SOP: Numerical Scoring Test

GIFSQ — Global Institute for Food Safety & Quality

Principle

One or more samples are presented to each panelist in random order or according to a statistical design, and the panelist evaluates each sample on a specific scale for a particular characteristic, indicating the rating of the sample. The panelists are trained to follow the sensory characteristics corresponding to the agreed quality descriptions and scores — without this understanding the rating is of no use.

Apparatus required

• Individual judging booths (identical, uniformly illuminated), each fitted with drinking water, a glass, clean towels and a basin or receptacle for expectoration
• Coloured lighting (where needed to mask small colour differences between samples)
• Stainless steel, glass or china serving dishes and cups; plain serving trays; small stainless steel forks and spoons
• Prepared evaluation cards for the numerical scoring test

Sample preparation

Prepare all samples in exactly the same manner. Code the samples with three- or five-digit numbers. Present the samples in random order or according to the statistical design (trained panel: 5–12 judges, 1–6 samples; untrained: 72–80 judges, 1–4 samples; for trained panels a larger number, 5–10 samples, only if the samples are mild-flavoured or are rated for texture only).

Procedure

Present the coded samples to the panelist in random order

↓

Ask the panelist to rate each sample according to the agreed descriptions: 90 excellent, 80 good, 70 fair, 60 poor

↓

Record the score and comments for each sample

Interpretation of results

Analyse the results by the analysis of variance (Tables 19-6, 19-7, 19-8 and 19-9). Determine which samples are significantly different from the others with Duncan’s Multiple Range Test.

Worked illustration from the book: canned tomato from three different manufacturers was rated for texture by 10 panelists (actual scores divided by 10 for convenience in calculation). Totals: sample 1 = 59, sample 2 = 66, sample 3 = 83; grand total 208. Analysis of variance: samples — df 2, SS 30.47, MS 15.24, F = 14.51 (tabulated 6.01 at the 1% level — significant); error — df 18, MS 1.05. Duncan’s test: sample means 5.9, 6.6, 8.3; standard error SE = √(1.05/10) = 0.330 as printed (the book’s value is carried as printed; the recomputed square root is 0.324); p from Table 19-8 at 18 degrees of freedom = 4.07 (for 2 means) and 4.27 (for 3 means); shortest significant ranges Rp = 1.343 and 1.409. A − C = 8.3 − 5.9 = 2.4 > 1.41 (R₃); A − B = 8.3 − 6.6 = 1.7 > 1.34 (R₂); B − C = 6.6 − 5.9 = 0.7 < 1.34 (R₂). Canned tomato sample No. 3 is significantly different from samples 1 and 2; samples 1 and 2 are not significantly different from each other.

• SE = standard error of the mean = √(mean square of error / N)
• p = tabulated Duncan’s value for the error degrees of freedom and the number of means compared
• Rp = shortest significant range = p × SE

Specimen evaluation card fields: score scale with quality descriptions (90 excellent, 80 good, 70 fair, 60 poor); table of sample, score and comments; signature.

Precautions

• Train the panelists on the sensory characteristics corresponding to the agreed quality descriptions and scores before the test; without this understanding the rating will not be of any use.
• Conduct judging in individual booths so that judgements are independent; allow no communication between panel members except consultation with the panel leader on any point of doubt.
• Test in the hour after a normal meal (e.g., 10.00 a.m. to 12 noon, or 3 to 5 p.m.).
• Panel members should not smoke or chew pan or supari for at least half an hour before the test.
• Judge quickly but not hurriedly; make odour observations by sniffing before tasting.
• Allow retesting, but avoid prolonged testing; tasters may swallow or spit out samples, and should rinse between samples (or use bread or puffed rice) to remove a strong flavour.
• Keep the evaluation card simple, clearly typed or printed, with unambiguous terms and directions in the desired sequence of action.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.