Selection of sampling procedure

Food Standard and Quality Control

Lesson 03 :Food Sampling

Selection of sampling procedure

The sampling procedure selected depends on the purpose of the inspection, the nature of the food being investigated. In general, increasing the sample size will increase the reliability of the final results. Sampling is usually the most variable step in the overall analysis process.

Factors that affect the choice of sampling plan

  • Purpose of the inspection,
  • Nature of the product,
  • Nature of the test method and
  • Nature of the food being investigated.

Homogeneous versus Heterogeneous populations

The ideal populations would be exactly the same at every location. Such a population would be homogenous. Sampling is simple in this. One can select a portion from any location and obtain results that are representative of the whole. Most populations are heterogeneous. Results obtained from these will depend on the location of sampling. Fortunately, there are several methods to make a heterogeneous population more homogeneous.

Manual versus Continuous sampling

Manual sampling is done by humans .The person taking the sample physically performs some process to select the sample. The unit being sampled will be made be as homogeneous to the maximum extent possible prior to sampling. If the samples are liquids in small containers, they are homologized by shaking prior to sampling, if they are in silos homogenization is done by aeration. But for grains in rail cars, mixing prior to sampling is impossible.

Liquids may be sampled by pipetting, pumping, a portion from the whole sample. Granular or powered samples may be taken with the help of probes that are inserted into the material.

Manual sampling of powdered or granular materials is subject to many errors. Round particles flow into sampler compartments more easily than do angular particles of similar size. Uncoated hygroscopic materials flow into the sampler compartment more readily than do similar non hygroscopic materials.

Continuous sampling is performed by mechanical sampling devices. Samples collected mechanically from flowing streams are preferred over manual sampling for several reasons: All of the material is accessible for sampling; material from all parts of the flowing stream are collected; there is no manual bias; and the mechanical sampling system works the same all the time.;

Last modified: Wednesday, 15 February 2012, 10:39 AM