Morphological changes of blocklets during the gelatinization process of tapioca starch

After combined hydrolysis by α-amylase and β-amylase at room temperature, spherical blocklets in diameters of 27-60 nm were observed on the surface of tapioca starch granules by scanning electron micrography (SEM). Tapioca starch (1%, w/w, db, distilled water) was heated by using a rapid visco analyzer (RVA) in four different programs, then the samples were settled and freeze dried, respectively. The SEM images showed that the blocklets swelled at 52 °C; the swollen blocklets deformed to olive shape, and linked by molecular chains, formed bead-like structure at 62 °C; they started to merge at 72 °C (pasting temperature); then the blocklets fused together and their shapes disappeared completely, and the gel network formed at 95 °C. Furthermore, the morphological changes of the blocklets were not simultaneously.