Commercial soy flours and grits are classified according to their Nitrogen Solubility Index (NSI), or their Nitrogen Dispersibility Index (NDI). These parameters indicate the extent of protein solubility
which is significantly affected by treatments used for its production. Moist heat treatments used to inactivate (denature) trypsin inhibitors and lipoxygenase will also denature and precipitate other soy proteins leading to lower protein solubility (Hettiarachchy and Kalapathy, 1999). Flours made from ‘‘white flakes’’ have NSI values of about 80%, while those made from toasted flakes show NSI levels of 10–20%. Other grades are available over the entire range of intermediate NSI values. The specification of a precise value of NSI reflects a compromise between the need to maintain the functional properties of the soy proteins or some enzyme activity, and the desire to inactivate anti-nutritional factors and eliminate the beany taste (Berk, 1992). Additional details on soybean processing conditions used to make human food fractions can be found in Appendix A, Supplementary data.