Biological evaluation of a protein isolate from cowpea (Vigna unguiculata) seeds

The present work was carried out to determine the nutritive quality of a protein isolate from cowpea (Vigna unguiculata) seeds. Previous data from our laboratory showed that cowpea protein isolate (CPI) presents good functional properties, including solubility, emulsifying and foaming activities. In this work, rats were divided into three groups that received, during 16 days, liquid diets containing casein or CPI as protein sources or a protein-free diet. The nutritional parameters measured for the diet containing CPI showed a positive nitrogen balance (NB=0.5), a net protein retention (NPR) of 0.7 and digestibility of 87%. Furthermore, CPI did not present detectable hemagglutinating activity and very low trypsin inhibitory activity (18 TIU/mg protein) after heat treatment. In terms of its essential amino acid content, CPI presented a better composition than purified cowpea vicilin. No significant histological differences were found in several internal organs of the rats that were fed a diet containing CPI when compared to the group fed with a casein-containing diet. Taken together, these results suggest that CPI may provide a new, inexpensive source of protein for use as a potential functional and nutritional agent in the food industry.