Sampling and Sample Preparation

Food quality is monitored at various processing stages but 100% inspection is rarely possible or even desirable. To ensure a representative sample of the population is obtained for analysis, sampling and sample reduction methods must be developed and implemented. Sampling is a vital process, since it is often the most variable step in the entire analytical procedure. The selection of the sampling procedure is determined by the purpose of the inspection, the nature of the population and product, and the test method. This chapter covers various aspects of sampling to be considered: homogenous vs heterogeneous samples; discrete vs. continuous populations; sampling for attributes vs. variables; consumer risk vs. vendor risk of sampling; manual vs. continuous sampling; probability vs. nonprobability sampling; numerous choices of sampling plans; precision analysis vs. power analysis to estimate sample size. Challenges continue after the sample is collected, including proper sample storage and identification, often followed by sample size reduction to an amount suitable for sample preparation. That sample preparation often involves grinding to a particle size appropriate for analysis and then storage prior to analysis, both of which must be done in ways to prevent sample degradation. The principles described in this chapter are intended to provide a basis for understanding, developing, and evaluating sampling plans and sample handling procedures for specific food analysis applications.