Algumas propriedades fisico-quimicas e nutricionais das proteinas da soja
Pedro Luiz Antunes
DATA DE PUBLICAÇÃO
Some physlcal-chemical properties and nutritive value (PER) or soy proteins were studied on products prepared in the laboratory and on soybeans and meals from differents stages of an oil industry processing line. In the processing of soy, heat-treatment is necessary to destroy anti-nutritional factors. However, an excess of heating will decrease the availability of soy nutrients. Therefore heat-treatment for two of the most well known anti-nutrutritional factors - trypsin inhibitor and hemagglutinin - was studied on samples at different physical states and water contents. It was found that 25, 15 and 10 minutes in boiling water were necessary for total destruction of trypsin inhibitor activity in unsoaked beans, beans soaked in water for 12 hours and beans soaked for 12 hours and dehulled, respectively. For total destruction of trypsin inhibitor, in solution, heating for 30 mi¬nutes in autoclave (121°C) was necessary. For destruction of hemagglutinin activity in unsoaked beans it was necessary to heat 45 minutes in bowling water, whereas, only 7.5 minutes of heating of a water extract, in boiling water, was needed for complete inactivation. As these determinations are not simple enough to be used as a rout1ne procedure for estimating the extent of heat-treatment and for quality control of soy products, industries use routinely, protein solubility and urease residual activity determination, as index or heat-processing. For comparison purposes, urease activity and protein solubility in water were determined in all samples studied. It was shown that good apparent correlations exist between inactivation or trypsin inhibitor and urease, and, decrease in solubility of the proteins, when heat-treatment is applied on unsoaked beans or soy products and by-products with low moisture" content. Good correlation seems not to exist on heated liquid products, because, within creasing water content of the beans or, or the products, urease activity and protein solubility decrease much faster than the activity of the trypsin inhibitor. For extraction of soybean proteins the best solid: solvent ratio round was 1:30 (w/v). Effects or concentration of KOH and pH on soy protein solubility (extraction) were also studied. It was found that the effect of increasing pH and KOH concentration on improving salubillty is more pronounced in denatured protein systems. It was shown that 0.1% KOH in water, extracted 70-80% of the pro¬teins of heat-treated soy products, whereas, solubility of the same proteins in water alone was lower than 10%. Heating soybeans in boi1ing water up to 30 minutes increased lysine availability and, further heating, decreased it. Heat-treatment applied by the oil industry decreased lysine avallability of soybean meals. Growth studies conducted with rats permitted the evaluation of protein efficiency ratio (PER) on by-products of the oil industry, as well as, on different products prepared in the laboratory. Calculated PER were as follows, for industry samples: 1. grinded soybean without heat-treatment (-1.08); 2. laminated grinded soybean with little heat-treatment, 2.24; 3.soybean meal after solvent extraction of oil 2.44; toasted soy bean mea1, 2.31; 5. commercial protein isolate, as sodium proteinate, 1.72. The following products prepared in the laboratory were all so tested: 6. defatted soybean flower, 2.66; 7.full-fat dried soymilk, 1.75; 8. isoelectric protein isolate, 2.02; 9. residue (insoluble) of soymilk,extraction, 1.30; 10. casein standard 3.36.