Starch morphological and molecular structural relations to amylolysis

• Author / Creator

  Naguleswaran, Sabaratnam

• The objective of this research was to investigate the impact of variation in starch morphology and molecular structure among starches isolated from triticale, wheat, corn and barley (normal, waxy, and high-amylose genotypes) on amylolysis. Native starch granules in their unfractionated and fractionated (large and small granules) forms were characterized in terms of their composition, morphology, physicochemical properties and molecular structure [amylopectin (AP) and amylose (AM)]. The degree of hydrolysis (DH) was determined (55oC for 1h and then at 30oC for 72h) using a mixture of α-amylase and glucoamylase. SEM and CLSM studies revealed that surface pores and internal channels were mainly present in large granules of triticale, wheat and corn starches. In corn starches, the surface pores and channels were filled with protein and phospholipids. AM content and crystallinity of starches varied among genotypes, and between large and small granules within a source. Regardless of genotypes, the DH at the initial stage (1h) of hydrolysis of unfractionated triticale was higher than wheat, corn and barley starches. In fractionated starches, small granules were hydrolyzed (at 1h) to a greater extent than large granules due to their larger surface area per unit mass. The data on AP molecular characteristics showed that the average chain length (average-CL) was negatively correlated to weight-average molecular weight (Mw), molecular-size or radius of gyration (Rz), molecular density (ρ) and degree of branching (DB). The enzyme hydrolysis data indicated that, at all stages of hydrolysis, AP was hydrolyzed to a greater extent than AM. Whereas, variation in DH among isolated AP or isolated AM from different starch sources was generally insignificant at all stages of hydrolysis. Furthermore, it was observed that the DH (at 1h) of native unfractionated starches was negatively correlated to average-CL, but positively correlated to Mw, Rz, ρ and DB. Overall, this study indicated that starch amylolysis is influenced by the interplay among: 1) composition (AM content), 2) morphological characteristics (granule size, channels/pores, and associated proteins and phospholipids) and 3) difference in granular architecture (resulting from variation in the AP average-CL).

• Subjects / Keywords

  • Starch
  • Amylolysis
  • Cereals

• Graduation date

  Spring 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R35Q8P

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.