Parameters Affecting Milling Qualities of Undefatted Soybeans (Glycine max, L. Merill) (2): Selected Physical Properties

Soybean protein is highly rich in the essential amino acid needed by human body. In the developing countries, its use will be more generally acceptable when converted to flour like wheat. This work focused on establishing the optimum conditions of some physical characteristics of soybean for high quality and acceptable soy flour. The characteristics studied for soybean samples subjected to heat treatment of boiling and oven drying were the effect moisture content (MC) and the hull thickness on the quality of the flours. Ten samples of Tax 1485 at different moisture levels ranging from 20.6% to 8.6% and five varieties (Tax 1440-1E, Tax 1740, Tax 1485, Tax 1456 and Tax 1448-2E) obtained from International Institute for Tropical Agriculture (IITA), having different hull thicknesses were used. Soybean with mixed varieties commonly found in the open markets was also used to compare the effects of MC on the studied parameters. Flours obtained from the samples milled in an attrition mill were subjected to proximate, sieve and organoleptic evaluations. The hull thickness was found to have no correlation with protein retention, acceptability and flour yield, but moisture content has a very significant effect on the qualities. Between moisture content of 20.6% and 8.6%, protein and acceptability reduced from 40.0% to 27.7% and 4.3 to 2.2 respectively while yield increased from 0.9% to 5.8%. Though protein was reducing with reduced MC, there was no significant difference (p<0.05) in protein retention between MC of 20.6% and 10.1% but it became significant at 9.4%. There was no significant difference in acceptability from 13.6% to 8.6% MC and between 8.9% and 11.0% MC for flour yield. Both Tax 1485 and mixed varieties followed the same trend only that they have different absolute values. The mixed varieties however had no significant difference in protein content between 19.8% and 10.2% MC. These results, therefore established that to obtain acceptable soyflour of high flour yield and protein content, moisture content of soybean after processing should be about 10% (dry basis).