SOP: Single Sample (Monadic) Test

GIFSQ — Global Institute for Food Safety & Quality

Principle

One sample at a time is presented to each panelist, who indicates the presence or absence and/or the intensity of a particular quality characteristic. The test is used for foods that have an after-taste or flavour carry-over which precludes testing a second sample at the same session. With trained panelists, the completed analyses of two or more samples evaluated at different times can be compared; in market and consumer analysis, the results of different samples evaluated at different times by different sets of untrained panelists can be compared. In consumer preference testing, the monadic procedure assumes that the consumer normally tastes just one type of food at a time.

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; watch glasses as covers; glass-stoppered bottles for odour tests (4 oz size)
• Prepared evaluation cards for the single sample test (off-flavour card for trained panels; hedonic scale card for consumer preference)

Sample preparation

Prepare each sample in exactly the same manner. Present a single coded sample per session. Where different formulations are compared, different groups of panelists receive the different formulations (consumer analysis), or the same panel evaluates the formulations in separate sessions.

Procedure

Serve one coded sample to the panelist (trained panel: 6–25 judges, 1 sample per session; untrained panel: 72–80 judges)

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Ask the panelist to sniff and taste the sample carefully

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Ask whether any off-flavour is detectable (Yes/No); if yes, ask for a description

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Ask the panelist to indicate intensity — Trace, Moderate or Strong — and to comment on whether the defect is due to off-odour, off-taste, residual taste or other defects

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For consumer preference: provide the hedonic-scale evaluation card and ask the panelist to record how acceptable the product is and the degree of acceptability or unacceptability

Interpretation of results

For trained-panel off-flavour work, tabulate presence/absence and intensity judgements per sample. For consumer preference, convert the hedonic values to numbers and analyse the results by the analysis of variance.

Worked illustration from the book: three carbonated orange-juice beverage formulations (A, B, C) were scored by three different groups of 100 panelists on a 5-point hedonic scale (+2 like very much, +1 like, 0 neither like nor dislike, −1 dislike, −2 dislike very much). Totals: formulation A Σx = 63, Σx² = 125; B Σx = 97, Σx² = 183; C Σx = 37, Σx² = 109. Total number of responses = 300; total sum of scores Σx = 197; correction factor C.F. = (197)²/300 = 129.36; uncorrected sum of squares of scores Σx² = 417; corrected sum of squares of scores = 417 − 129.36 = 287.64; uncorrected sum of squares of each sample = (63)²/100 + (97)²/100 + (37)²/100 = 147.47; corrected sum of squares of samples = 147.47 − 129.36 = 18.11; replicate error = 287.64 − 18.11 = 269.53. The analysis of variance gives: between formulations — degrees of freedom 2, variance 18.11, mean variance 9.055; replicate error — degrees of freedom 297, variance 269.53, mean variance 0.907; F = 9.055/0.907 = 9.983. The tabulated values at degrees of freedom (2, infinity) (Tables 19-6/19-7) are 3.00 at the 5% level and 4.60 at the 1% level — there is a significant difference between the formulations.

• n = number of samples
• Σx = sum of numerical scores
• Σx² = sum of squares of numerical scores
• C.F. = correction factor = (Σx)²/N

Specimen evaluation card fields: off-flavour present (circle Yes/No); description; intensity (circle Trace/Moderate/Strong); comments on the source of the defect; signature.

Precautions

• 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.
• Where a pronounced after-effect precludes a second sample in the same session, never serve a second sample — that is the reason for choosing this test.
• 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.