Correction of wheat meal falling number to a common barometric pressure at simulated laboratory elevations of 0 to 1500 meters

Authors: Delwiche, Stephen - Steve; Rausch, Steven - Steve; Vinyard, Bryan

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2018
Publication Date: 3/1/2018
Citation: Delwiche, S.R., Rausch, S.R., Vinyard, B.T. 2018. Correction of wheat meal falling number to a common barometric pressure at simulated laboratory elevations of 0 to 1500 meters. Cereal Chemistry. 95(3):428-435.

Interpretive Summary: Of the many tests used worldwide to evaluate the quality and soundness of harvested wheat, one test known as 'falling number' determines the integrity of starch, the primary component of seed endosperm and hence, the primary component of flour. Falling number is a measurement of the viscosity of a heated mixture of ground wheat and water, with the viscosity greatly influenced by the level of an enzyme that degrades (breaks down) starch. The test requires a tightly controlled heating regiment, accomplished by immersing the test sample in boiling water. Because boiling point varies with barometric pressure and hence land elevation, it has long been known that the falling number result is influenced by the elevation of the laboratory conducting the test. A study was recently completed that quantified the effect of elevation, from which a correction equation was developed to permit falling number readings reported on a single elevation (sea level) basis. When evaluated on a historical set of data, the correction was found to reduce falling number variation caused by elevation by more than 70%. The correction is now available for use in official grain inspection services. It will improve the confidence of buyers and sellers of wheat in the world marketplace.

Technical Abstract: Falling number, a procedure that indirectly gauges germination enzyme activity in wheat by its measurement of the viscous behavior of a heated starch-water mixture, is affected by the immersion water bath temperature. Maintained at boiling point, the water bath temperature is determined by barometric pressure which changes with land elevation. A study was conducted to quantify the effect of elevation, hence barometric pressure on falling number over a simulated elevation range of near sea level (760 mm Hg) to 1,524 m (632.4 mm Hg). Five evenly spaced elevations were simulated in a walk-in hypobaric chamber, in which falling number measurements were collected on 12 samples of U.S. grown wheat meal from three market classes (hard red spring, hard red winter, and soft white), and verified with 4 additional wheat meal samples. First order polynomial linear regression equations were developed on log transformed mean falling number readings to correct non-sea level readings to sea level. Separate regressions were performed for corrections of data initially represented by pressure, elevation, and water bath boiling temperature. With correction, the range in standard deviation of falling number over the five simulated elevations declined to 0.9 to 14.1 s, from a pre-correction range of 13.2 to 50.9 s. The correction functions are continuous linear relationships in the log domain and applicable to the entire simulated elevation range. When the correction model was applied to a historical data set consisting of falling number readings collected on 23 field instruments at elevations ranging between 0 and 1,006 m and compared to readings collected on a central instrument at 305 m (2,274 test samples altogether), it was found that the estimated variance of the mean differences between field and central instruments declined by 77%, compared to no correction.