H: Health, Nutrition, & Food JFS H: Health, Nutrition, and Food Cholesterol-Lowering Properties of Whole Cowpea Seed and Its Protein Isolate in Hamsters K.M.G. FROTA, S. MENDONC ¸A, P.H.N. SALDIVA, R.J. CRUZ, AND J.A.G. ARˆ EAS ABSTRACT: Hypercholesterolemic hamsters were fed for 4 wk on diets rich in saturated fatty acids and cholesterol, differing only in protein source (20%): casein (control group, HC), whole cowpea seed (HWS), and cowpea protein isolate (HPI). Hamsters fed on HWS and HPI presented significant reductions in plasma total cholesterol and non- HDL cholesterol. HPI and HC presented similar protein digestibility, which were significantly higher than that of HWS. Animals fed on HWS presented significantly higher levels of bile acids and cholesterol in feces than did the animals fed on casein or HPI diets. Histological analyses of the liver showed that HC diet resulted in steatosis widely distributed throughout the hepatic lobule, while HWS and HPI diets promoted reductions in liver steatosis. The ef- fectiveness of HWS for modulating lipid metabolism was greater than that of HPI, as measured by plasma cholesterol reduction and liver steatosis. Keywords: cholesterol, cowpea, hypocholesterolemia, protein isolate, steatosis Introduction M uch attention has been paid to dietary interventions that lower plasma cholesterol concentration among the popula- tion as a tool to prevent and treat coronary heart diseases (Kerck- hoffs and others 2002). Legumes are candidates to such interven- tions as they have shown hypocholesterolemic effects in humans and animals. Soy protein intake, for example, affects serum lipid levels and presents a significant relationship with decreases in total and LDL cholesterol and the risk of coronary heart disease. Soy consumption, however, is not part of dietetic habits of West- ern population and other seeds may play an effective role in con- tributing to lower plasma cholesterol concentration. The cowpea (Vigna unguiculata L. Walp) is a tropical legume native to West Africa whose mature seeds are rich in protein (about 25%) and carbohydrates (about 65%) (Bressani 1985; Frota and others 2008). Cowpeas grow well under a diverse range of conditions and envi- ronments, including arid regions and areas unsuited for growing soybeans (Prinyawiwatkul and others 1996; Sarr and others 2001). This grain is an important component of the diets for populations in Brazil’s Northeastern and Northern regions, sub-Saharan Africa, and India, where it is especially valuable as a source of dietary protein to complement cereals, starchy roots, and tubers (Bressani 1985; Phillips and McWatters 1991; Frota and others 2008). Among the mechanisms that have been proposed to explain the cholesterol-lowering effect of soy, and possibly other legume seeds, the most commons are the physiological action of legume components such as phytic acid, dietary fiber, saponins, phytos- terols, proteins, peptides, and their amino acid profiles (Reynolds and others 2006). In our studies on amaranth, a powerful hypoc- holesterolemic seed, we found that protein was the major com- MS 20080438 Submitted 6/13/2008, Accepted 8/14/2008. Authors Frota, Mendonc ¸a, and Arˆ eas are with Dept. de Nutric ¸˜ ao, Faculdade de Sa´ ude P´ ublica, Univ. de S˜ ao Paulo, Av. Doutor Arnaldo 715, 012406-904, S˜ ao Paulo, Brazil. Author Saldiva is with Dept. de Patologia, Faculdade de Medicina, Univ. de S˜ ao Paulo, Av. Doutor Arnaldo 455, 012406-903, S˜ ao Paulo, Brazil. Author Cruz is with Centro de Bioterismo, Faculdade de Medicina, Univ. de S˜ ao Paulo, Av. Doutor Arnaldo 455, 012406-903, S˜ ao Paulo, Brazil. Direct inquiries to author Arˆ eas (E-mail: jagareas@usp.br). ponent responsible for this cholesterol-lowering effect (Plate and Arˆ eas 2002; Mendonc ¸a 2006). Although cowpeas have been con- sumed by humans since the earliest times of agriculture practices and medicinal and nutritional properties have been ascribed to this crop (Phillips and McWatters 1991; Frota and others 2008) lit- tle research has been undertaken to test the effect of cowpeas on cholesterol metabolism. There is a clear need to assess whether this crop is able, like soy, to reduce plasma cholesterol levels and which is the main component responsible for this effect, should it exist. The aim of the present study was therefore to investigate the oc- currence of hypocholesterolemic effects from whole cowpea seed or its protein isolate, among hamsters that had been fed on a diet rich in saturated fatty acids and cholesterol. Hamsters have been extensively used as animal model for studying the effects of diet on plasma lipid levels and the mechanism involved, because they are sensitive to high-fat cholesterol-supplemented diets (Dorfman and others 2005) and carry a significant portion of its plasma choles- terol in the LDL lipoprotein fraction, presenting thus metabolism close to that observed in humans (Lock and others 2005). High- fat or high caloric diets usually result in triacylglycerol deposition in liver, which is termed ectopic fat deposition or steatosis that is present in one-third of U.S. population (Browning and others 2004) and may occur by distinct mechanisms: high dietary fat, fatty acid released from adipose tissue, and from de novo hepatic lipogenesis. An imbalance of any of the pathways involved in fatty acid and tria- cyglycerol delivery, synthesis, export, or oxidation could contribute to lipid accumulation in the liver. Thus, steatosis is expected to oc- cur in the high-fat diets employed in this study. Therefore, both the mechanisms involved in cholesterol reductions and the potential of cowpeas to prevent steatosis were investigated. Materials and Methods Protein isolate preparation Cowpea protein isolate was obtained by means of the conven- tional methods of alkaline solubilization and isoelectric precipita- tion of the proteins, followed by solvent extraction, as described in C  2008 Institute of Food Technologists R  Vol. 73, Nr. 9, 2008—JOURNAL OF FOOD SCIENCE H235 doi: 10.1111/j.1750-3841.2008.00953.x Further reproduction without permission is prohibited