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Impact of Sprout Damage on Wheat and Durum Quality
Germination of wheat generally occurs after the kernel has matured and moisture levels have dropped to around 12 to 15%. Water adsorption is the first step in germination and initiates many biochemical processes; such as, activation and synthesis of enzymes, one in particular is alpha-amylase. Starch is degraded to glucose, protein to amino acids and oil to fatty acids. This process is necessary for growth of the embryo.
The most obvious change in quality resulting from sprouting is reduced test weight. When the germination starts energy is required. As a result of respiration carbon stores are depleted and the total biomass of the seed is reduced, primarily a loss of starch.
The degradation of the starch and protein during germination in the wheat endosperm results in flour or semolina that produces inferior quality products. Since durum and bread wheat are used differently, the effects of sprouting on end products are different. However, sprouting results in lowered test weight of both crops. Sprouting in durum result in increased cooking loss, softer cooked spaghetti, increased speck count and decreased spaghetti shelf stability. Sprouted bread wheat results in dough stickiness or bread loaves with gummy insides and large voids. Sprouting in bread wheat also results in less water absorption during dough preparation, resulting in decreased bread yield. Compounding the problem is the fact that sprout damage—the germination process—can affect the inside composition of a kernel even though the exterior of the kernel appears sound.
There are subtle indicators to look for when sprouting is suspected but not visible. Weathered kernels, of course, is the first clue. Additionally, weather conditions that lead to sprouting also favor development of fungi that cause black point. Wheat with a weathered appearance and black point is likely to also have sprout damage. Sprouting counts as "damaged kernels" when grading wheat. U.S. No. 1 grade wheat can have up to 2% damaged kernels while No. 2 wheat can have 2.1 to 4% damaged kernels. Wheat graded No. 3 can have 4.1 to 7% damaged kernels, No. 4 wheat can have 7.1 to 10% and No. 5 wheat can tolerate 10.1 to 15% damaged kernels.
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