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

A unique wheat genotype carrying waxy-type allelic composition at the Wχ 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 Wχ 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 with 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. Retrogradation 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 Gunji-1 were much smaller than the wild-type parent.