Role of Endogenous Protein in the Spherical Aggregation of Taro Starch Granules upon Spray-Drying and in In Vitro Digestibility

The role of endogenous protein in the formation of spray-dried taro starch spherical aggregates is studied in this work. Taro starch dispersions (30 g per 100 mL water) are added with different protease concentrations (0.0, 1.0, and 5.0 × 10³ IU protease per g starch) for degrading the surface protein of the starch granules. Protease treatment has a negative effect on the formation of starch aggregates, which are scarce and irregular. The incorporation of exogenous protein in the form of whey protein isolate (WPI) improved the formation of starch aggregates, but with non-spherical morphology. Fourier transformed infrared (FTIR) analysis reveals that the formation of random structures at the expense of β-structures (up to 65%) in proteins is the mechanism responsible for the spherical aggregates formation. In vitro digestibility tests show that spherical aggregates are less digestible (≈19% of RDS) than native taro starch (≈40% of RDS), an effect that might be attributed to increased ordering and crystallinity (≈34% for spray-dried starch) induced by thermal modifications in the spray-drying process.