Effect of succinylation of cottonseed flour during protein extraction on the yield and some of the properties of protein isolates

A new method has been developed to improve extraction and recovery of protein isolates, which are highly water‐soluble, low in sensitivity to calcium precipitation and light‐colored, from defatted cottonseed flour. Optimal conditions include extraction of flour with acidified n‐butanol (pH 4.5) to remove chromophores, succinylation of proteins at pH 8.5 using succinic anhydride at a concentration of 30% on protein basis, and precipitation of protein at pH 4.5. The resulting succinylated isolates contain more hydrophobic and neutral amino acids than untreated isolates. Gel filtration chromatography and polyacrylamide gel electrophoresis of protein isolates (water‐, salt [4% NaCl]‐ and alkali [0.2% NaOH]‐soluble), sequentially fractionated from succinylated and untreated flours, suggest that succinylation converts much of the salt‐ and alkali‐soluble proteins to water‐soluble forms. Succinylation increases emulsion stability of isolates. The 3 succinylated isolates showed similar Chromatographie patterns on Sephadex G‐100 columns and clectrophoretic mobilities in polyacrylamide gels, whereas the corresponding 3 isolates from untreated flour had different gel patterns and mobilities. Mobilities of major protein components of the 3 isolates were increased by succinylation.