The Sensory Analysis of Four Chocolate varieties using Qualitative Descriptive Analysis.

The Sensory Analysis of Four Chocolate varieties using Qualitative Descriptive Analysis.

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School of Food and Nutrition

SENSORY EVALUATION EXPERIMENTAL PLAN

141.312

Introduction:

The purpose of these experiments is to obtain experience and knowledge in running Quantitative Descriptive Analysis. The issues of screening and training will be investigated with a strong emphasis on analysis of the data. However, remember the screening and training of panel members takes usually between 40-120 hours of time (Meilgaard and Morton, 2007), so this practical cannot expect to produce fully trained panel members.

Procedure:

You have 3 x 3 hour sessions. Each of the practical is interconnected, but the focus of each session is as follows (remember descriptive analysis is run with a trained panel not a consumer panel):

  • Laboratory 1: Screening of panellists
  • Laboratory 2: Development of descriptors
  • Laboratory 3: Training of panellists , running of descriptive  panel and analysis of data

General Laboratory Procedures:

You will be working in groups and you will run the screening sensory experiment on everyone else in the class. In industry normally you would screen 60 -120 people to get to a panel size of approximately 15. In this practical series see if how many people you get from screening 20+ people in the class.

 


 

Laboratory 1: Panel Screening

Introduction

This experiment involves the screening of potential panel members for possible inclusion into a descriptive panel. It is not a comprehensive list of tests, but more an example of the types of tests you might run.

  1. Screening Questionnaire

Procedure – Prepare a screening questionnaire similar to the one attached in Appendix 1 remembering you will be evaluating chocolate. It will help if you have thought about this prior to the session and come with ideas.

  • Please nominate one person to lead the team. Get all the people in your group to complete the questionnaire and screen down the number of participants based on the test’s objective (motivation, availability and exhibiting an allergic reaction to a substance). Give result and reasons for your choice of why you have eliminated those subjects (add this into your final write up). Ensure your screening questionnaire has appropriate ethics and consent given (Example is given on Stream).

 

  1. Identification of tastes

Procedure – To test panel sensitivity to taste substances (panel is able to perceive and differentiate the basic tastes), preparing the following taste reference solutions (Table 1) by following STANDARD SENSORY PRACTICE (Appendix 8 and 9) and examining the test sheet for instructions on running a taste test as described on the test sheet (Appendix 2). As you have prepared the sample sit would not be appropriate to run the test ion yourselves.  Instead you will evaluate the samples prepared by another group in your class and they will provide you with the results for your write up.    Although all of the group will carry out the tests remember that only data from those people in your group who passed the initial screening are valid

Table 1 Reference substance and concentration for identification of tastes

Reference Substance Concentration g/L
Caffeine 0.19g/litre
Sodium Chloride (NaCl) 1.19g/litre
Sucrose 5.76g/litre
Citric Acid 0.43g/litre
Monosodium glutamate (MSG) 0.60g/litre
Deionised water

 

Equipment and Reagents:

  • Caffeine (food grade)
  • Sodium Chloride (food grade)
  • Sucrose (food grade)
  • Citric acid (food grade)
  • Monosodium glutamate (food grade)
  • Deionised water/spring water (food grade)
  • Kitchen – approved for preparation of foods and tasting
  • Unsalted crackers
  • Tasting cups and lids

 

Remember for standard sensory practice all sensory preparation needs to be standardised: use the same tasting cups (size, colour, and material) for all samples and all panellists; random three digit numbers for identification of the samples; standard volume of the taste solution (approx. 30mls); the order of presentation of the samples also needs to be randomised. Use appendix 3 to help you set up the experiment.

In this experiment, each participant will get to taste 9 samples made up from the above six solutions, i.e. participant 1 will taste water first following by citric acid, MSG, caffeine, sucrose, citric acid, water, salt and sucrose, respectively (appendix 3 and figure 1). The number of correct response should be recorded for each subject (add this into your final write up).

Figure 1 the presentation order of taste reference solutions for participant number 1

  1. Ranking to determine ability to discriminate different intensities of taste

Procedure – To further investigate the panel sensitivity, prepare as many of the following solutions as you can in the remaining time, carry out an experiment using standard sensory practice (see Appendix 8 and 9), and examining the test sheet for instructions, run a taste test as described on the test sheet (see Appendix 4) for screening your panellists further. In this experiment, each panellist will taste a total of 16 samples (4 concentrations and 4 tastes) and then will be asked to rank the intensity of each taste on the scale (Appendix 4).

Equipment and Reagents:

  • Caffeine (food grade)
  • Sodium Chloride (food grade)
  • Sucrose (food grade)
  • Citric acid (food grade)
  • Deionised water/spring water (food grade)
  • Kitchen – approved for preparation of foods and tasting
  • Tasting cups
  • Sensory booths
  • Access to computers/printer

Table 2 Reference substance and concentration for ranking of taste substances. The random three digit numbers should be created and the presentation should be randomised (add this into your final write up).

Sample order

(for one judge)

Example of three digit random number to identify sample Concentration Taste
a)      3 223 10g/litre Sweet (ranking)

Sucrose

         1 793 0 (water only)
         4 246 20g/litre
         2 970 5g/litre
b)      2 0.35g/litre Sour (ranking)

Citric Acid

         4 1.40g/litre
         1 0 (water only)
         3 0.7g/litre
c)      2 1g/litre Salty (ranking)

Salt

         1 0 (water only)
         4 4g/litre
         3 2g/litre
d)      2 0.35g/litre Bitter (ranking)

Caffeine

         1 0 (water only)
         4 1.4g/litre
         3 0.7g/litre

 

Data Analysis

Collect the results of the screening tests which you performed. Complete an excel spread sheet for your panellists (Table 3). Add your summary and discussion of below table and questions into your final write up

 

Table 3 Example of result table for panel screening

Panellist Screening Questionnaire Screening

Identification

Of tastes

Screening – Ranking experiment Overall decision
Sweet Sour Salt Bitter
1 Pass/Fail % % % % %
2
3
….

Note: “It has been proven that the concentrations recommended in this experiment were detected and recognised by 50% of novice assessors”

Question:

  • How does the result help you make a decision about who to keep on your panel?
  • What other screening test could you have carried out?


 

Laboratory 2:  Training your panel on descriptors – CHOCOLATE EXAMPLE

Introduction

The descriptive technique we are going to practice today is called “Quantitative Descriptive Analysis (QDA). Once you have screened your panellists you are ready to start to develop descriptors on the product of interest. To begin the process, nominate a panel leader for your group. The panel leader will not taste the product but will guide the team through the tasting and discussion. Panellists are normally exposed to many variations of the product over several sessions to encourage adequate concept formation. The panellist then will

Figure 2 Descriptive analysis procedures

At the end of training stages, a series of trial evaluations are performed to assess the panellist’s performances. The results are statistically analysed to ascertain which panellists need further training. In general, the standard deviation of well-trained panel should not be over 1.0 and repeat measures within 10% of the scale used. Add the discussion in your final report.

Procedure

Familiarise yourself with the type of descriptive form you are trying to prepare (examples are given in Appendix 5, 6 and 7). Appendix 5 shows the form you will use to generate the descriptors. Appendix 6 shows the tables you are trying to complete once you have generated the descriptor, definition, tasting procedure and reference standard Appendix 7 shows an evaluation scale. This is a line scale where the panellists can mark their score anywhere on the scale.  Ensure all members of your team have these forms for future evaluations.

Equipment and Reagents:

  • Four chocolate samples
  • Some examples of references e.g.
  • Cream
  • Caffeine (food grade)
  • Sodium Chloride (food grade)
  • Sucrose (food grade)
  • Caramel flavouring
  • Cocoa
  • Deionised water/spring water (food grade)
  • Kitchen – approved for preparation of foods and tasting
  • Tasting cups
  • Sensory booths
  • Access to computers/printers

Quantitative Descriptive Analysis (QDA)

  1. Prepare your samples (4 chocolate samples) and references ready for the panel training. (You may have already identified some potential references for the training – e.g. sucrose solution, salt solution, caffeine solution etc.). Chocolates will be cut to the same size (1 block) and kept in cups covered with lids. All external factors should be controlled, i.e. temperature, cup size, etc.
  2. Get your group of screened panellists all in a circle around a table. Other members of your group should however still participate to gain experience of the process.
    • Participants are presented with the product of interest (chocolate in this experiment). Normally panellists are exposed to a wide range of products which are representative of the product category under investigation
    • References available for anticipated attributes, although more ideas normally come up once panel discussions regarding the attributes begin.
    • Familiarise the panel with the basic scale to be used – a continuous line scale
  3. Get the panellists to taste the chocolates in turn and write down a list of attributes they perceive with a definition (description) for that attribute if they can,  for the general categories of odour, texture (in the hand), texture (in the mouth), flavour, taste, mouth coating. What other categories of attributes could you have included? Include these if appropriate. Ensure panellists do not discuss the attributes at this stage – they would normally do this in sensory booths.
  4. When everyone is finished writing down their attributes and definitions get every member of the panel to read out all their attributes for every product and write a combined list on the board. Write down everything tallying words that are the same and thus popular as you go. Next ask for clarification from the panel if there are similar ones and make a list which everyone agrees is the same (consensus). New attributes may arise during these discussions – e.g. people may understand different things by the term creamy.
  5. Once the list of attributes is finalized. validate the testing protocol for each attribute (add this information into your final write up)
    • Is there a reference standard that you can use to represent that attribute – use what is available or discuss what you think might be a suitable reference – you can then purchase these and bring them to the next session (together with the receipt for reimbursement (no receipt greater than $125)
  6. Now prepare a test sheet (using word format and similar to appendix 6) and definitions for your sample (use the template in appendix 7) ready for independent analysis of the samples.
  7. Using sensory booths and STANDARD SENSORY PRACTICE (appendix 8 and 9) get each of the panel members using your test sheet to evaluate the samples independently as part of their initial training
  8. Usually multiple trainings should be performed until the panels are close to ready for the final evaluation. Are panellists scoring consistently and similarly e.g. within 10% or 1SD.

Data Analysis

Collate the data from each descriptor using your screened panellists only. Present the result in a table similar to Table 4 (any format you think that is appropriate). Calculate the mean and standard deviation for each descriptor for your panel. Add your result and discussion of below questions into your final write up

Table 4 Example of result table for product evaluation

Descriptors Sample code Panel score Mean Std.
Caramel S1 3,4,3,4,3,4,5,6,7,3 …. 4.2 0.5
S2
S3
….

 

Question:

  • Look at the raw panel data:
    • How does the range vary? Comment on the panel’s performance
    • Does the data look normally distributed? Use your observation and statistical test for normality (Shapiro-wilk and Kolmogorov-Smirnov test) to conclude and discuss.
    • Are there any judges who are not performing particularly well (you may want to re-plot the panel data to look at individual judge performance – plot attribute intensity on the y axis and sample type on the x axis for each judge (on the same graph) and see how the judges vary)? Select at least 2 attributes to plot and discuss on judge performance.
  • Now look closer to the sample means and standard deviations:
    • Are the panel discriminating between samples? Please observe the size of standard deviation of your team member and discuss how to improve panellist’s performances. Explain how you could lower the standard deviation to get more consistency among panel rating.
    • Is the panel performing well as an objective instrument?
  • Are there any descriptors that seem to be used by panellist in the same way (redundant descriptors)?
  • Do you think you need to discuss any attributes further as a panel and/or find more attribute references?

 

Laboratory 3:  Training your panel on descriptors

Introduction

You are still training your panel here. You have some data and some training information from the previous lab.

Procedure

  1. Prepare any additional reference standards that you have brought to the session and consider important for your descriptive panel
  2. Get together the same group of screened panellists all in a circle around a table and provide:
  • Feedback from the last test (show the panel average and where each member falls in respect to the group. Are there particular attributes where the panel disagree e.g. on rank order of the 4 samples?
  • Do you need additional reference standards to help define any attributes panellist were unsure of
  • Any attributes with a high degree of covariance (which you observed from the last test)?
  1. Now MODIFY your original test sheet as needed (using word format) ready for independent analysis which includes all the consensual attributes that you have agreed on.
  2. Using sensory booths get each of the panel members using your test sheet to evaluate the samples independently.
  3. Replicate evaluation should be done at least 2-3 times to be able to calculate the standard deviation within a panellist.

 

Data Analysis (add this information into your final write up).

  • Analyse the data similarly to Laboratory Session 2 and compare the results of this new panel data from laboratory session 3 following the feedback, further training and discussions. Draw conclusions on the role of training in descriptive analysis.
  • Discuss the importance of replicates (Lab session 2 vs. Lab session 3 for same attribute) in sensory descriptive analysis.
  • Prepare a radar plot for all attributes and plot the four samples on this diagram (Figure 3) and discuss what the radar plot tells you.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3 Radar plot for the flavour profile analysis of coloured carrot varieties

  • Please complete a two way ANOVA (judges, sample) for all attributes. In this case the judges are the row values and the samples are the column values. In SPSS/Minitab fill out the data as below

SPSS/Minitab:         Analyse         General Linear Model        Univariate or Multivariate

(Go to the lecture on Stream “Sensory Lab Guideline” for example)

Please provide a summary of ANOVA result (Table 5) for all attributes. What does this data tell you?

Table 5 Summary table of Analysis of Variance (ANOVA) for each attribute

Attributes Significance level (p value) R squared
Sample Panellist Sample * Panellist
Odour
Colour
….

 

Please provide a summary of multiple paired comparison (Tukey’HSD) result (similar to table below)

Table 6 Summary table of multiple pair comparison (Tukey’s HSD) for each sample and each panellist

Colour Caramel ….
Sample 1 (Intensity score) x
2 (Intensity score) x
3
Panellist 1 (Intensity score) x
2 (Intensity score) x
3

X = superscript to show significant differences if any.

Different letter shows significantly different at 95% confidence interval. By indicating the intensity score in the table along with the significant letter would help the reader to understand whether they are significantly higher or lower.

Useful References

Kemp, Hollowood and Hort (2009) Sensory Evaluation: A practical handbook.  Wiley

Meilgaard, GVC and Morten, C. (2007). Sensory evaluation techniques. Fourth edition, Taylor and Francis, Boca Raton.

Labbe, D.,  Rytz, A.and Hugi, A.(2004). Training is a critical step to obtain reliable product profiles in a real food industry context. Food Quality and Preference 15, 341-348.

GUIDELINES FOR WRITING UP THESE THREE EXPERIMENTS

I would like one report from each person. The data collecting from screening and evaluation will be shared among team members. So ensure you have all results from the group practical. The Report should be submitted in MS word format

Assessment Criteria

  • To demonstrate a working knowledge of descriptive analysis
  • To understand why training of panellists may need to be carried out
  • To be able to analyse the data from panels
  • To reflect on learning
  • Professional written format (recommend to look for some publications as a guideline)
  • Good grammar and spelling, no typo
  • Appropriate referencing

 

WRITE UP AS A GROUP BUT INCLUDE IN THE INDIVIDUAL REPORTS

Title: Concise, relevant and specific and contain key words

Authors:

Summary/abstract: Objectives, key findings and recommendations. No more than 1 side of A4

Objectives

Background/Introduction: This should include why the project was undertaken; the broader context, scientific state of knowledge, constraints and their implications and advantages and limitations of the approach with appropriate references

(No more than 1 side of A4)

Methods: No more than 2 sides of A4

Experimental design, e.g. design, number and type of replications etc. (you have learnt from statistic class in previous semester)

Sensory method, e.g. type, number, scales used, data collection method etc.

Assessors, e.g. type, number, screening, selection, level of training, instructions given etc.

Samples, e.g. formulations, coding, preparation, serving and so on

Standard reference for your evaluation (not screening), e.g. preparation, concentration, score and so on

Testing Conditions e.g. test procedure (generating of descriptors, definition of each, way of sample testing), test location, environment etc.

Data handling e.g. coding, transformations, treatment of missing data

Data statistical analysis technique and hypothesis

 

THIS WRITTEN UP INDIVIDUALLY

Results and Discussion:  No more than 4 sides of A4

Make sure you include the following:

Probability levels, degrees of freedom, test statistics and where appropriate direction of the effect should be reported

Ensure you complete the analysis as requested for the individual laboratory sessions. Then discuss in general the process of training panels and the justification or not for having a trained sensory panel as related to the experiences and results you have obtained through these three laboratory sessions.

Interpret, discuss and briefly summarise the result. Where applicable, please provide the reference to support the idea.

Summary tables to illustrate result (do not directly copy the output from SPSS except for figures, report score with appropriate subscription with proper confidence level stated).

Conclusions and recommendations No more than 1 side of A4

APPENDICES ARE ALLOWED (to include all relevant information to the report)

 

 

 

 

 

APPENDIX 1 – SCREENING QUESTIONNAIRE

THIS IS ONLY AN EXAMPLE MODIFY AS TUTOR AND YOU SEE BEST

HISTORY:

Name: __________________________________________________________________________________

TIME:

When are you available for tasting?

__________________________________________________________________________________

HEALTH:

Do you have any of the following?

Dentures                                             _______

Diabetes                                              _______

Oral or gum disease                        _______

Hypoglycaemia                                 _______

Food Allergies*                                  _______

Hypertension                                    _______

* = please list if yes __________________________________________________________________________________

Do you take any medications which affect your senses, especially taste and smell?

__________________________________________________________________________________

Do you smoke?

__________________________________________________________________________________

FOOD HABITS:

Are you currently on a restricted diet? If yes, explain.

_________________________________________________________________________________

How often do you eat out in a month? __________________________________________________

How often do you eat fast food in a month?_________________________________________

What are your favourite foods _____________________________________________________

What foods can you not eat _______________________________________________________

What foods do you not like to eat___________________________________________________

 

 

Is your ability to distinguish smell and tastes?

SMELL                   TASTE

Better than average                                                       ______                                _______

Average                                                                               ______                                _______

Worse than average                                                       ______                                _______

FLAVOUR QUIZ

If a recipe calls for thyme and there is none available, what would you substitute?

______________________________________________________________________________

What are some other foods that taste like yoghurt?

______________________________________________________________________________

How would you describe the difference between flavour and aroma?

______________________________________________________________________________

What is the best one or two word description of grated Italian cheese?

______________________________________________________________________________

Describe some of the noticeable flavours in mayonnaise

______________________________________________________________________________

Describe some of the noticeable flavours in sausage

______________________________________________________________________________

Describe some of the noticeable flavours in Corn Flakes

______________________________________________________________________________

Describe some noticeable flavours in Coke

______________________________________________________________________________

Thank you for your time

APPENDIX  2 – IDENTIFICATION OF TASTES

Name: ……………………………………………………………………

Date: ……………………………………………………………………..

Time: …………………………………………………………………….

Instruction:

  • Sample each solution in the order provided, taking a mouthful (approximately 15mls) of each, and spit out the sample in the spittoon provided.
  • Take approximately 30 seconds per sample, but do not go back to the previously sampled vessels.
  • You may rinse out your mouth at the beginning and end of the sample set with the water provided.

Each coded sample may or may not have one of the following tastes: Bitter, Salty, Sweet, Sour, umami. If you identify a taste in the coded sample place a X next to the taste identified

Code number of vessel Taste not identified Acid Bitter Sweet Salty Umami

 

 

Thank you for your attention and participation

 


 

Appendix 3

Presentation Order
Panel 1 2 3 4 5 6 7 8 9
1 Water

390

Acid

403

Umami

289

Bitter

738

Sweet

112

Acid

938

Water

945

Salt

450

Sweet

778

2 W

645

W

989

A

955

B

997

S

131

S

644

U

445

U

245

A

852

3 B

447

A

124

W

594

A

714

B

764

W

735

S

415

S

197

U

564

4 U

365

B

965

S

895

W

200

A

498

B

645

A

834

W

946

S

089

5 U

095

B

930

W

990

A

508

W

241

A

298

B

809

S

546

S

915

6 B

644

A

545

S

974

W

709

U

753

W

155

A

739

B

937

S

614

7 A

543

W

213

S

661

W

566

B

454

U

999

S

403

A

615

B

342

8 S

982

S

142

A

544

B

341

B

164

W

984

U

153

W

165

A

232

9 S

489

U

512

B

516

A

157

A

356

W

345

S

896

U

204

W

105

10 U

012

U

087

S

294

W

465

S

067

W

978

A

984

A

941

B

560

11 B

689

B

186

S

725

S

357

W

354

A

754

W

348

A

944

U

195

12 S

879

A

159

B

848

S

897

W

846

U

259

A

574

W

789

U

156

13 W

871

W

987

B

823

S

479

U

617

A

102

U

935

S

763

B

926

14 A

300

B

902

S

451

U

620

W

940

S

798

A

097

B

491

W

981

15 U

045

W

689

S

925

B

887

A

141

S

604

W

745

U

015

A

150

 

 

 

Appendix 4  – BASIC TASTE – SCREENING

THIS IS ONLY AN EXAMPLE MODIFY AS TUTOR AND YOU SEE BEST

 

NAME:                                                                                                      DATE:                                                

 

Please taste the following samples and rank them in order of increasing intensity (lowest to highest) for SWEETNESS.

 

 

223

 

798

 

145

 

607

 

 

 

 

 

SAMPLE NUMBER

 

(Least Sweet)
 

(Most Sweet)

 

 

THANK YOU

 

 

Appendix 5

Product Profiling

Name: ……………………………………………………………………

Date: ………………………………………………………………………

Product number: ……………………………………………………

Instruction: Please describe the sensations given by the (these) product (s) following the properties indicated below, using your own vocabulary.

Before tasting During tasting After tasting
Appearance
Odour
Flavor

(taste + aroma)

Texture

(in mouth)

Texture

(by finger and possibly with a spoon)

 

APPENDIX 6

 

Attribute Description When/how to assess Scale to be used/Anchors Reference
Odour and Flavour
e.g. Sweet Basic taste of sweetness 15 cm line intensity scale

 

Sucrose solution (define brand, concentration, preparation)

 

 

Attribute Description When/how to assess Scale to be used? Anchors Reference
Texture
e.g. Hardness Force required to break down on initial bite Force required to break down on initial bite 15 cm line intensity scale

 

 

Attribute Description When/how to assess Scale to be used? Anchors Reference
Mouthcoating
e.g. fatty Flavour associated with vegetable fat Once melted in mouth 15 cm line intensity scale Vegetable fat (define brand)

 

 

 

 

Appendix 7

THIS IS ONLY AN EXAMPLE MODIFY AS TUTOR AND YOU SEE BEST

 

EVALUATION FORM – ______________________

 

Name:____________________________________

Date: ____________________________________

Please evaluate the ___________________ for Odour, Flavour and Texture using the attributes and scales below:

SAMPLE  _____________

ODOUR

 

____________

 

 

____________

 

 

 

____________

 

 

 

FLAVOUR

____________

 

 

____________

 

 

____________

 

 

 

 

 

 

TEXTURE (in the hand)

 

____________

 

 

____________

 

 

 

____________

 

 

 

 

TEXTURE (in the mouth)

 

____________

 

 

____________

 

 

 

____________

 

 

 

 

MOUTHCOATING

 

____________

 

 

____________

 

 

 

 

 

APPENDIX 8

Complete the below sensory checklist for all experiments that have been carried out.

SENSORY CHECKLIST

TEST OBJECTIVE ___________________________________________________________

PANELLIST  (Comment on what they have completed already )

Recruitment

Screening

Training

SAMPLE   (describe the sample characteristics – all standardised throughout testing)

Size and shape

Volume

Carrier

Serving temperature

Maximum holding time

TEST SETUP (describe the below how they were standardised)

Palate cleanser

Instructions to technicians

Instructions to panellists

Score Sheets

Instructions

Types of scales

Attribute words

Anchor words

Coding

Randomisation

Booth items

Pencils

Napkins

Spittoons

Panellist debriefing

 

TEST AREA

Separation of panellists

Temperature

Humidity

Light conditions

Noise

Background odour/clean-air handling/positive pressure

Accessibility

Security

 

 

Appendix 9

 

Date Test Code
Type of Test
Post this sheet where the trays are prepared. Code score sheets and serving containers ahead of time
 

Product type:

 

Sample identification

Sample 1 = _________        Sample 2 = ________        Sample 3 = _________

Panellist Sample – codes
1
2
3
4

 

 

 

School of Food and Nutrition

SENSORY EVALUATION EXPERIMENTAL PLAN

141.312

Introduction:

The purpose of these experiments is to obtain experience and knowledge in running Quantitative Descriptive Analysis. The issues of screening and training will be investigated with a strong emphasis on analysis of the data. However, remember the screening and training of panel members takes usually between 40-120 hours of time (Meilgaard and Morton, 2007), so this practical cannot expect to produce fully trained panel members.

Procedure:

You have 3 x 3 hour sessions. Each of the practical is interconnected, but the focus of each session is as follows (remember descriptive analysis is run with a trained panel not a consumer panel):

  • Laboratory 1: Screening of panellists
  • Laboratory 2: Development of descriptors
  • Laboratory 3: Training of panellists , running of descriptive  panel and analysis of data

General Laboratory Procedures:

You will be working in groups and you will run the screening sensory experiment on everyone else in the class. In industry normally you would screen 60 -120 people to get to a panel size of approximately 15. In this practical series see if how many people you get from screening 20+ people in the class.

 


 

Laboratory 1: Panel Screening

Introduction

This experiment involves the screening of potential panel members for possible inclusion into a descriptive panel. It is not a comprehensive list of tests, but more an example of the types of tests you might run.

  1. Screening Questionnaire

Procedure – Prepare a screening questionnaire similar to the one attached in Appendix 1 remembering you will be evaluating chocolate. It will help if you have thought about this prior to the session and come with ideas.

  • Please nominate one person to lead the team. Get all the people in your group to complete the questionnaire and screen down the number of participants based on the test’s objective (motivation, availability and exhibiting an allergic reaction to a substance). Give result and reasons for your choice of why you have eliminated those subjects (add this into your final write up). Ensure your screening questionnaire has appropriate ethics and consent given (Example is given on Stream).

 

  1. Identification of tastes

Procedure – To test panel sensitivity to taste substances (panel is able to perceive and differentiate the basic tastes), preparing the following taste reference solutions (Table 1) by following STANDARD SENSORY PRACTICE (Appendix 8 and 9) and examining the test sheet for instructions on running a taste test as described on the test sheet (Appendix 2). As you have prepared the sample sit would not be appropriate to run the test ion yourselves.  Instead you will evaluate the samples prepared by another group in your class and they will provide you with the results for your write up.    Although all of the group will carry out the tests remember that only data from those people in your group who passed the initial screening are valid

Table 1 Reference substance and concentration for identification of tastes

Reference Substance Concentration g/L
Caffeine 0.19g/litre
Sodium Chloride (NaCl) 1.19g/litre
Sucrose 5.76g/litre
Citric Acid 0.43g/litre
Monosodium glutamate (MSG) 0.60g/litre
Deionised water

 

Equipment and Reagents:

  • Caffeine (food grade)
  • Sodium Chloride (food grade)
  • Sucrose (food grade)
  • Citric acid (food grade)
  • Monosodium glutamate (food grade)
  • Deionised water/spring water (food grade)
  • Kitchen – approved for preparation of foods and tasting
  • Unsalted crackers
  • Tasting cups and lids

 

Remember for standard sensory practice all sensory preparation needs to be standardised: use the same tasting cups (size, colour, and material) for all samples and all panellists; random three digit numbers for identification of the samples; standard volume of the taste solution (approx. 30mls); the order of presentation of the samples also needs to be randomised. Use appendix 3 to help you set up the experiment.

In this experiment, each participant will get to taste 9 samples made up from the above six solutions, i.e. participant 1 will taste water first following by citric acid, MSG, caffeine, sucrose, citric acid, water, salt and sucrose, respectively (appendix 3 and figure 1). The number of correct response should be recorded for each subject (add this into your final write up).

Figure 1 the presentation order of taste reference solutions for participant number 1

  1. Ranking to determine ability to discriminate different intensities of taste

Procedure – To further investigate the panel sensitivity, prepare as many of the following solutions as you can in the remaining time, carry out an experiment using standard sensory practice (see Appendix 8 and 9), and examining the test sheet for instructions, run a taste test as described on the test sheet (see Appendix 4) for screening your panellists further. In this experiment, each panellist will taste a total of 16 samples (4 concentrations and 4 tastes) and then will be asked to rank the intensity of each taste on the scale (Appendix 4).

Equipment and Reagents:

  • Caffeine (food grade)
  • Sodium Chloride (food grade)
  • Sucrose (food grade)
  • Citric acid (food grade)
  • Deionised water/spring water (food grade)
  • Kitchen – approved for preparation of foods and tasting
  • Tasting cups
  • Sensory booths
  • Access to computers/printer

Table 2 Reference substance and concentration for ranking of taste substances. The random three digit numbers should be created and the presentation should be randomised (add this into your final write up).

Sample order

(for one judge)

Example of three digit random number to identify sample Concentration Taste
a)      3 223 10g/litre Sweet (ranking)

Sucrose

         1 793 0 (water only)
         4 246 20g/litre
         2 970 5g/litre
b)      2 0.35g/litre Sour (ranking)

Citric Acid

         4 1.40g/litre
         1 0 (water only)
         3 0.7g/litre
c)      2 1g/litre Salty (ranking)

Salt

         1 0 (water only)
         4 4g/litre
         3 2g/litre
d)      2 0.35g/litre Bitter (ranking)

Caffeine

         1 0 (water only)
         4 1.4g/litre
         3 0.7g/litre

 

Data Analysis

Collect the results of the screening tests which you performed. Complete an excel spread sheet for your panellists (Table 3). Add your summary and discussion of below table and questions into your final write up

 

Table 3 Example of result table for panel screening

Panellist Screening Questionnaire Screening

Identification

Of tastes

Screening – Ranking experiment Overall decision
Sweet Sour Salt Bitter
1 Pass/Fail % % % % %
2
3
….

Note: “It has been proven that the concentrations recommended in this experiment were detected and recognised by 50% of novice assessors”

Question:

  • How does the result help you make a decision about who to keep on your panel?
  • What other screening test could you have carried out?


 

Laboratory 2:  Training your panel on descriptors – CHOCOLATE EXAMPLE

Introduction

The descriptive technique we are going to practice today is called “Quantitative Descriptive Analysis (QDA). Once you have screened your panellists you are ready to start to develop descriptors on the product of interest. To begin the process, nominate a panel leader for your group. The panel leader will not taste the product but will guide the team through the tasting and discussion. Panellists are normally exposed to many variations of the product over several sessions to encourage adequate concept formation. The panellist then will

Figure 2 Descriptive analysis procedures

At the end of training stages, a series of trial evaluations are performed to assess the panellist’s performances. The results are statistically analysed to ascertain which panellists need further training. In general, the standard deviation of well-trained panel should not be over 1.0 and repeat measures within 10% of the scale used. Add the discussion in your final report.

Procedure

Familiarise yourself with the type of descriptive form you are trying to prepare (examples are given in Appendix 5, 6 and 7). Appendix 5 shows the form you will use to generate the descriptors. Appendix 6 shows the tables you are trying to complete once you have generated the descriptor, definition, tasting procedure and reference standard Appendix 7 shows an evaluation scale. This is a line scale where the panellists can mark their score anywhere on the scale.  Ensure all members of your team have these forms for future evaluations.

Equipment and Reagents:

  • Four chocolate samples
  • Some examples of references e.g.
  • Cream
  • Caffeine (food grade)
  • Sodium Chloride (food grade)
  • Sucrose (food grade)
  • Caramel flavouring
  • Cocoa
  • Deionised water/spring water (food grade)
  • Kitchen – approved for preparation of foods and tasting
  • Tasting cups
  • Sensory booths
  • Access to computers/printers

Quantitative Descriptive Analysis (QDA)

  1. Prepare your samples (4 chocolate samples) and references ready for the panel training. (You may have already identified some potential references for the training – e.g. sucrose solution, salt solution, caffeine solution etc.). Chocolates will be cut to the same size (1 block) and kept in cups covered with lids. All external factors should be controlled, i.e. temperature, cup size, etc.
  2. Get your group of screened panellists all in a circle around a table. Other members of your group should however still participate to gain experience of the process.
    • Participants are presented with the product of interest (chocolate in this experiment). Normally panellists are exposed to a wide range of products which are representative of the product category under investigation
    • References available for anticipated attributes, although more ideas normally come up once panel discussions regarding the attributes begin.
    • Familiarise the panel with the basic scale to be used – a continuous line scale
  3. Get the panellists to taste the chocolates in turn and write down a list of attributes they perceive with a definition (description) for that attribute if they can,  for the general categories of odour, texture (in the hand), texture (in the mouth), flavour, taste, mouth coating. What other categories of attributes could you have included? Include these if appropriate. Ensure panellists do not discuss the attributes at this stage – they would normally do this in sensory booths.
  4. When everyone is finished writing down their attributes and definitions get every member of the panel to read out all their attributes for every product and write a combined list on the board. Write down everything tallying words that are the same and thus popular as you go. Next ask for clarification from the panel if there are similar ones and make a list which everyone agrees is the same (consensus). New attributes may arise during these discussions – e.g. people may understand different things by the term creamy.
  5. Once the list of attributes is finalized. validate the testing protocol for each attribute (add this information into your final write up)
    • Is there a reference standard that you can use to represent that attribute – use what is available or discuss what you think might be a suitable reference – you can then purchase these and bring them to the next session (together with the receipt for reimbursement (no receipt greater than $125)
  6. Now prepare a test sheet (using word format and similar to appendix 6) and definitions for your sample (use the template in appendix 7) ready for independent analysis of the samples.
  7. Using sensory booths and STANDARD SENSORY PRACTICE (appendix 8 and 9) get each of the panel members using your test sheet to evaluate the samples independently as part of their initial training
  8. Usually multiple trainings should be performed until the panels are close to ready for the final evaluation. Are panellists scoring consistently and similarly e.g. within 10% or 1SD.

Data Analysis

Collate the data from each descriptor using your screened panellists only. Present the result in a table similar to Table 4 (any format you think that is appropriate). Calculate the mean and standard deviation for each descriptor for your panel. Add your result and discussion of below questions into your final write up

Table 4 Example of result table for product evaluation

Descriptors Sample code Panel score Mean Std.
Caramel S1 3,4,3,4,3,4,5,6,7,3 …. 4.2 0.5
S2
S3
….

 

Question:

  • Look at the raw panel data:
    • How does the range vary? Comment on the panel’s performance
    • Does the data look normally distributed? Use your observation and statistical test for normality (Shapiro-wilk and Kolmogorov-Smirnov test) to conclude and discuss.
    • Are there any judges who are not performing particularly well (you may want to re-plot the panel data to look at individual judge performance – plot attribute intensity on the y axis and sample type on the x axis for each judge (on the same graph) and see how the judges vary)? Select at least 2 attributes to plot and discuss on judge performance.
  • Now look closer to the sample means and standard deviations:
    • Are the panel discriminating between samples? Please observe the size of standard deviation of your team member and discuss how to improve panellist’s performances. Explain how you could lower the standard deviation to get more consistency among panel rating.
    • Is the panel performing well as an objective instrument?
  • Are there any descriptors that seem to be used by panellist in the same way (redundant descriptors)?
  • Do you think you need to discuss any attributes further as a panel and/or find more attribute references?

 

Laboratory 3:  Training your panel on descriptors

Introduction

You are still training your panel here. You have some data and some training information from the previous lab.

Procedure

  1. Prepare any additional reference standards that you have brought to the session and consider important for your descriptive panel
  2. Get together the same group of screened panellists all in a circle around a table and provide:
  • Feedback from the last test (show the panel average and where each member falls in respect to the group. Are there particular attributes where the panel disagree e.g. on rank order of the 4 samples?
  • Do you need additional reference standards to help define any attributes panellist were unsure of
  • Any attributes with a high degree of covariance (which you observed from the last test)?
  1. Now MODIFY your original test sheet as needed (using word format) ready for independent analysis which includes all the consensual attributes that you have agreed on.
  2. Using sensory booths get each of the panel members using your test sheet to evaluate the samples independently.
  3. Replicate evaluation should be done at least 2-3 times to be able to calculate the standard deviation within a panellist.

 

Data Analysis (add this information into your final write up).

  • Analyse the data similarly to Laboratory Session 2 and compare the results of this new panel data from laboratory session 3 following the feedback, further training and discussions. Draw conclusions on the role of training in descriptive analysis.
  • Discuss the importance of replicates (Lab session 2 vs. Lab session 3 for same attribute) in sensory descriptive analysis.
  • Prepare a radar plot for all attributes and plot the four samples on this diagram (Figure 3) and discuss what the radar plot tells you.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3 Radar plot for the flavour profile analysis of coloured carrot varieties

  • Please complete a two way ANOVA (judges, sample) for all attributes. In this case the judges are the row values and the samples are the column values. In SPSS/Minitab fill out the data as below

SPSS/Minitab:         Analyse         General Linear Model        Univariate or Multivariate

(Go to the lecture on Stream “Sensory Lab Guideline” for example)

Please provide a summary of ANOVA result (Table 5) for all attributes. What does this data tell you?

Table 5 Summary table of Analysis of Variance (ANOVA) for each attribute

Attributes Significance level (p value) R squared
Sample Panellist Sample * Panellist
Odour
Colour
….

 

Please provide a summary of multiple paired comparison (Tukey’HSD) result (similar to table below)

Table 6 Summary table of multiple pair comparison (Tukey’s HSD) for each sample and each panellist

Colour Caramel ….
Sample 1 (Intensity score) x
2 (Intensity score) x
3
Panellist 1 (Intensity score) x
2 (Intensity score) x
3

X = superscript to show significant differences if any.

Different letter shows significantly different at 95% confidence interval. By indicating the intensity score in the table along with the significant letter would help the reader to understand whether they are significantly higher or lower.

Useful References

Kemp, Hollowood and Hort (2009) Sensory Evaluation: A practical handbook.  Wiley

Meilgaard, GVC and Morten, C. (2007). Sensory evaluation techniques. Fourth edition, Taylor and Francis, Boca Raton.

Labbe, D.,  Rytz, A.and Hugi, A.(2004). Training is a critical step to obtain reliable product profiles in a real food industry context. Food Quality and Preference 15, 341-348.

GUIDELINES FOR WRITING UP THESE THREE EXPERIMENTS

I would like one report from each person. The data collecting from screening and evaluation will be shared among team members. So ensure you have all results from the group practical. The Report should be submitted in MS word format

Assessment Criteria

  • To demonstrate a working knowledge of descriptive analysis
  • To understand why training of panellists may need to be carried out
  • To be able to analyse the data from panels
  • To reflect on learning
  • Professional written format (recommend to look for some publications as a guideline)
  • Good grammar and spelling, no typo
  • Appropriate referencing

 

WRITE UP AS A GROUP BUT INCLUDE IN THE INDIVIDUAL REPORTS

Title: Concise, relevant and specific and contain key words

Authors:

Summary/abstract: Objectives, key findings and recommendations. No more than 1 side of A4

Objectives

Background/Introduction: This should include why the project was undertaken; the broader context, scientific state of knowledge, constraints and their implications and advantages and limitations of the approach with appropriate references

(No more than 1 side of A4)

Methods: No more than 2 sides of A4

Experimental design, e.g. design, number and type of replications etc. (you have learnt from statistic class in previous semester)

Sensory method, e.g. type, number, scales used, data collection method etc.

Assessors, e.g. type, number, screening, selection, level of training, instructions given etc.

Samples, e.g. formulations, coding, preparation, serving and so on

Standard reference for your evaluation (not screening), e.g. preparation, concentration, score and so on

Testing Conditions e.g. test procedure (generating of descriptors, definition of each, way of sample testing), test location, environment etc.

Data handling e.g. coding, transformations, treatment of missing data

Data statistical analysis technique and hypothesis

 

THIS WRITTEN UP INDIVIDUALLY

Results and Discussion:  No more than 4 sides of A4

Make sure you include the following:

Probability levels, degrees of freedom, test statistics and where appropriate direction of the effect should be reported

Ensure you complete the analysis as requested for the individual laboratory sessions. Then discuss in general the process of training panels and the justification or not for having a trained sensory panel as related to the experiences and results you have obtained through these three laboratory sessions.

Interpret, discuss and briefly summarise the result. Where applicable, please provide the reference to support the idea.

Summary tables to illustrate result (do not directly copy the output from SPSS except for figures, report score with appropriate subscription with proper confidence level stated).

Conclusions and recommendations No more than 1 side of A4

APPENDICES ARE ALLOWED (to include all relevant information to the report)

 

 

 

 

 

APPENDIX 1 – SCREENING QUESTIONNAIRE

THIS IS ONLY AN EXAMPLE MODIFY AS TUTOR AND YOU SEE BEST

HISTORY:

Name: __________________________________________________________________________________

TIME:

When are you available for tasting?

__________________________________________________________________________________

HEALTH:

Do you have any of the following?

Dentures                                             _______

Diabetes                                              _______

Oral or gum disease                        _______

Hypoglycaemia                                 _______

Food Allergies*                                  _______

Hypertension                                    _______

* = please list if yes __________________________________________________________________________________

Do you take any medications which affect your senses, especially taste and smell?

__________________________________________________________________________________

Do you smoke?

__________________________________________________________________________________

FOOD HABITS:

Are you currently on a restricted diet? If yes, explain.

_________________________________________________________________________________

How often do you eat out in a month? __________________________________________________

How often do you eat fast food in a month?_________________________________________

What are your favourite foods _____________________________________________________

What foods can you not eat _______________________________________________________

What foods do you not like to eat___________________________________________________

 

 

Is your ability to distinguish smell and tastes?

SMELL                   TASTE

Better than average                                                       ______                                _______

Average                                                                               ______                                _______

Worse than average                                                       ______                                _______

FLAVOUR QUIZ

If a recipe calls for thyme and there is none available, what would you substitute?

______________________________________________________________________________

What are some other foods that taste like yoghurt?

______________________________________________________________________________

How would you describe the difference between flavour and aroma?

______________________________________________________________________________

What is the best one or two word description of grated Italian cheese?

______________________________________________________________________________

Describe some of the noticeable flavours in mayonnaise

______________________________________________________________________________

Describe some of the noticeable flavours in sausage

______________________________________________________________________________

Describe some of the noticeable flavours in Corn Flakes

______________________________________________________________________________

Describe some noticeable flavours in Coke

______________________________________________________________________________

Thank you for your time

APPENDIX  2 – IDENTIFICATION OF TASTES

Name: ……………………………………………………………………

Date: ……………………………………………………………………..

Time: …………………………………………………………………….

Instruction:

  • Sample each solution in the order provided, taking a mouthful (approximately 15mls) of each, and spit out the sample in the spittoon provided.
  • Take approximately 30 seconds per sample, but do not go back to the previously sampled vessels.
  • You may rinse out your mouth at the beginning and end of the sample set with the water provided.

Each coded sample may or may not have one of the following tastes: Bitter, Salty, Sweet, Sour, umami. If you identify a taste in the coded sample place a X next to the taste identified

Code number of vessel Taste not identified Acid Bitter Sweet Salty Umami

 

 

Thank you for your attention and participation

 


 

Appendix 3

Presentation Order
Panel 1 2 3 4 5 6 7 8 9
1 Water

390

Acid

403

Umami

289

Bitter

738

Sweet

112

Acid

938

Water

945

Salt

450

Sweet

778

2 W

645

W

989

A

955

B

997

S

131

S

644

U

445

U

245

A

852

3 B

447

A

124

W

594

A

714

B

764

W

735

S

415

S

197

U

564

4 U

365

B

965

S

895

W

200

A

498

B

645

A

834

W

946

S

089

5 U

095

B

930

W

990

A

508

W

241

A

298

B

809

S

546

S

915

6 B

644

A

545

S

974

W

709

U

753

W

155

A

739

B

937

S

614

7 A

543

W

213

S

661

W

566

B

454

U

999

S

403

A

615

B

342

8 S

982

S

142

A

544

B

341

B

164

W

984

U

153

W

165

A

232

9 S

489

U

512

B

516

A

157

A

356

W

345

S

896

U

204

W

105

10 U

012

U

087

S

294

W

465

S

067

W

978

A

984

A

941

B

560

11 B

689

B

186

S

725

S

357

W

354

A

754

W

348

A

944

U

195

12 S

879

A

159

B

848

S

897

W

846

U

259

A

574

W

789

U

156

13 W

871

W

987

B

823

S

479

U

617

A

102

U

935

S

763

B

926

14 A

300

B

902

S

451

U

620

W

940

S

798

A

097

B

491

W

981

15 U

045

W

689

S

925

B

887

A

141

S

604

W

745

U

015

A

150

 

 

 

Appendix 4  – BASIC TASTE – SCREENING

THIS IS ONLY AN EXAMPLE MODIFY AS TUTOR AND YOU SEE BEST

 

NAME:                                                                                                      DATE:                                                

 

Please taste the following samples and rank them in order of increasing intensity (lowest to highest) for SWEETNESS.

 

 

223

 

798

 

145

 

607

 

 

 

 

 

SAMPLE NUMBER

 

(Least Sweet)
 

(Most Sweet)

 

 

THANK YOU

 

 

Appendix 5

Product Profiling

Name: ……………………………………………………………………

Date: ………………………………………………………………………

Product number: ……………………………………………………

Instruction: Please describe the sensations given by the (these) product (s) following the properties indicated below, using your own vocabulary.

Before tasting During tasting After tasting
Appearance
Odour
Flavor

(taste + aroma)

Texture

(in mouth)

Texture

(by finger and possibly with a spoon)

 

APPENDIX 6

 

Attribute Description When/how to assess Scale to be used/Anchors Reference
Odour and Flavour
e.g. Sweet Basic taste of sweetness 15 cm line intensity scale

 

Sucrose solution (define brand, concentration, preparation)

 

 

Attribute Description When/how to assess Scale to be used? Anchors Reference
Texture
e.g. Hardness Force required to break down on initial bite Force required to break down on initial bite 15 cm line intensity scale

 

 

Attribute Description When/how to assess Scale to be used? Anchors Reference
Mouthcoating
e.g. fatty Flavour associated with vegetable fat Once melted in mouth 15 cm line intensity scale Vegetable fat (define brand)

 

 

 

 

Appendix 7

THIS IS ONLY AN EXAMPLE MODIFY AS TUTOR AND YOU SEE BEST

 

EVALUATION FORM – ______________________

 

Name:____________________________________

Date: ____________________________________

Please evaluate the ___________________ for Odour, Flavour and Texture using the attributes and scales below:

SAMPLE  _____________

ODOUR

 

____________

 

 

____________

 

 

 

____________

 

 

 

FLAVOUR

____________

 

 

____________

 

 

____________

 

 

 

 

 

 

TEXTURE (in the hand)

 

____________

 

 

____________

 

 

 

____________

 

 

 

 

TEXTURE (in the mouth)

 

____________

 

 

____________

 

 

 

____________

 

 

 

 

MOUTHCOATING

 

____________

 

 

____________

 

 

 

 

 

APPENDIX 8

Complete the below sensory checklist for all experiments that have been carried out.

SENSORY CHECKLIST

TEST OBJECTIVE ___________________________________________________________

PANELLIST  (Comment on what they have completed already )

Recruitment

Screening

Training

SAMPLE   (describe the sample characteristics – all standardised throughout testing)

Size and shape

Volume

Carrier

Serving temperature

Maximum holding time

TEST SETUP (describe the below how they were standardised)

Palate cleanser

Instructions to technicians

Instructions to panellists

Score Sheets

Instructions

Types of scales

Attribute words

Anchor words

Coding

Randomisation

Booth items

Pencils

Napkins

Spittoons

Panellist debriefing

 

TEST AREA

Separation of panellists

Temperature

Humidity

Light conditions

Noise

Background odour/clean-air handling/positive pressure

Accessibility

Security

 

 

Appendix 9

 

Date Test Code
Type of Test
Post this sheet where the trays are prepared. Code score sheets and serving containers ahead of time
 

Product type:

 

Sample identification

Sample 1 = _________        Sample 2 = ________        Sample 3 = _________

Panellist Sample – codes
1
2
3
4