Physicochemical and functional properties of tetraploid and hexaploid waxy wheat starch

Waxy wheats possess unique starch functional properties that may be useful in specific end-uses. To assess the physicochemical, thermal, and pasting properties, starches from seven waxy genotypes originating from two wheat classes, tetraploid durum and hexaploid hard red spring (HRS), were evaluated and compared with their counterpart non-waxy wild types. The amylose content ranged from 2.3% to 2.6% in waxy durum lines, compared to 29.2% in normal durum control, and 2.1% to 2.4% in waxy HRS, compared with 26.0% in normal HRS control. Significant differences in the degree of crystallinity were observed between the waxy and control starches, despite similar A-type X-ray patterns, although differences between the two wheat classes were non-significant. Both, control and waxy starches displayed an X-ray peak corresponding to the amylose-lipid complex, but the intensity of the peak was markedly lower in the waxy starches. The waxy durum starches exhibited the highest transition temperatures as measured by Differential Scanning Calorimetry (DSC), whereas, the enthalpy of gelatinization of most waxy genotypes was statistically higher than that of the controls. All waxy starches displayed high peak viscosity, high breakdown, and low setback profile as measured by the Rapid Visco Analyser (RVA). Texture analysis of RVA gels revealed significant differences between waxy and non-waxy wheats, as well as between waxy tetraploid and hexaploid wheats, confirming that the nature and class of wheat starch would play a significant role when using waxy wheat blends in different wheat-based products.