Sampling & Sample Preparation (Lect. 5)

Importance of Sampling

  • Essential to monitor and evaluate the food quality and characteristics of a product or ingredient.

    • Monitor the composition of the lot.

    • Evaluate samples to decide acceptance/rejection of lots.

    • Determine sample size and selection based on product nature and inspection purpose.

Sample Preparation Principles

  • Reduce particle size to 20-mesh.

  • Control enzyme activity.

  • Prevent lipid oxidation.

Sampling Feasibility

  • Consider homogeneity/heterogeneity, unit size, cost, and past specifications to decide on sampling.

Risk Assessment

  • Vendor Risk: Accepting poor quality (< 5%)

  • Consumer Risk: Rejecting good quality (5–10%)

Sampling Plans

  • Acceptance Sampling Types: Single, Double, and Sequential sampling.

    • Attribute Sampling: Acceptability checks for presence/absence of variables (e.g., pathogens).

    • Variable Sampling: Quantitative estimation of characteristics (e.g., color, salt).

Mechanical vs Manual Sampling

  • Mechanical: Continuous, higher error probability.

  • Manual: Less bias, more reliable.

Considerations for Sample Preparation

  • Control factors like enzyme activity, lipid oxidation, and microbial growth to prevent sampling errors.

  • Sample size affects reliability; smaller samples for normally distributed attributes.

Common Problems in Sampling

  • Non-statistical methods.

  • Poor storage.

  • Mislabeling reduce reliability.

Preparation Techniques

  • Use of grinding for particle size.

  • Consideration of sample type (moist vs. dry).

  • Storage conditions.

Questions

  • To determine food quality and acceptance, it is essential to:

    • Monitor the composition and characteristics of the whole lot of a food product or raw ingredient

    • Evaluate a sample/samples of a lot and then decide to accept or reject a particular lot

    • Determine sample size and selection protocol based on factors such as the nature of the product and the purpose of inspection

    • All of the above

  • For sample preparation, prior to analysis, the following is true:

    • For all types of analyses, particle size should be reduced to a 20-mesh size

    • Enzyme activity should be eliminated or controlled

    • Lipid oxidation should be prevented

    • All of the above

  • When monitoring food safety by measuring mycotoxins

    1. Many randomly selected samples are required

    2. A single sampling plan is required

    3. Sampling error is many times greater than the analytical error

    4. 1 and 2

    5. 2 and 3

    6. 1 and 3

  • The following are potential problems associated with sampling that may result in reduced reliability

    • Non-statistically viable convenience

    • Poor storage conditions

    • Mislabeling of samples

    • All of the above

Study Question:

You are to collect and prepare a sample of cereal produced by your company for the analyses required to create a standard nutritional label. Your product is considered “low fat” and “high fiber” (see regulations for nutrient claims and FDA compliance procedures in Chapter 3).


  • What kind of sampling plan will you use?

  • Will you do attribute or variable sampling?

  • What are the risks associated with sampling in your specific case?

  • Would you use probability or nonprobability sampling, and which specific type would you choose?

  • What specific problems would you anticipate in sample collection and in preparation of the sample?

  • How would you avoid or minimize each of these problems?