Composição e caracterização nutricional de três cultivares de Vigna unguiculata (L.) Walp. epace 10, olho de ovelha e ipa-206.

Abstract

Cowpea [Vigna unguiculata (L.)] Walpi, is a legume which constitutes an important human and animal dietary constituent supplying protein and energy. Due to its importance many cultivars were developed aimed to obtain new varieties with higher germination index, shorter flowering time, higher number of pods per plant, improved seed quality, and traits such as resistance to several pests and diseases, resistance to drought environments, etc. However, studies on the nutritional quality of these improved varieties are scanty. Thus, in this study the seeds of three Brazilian cultivars of Vigna unguiculata (EPACE 10, Olho de ovelha, and IPA-206) were analyzed with respect to the proximate composition, amino acid composition, presence of antinutritional factors, net protein utilization (NPU), true digestibility, and biological value. Moreover, the main seed protein classes were fractionated and compared within cultivars. The seed carbohydrate and protein contents varied from 68.14 to 70.65% and 23.72 to 26.10%, respectively, and were not significantly distinct among the cultivars. Regarding to the main types of seed protein the globulin has the highest content (49.8 to 53.1%) followed by albumin (24.3 to 27.6%) and basic glutelin (10.8 to 14.3%). Polyacrylamide gel electrophoreses of the flours and protein fractions (crude extract, globulin, albumin, basic glutelin, acidic glutelin, and prolamin), in presence of SDS and β-mercaptoethanol, showed that no qualitative differences were found among the studied cultivars. Furthermore similarities between their amino acid profiles were found and all the fractions were poor in essential amino acids with albumin showing to be the less deficient. The presence of antinutritional factors such as lectins and tryp sin inhibitors was also observed. The hemagglutinating activity against trypsinized rabbit erythrocytes was detected only in the seed crude extracts, globulin, and alb:1min. The highest titer was found for the albumin fraction from Olho de ovelha and IPA-206, while for EPACE 10 there was a similar distribution among globulin and albumin. The crude extract trypsin inhibitory activities were 7.62, 6.00, and 8.39 UI/g flour for EPACE 10, Olho de ovelha, and IPA-206, respectively. The seed flour amino acid compositions of the three cultivars were deficient in methionine + 1/2 cystine, (first limiting), and valine, with chemical scores varying from 57.1 to 67.0, and 83.9 to 88.7, respectively, compared to the hypothetical protein established by FAO (1973). The feeding trials conducted with growing rats fed the experimental diets containing the seed flours as the sole protein with the chemical score varing from 57.1 to 67.0 at 10% level induced to lost of appetite, impaired growth, low values of NPU (41.5, 40.1, and 43.4), low digestibility (56.2%, 59.3%, and 59.2%) and biological value (72.3, 67.6, and 72.1) for EPACE 10, Olho de ovelha, and IPA-206, respectively, when compared to the animals fed the high quality diet containing egg white. From the data presented one can conclude that the raw seeds of Vigna unguiculata cv. EPACE 10, Olho de ovelha, and IPA-206 are of poor nutritional quality, apparently due to the low digestibility of their proteins, sulphur amino acid deficiency, and at the less extent to the presence of antinutritional factors.