25.3 Sensory Evaluation, Objective Food Tests, and Quality Assurance in Food Production
Key Takeaways
Sensory tests are grouped as difference (discriminative) tests, descriptive tests, and affective (acceptance or preference) tests.
In a triangle test, panelists receive three coded samples, two identical, and must identify the odd one, so the chance of guessing correctly is one in three.
The 9-point hedonic scale runs from 9 (like extremely) through 5 (neither like nor dislike) to 1 (dislike extremely).
Samples are labeled with random three-digit codes and served in randomized order, with water or unsalted crackers between samples.
A refractometer measures soluble solids in degrees Brix, a pH meter measures acidity, and a water activity meter measures available water.
Quality assurance and food evaluation are part of Foods and Food Service Systems. Total quality management and the plan-do-check-act cycle are covered in the facility and quality management section; this section focuses on evaluating food products.
Sensory Attributes
- Appearance: color, size, shape, gloss, consistency.
- Flavor: taste (sweet, sour, salty, bitter, umami) combined with aroma; also chemical sensations such as the heat of chili.
- Texture: hardness, crispness, chewiness, smoothness, and mouthfeel.
- Sound: crunch of chicharon or fresh vegetables.
Sensory Panels
| Panel | Members | Purpose |
|---|---|---|
| Trained or expert panel | Small group (often 5-15) screened and trained | Difference and descriptive tests |
| Semi-trained panel | Staff familiar with the product | Routine quality checks |
| Consumer (untrained) panel | Large group (often 50 or more) from the target market | Acceptance and preference |
Types of Sensory Tests
Difference (discriminative) tests: is there a detectable difference?
- Paired comparison: which of two samples is sweeter (or saltier, firmer)?
- Duo-trio: which of two samples matches the reference?
- Triangle test: three coded samples, two alike; identify the odd one. The chance of guessing correctly is 1/3. With 30 panelists, at least 15 correct answers are generally needed to conclude a significant difference at the 5% level.
Descriptive tests: how do products differ?
- Scoring or rating scales for intensity of attributes (such as saltiness from 1 to 7).
- Descriptive analysis by a trained panel that profiles many attributes.
Affective tests: do consumers like it?
- Paired preference: which sample do you prefer?
- Ranking: order samples from most to least liked.
- 9-point hedonic scale:
| Score | Description |
|---|---|
| 9 | Like extremely |
| 8 | Like very much |
| 7 | Like moderately |
| 6 | Like slightly |
| 5 | Neither like nor dislike |
| 4 | Dislike slightly |
| 3 | Dislike moderately |
| 2 | Dislike very much |
| 1 | Dislike extremely |
Facial hedonic scales with smiling and frowning faces are used for children.
Example. Fifty students rate a squash-enriched pandesal: the sum of scores is 360, so the mean score is 360 ÷ 50 = 7.2, between "like moderately" and "like very much".
Testing Conditions
- Individual booths with uniform lighting; colored lights mask color differences when color is not being tested.
- Samples coded with random three-digit numbers to avoid bias.
- Randomized or balanced serving order.
- Equal sample sizes served at the same temperature.
- Water or unsalted crackers to cleanse the palate between samples.
- Panelists should not be very hungry or full and should avoid smoking, coffee, and strong flavors just before testing.
Objective (Instrumental) Tests
| Property | Instrument or test |
|---|---|
| Color | Colorimeter; color charts |
| Texture | Texture analyzer, penetrometer, shear press |
| Viscosity and spread | Viscometer; line-spread test for sauces and batters |
| Sugar content | Refractometer (degrees Brix) |
| Acidity | pH meter |
| Water activity | Water activity meter |
| Volume | Seed displacement for breads and cakes |
| Moisture | Drying oven or moisture analyzer |
Objective tests give reproducible numbers, while sensory tests show how people perceive the food. Both are used together.
Quality Control and Quality Assurance in Food Production
- Quality control inspects products against standards, such as checking portion weights and temperatures.
- Quality assurance builds quality into the whole process through standards, training, and monitoring.
Common tools in food services:
- Standardized recipes and purchase specifications
- Portion control tools and plate diagrams
- Temperature and sanitation logs
- Tray accuracy and taste-panel checks before service
- Plate waste studies and customer satisfaction surveys
- Product standards, including Philippine National Standards issued by the DTI Bureau of Philippine Standards and agricultural standards from the Bureau of Agriculture and Fisheries Standards
Product development stages: idea generation, screening, concept development, formulation, sensory testing, shelf-life and safety testing, costing, labeling, pilot production, and launch.
Sources of Error in Sensory Testing
| Error | Description | How to reduce it |
|---|---|---|
| Expectation error | Panelists expect a difference because of information they were given | Give only the information needed |
| Stimulus error | Irrelevant cues such as sample size or container influence judgments | Serve identical portions in identical containers |
| Halo effect | Liking one attribute colors the rating of others | Evaluate one attribute at a time when possible |
| Positional (order) bias | The first or middle sample is rated differently | Randomize or balance serving order |
| Contrast effect | A sample tastes worse after a very good one | Randomize order; provide rest periods |
| Sensory fatigue and adaptation | Senses dull after many samples | Limit the number of samples; use palate cleansers |
Planning a Sensory Evaluation
- State the objective, such as "Is the reduced-sugar leche flan acceptable to customers?"
- Choose the test type (difference, descriptive, or affective).
- Select and, if needed, train panelists.
- Prepare samples under identical conditions, coded and randomized.
- Prepare score sheets with clear instructions.
- Conduct the test in a controlled area.
- Analyze the data with suitable statistics.
- Report results and decide on the next step, such as reformulating or launching the product.
Shelf-life testing stores products under expected conditions and checks sensory quality, microbial counts, and chemical changes such as rancidity over time to set the "best before" or "use by" date.
A food service wants to know whether replacing 30% of the salt in its pancit canton with herbs creates a difference tasters can detect. Panelists receive three coded samples, two of which are the same. Which test is this?
Hedonic rating test
Ranking test
Triangle test
Descriptive profile
Why are sensory samples labeled with random three-digit codes?
To prevent bias from labels such as "A" or "1"
To show panelists which sample is the control
To record the price of each sample
To identify each panelist's name
Forty adults rate a new kakanin on a 9-point hedonic scale, and the scores total 248. What is the mean score and its meaning?
5.2, neither like nor dislike
7.2, like moderately to very much
8.2, like very much
6.2, like slightly
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