Making the grade

EXPLORING HOW MILDEW, SPROUTING AND FUSARIUM AFFECT QUALITY

with wheat harvest nearing completion, farmers and end-users alike are analyzing the quality of this year’s crop. Mildew, sprouting, and Fusarium are the three most relevant grading factors to wheat producers in Ontario. The tolerances for these grading factors are set by the Canadian Grain Commission (CGC) based on their impact on end-use quality and safety. The CGC performs a great deal of research to make certain that the grades assigned to wheat within a specific class accurately reflect its potential for end-use. A closer look at how mildew, sprouting and Fusarium affect end-use quality and safety helps provide  some insight into the difficulty they can cause for millers, bakers and other end-users.

mildew
Mildew is a subjective grading standard that is based upon a comparison to a visual standard created every year by the Chief Grain Inspector at the CGC.  The presence of mildew damage is indicative of a wet harvest and, therefore, may also be a flag for other grading factors such as sprout damage. This finding has been supported by research performed at the CGC’s Grain Research Laboratory, which determined that as mildew increases, test weight and falling number decrease.

Mildew damage is triggered by a non-toxic fungus that causes the heads of the wheat kernel to turn grayish in colour.  The primary impact of mildew on end-use quality is largely aesthetic and involves discoloration. When milled, wheat with mildew damage will produce an off colour, darker flour. Similarly, mildew-damaged wheat may also produce undesirable discoloration in food products such as breakfast cereals and whole grain snacks.

sprout damage
As with mildew, sprout damage occurs when wet harvest conditions are encountered. Grain inspectors determine the extent of the sprout damage through objective measurements that involve calculating the percentage of sprouted wheat kernels in a sample. A kernel is deemed to be sprouted by an inspector if it is showing evidence of growth in the germ area.

Sprouted wheat kernels contain high levels of an enzyme called alpha-amylase, which works to breakdown the starch in the wheat. The most common way of measuring the effect of sprout damage is a procedure called the Hagberg falling number test. The falling number test measures the time (in seconds) that it takes for a plunger to travel, or fall, a set distance in a test tube through a hot slurry of ground wheat. The more alpha-amylase that is present, the more starch that is broken down thereby resulting in a thinner paste that requires the plunger less time to travel through. In general, a falling number of 300 seconds or higher will indicate sound wheat.

The affects of sprout damaged wheat with a low falling number will be more evident in fermented baking processes, such as those used in making pan bread. During long fermentation processes the alpha-amylase will continue breaking down starch, creating a sticky dough and a bread loaf that has a large openings within it and a gummy texture. Although more pronounced in fermented baked goods, it has been claimed that high alpha-amylase in soft wheat flour will produce cookies and crackers that brown excessively.

fusarium head blight
Unlike mildew and sprout damage, Fusarium is a grading factor primarily because it poses a health risk. Fusarium is a fungal disease that becomes more prevalent when there is precipitation during the flowering period of the wheat crop. The Fusarium fungi species can produce mycotoxins, the most common of which is called deoxynivalenol (DON) or vomitoxin, which have been shown to cause adverse health effects in both humans and animals. 

The tolerance for Fusarium-damaged kernels (FDK) in a wheat sample is set based on the correlation between FDK and DON levels, which is currently understood to be approximately one percent FDK to one part per million DON. However, this correlation will vary depending on factors such as wheat class, variety and growing location. Given the variability of this relationship it is imperative that ongoing research is conducted to monitor changes in this relationship.  

According to the Official Grain Grading Guide, the tolerance for Grade 1, 2 and 3 eastern wheat is one percent FDK. As with sprout damage, an objective grading procedure is used to determine total Fusarium damage. Inspectors will determine total FDK by calculating the percentage of Fusarium-damaged kernels in a representative sample. Fusarium damage presents itself as thin or shrunken kernels that have a white or pinkish fibrous growth.

For a more in depth explanation of Eastern grain grading standards, go to the “publications and forms” section of the Canadian Grain Commission’s website at www.grainscanada.gc.ca. •

About Mike Reimer 3 Articles
Ontario Wheat Technical Specialist, Canadian International Grains Institute