Charge and zeta-potential distribution in starch modified with octenyl succinic anhydride (OSA) determined using electrical asymmetrical flow field-flow fractionation (EAF4)

Starch modified with octenyl succinic anhydride (OSA) is extensively used due to its emulsifying capacity. Modification with OSA renders the starch surface active but also anionic at intermediate pH. The amount of OSA that is grafted to the starch polymer backbone will influence the functionality. Likewise, it can be expected that the distribution of the substituents over the molar mass distribution will play an important role for the behavior and functionality. Electrical asymmetrical flow field-flow fractionation (EAF4) could provide charge-size dependent separation of samples with different charges. A major advantage is that zeta-potential and size/molar mass distribution can be simultaneously determined. The present study investigates if EAF4 can be used to determine the charge properties over molar mass (or size) distribution of barley starch modified with OSA. The results show that zeta potential and net charge could be estimated over the larger part of the OSA-starch molar mass distribution. Furthermore, the OSA substituents do not appear to be evenly distributed at or close to the "surface" of the polymers, which may have implications for the adsorption behavior and functionality of OSA-starch in emulsions. To the best of our knowledge, this is the first report on applying EAF4 for the characterization of biopolymers and the first time that zeta potential can be determined over the molar mass distribution.