The sampling, subsampling, and analytical variance associated with testing cottonseed for aflatoxin were estimated by use of 4.54 kg samples, 100 g subsamples, and the Velasco method of analysis. Regression analysis indicated that each of the above variance components is a function of the concentration of aflatoxin in the populations tested. Functional relationships are presented to determine the sampling, subsampling, and analytical variance for any size sample, subsample, and number of analyses.

Large samples called “sublots” were drawn from 41 commercial lots of contaminated cottonseed. Each sublot was subdivided into twenty 5 lb samples which were analyzed for aflatoxin. The mean, median, variance, coefficient of variation, and the estimated range among the sample concentrations were computed. The results indicated that: (A) the variance among sample concentrations was large and was found to be a function of sample concentration and (B) the distribution of sample concentrations was skewed; the density of sample values was greater below the sublot concentration.

AND SUMMARYA computer model was developed to simulate cottonseed aflatoxin testing programs. By use of the model, probabilities of obtaining, certain aflatoxin test results for various lot concentrations and sample sizes were determined. Also, the effects of sample size and the definition of good and bad sample quality on the probability of lot acceptance were demonstrated.

A rapid screening method for detecting ariatoxins in cottonseed has been developed. Using long-wave ultraviolet light and samples containing aflatoxins, the fibers on a few cottonseed fluoresced a greenish yellow and the ends of some sticks and stems (foreign material) fluoresced with a bluish color. Nine out of 10 of the 2300 samples of cottonseed were correctly screened during the last two years of the study. In only one category, 1-10 ppb aflatoxins, was there an appreciable error in the screening method.

In central California, neither fungal infections nor aflatoxins are significant problems in cottonseed during the receiving and storage seasons. However, in southern California, the 1967 harvest contained a relatively high percentage of seed which were invaded before harvest by fungi, includingAspergillus flavus. Seed infection and concentrations of aflatoxins in seed increased significantly during the time between harvest and storage in southern California. For a short time during storage, seed infection byA. flavus increased because of the moisture the seed received late in the season; however, aflatoxin concentrations in seed did not increase in storage. The aflatoxin content of the seed removed from storage was a reflection of the relative amount of aflatoxins the seed contained when they were received for storage. In 1967, the conditions that existed in the large, densely packed seed pile did not favor accummulation of aflatoxins in seed, even thoughA. flavus was active.