Testing Green Coffee for Ochratoxin A, Part I: Estimation of Variance Components

Abstract

The variability associated with testing lots of green coffee beans for ochratoxin A (OTA) was investigated. Twenty-five lots of green coffee were tested for OTA contamination. The total variance associated with testing green coffee was estimated and partitioned into sampling, sample preparation, and analytical variances. All variances increased with an increase in OTA concentration. Using regression analysis, mathematical expressions were developed to model the relationship between OTA concentration and the total, sampling, sample preparation, and analytical variances. The expressions for these relationships were used to estimate the variance for any sample size, subsample size, and number of analyses for a specific OTA concentration. Testing a lot with 5 μg/kg OTA using a 1 kg sample, Romer RAS mill, 25 g subsamples, and liquid chromatography analysis, the total, sampling, sample preparation, and analytical variances were 10.75 (coefficient of variation [CV] = 65.6%), 7.80 (CV = 55.8%), 2.84 (CV = 33.7%), and 0.11 (CV = 6.6%), respectively. The total variance for sampling, sample preparation, and analytical were 73, 26, and 1%, respectively.

Sampling of cereals and cereal-based foods for the determination of ochratoxin A: an overview

“…The subsampling variance was the next largest, followed by the variance of the analytical test. The fact that both aflatoxins ( Dickens and Whitaker 1986 ) and OTA ( Vargas et al 2004 ) appear to display similar heterogeneity in sample lots indicate sampling is also likely the largest source of variance for the measurement of OTA in food items.…”

“…The nominal value of the sampling variance depends upon the specific experimental conditions, including analyte concentration, sample sizes, and OTA test procedure used. The rank order of sampling > subsampling > analytical variance has been observed in many situations, including aflatoxins in peanuts ( Whitaker and Dickens 1974 ), cottonseed ( Whitaker and Dickens 1976 ), almonds ( Whitaker et al 2006 ), and OTA in green coffee ( Vargas et al 2004 ). Therefore, improvements in analytical variance will have a small effect on the total variance of results ( Vargas et al 2004 ; Whitaker et al 2006 ).…”