Effect of some variables on the extractability of proteins,urease activity,free alpha-amino groups and soluble carbohydrates from soybean meals

The effect of several variables on the extraction of soybean meal protein has been investigated. Solubility studies of the meal show that globulin is the main protein component. Overnight suspension and a meal to solvent ratio 1:10 (w/v) were found to extract maximum amount of protein in distilled water adjusted to pH 6.4 (91.07%). More protein was extracted by diluted sodium hydroxide solutions (0.02 M) adjusted to various alkaline pH-values. Results with several other salts show that concentration as well as pH are very important factors in controlling the percentage of protein extracted. The optimum temperature of extraction was 70°C for 30 minutes, although over a temperature range of 60–75°C the extraction remains essentially constant. Destruction of urease activity was achieved by heating the suspended meal at 75°C for 45 Min. The kinetic inactivation of the enzyme was studied and the energy of inactivation was found to be 32.575 K cal. The level of free alpha amino groups in soybean meals ranged from 5.50 grams: 16 gram nitrogen in meal extracted with 0.1 N HCL adjusted to pH 5.0 to 1.71/100 grams protein (in meal extracted with distilled water.). Their level correlated significantly (p=0.01) upon heat treatment with the carbohydrate content of the corresponding meal. Contrary tothe protein solubility pattern, the -NH₂ groups decrease considerably upon longer exposure to temperatures between 60–75°C.