PROTEIN-QUALITY OF IRRADIATED BRAZILIAN BEANS

Beans are a major source of dietary protein in Brazil. However, high l osses due to insect infestation occur after each harvest. To combat th ese losses, radiation processing of beans offers promise as an alterna tive to chemical treatment, provided the nutritional quality of beans is not impaired by the radiation treatment. Conflicting results have b een published about the effect of radiation on the biological value of legume proteins. Therefore, two varieties of Brazilian beans were stu died: 1) Phaseolus vulgaris L., var. carioca and 2) Yigna unguiculata (L.) Walp, var. macacar. The beans were irradiated with doses of 0, 0. 5, 1.0, 2.5, 5.0 and 10 kGy. Since irradiated beans will be consumed a fter appropriate storage, the beans under study were stored for 6 mont hs at ambient temperature. Protein quality was measured by a biologica l assay employing the nitrogen balance approach in weanling rats. The animals were fed with optimally cooked beans, which were the only sour ce of protein (similar to 10%). Nitrogen contents of legumes, diets, a nimal urine and faeces were determined by Kjeldahl analysis. The indic es for apparent protein quality: net protein utilisation, digestibilit y and biological value were not influenced by irradiation. Thus, radia tion treatment of Brazilian beans offers considerable promise as an ef fective insect disinfestation process, without impairing the biologica l quality of the valuable bean protein.