| Fourteen varieties of wheat, and one sample each of triticale and corn, grown in western Canada were assessed for differences in starch content and structure and their susceptibility to industrial alpha-amylase once gelatinized. Starch content was found to vary significantly between samples and correlated strongly with protein content (r=-0.895, P<0.001). AC Andrew, a soft white spring (SWS) wheat, possessed high starch (68.6+/-0.09%) and low protein (10.1%) characteristics more similar to Central Manitoba Corn (CMC) than other measured wheat cultivars. Physicochemical properties of starch such as amylopectin to amylose ratio, starch granule morphology, and thermal and pasting properties were all found to vary significantly between varieties. The branch chain length distribution of amylopectin was not found to be significantly different between samples. Amylopectin to amylose ratio for wheat starch ranged from 73.60:26.40 to 69.47:30.53 and was found to be different and lower than CMC at 74.51:25.49. Enzymatic susceptibility was measured using industrial alpha-amylase to hydrolyze gelatinized starches and resultant reducing sugar content ranged from approx. 407 to 500mg glucose equivalents per gram starch, indicating different patterns of oligosaccharide chain lengths present after hydrolysis. However, liquefaction performance was measured and found to be similar between samples, indicating no major differences in the quantities of maltose, maltotriose, maltotetrose or larger dextran concentrations in the respective worts prior to saccharification and fermentation. During fermentation striking differences in glucose generation were observed, the high glucose cohort averaged 1.21 g/g-starch for the initial time point, compared to a range of 0.83 to 1.05 g/g-starch for the low glucose cohort. In general, the pattern of glucose generation appears to be consistent with ethanol and biomass production. CMC and Buteo, observed to have the highest ethanol and biomass yields, achieved conversion efficiencies between ∼95.6--97%, compared to the low glucose cohort which achieved 85.64--88.42% conversion efficiency. Amylose content is observed in this study to have a moderate negative correlation with ethanol yield (r=-0.784, P<0.05), suggesting even subtle decreases in wheat starch amylose content (∼4%) correspond to increases in generated ethanol. Reducing sugar yield also showed a strong negative correlation (r=-0.921, P<0.01) with ethanol yield. Reducing sugar yield, however, appears to be influenced by amylopectin to amylose ratio. Correlating structural attributes with fermentation performance suggests that amylopectin to amylose ratio is the most predictive factor in the pattern of wheat starch hydrolysis. |
