No abstract

In this work we have determined the phenolic composition of raw cowpeas (Vigna sinensis L) of the variety Carilla by HPLC/PAD/MS and have studied the effect of fermentation, both spontaneous and with Lactobacillus plantarum ATCC 14917, on the phenolic compounds. This variety contains mainly ferulic and p-coumaric acids esterified with aldaric acids, together with the cis and trans isomers of the corresponding free acids. Hydroxybenzoic acids such as gallic, vanillic, p-hydroxybenzoic and protocatechuic were also found, along with flavonols such as a myricetin glucoside, mono-and diglycosides of quercetin and a quercetin diglycoside acylated with ferulic acid. Fermentation, both spontaneous and inoculated, modifies the content of phenolic compounds, but differently in each case. The antioxidant activity as free radical-scavenging activity has also been evaluated. Fermentation followed by heating has been shown to be a very effective process to increase the functionality of this variety of V sinensis. For this reason, this cowpea variety could be used as an ingredient to obtain high value-added flours.

Studies were carried out to determine the possible relationship between the color of the seed coat of beans and the nutritive value of its protein. Beans with white, red and black seed coats and a black coated bean and its white mutant were chosen for the study. Hemagglutinin activity was located in the cotyledons of all samples with low activity in the seed coat. No activity was found in the cooked beans or in the cooking broth. Trypsin activity was influenced by a heat labile factor (true trypsin inhibitor) and by a heat resistant factor (tannins). The heat labile factor or true trypsin inhibitor was higher in the cotyledons (16-18 TUI/mg sample) than in the seed coat, while the heat resistant factor was found in highest concentration in the seed coat. Red and black seed coats had a higher concentration (23-31 TUI/mg sample) of the heat resistant factor than the white seed coat of the normal white bean and of the mutant (7-9 TUI/mg sample). Cooked beans and their broth showed trypsin inhibitor activity of the heat resistant type. Cooked cotyledons had 5-9 TUI/mg sample. Tannin concentration was high in colored seed coats (38-43 mg/g) and low in white coated beans (1.3 mg/g) while values ranged from 3.8-5.9 mg/g in the cotyledons. A highly significant correlation (r = 0.88) was found between tannin concentration in the seed coat and trypsin inhibitor activity. No correlation between these two components was found in the cotyledons. Samples of cooked beans supplemented with methionine without the cooking broth had higher protein quality values (2.9-3.3) than samples fed with the broth (1.7-2.1). Protein digestibility was lower for red (70.4%) and black beans (75.0%) fed with the broth than beans fed without the broth (78.7% and 77.9% respectively), but the broth had no effect on the protein digestibility of white coated beans (81.3 and 81.4%). The data suggest that color of the seed coat is related to the protein quality of beans.