Canadian Grain Commission
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The implications of frequently encountered grading factors on the processing quality of common wheat

1. Abstract

Grading factors associated with adverse growing conditions in Canada and the United States affect the edibility and end-use performance of common wheat. Mycotoxins are associated with fungal infections like fusarium head blight and ergot. Mycotoxins partition themselves among wheat milling products, and are relatively stable throughout wheat end-use processing. Fusarium head blight also has adverse effects on wheat milling and baking performance. Mildew and smudge and black-point are common fungal infections that present no toxicological danger. Mildew is a marker of potential sprout damage. The quality effects of all three forms of damage are relatively minor except when infections are severe, but they are an impediment to marketing wheat because they are aesthetically unappealing. The orange wheat blossom midge, whose larvae feed on developing wheat kernels, can result in devastating yield losses and also impart nonfunctional gluten properties and unsatisfactory baking quality when damage is severe. Farmers can reduce yield losses and quality deterioration by timely application of insecticides. Hard vitreous kernel (HVK) limits have been in place in common wheat grades for many years because vitreousness is directly related to protein content. Aside from a slight effect on kernel hardness, the level of HVK is not associated with wheat processing quality, and is redundant when protein content guarantees are a part of wheat transactions. Frost damage is one of the most serious grading factors. Severely frosted wheat is very hard, making reduction into flour difficult. Flour refinement and baking performance are also adversely affected. Pre-harvest sprouting causes processing problems because of high levels of the starch degrading enzyme a-amylase. The action of the enzyme during baking reduces the water holding capacity of the starch, resulting in lower baking absorption (lower bread yield) and handling problems due to sticky dough properties. In years of wet harvest improper use of hot air dryers can damage gluten functionality and baking quality without visibly altering wheat appearance. Rapid tests are available to detect gluten damage due to improper drying.