Effect of amylose and amylopectin content on the colloidal behaviour of emulsions stabilised by OSA-Modified starch

Abstract

The impact of the amylose content (AC) of hydrophobically modified starch on its emulsion stabilising behaviour has been examined in this study. Waxy maize (W) and normal corn starches (N) with different amylose contents, 5.48% and 28.37% respectively, were hydrophobically modified with Octenyl Succinic Anhydride (OSA) (3%) and used to fabricate oil-in-water emulsions. Emulsion samples were compared for their colloidal stability against pH change, increase of electrolyte concentration and enzymatic treatment by amylase. The amylose content of the OS-starch made a pronounced difference to emulsion stability in all cases. Increases in the electrolyte concentration, or decrease of pH to low values, left emulsions stabilised by OS-N (medium AC) strongly flocculated. However, little coalescence of droplets was detected, even after 21 days. In comparison, the OS-W (low AC) stabilised emulsion remained well dispersed throughout the entire storage period, following changes to pH or raised salt concentrations. The contrast between the behaviour of the samples is attributed to the provision of sufficient steric interactions by OS-W emulsifier but not OS-N. Destabilisation following α-amylase treatment revealed a different trend, with both in vitro and in vivo digestion experiments leaving the low AC (OS–W) stabilised droplets showing extensive coalescence immediately post treatment. Over the same short period, the OS-N stabilised emulsions became flocculated, but again without much droplet coalescence. The enzymatic degradation of OS-N interfacial layers seems to proceed more slowly than the OS-W samples. Varying destabilisation rates provide a means for realising tailored release profiles of flavours or active ingredients, achieved in principle by appropriate mixing of several emulsions stabilised by different AC modified starch.