Ya-Jane Wang Meng-I Kuo* Linfeng Wang James Patindol Department of Food Science, University of Arkansas, Fayetteville, AR, USA Chemical Composition and Structure of Granule Periphery and Envelope Remnant of Rice Starches as Revealed by Chemical Surface Gelatinization In this work the contribution of molecular structures to the swelling behavior of rice starches was investigated. Rice starches with different amylose contents (0 - 23.4 %) were gelatinized to various degrees (approximately 10, 20, and 50 %) with 13 M aqueous LiCl, and the surface-gelatinized starch and ungelatinized remaining granules were separated and characterized. The native starches were heated at 85 or 957C for 30 min in excess water, and the granule envelope remnants were recovered by cen- trifugation for further characterization. The remaining granules after surface removal exhibited a lower gelatinization temperature and enthalpy, and swelled to a greater extent upon heating than the native counterpart. The amylopectin molecules in granule envelope remnants obtained at 957C had larger M w (weight-average molar mass) and R z (z-average gyration radius) than those in remnants obtained at 857C. The chemical composition and structure of granule envelope remnants obtained at 857C were dif- ferent from those obtained at 957C for the same rice starch cultivar. The results imply that starch periphery may not be responsible for maintaining starch granule integrity during gelatinization and swelling. It is proposed that the composition and structure of the granule envelope remnant that maintains granule integrity are not constant but dynamic. The formation of a semi-permeable membrane-like surface structure during gelatinization and swelling is proposed to be a result of molecule entanglement after gelatinization. Keywords: Rice starch; Surface chemical gelatinization; Starch granule periphery; Swelling; Starch granule envelope Starch/Stärke 59 (2007) 445–453 445 1 Introduction Starch occurs as discrete, semi-crystalline granules that are insoluble in cold water but absorb water reversibly to a limited extent [1]. When starch slurry is heated above its gelatinization temperature, the hydrogen bonds between the crystalline lamellae of the granules are disrupted, allowing the penetration of water and hydration of the lin- ear segments of the amylopectin molecules, thus result- ing in granule swelling and leaching of soluble compo- nents [2]. It is the swelling function that contributes to the major development of functional properties of starch, such as water-holding capacity and rheological proper- ties. Starch swelling is a property of amylopectin, and amy- lose acts as a diluent [3]. Previous reports [4, 5] sug- gested that increased proportions of long B chains and longer average chain length in amylopectin may provide a stronger association of the amylopectin molecules with each other and with amylose, consequently increasing the resistance of the granule to gelatinization and swel- ling. However, Sasaki and Matsuki [6] reported that larger proportions of long chains (degree of polymerization, DP, 35) contributed to increased wheat starch swelling. Murugesan et al. [7] compared the molecular size dis- tribution of leached amyloses with those of whole amy- loses from maize, wheat, potato and sweet potato starches, and found that less branched, smaller amylose molecules leached first. They suggested that the frac- tions of large amylose molecules remaining in the insol- uble residues probably controlled the swelling of the granules during gelatinization. Mizukami et al. [8] studied the structure of leached materials in six new Japanese rice cultivars and reported that small amylopectin mole- Correspondence: Ya-Jane Wang, Department of Food Science, University of Arkansas, Fayetteville, AR 72704, USA. Phone: 11- 479-575-3871, Fax: 11-479-575-6936, e-mail: yjwang@uark. edu. * Current address: Department of Nutrition and Food Science, Fu-Jen University, Taipei, Taiwan  2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.starch-journal.com Research Paper DOI 10.1002/star.200700613