 24 walnut trees (2 of cvs. Mellanaise, Marbot, Mayette, cis-11-octadecenoate C18:1ω7 and Parisienne; 4 of cv. Lara; and 12 of cv. Franquette) with a planting cis-11-eicosenoate C20:1 density of 7 × 7 m. All trees are >18 years old. They are pruned when cis-13-docosenoate C22:1ω9 necessary, and they receive organic fertilization but not phytosanitary cis-15-tetracosenoate C24:1ω9 treatments. The surrounding soil is tilled to control infestation and polyunsaturated trans-9,12-octadecadienoate C18:2ω6tt irrigated in summer (July and August). cis-9,12-octadecadienoate C18:2ω6 The walnut fruits were harvested in the crop year 2001 (September), cis-9-trans-12-octadecadienoate C18:2ω6ct and a final sample of ∼2 kg was taken. After harvest, walnut fruits trans-9-cis-12-octadecadienoate C18:2ω6tc were immediately transported to the laboratory and held in an oven cis 6,9,12-octadecatrienoate C18:3ω6 (UL60, Memmert, Germany) for 3 days at 30 °C. The fruits were stored cis-9,12,15-octadecatrienoate C18:3ω3 - ° cis-11,14,eicosadienoate C20:2ω6 in the shell, closed in plastic bags, and frozen to 20 C, until the cis-8,11,14-eicosatrienoate C20:3ω6 analyses. cis-11,14,17-eicosatrienoate C20:3ω3 Sample Preparation. Before chemical analysis the walnuts were cis-5,8,11,14-eicosatetranoate C20:4ω6 manually cracked and shelled and then chopped in a 643 MX coffee cis-13,16-docosadienoate C22:2ω6 mill (Moulinex, Spain). To obtain oil for further analysis, finely chopped cis-5,8,11,14,17-eicosapentaenoate C20:5ω3 nuts (∼15 g) were extracted with light petroleum ether (bp 40-60 °C) cis-4,7,10,13,16,19-docosahexenoate C22:6ω3 in a Soxhlet apparatus, and the remaining solvent was removed by vacuum distillation. The extracted oil was kept in tubes over anhydrous sodium sulfate and flushed with nitrogen. The tubes were carefully Fatty Acid Composition. Fatty acids were determined by gas-liquid wrapped in aluminum foil and stored at 4 °C until the analyses. chromatography with flame ionization detection (GLC-FID)/capillary Chemical Analysis. Analyses of moisture, total fat, ash, and protein column based on the method used by Oliveira et al. (30) with minor contents were carried out in duplicate. Moisture was determined at 100 modifications. Fatty acid methyl esters (FAMEs) were prepared by ( 2 °C(∼5 g test sample) with an SMO 01 infrared moisture balance hydrolysis with a 11 g/L methanolic potassium hydroxide solution, (Scaltec, Goettingen, Germany) (25). Ash, crude protein (N × 5.3), methyl esterification with BF3/MeOH, and extraction with n-heptane. and total fat contents were