Repeatability Precision of the Falling Number Procedure Under Standard and Modified Methodologies

Abstract

The falling number (FN) procedure is used worldwide to assess the integrity of the starch stored within wheat seed. As an indirect measurement of the activity level of α‐amylase, FN relies on a dedicated viscometer that measures the amount of time needed for a metal stirring rod of precise geometry to descend a fixed distance through a column of water–flour or water–meal slurry that undergoes enzyme‐activated starch hydrolysis under controlled mixing and heating conditions. For U.S. wheat, FN values of 300 s and above generally indicate soundness in the condition of the seed starches, whereas values less than 300 s often indicate that some seeds have broken dormancy, which deleteriously affects bread‐, cake‐, and noodle‐making quality of products derived from their flour. Domestic and especially overseas sales contracts will often specify a minimum FN value for consignments, thus making it critical to ensure that the FN procedure be highly precise. The study described herein examined the level of repeatability precision of the FN procedure under strictly controlled laboratory conditions as a means to establish precision levels arising alone from the random nature of the viscous properties of starchy meal undergoing mixing and heating. Six representative samples of Pacific Northwest–grown soft white and club wheat, ranging in FN between 168 and 404 s, were repeatedly measured with the conventional FN procedure and three modifications thereof, with the modifications being increased meal and water amounts (8 g of meal + 30 mL of H2O instead of 7 g + 25 mL) or the addition of a polysorbate surfactant (0.1% Tween 20) to the mixture water. Based on 16 FN runs for each sample and treatment, estimated variances and coefficients of variation (CV) were determined for each treatment–sample combination. The results indicated that CVs between 1 and 4% were achieved for all treatments and samples. The treatment modification of an augmented test sample size improved precision, whereas incorporating a surfactant had a negligible effect. Precision and treatment (conventional versus augmented) findings were corroborated by two external laboratories with two of the six original samples and by the main laboratory on an independent set of 14 wheat meal samples of commercial origin. Another possible improvement in precision is in the sequencing of water and meal addition to be half the volume of water, then the meal, followed by the remaining volume of water, all at the conventional levels of meal and water. Preliminary experimental results indicate an improvement in precision by using the “sandwich” approach; however, further testing is warranted to substantiate this discovery.

Falling number of soft white wheat by near‐infrared spectroscopy: A challenge revisited

“…Meal and water were combined in a standard FN test tube using the layering procedure described in Delwiche, Vinyard, and Bettge (2015) to ensure the complete wetting of meal. A Perten model 1000 instrument with cooling tower was used.…”

Correction of wheat meal falling number to a common barometric pressure at simulated laboratory elevations of 0–1,500 m

“…Previously, the authors demonstrated that with good laboratory practice, the repeatability precision of the falling number method, defined as a coefficient of variation from expected variance, is typically <3% (Delwiche, Vinyard, & Bettge, 2015). For example, a wheat lot possessing a raw falling number of 300 s when tested at a barometric pressure of 733 mm Hg, which corresponds to an elevation of 305 m (1,000 feet), would be equivalent to a falling number of 288 s at sea level.…”

“…For example, a wheat lot possessing a raw falling number of 300 s when tested at a barometric pressure of 733 mm Hg, which corresponds to an elevation of 305 m (1,000 feet), would be equivalent to a falling number of 288 s at sea level. Previously, the authors demonstrated that with good laboratory practice, the repeatability precision of the falling number method, defined as a coefficient of variation from expected variance, is typically <3% (Delwiche, Vinyard, & Bettge, 2015). While such a value for precision is low compared to other procedures in cereals analysis, it does imply that the uncertainty of measurement from random variability in the procedure (i.e., repeatability precision) may be larger than the barometric pressure-elevation-boiling point effect when the difference between prevailing and sea level conditions is small.…”

Falling Number Sampling Variation Within Trucks at First Point of Sale

“…Other minor measures taken to maximize instrument precision were reported by Delwiche et al (2015). FN analyses were performed according to AACCI Approved Method 56-81.03, with additional practices to improve repeatability precision, described as follows.…”

“…Our previous study examined the repeatability and reproducibility precision of FN under highly controlled operating conditions (Delwiche et al 2015). In actual commercial practices, however, variation in reported values arises from sampling variability in addition to that of the analytical procedure.…”