Effect of different alcoholic-alkaline treatments on physical and mucoadhesive properties of tapioca starch

Alcoholic-alkaline treatment (AAT) is a physical modification method for the production of granular cold water swelling starch and should be optimized for each starch source. The main objective of this research was to investigate physical and mucoadhesive properties of tapioca starch (TS) modified by different AATs. Improvement of cold-water absorption, solubility, rheological properties at low temperatures, clarity, freeze-thaw stability, and mucoadhesion was positively correlated with the alkali amount and reaction temperature and negatively correlated with ethanol content. Morphological studies demonstrated different degrees of swelling, birefringence loss, and surface wrinkling of granules depending on modification degree. Starch pastes, modified in a higher degree, showed a change from rheopexy to thixotropy and from translucency to turbidity over time. The highest quality along with maintaining granular integrity was obtained by treating starch (10 g) with 30 g alkaline solution (2.5 M) and 110 g aqueous ethanol (40%) at 25 °C. The characteristics of this sample were higher than those of corn counterpart except for viscosity, consistency, and freeze-thaw stability and were almost similar to those of thermally gelatinized TS (TGTS). Therefore, this AA-modified TS can be an alternative for TGTS in instant and heat-sensitive foods and delivery of bioactives as a mucoadhesive polymer.