title: Correlated changes in structure and viscosity during gelatinization and gelation of tapioca starch granules.
abstract: Melting of native tapioca starch granules in aqueous pastes upon heating is observed in situ using simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) and solution viscometry. Correlated structure and viscosity changes suggest closely associated amylose and amylopectin chains in the semicrystalline layers, and the release of amylose chains for enhanced solution viscosity occurs largely after melting of the semicrystalline structure. Before melting, WAXS results reveal mixed crystals of A- and B-types (∼4:1 by weight), whereas SAXS results indicate that the semicrystalline layers are composed of lamellar blocklets of ca 43 nm domain size, with polydisperse crystalline (≃7.5 nm) and amorphous (≃1.1 nm) layers alternatively assembled into a lamellar spacing of ≃8.6 nm with 20% polydispersity. Upon melting, the semicrystalline lamellae disintegrate into disperse and molten amylopectin nanoclusters with dissolved and partially untangled amylose chains in the aqueous matrix which leads to increased solution viscosity. During subsequent cooling, gelation starts at around 347 K; successively increased solution viscosity coincides with the development of nanocluster aggregation to a fractal dimension ≃2.3 at 303 K, signifying increasing intercluster association through collapsed amylose chains owing to decreased solvency of the aqueous medium with decreasing temperature.
authors.affiliation: Department of Chemical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan.
authors.forename: Hsien-Kai
authors.initials: HK
authors.lastname: Huang
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: Hwo-Shuenn
authors.initials: HS
authors.lastname: Sheu
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: Wei-Tsung
authors.initials: WT
authors.lastname: Chuang
authors.affiliation: Department of Chemical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan ; National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: U-Ser
authors.initials: US
authors.lastname: Jeng
authors.affiliation: Department of Chemical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan.
authors.forename: An-Chung
authors.initials: AC
authors.lastname: Su
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: Wei-Ru
authors.initials: WR
authors.lastname: Wu
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: Kuei-Fen
authors.initials: KF
authors.lastname: Liao
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: Chun-Yu
authors.initials: CY
authors.lastname: Chen
authors.affiliation: Department of Agricultural Chemistry, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Shing-Yun
authors.initials: SY
authors.lastname: Chang
authors.affiliation: Department of Agricultural Chemistry, National Taiwan University, Taipei 106, Taiwan.
authors.forename: Hsi-Mei
authors.initials: HM
authors.lastname: Lai
keywords: SAXS/WAXS; gelatinization; gelation; tapioca starch granules; viscosity