Emulsifying properties of soy protein isolate fractions obtained by isoelectric precipitation

Soy protein isolate (SPI) fractions were produced by isoelectric precipitat ion based on results of isoelectric focusing carried out on the crude soy e xtract. The fractions were produced from crude protein extract (pH 9.0) seq uentially and non-sequentially at isoelectric points (pIs) of 5.6, 5.1 and 4.5. Emulsions stabilised by soy proteins with pIs between 5.6 and 5.1 had the highest (P <0.01) emulsion stability index (ESI), while those stabilise d with proteins having pIs between 5.1 and 4.5 resulted in the lowest ESI f or sequentially precipitated fractions. Non-sequential fractionation at pI 5.1 produced fractions with higher emulsifying activity index (EAI) than se quential fractionation. SDS-PAGE profiles indicated that the fractions exhi biting high functionality in terms of ESI and EAI were also richer in 7S gl obulin protein subunits. (C) 2001 Society of Chemical Industry.