Surface properties of water soluble maltodextrin, starch acetates and starch acetates/alkenylsuccinates

Surface and interfacial tensions with hexadecane were measured for water soluble maltodextrin and starch ester solutions in order to determine their potential as stabilizers or emulsifiers. The surface tension for an acid hydrolysed starch (maltodextrin) initially declined with concentration and then reached an equilibrium value of 56 mN/m at 20–40 wt.%, suggesting that hydrated starch has this surface energy. Surface and interfacial tensions of starch acetates decreased more rapidly with concentration reaching values of 41–44 and 11–13 mN/m, respectively, at 40 wt.%. There was little dependence of surface or interfacial tensions on degree of substitution between 0.3 and 0.8 and amylose content of starch acetates. Surface and interfacial tensions for starch acetate/alkenylsuccinates were lower than those for starch acetates, particularly at low concentrations. Emulsions of soybean oil/water mixtures were stabilized for >1 day by waxy starch acetate/octenylsuccinate and acetate/dodecenylsuccinate but not starch acetates. In summary, these starch esters may represent biodegradable, economical alternatives to some emulsifiers and coating polymers currently in use.