Behaviour and application of colloids stabilised by hydrophobically modified starch: Impact of amylose content

Normally hydrophilic starch is modified with octenyl succinic anhydride (OSA) to provide it with emulsifying and colloid stabilising properties. As a biopolymer emulsifier, OS-starch stabilised emulsions have higher resistance to changes in environmental conditions such as pH and electrolyte, when compared to protein-based emulsifiers. This is thought to be mainly due to the provision of stronger steric stabilisation. There has been much interest in seeking the most fundamental factors leading to further improvement of OS-starch functionality, as well as its novel applications. As an example of the latter, a truly reconstitutable O/W emulsion that can be stored and transported as dried powder, and upon simple rehydration can be restored to its original droplet size, was studied here. The storage temperature of emulsion powder was found to greatly affect the rehydrated droplet size, with a powder storage temperature below the supercooling point of the oil phase being successful in fabrication of such truly reconstitutable emulsion. The achieved oil droplets were of 2 m post rehydration. In the effort to fundamentally understand and enhance the functionality of OS-starch, a systematic investigation into the relationship between the amylose content (AC) of OS-starch and its colloidal stabilising behaviour was conducted. Changes in pH and electrolyte concentration revealed that the OS-starch with lower AC exerted stronger steric stabilisation, but the interfacial layers it formed were more rapidly degraded by α-amylase. The results were further examined in light of a theoretical study concerning the impact of polymer architecture on their ability to stabilise colloids/emulsions. Linear, star-like, and dendritic amphiphilic polymers were compared for their surface affinity using Self-Consistent Field (SCF) calculations. A method for extrapolating Henry’s constant from SCF calculated adsorption isotherms was established. Just as linear diblock polymers have higher affinity for adsorption than their triblock or multi-block counterparts, the same seemed to apply for the more complex architectures. Those chains, having all hydrophobic residues concentrated in a single block, provided higher surface affinity than those with hydrophobic groups distributed in several smaller blocks. Understanding the behavioural difference of OS-starch of varying AC not only provides opportunity for further improving its functionality, but also opens possibility for customising tailored release profiles. This can be achieved by suitable mixing of multiple OS-starch emulsions, stabilised by OS-starch of disparate amylose contents.