Cereal Chem 43:261 - 269.  |  VIEW ARTICLE

Nitrogen Solubility Index, Isolated Protein Yield, and Whey Nitrogen Content of Several Soybean Strains.

A. K. Smith, J. J. Rackis, P. Isnardi, J. L. Cartter, and O. A. Krober. Copyright 1966 by the American Association of Cereal Chemists, Inc. 

Two modified procedures were developed to determine nitrogen solubility index (NSI). Both methods used a double extraction of dehulled, defatted soybean flakes. The first, on a 40-g. sample, had water-to-meal ratios of 20:1 and 10:1, with slow paddle stirring at 30 C. and pH 7.2; the second, on a 2-g. sample, ratios of 60:1 and 50:1, with magnetic stirring at room temperature. Flaking cracked beans tempered to 14% moisture facilitated rapid extraction of oil and elimated the need for grinding defatted flakes to obtain maximum and reproducible NSI values. Lower water-to-meal ratios, pH, and other type of grinding reduced NSI values somewhat. Average NSI values of 93.6 (range 91-97) were obtained with both methods on 26 soybean strains. Their yield of isolated protein varied from 39 to 56 g./100 g. dehulled, defatted meal (moisture-free basis). The nitrogen content of isolated protein varied between 13.4 and 15.2%. The small differences between strains in NSI would not aid in genetic selection of soybeans suitable for food and industrial use; however, the large differences in yield of isolated protein correlate directly with the protein content of the meal.