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Sprout Damage In Cereal Grains and the Falling Number Assay

Sprouting in grain can occur once the kernel has reached maturity; therefore, when mature kernel is subjected to proper moisture, temperature and time it begins to sprout.  The physiological changes needed to produce a new plant require energy and nutrients, which is why the wheat kernel produces enzymes to breakdown starch (amylases), oil (lipases) and protein (proteases).  This process is exploited in the production of barley malt, which is an enzyme and nutrient �package� vital to the brewing of beer.  When moisture levels in the wheat decrease prior to threshing, the sprouting process stops, and if it stops before there are visible signs of sprouted kernels it is called incipient sprouting. 

The impact of sprouting on foods produced from wheat depends on the amount of enzymes present and breakdown of the kernel.  Sprouting lowers test weight and flour yield, lowering the grade and value to the processor.  The impact on baking quality is observed by lower absorption (water added in baking, which reduces bread yield), reduced mixing strength and tolerance, and sticky dough.  It can also affect loaf volume, crust strength and crumb texture, whereas a wet and gummy crumb causes problems with slicing and shelf life.  The starch degradation and enzyme activity also reduce the quality of Asian noodles.  The effects on durum are lower test weight, reduced semolina yield and color.  In the processing of semolina and pasta, sprouting increases semolina speck counts, reduces shelf life of dried pasta (due to checking or cracking), increases cooking loss, and produces softer cooked pasta.

Much of the frustration and confusion centers on the falling number test used to detect sprouting.  The level and impact of sprout damage is not fully realized until it is processed into bread or pasta.  The Falling number test does not directly measure amylase enzyme activity, but measures changes in the physical properties of the starch portion of the wheat kernel caused by these enzymes during the test.    

When a cereal grain is ground into flour and mixed with water it forms a slurry.  Upon heating, the viscosity of the slurry increases due to cooking or �gelatinization� of the starch.  This is the basis for preparing gravy.  The falling number test begins with the mixing of ground sample and water in test tubes to form the slurry.  The tubes are placed in a boiling water bath (212^oF) and automatically stirred for 60 seconds, causing the starch-water slurry to thicken due to starch swelling or �gelatinization�.  When starch granules become gelatinized, they are increasingly susceptible to degradation by amylase enzymes, which increases the rate of thinning in the slurry.  After mixing, the stirrers are released at the top of the slurry and begin to fall.  The falling number apparatus records the time for the stirrer to fall through the slurry.  The rate at which the stirrer falls is directly related to the amount of starch degradation by amylase enzymes.

There are no standards for falling number, as it is not an official grading factor in FGIS grain inspection and grading process.  Generally speaking for wheat, a falling number value of 350 seconds or longer indicates low enzyme activity and very sound wheat.  As the amount of enzyme activity increases, the falling number decreases.  Values below 200 seconds indicate high levels of enzyme activity.  In the past several years, grain buyers have discounted wheat for falling number values below 300 seconds.    Falling number values are also important overseas, as many of the buyers from export markets have written minimum tolerances of 300 to 350 seconds into their purchase contracts. 

When correctly run, the falling number test is fairly repeatable; however, contamination of the sample from a multitude of sources, including the grinder used to make the test flour, can decrease the falling number value.  Tests conducted at the Department of Cereal Science at NDSU on durum illustrate how contamination can affect the test results.  Two visibly sprouted wheat kernels added to 200 grams of sound wheat (.03%) reduced the falling number (FN) by 100 seconds.  In another test, sprouted durum flour (FN = 66 seconds) was added at a level of only 1.6% to a sound sample, lowering FN by 34 seconds. 

Flushing the grinder by grinding a certain amount of wheat can affect subsequent samples.  This was observed in a test in which a sprouted sample (FN = 66 seconds) was followed by a grinder flush of 300 grams of sound wheat.  Enough flour was in the system to reduce the falling number from 344 to 325 seconds.  Values of 19 and 34 seconds seem small, unless the wheat to be tested is 10 seconds above a discount threshold level.  If a small sample of undamaged wheat is ground immediately following a sample with severe sprout damage, without adequate flushing or cleaning of the grinder, substantial contamination is possible.

Proper cleanout of the grinder is time consuming, but may be necessary after grinding a sample with a very low falling number.  Effective grinder cleaning requires removing the grinding head cover and sample collector to remove flour reside using a brush, compressed air or a vacuum cleaner.  Remember, taking precautions to minimize contamination can greatly improve the accuracy of the falling number test, which is important for all parties involved.

Brian Sorenson

Technical Director, Northern Crops Institute

Crop Quality Specialist, NDSU Extension Service

North Dakota State University

Fargo, ND  58105

Phone (701) 231-6048

Fax   (701) 231-7235

bsorenso@ndsuext.nodak.edu

North Dakota State University
NDSU Extension Service