Lecture 6 - Discrimination tests-itel_250204_213448

Discrimination Tests Notes

Introduction to Sensory Evaluation Methods

  • Multiple sensory evaluation methods exist; none are universally applicable.

  • Before testing, clearly define:

    • Objective: Purpose of the test.

    • Information needed: Desired outcomes from the test.

Fundamental Types of Sensory Tests

  1. Discrimination Tests

  2. Difference Tests

  3. Affective Tests:

    • Includes acceptance/preference tests and descriptive tests.

Product and Consumer Oriented Tests

  • Product Oriented:

    • Discrimination, descriptive tests.

    • Equivalence and difference tests.

  • Consumer Oriented:

    • Preference tests, acceptance tests.

Discrimination Tests Overview

  • Aimed at determining perceptible differences between products.

  • Extremely sensitive for identifying small differences.

  • Not suitable when obvious differences exist.

  • Common application areas:

    • Screening and training panels

    • Investigating taints

    • Determining sensitivity thresholds

    • Quality assurance/control in raw materials.

Application in the Food Industry

  • Used to assess the impact of changes such as:

    • Ingredient replacements

    • Packaging changes

    • Process alterations or storage changes.

Types of Discrimination Tests

  1. Paired Comparison Tests

  2. Duo-Trio Test

  3. Triangle Test

  4. Two-Out-of-Five Tests

  5. "A-Not-A" Test

  6. Same/Different Test

  7. Difference-From-Control Test

Paired Comparison Tests

  • Two forms of this test:

    • Directional Paired Comparison (two-alternative forced choice).

    • Difference Paired Comparison (same/different).

  • Choice of form depends on the study's objective.

  • Probability of random selection is always 50%.

Directional Paired Comparison Test

  • Objective: Determine differences regarding specific attributes (e.g., sweetness, hardness).

  • Procedure: Present two coded samples and let panelists evaluate which is more intense in a specific attribute.

  • Requires a minimum of 30 panelists for significant results.

  • Must control for other sensory attributes to ensure clarity.

Example of a Directional Test

  • Example scenario: Determine softness between a company's croissant and a competitor’s.

    • 60 assessors judged softness, with a majority favoring sample A (the company's croissant).

Data Analysis

  1. Count how often each sample is selected.

  2. Two analysis methods:

    • Manual calculation against statistical tables for significance.

    • Use software for error probability assessment.

Duo-Trio Test

  • Objective: Determine if a sample differs from a reference.

  • Procedure: Present one reference sample (R) and two coded samples. Panelists assess which coded sample is closest to the reference.

  • Two formats:

    1. Constant Reference Duo-Trio Test: All panelists use the same reference sample.

    2. Balanced Reference Duo-Trio Test: Half of panelists receive each sample as the reference.

Triangle Test

  • Objective: Identify if there is a difference between three samples (two identical, one different).

  • Assessors determine which sample is different.

  • Good for assessing small differences.

  • Requires a panel size of 24-30; larger numbers improve discriminatory ability.

"A-Not-A" Test

  • Assessors evaluate samples conditioned as ‘A’ and ‘Not A’ before comparative testing.

  • Useful when samples are complex or carry-over effects are present.

Two-Out-Of-Five Test

  • Objective: Identify the two different samples among five.

  • Probability of randomly choosing correctly is low, making the test effective.

  • Works better visually or through tactile means rather than taste or smell.

Difference-From-Control Test

  • Objective: To identify differences between multiple test samples and a control/reference sample.

  • Gather subjective ratings for differences from the control, particularly useful in quality assurance.

Conclusion

  • Discrimination tests are vital for sensory evaluation in food products to ensure quality and consistency.

  • Understanding the methodologies and conditions under which each test is applicable is crucial for accurate results.

References

  • Meilgaard, M., Civille, G.V. & Carr, B.T. 2007. Sensory Evaluation Techniques. 4th Ed. Boca Raton, Florida: CRC Press.

  • Kemp, S. E., Hollowood, T. & Hort, J. 2009. Sensory Evaluation: A Practical Handbook. United Kingdom: Wiley-Blackwell.

  • Lawless, H.T. & Heymann, H. 2010. Sensory Evaluation of Food: Principles and Practices. 2nd Ed. New York: Springer.