Physiochemical and thermal characteristics of starch isolated from a waxy wheat genotype exhibiting partial expression of Wx proteins

Authors: JUNG, TAEK-HEE - Chonbuk National University; KIM, JAE - Korea University; Baik, Byung-Kee; PARK, CHUL - Chonbuk National University

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2014
Publication Date: 1/1/2015
Publication URL: http://handle.nal.usda.gov/10113/60567
Citation: Jung, T., Kim, J.Y., Baik, B.-K., Park, C.S. 2015. Physiochemical and thermal characteristics of starch isolated from a waxy wheat genotype exhibiting partial expression of Wx proteins. Cereal Chemistry. 92(1):14-21.

Interpretive Summary: The discovery and development of waxy and partial waxy wheat genotypes have provided us with starches possessing a wide range of amylose content and functional properties, which could be useful for improvement of cooking, textural and shelf-life qualities of many wheat foods, and also as sources of starch exhibiting unique functional properties. Being a hexaploid crop, common wheat carries three different genomes called A, B and D, and accordingly three waxy genes, one in each genome. The waxy genes encode granular-bound starch synthases (GBSS), which are responsible for synthesis of amylose during the grain-filling period. A wild type genotype carries all three fully active waxy genes and produces starch of about 25% amylose, while a waxy wheat genotype is null in all three waxy genes and consequently produces starch composed mainly of amylopectin with little to no amylose. Partial waxy wheat genotypes, carrying one or two null waxy genes, produce starch composed of 17 to 25% amylose. Waxy wheat genotypes, on the other hand, contain less than 3% amylose; thus there is a significant gap in starch amylose content between less than 3% amylose in waxy wheat starch and about 17% amylose in double-null partial waxy wheat starch. Through a cross between waxy and wild type parental genotypes, and subsequent intensive selection, a unique waxy wheat genotype, which carries uncommon and different alleles on waxy loci from those of wild type wheat, was developed and compared to the parental waxy and wild type wheat genotypes for starch characteristics. The mutant waxy genotype exhibited a lower degree of waxy gene expression and consequently a lower level of GBSS than wild type wheat, and yielded starch composed of an intermediate amylose content (of about 10%) between waxy and wild type wheat. As expected from its amylose content, the starch pasting properties, gel hardness, swelling volume and power, paste clarity, degree of crystallinity, starch gelatinization and retrogradation characteristics of the mutant waxy genotype were all significantly different from, and intermediate between, those of the waxy and wild type parental varieties. With amylose content of starch not available from the existing wild type, waxy and partial waxy wheat genotypes, this new genotype of wheat would contribute to the increased genetic diversity in starch characteristics of wheat and would be a valuable resource for production of flour with starch of about 10% amylose, which is ideal for foods requiring intermediate starch properties between wild type and waxy wheat.

Technical Abstract: A unique wheat genotype carrying waxy type allelic composition at the Wx loci, Gunji-1, was developed and its starch properties were evaluated in comparison to parental waxy and wild type wheat varieties. Gunji-1 was null in all three of the Wx genes, but exhibited a lower level of Wx proteins than the wild type. Starch amylose content and cold water retention capacity were 10.1% and 70.5% for Gunji-1, 4.2% and 76.6% for waxy, and 27.9% and 65.0% for wild type, respectively. No significant differences were observed in microstructure, granule size distribution and X-ray diffractograms of the starch granules isolated from Gunji-1 compared to those of waxy and wild type wheat varieties. Starch pasting peak, breakdown and setback viscosities and peak temperature of Gunji-1 were intermediate between waxy and wild type wheat. In starch gel hardness, Gunji-1 (1.1 N) was more similar to waxy wheat (0.5 N) than to the wild type variety (17.6 N). Swelling power, swelling volume, paste transmittance during storage, and gelatinization enthalpy of Gunji-1 were lower than those of waxy wheat but greater than those of wild type wheat. Retgrogradation of starch stored for one week at 4'C expressed with DSC endothermic enthalpy was absent in the waxy wheat variety, whereas Gunji-1 exhibited both retrogradation of amylopectin and amylose-lipid complex melting similar to the wild type parent, even though enthalpies of the former were much smaller than the latter.