Lipid components that reduce protein solubility of soy protein isolates

A lipid fraction from a commercial soy protein isolate (SPI), previously found to be detrimental to SPI solubility, was analyzed by size-exclusion liquid chromatography, by high-performance liquid chromatography (HPLC), and for chemical composition. The molecular weight of most of this material was greater than 1,100 daltons. This lipid fraction was water-soluble yet required a strong nonpolar solvent mixture to elute it from a C-18 HPLC column. The lipid material was alkaline (pH 8.7) and composed of 3.0% nitrogen, 1.6% phosphorus, 17.5% nonvolatile crude fatty acids (primarily hydroxylated), 10.4% long-chain bases, 9.9% hexuronic acid, 3.2% hexosamine, and 6.6% total sugar. The molecular weight, chemical composition, and physical characteristics (solubility characteristics, surfactant characteristics, and appearance) of this material were all similar to those reported for phytoglycolipid.