Falling number sampling variation within trucks at first point of sale

Authors: Delwiche, Stephen - Steve; Vinyard, Bryan

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2016
Publication Date: 5/1/2017
Citation: Delwiche, S.R., Vinyard, B.T. 2017. Falling number sampling variation within trucks at first point of sale. Cereal Chemistry. 94(3):480-484.

Interpretive Summary: A post harvest wheat quality procedure known as falling number (FN) is used throughout the United States and elsewhere. The procedure is an indirect measurement of the susceptibility of seeds to break dormancy, germinate, and consequently compromise the value of these raw resources as ingredients in processed goods. Sales contracts, from first point of sale to export destination, often specify a minimum value for FN whereby grain failing to meet the value is either discounted in price or rejected altogether. One aspect of ensuring reliability and confidence in FN lies with the steps for obtaining a sample of grain (typically weighing 2 lbs) that is representative of the cargo lot from which it was drawn. When applied to the first point of sale (that is, wheat arriving by tandem wheel truck to the country elevator), sampling should be performed according to a USDA protocol that specifies probing at several locations throughout the truck bed. This study had two goals: first, to determine the degree of uncertainty associated with obtaining a representative sample of wheat from a truck bed; and second, to provide recommendations on whether retesting by re-probing is warranted in cases when FN is lower than the prescribed minimum. Both goals are aimed at facilitating the efficiency and fairness of U.S. wheat commerce. Results indicate that when probing is performed correctly, sampling error is quite low, so much so that retesting is usually not advised.

Technical Abstract: Falling number (FN) is a test widely performed on raw samples of wheat and barley as a means to indicate the level of enzyme activity, alpha-amylase, associated with seed germination. In most circumstances of wheat, high activity levels are associated with decreased quality of the end products, and because of this, grain lots with low FN are discounted at points of sale, including the first point of delivery when wheat is brought in from the field. Confidence in the validity of a FN assessed on a grain lot is dependent on knowledge of the precision of the analytical method as well as the sampling protocol. The current study examined the latter component, that is, the variation caused by sampling. Soft red and white commercial wheats from two seasons and two regions (states of Washington and Ohio) were sampled upon arrival at country elevators and a flour mill. By catch stream sampling or probe sampling, catches and probings were run in quadruplicate according to standard methodology for FN. Among-catches and among-probings variance estimates, inclusive of sampling error and method error, were typically less than 100 s^2, corresponding to a coefficient of variation of 3% or less. Estimated variances due to sampling alone, as determined by a mixed-effects ANOVA, were typically less than 50 s^2. Based on the among-probings variance estimates and a simple model that assumes normality of FN and linearity in mathematically combining individual probe readings into the equivalent composite reading for a truck, retesting a truck in borderline FN conditions (i.e., FN less than or equal to 294 s) will not yield a new FN value of 300 s or greater more than 95% of the time.