Measuring wheat starch size distribution using image analysis and laser diffraction technology: Quality of spelt wheat and its starch

Starch was isolated (85--87% recovery) from four flours representing four of classes of wheat; hard red winter (Karl), hard red spring (Gunner), durum (Belfield 3), and spelt (WK 86035-8). Digital image analysis coupled to light microscopy was used to determine starch size distributions calculated as both spherical and oblate-spheroidal volumes. Wheat starch showed a trimodal distribution of granules (A-type granules, >15 mum; B-type granules, 5--15 mum; and C-type granules <5 mum). Measurement errors associated with starch granules touching the edge of field of view were investigated and corrections made. The perimeter of starch granules touching the edge of the field of view (PTE) were manually "replaced" into the field, and their measurements entered into the data base. The results show differences between the classes of wheat evaluated, as well as an effect of the total number of starch granules counted. Identical samples of isolated wheat starch were analyzed on four different laser diffraction sizing instruments to ascertain reproducibility between instruments. Laser diffraction sizing resulted in a ∼40% underestimation of the peak diameter for the A-type granules and a ∼50% underestimation for the B granule populations. An adjustment was developed from image analysis data to correct volume% of granules determined by laser diffraction. Before an adjustment of laser diffraction data correlations to image analysis ranged from R2 = 0.02ns to 0.55*** depending on the instrument evaluated. After correction these correlations improved to a range of R2 = 0.79*** to 0.93***' depending on class of wheat starch.; Flour from 5 spelt cultivars grown over 3 years were evaluated for breadbaking quality and starch properties such as amylose content, gelatinization properties, starch size distribution and pasting properties. Milled flour contained highly variable protein content, and showed short dough mix times indicating weak gluten. High protein cultivars resulted in good crumb scores, some of which surpassed the HRW baking control. Loaf volume also correlated positively to protein with all spelt varieties. Isolated starch properties revealed an increase of percent amylose in the spelt of between 4--7% over the HRW control. Significant negative correlations were found in large A-type granules, to crumb score, percent amylose, and final pasting viscosity for cultivars grown in year 1999 and pasting temperature in 1998. Significant positive correlations of the smaller B and C-type granules with bread crumb score, loaf volume, percent amylose, and RVA final pasting viscosity for cultivars grown in year 1999, and RVA pasting temperature in 1998. Growing environment seemed to have a greater impact on the tested spelt wheat than genetic control.