Enhancing storage stability of emulsions by binding detergents with soy protein isolate and its hydrolysates

Abstract

AbstractSodium dodecyl sulfate (SDS) is a frequently used anionic detergent, and proteins are among the widely used minor ingredients in cosmetic products. Proteins may enhance the detergent functions and protect human skin from irritation caused by detergents. Soy protein hydrolysates (SPH) were prepared by modifying soy protein (SP) with papain. Varying concentrations of SP or SPH were mixed with various concentrations of SDS at different pH values to determine: (i) molecular characteristics, degree of hydrolysis (DH), and surface hydrophobicity (S0) of SP and SPH; (ii) the effect of SDS concentrations on the S0 of SP; (iii) the storage stabilities of oil‐in‐water emulsions formed by SDS, SP, SPH, SP‐SDS, and SPH‐SDS; and (iv) the effect of protein concentration (0.01 to 1.5%), DH (1.2 to 12.5%), and pH (3.0, 5.0, 7.0, and 9.0) on storage stabilities of emulsions formed by SP‐SDS or SPH‐SDS. An increase in emulsion stability (ES) with increasing protein concentration was observed. The ES values of emulsions formed by SPH‐SDS complexes were significantly higher than those formed by SP‐SDS at pH 7.0 and 9.0. The ES of emulsions formed by the complexes were low at pH 5.0 and increased with increasing pH. At pH 3.0 the emulsions formed by SP‐SDS at 1 to 1.5% protein concentration and by SPH‐SDS at 1.5% protein concentration were very stable. The results indicate that at least one‐half of SDS content can be replaced by SP or SPH while maintaining emulsion stability.