Composição e propriedades nutricionais das proteinas do feijão rosinha G2 (Phaseolus vulgaris, L.)

AUTOR(ES)
DATA DE PUBLICAÇÃO

1978

RESUMO

Percent composition, toxicity, effect of heat-treatment on the inactivation of toxic components and on the improvement of nutritional value of the raw bean (Phaseolus vulgaris, L.), variety Rosinha G2 was studied. The above investigation was extended also to different fractions obtained from the integral flour, i.e., total protein isolate, albumin, globulin, total water soluble solids, water insoluble solids and the total dialyzable solids. Influence of the storage conditions and addition of free methionine on the biological value of the bean proteins, as well as on the organoleptic and cooking properties of the bean kernels was also studied. The integral flour contained 26% protein (dry basis) and the above mentioned fractions 82, 70, 90, 50, 15 and 20%, respectively. The a¬mino acid composition was similar in all materials being, characterized by a low content of sulfur-containing amino acids 0.84g/16g N of methionine, and 0.54g/16g N of cyteine and a high content of lysine (7.9g/16g N). Heat-treatment reduced available lysine from 6.0 to 3.5g/16g N. The activity of the antinutritional factors (trypsin, chymotrypsin inhibitors and phytohemagglutinin) was highest in the a1bumin fraction, where 376 units of trypsin and 115 units of chymotrypsin were inhibited per mi1igram of protein. Hemagg1utination occurred with 0.12μg protein per milliliter. Heat resistance of hemagglutinins was low (5-l0min at 97°C). The trypsin and chymotrypsin inhibitors were easily inactivated in the whole bean (10min at 97°C) whereas in aqueous solu¬tion the heat resistance was very high; one hour at l2l°C not being sufficient for their complete inactivation. The digest¬ibility of the bean protein increased significantly with heat treatment particularly for the isolated protein fractions reaching values as high as 80%. In the integral flour the di¬gestibility remained low (61%) even after heat-treatment. Short heat-treatment (5-l0min, l2l°C) improved the protein nutritive value, whereas treatment beyond 10min in an autoclave was detrimental to the nutritive value, even though these treat¬ments were not sufficient to completely eliminate the activity of the known antinutritional factors. Unheated material killed all the experimental rats in a period ranging from three to twenty three days. Storage of the beans under different condition ad¬versely affected the biological value of the proteins. The e¬ffect was greater as the storage temperature and humidity in¬creased. The conditions used were: l2°C and 52% R.H., 22-25/C and 65-70% R.H. and 37°C at 76% R.H. during six months. At 37°C and 76% R.H., the PER value dropped from 1.0 to 0.1 while the available methionine decreased from 46 to 28% and available cysteyne from 52 to 30%. For the same sample the cooking time increased from 60 to 240min and the texture, extrusion in the Instron, from 238 to over 500kg-force. Percentage of hard shell kernels increased only for the sample stored at environmental conditions of the laboratory (22-25°C and 65-70% H.R.). Incorporation of methionine (3% of the protein) raised PER of the bean to the level of 2.5 even in beans that previously stored for six months. Addition of methionine the were to the isolated protein fractions had still a much greater effect raising the PER values from 0.72, 0.59 and 0.68 to 4.0, 4,3, and 4.4 for the albumin, globulin and total protein isolate , respectively. A set of conditions was established to introduce methionine to the whole bean by infusion. The best approach was to soak the bean in a5% methionine solution (1:2 ratio) at 50°C for 1 hour. By this procedure the methionine content of the bean was increased from 1.5 to 24g methionine per l00g bean protein. The infused beans when mixed with the non-infused ones at a 1:7 ratio gave a product with approximately 3g methionine per 100g bean protein with a PER of 2.4.

ASSUNTO(S)

proteinas feijão

ACESSO AO ARTIGO

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