The influence of presentation factors on the sensory assessment of beverages

Food Quality and Refmnce 3 (1991/2) 101-107

THEINFLUENCEOFPRESENTATIONFACTORSONTHE SENSORYASSESSMENTOFBEVERAGES

Anthony A. Williams

Sensory Research Laboratories Ltd, 4 High Street, Nailsea, Bristol, UK BS19 1BW

&

Gillian M. Arnold

Department of Agricultural Sciences, University of Bristol, AFRC Institute of Arable Crops Research, Long Ashton Research Station, Long Ashton, Bristol, UK BS19 9AF

(Received 23 Novenrber 1990; accepted July 1992)

ABSTRACT

Presentation order and preceding samples are known to influence the perception of sensory attributes. In conventional tasting procedures these effects are normally al- lowed for by the use of suitable experimental designs for assessment order and b averaging responses over assessors. Howevq it is also important to know how these effects influence perception. Ex@iments to evaluate and differ- entiate these order effects when assessing eiders indicated order effects to be most pronounced between$rst and sub sequent samples, with strong characteristics building up during a session. The effect of a peceding sample appeared greater than later order effects and tended to amplifj opposite characteristics.

Keywords: order effects; carry-over effects; semij-ee-choice profiling; generalised Procrustes analysis; perception.

INTRODUCTION

Order effects in sensory evaluation have been exten- sively described by many authors (see, for example, Amerine et al., 1965; Lea & Arnold, 1978; O’Mahoney, 1986). With the current surge in interest in time intensity evaluation, a number of authors have used this technique to determine the effects of repeated ingestion of a particular stimulus on both perceived intensity and duration of sensation (Guinard et al., 1986a,& Leach 8c Noble, 1986; Lyman & Green, 1990; Noble, 1990). Order effects in triangular tests have also been

0 1992 Elsevier Science Publishers Ltd 095O-3293/92/$05.00

investigated by O’Mahoney and Odhert (1985) and O’Mahoney and Goldstein (1987). Poulton (1988) in his discussion of scaling biases discusses the effect of presenting very weak samples after strong ones and vice versa. In practice, practitioners try to allow for such effects by either presenting samples singly or balancing position and preceding sample across a complete experiment so that each sample is assessed in a particular position or environment an equal number of times. By taking means across the whole panel of assessors such effects, if present, do not influence the mean value, although of course precision of estimation is likely to be decreased. Interactions of assessors with order or preceding sample are not, however, generally accounted for. Experimental designs to allow for such positional effects are based on some form of Latin Square, examples of which are documented by Cochran and Cox (1957)) Williams (1949) and MacFie et al. (1989). However, these designs vary in complexity and in their ability to take into account adequately both carry-over effects from the preceding sample and position effects. When exploring individual variability in perceptions of products, an increasingly important aspect of sensory assessment, it is impossible to distinguish all such order and environment effects unless each assessor evaluates all samples in all possible orders and combinations, a procedure which is impractical in everyday product evaluation.

It is especially important to be able to estimate position and carry-over effects when assessing aroma and flavour using freechoice profiling (Williams & Langron, 1984; Williams & Arnold, 1985). In such investigations each assessor is treated as an individual and not assumed to be acting in an identical manner to all other panel members, either in respect of how they scale the terms they use or how they use apparently similar terms. As a consequence, averaging results over the panel is meaningless without some form of prior rationalisation of descriptors. Without balancing order and position for each assessor such rationalisation processes can be

101

102 Anthony A. Williams, Giilian 44. Arnold

substantially affected if significant order/position effects are present. Such effects became obvious in a simple experiment where a set of samples of commercial alcoholic cider and perry (fermented juice of the pear) were being assessed by a panel of assessors. The results indicated rather disturbing anomalies in respect of replicate samples when evaluating aroma and flavour, but not for appearance. Although there were no obvious overall differences between assessors with respect to the set of samples, it did appear that one sample was being perceived as having a very different flavour depending on its position within a session. When evaluated early in a session it appeared to have an apple-like, astringent and full-bodied flavour but if assessed towards the end of a session these characteristics were less detectable. Although, as reported above, order effects have been investigated in respect of individual stimuli, little work has been conducted to show how order and preceding sample affect the perception of the complex array of stimuli in real foods and beverages. The following research, of which a preliminary presentation was made at ECRO (Williams et aZ., 1988), was set up to investigate order and sample environment effects in profiling to give further insight into just how important each of these effects might be and how they might vary depending on the characteristics of the products being assessed. Salient information from such research would not only be of value in the interpretation of free choice profiling but could also help in improving experimental design in sensory analysis in general.

EXPERIMENTAL PROCEDURES

Two experiments were set up, the first to investigate the influence of position in an experimental presentation,

TABLE 1. Terms Used for Evaluating Flavour in Experiment 1

: : 3. 4. 5. 6. 7. 8. 9.

10. 11. 12. 13. 14. 15. 16. 17. 18.

:“o: 21.

Overall intensity Carbonation Acidity/sharpness Acetic Saccharin/artificial sweeteners Sugary sweetness Fruity-peardrops Fruity-raw apple Fruity-banana/strawberry Fruity-cooked apple Fruity-bittersweet apple Fruity-diacetyl/treacle Bitterness Astringency Musty/mouldy Mousy Rancid/butyric/old horse Soapy Battery acid/metallic Woody Burnt

TABLE 2. Design for Assessing Samples in Experiment 1

!kWiOll order of preselltalion

1st 2nd 3rd 4th 5th

I A D B C II D C E : B

III C B A D E IV E A C B D V B E D C A

and the second to determine the effects of both position and preceding sample on sensory perception. Five commercial eiders were purchased through normal commercial outlets; (A) Long Ashton, (B) Bulmer’s Woodpecker, (C) Coates’ Festival Vat, (D) Weston’s Vat 53 and (E) Taunton Autumn Cold.

In the first experiment a panel of 10 trained assessors (6 female and 4 male selected according to taste and odour acuity using standard solutions, trained in profiling and experienced in the evaluation of eiders) carried out a sensory profile analysis for the flavour of the five samples using a semi-fixed language profiling approach. Each assessor was presented with each of the five samples on five separate occasions. The samples (30 ml) were served in straight-sided red glasses to lessen any influence of appearance, and assessors scored the samples for flavour intensity using as many of the terms given in Table 1 as they individually felt appropriate.

On each occasion the set of samples was presented in a different order; the design for order of presentation

TABLE 3. Terms Used to Evaluate Flavour in Experiment 2

:. 3:

2: 6. 7. 8. 9.

10.

::. 13: 14. 15. 16. 17. 18. 19. 20. 21.

Z:

fi:

Z: 28. 29.

Sweet (sweet/sugary/artificial) Diacetyl/treacle Lemonade Raw/green apple (fruity-raw apple-apple juice) Fruity-bittersweet Fruity-peardrops Bruised apple (fiuity-oxidised/bruised apple) Rotting apple (fruity-rotting apple) Stewed apple (fruity-cooked/stewed) Fruity-banana/ripe Tangerine/orange Bitterness (bitter/astringent) Acidity (acidic/sharp/sour) Battery acid/metallic Acetic/vinegar Elderflower Alcoholic Oily/soapy Mousy Musty/mouldy Dry Rancid/old horse/stale Woody Sulphur dioxide Phenolic Hydrogen sulphide Burnt Smoked Insipid

The Influence of Presentation Factors on the Sensory Assessment of Beverages 103

TABLE 4. Example of Design Used in Experiment 2

Session order of presentation

1st 2nd 3rd 4th

I II

III N V

VI VII

VIII IX X

XI XII

B C D A D A B B A C D C

A D C B A C C D D A B B

D A B C C D A C B B A D

over the five sessions comprised a Latin Square, as given in Table 2, so that position effects could be directly evaluated for each individual. Within each session different random three-digit codes were used to label any given sample for each panel member. Assessors were asked to concentrate on flavour evaluation, and to take a normal mouthful, swill around and expectorate or swallow as they felt appropriate. Once they had established their own protocol they were instructed to maintain it throughout the experiment. To exacerbate any carryover effects, samples were assessed without intermediate palate cleansers and with a minimum time interval between assessments (approximately 15 s) .

For the second experiment four of the eiders were assessed (A, B, C and D). These four samples were evaluated by a similarly selected and trained panel of eight different assessors using the attributes listed in Table 3, again using a semi-fixed choice profile procedure. In this experiment the assessors did not have the same experience in evaluating eiders as did the panel in the first experiment. A similar presentation protocol to that used in the first experiment was adopted.

All four samples were presented at each of 12 sessions. Over these 12 sessions every assessor evaluated each sample three times in each of the four possible positions in the presentation order. For the second, third and fourth positions, the three assessments each had a different preceding sample, thus enabling all possible position and carry-over effects to be investigated. An example of the resulting design for an individual assessor is given in Table 4; the design was different for each assessor, so, although sessions effects could not be removed from the analysis, they were not aliased with any positional or carry-over effect.

As the profile terms were not used by all assessors in a prescribed way it was not appropriate to analyse the terms directly for the panel as a whole. Also, as the inter-relations between the terms are of primary importance in such a multi-variate situation, it was not of interest to analyse individual attributes for individual assessors. The data from both experiments were there- fore examined using generalised Procrustes analysis (Cower, 1975; Arnold & Williams, 1986). For the first

FIG. 1. Plot of the two-dimensional consensus scores for each of the sample-by-position units (Al, A2 etc. where letter denotes sample and digit denotes position) from Experiment 1. The mean for each sample is shown by the appropriate single letter and joined to each of the individual positions.

104 Anthony A. Williams, Gillian M. Arnold

experiment each sample-by-position combination was treated as a separate unit in the analysis. Similarly, for the second experiment, each sample-by-position-and- preceding-sample combination defined a separate unit.

RESULTS

For the first experiment the first two principal axes of the consensus configuration after generalized Procrustes analysis accounted for 40% of the total variation; scores for each sample-by-position unit on these first two dimensions are plotted in Fig. 1. Samples of cider A are well separated from the rest, with those for C being well separated from B and E.

This plot can be interpreted in terms of the fitted projection of each individual’s original attributes on these new axes (Arnold 8c Collins, 1993). The projections of the most important attributes for each assessor are shown in Fig. 2. There were selected initially as the group of nine attributes of most importance across the whole panel, with those from this subset of importance to each individual shown on the plot (there being too many individual projections overall to show clearly on one graph, this was felt to give a representative picture). From this plot it appears that the first axis is largely a contrast of saccharin and sweetness (positive direction) with bitter and astringent fruity acid flavours (negative direction) and the second a decreasing trend of overall intensity of flavour and possibly burnt character. Overall it appears that A was perceived as the most bitter, acid and astringent sample with leastsweetness, with C having least intensity of flavour.

Apart from these overall sample differences, some effects of position of sample within a session are apparent.

11 03

14 03 06

I _ 03 IlOJoss ,I4

,.I ! I '4 _. 06 "?3

13 5511, 03" $4 OS

21 06 01

21 06 01

13 01 '3

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FIG. 2. Twodimensional projection plot for the main attributes used by the assessors by defining the first two consensus dimensions for Experiment 1. Numbers denote attributes as listed in Table 2. The fitted projection for any attribute shown is given by a line joining the origin to that point; the longer the line, the more important the attribute.

The scores on the first three dimensions have been analysed with respect to session, sample, order in sessions and preceding sample, using repression techniques to allow for the lack of balance for preceding sample. The variance ratios (VR) and corresponding F probabilities are shown in Table 5 and it can be seen that, although sample tasted is highly significant in the first two dimensions as described, there is also some evidence of an overall effect due to preceding sample in dimension 1. There is little indication of differences due to known factors in the third dimension, so this two-dimensional representation is likely to be adequate for interpreting the results of Experiment 1.

There is an indication in Fig. 1 of a pure order effect in the first dimension for A, with the sample presented first in a session being perceived as less bitter and astringent than when presented last. This could simply be a build-up of astringency on the palate as has been noticed in other sensory experiments (for example, Lea & Arnold, 1978). Although order effects were apparent with other samples, they were rather more complex in nature. In respect of effects of preceding samples, these are quantified in Table 6. It appears that the effect of having tasted A prior to another sample has a significant effect in increasing the score on dimension 1. For example, B5, C3 and D2 are preceded by A, the most bitter and astringent sample, and these all appear further to the right along the first axis than others of the same sample (no sample of E is preceded by A). This indicates they are being perceived as less bitter and astringent and possibly more sweet when

TABLE 5. Test of Significance for Sample and Order Effects

Experiment 1 Source df Dimension 1 Dimension2 Dimension3

VR Fprob. VR Fprob. VR Fprob.

Session 4 2.25 0.153 3.54 0.060 1.13 0409 Sample 4 82.70 <O.OOl 29.21 <OXKU 4.07 0.043 Order 4 1.03 0448 0.70 0.616 2.71 0.107 Preceding

sample 4 5.04 0.025 0.60 0.676 1.50 0.290 Residual 8

Experiment 2 Source df Dimension 1 Dimension 2 Dimension 3

VR Fprob. VR Fprob. VR Fprob.

Sample 3 343.53 <O.OOl 6.84 0902 0.10 0.957 Order 3 2.00 0.141 13.36 <0601 1.25 0.315 Sample

Order 9 3.37 0.008 1.23 0.324 2.08 0.073 Preceding

sample 3 14.65 <O.OOl 544 0605 0.80 0.504 Sample

Preceding sample 5 3.34 0.020 1.32 0.288 2.35 0.071

Residual 24

The Influence of Presentation Factors on the Sensory Assessment of Beverages 105

TABLE 6. Quantification of Effects of Preceding Samples

Experiment 1 Recediq sample Dimension 1 Dimension 2 Dimension 3

A +1.96 -0.31 -0.72 B -0.08 +0*07 -0.39 C -1.05 +O. 65 +1.05 D -0.28 -0.47 +1.27 E -0.55 +0.06 -1.21

Approx. SED (8 df) 0.740 0.805 1.255

Eqeriment 2 Dimension 1 Preceding sample

Sample 1st A B C D A -3.55 * -5.29 -6.00 -5.20 B +0.92 +2.70 * +0.62 t1.85 C t2.69 t3.35 +2.89 * +3&O D t1.15 t2.06 -1.18 -0.60 *

SED (24 df) 0.539

Dimension 2

Overall effect SED (24 df)

Preceding sample 1st A B C D _ +0.68 to.57 -0.59 to.98

0.384

tasted after a more bitter and astringent sample than elsewhere. Similarly A5, B2 and E3 are preceded by C, the sample with least intense flavour, and these all appear further to the left along the first axis than other similar samples (no sample of D is preceded by C). This implies these samples have stronger bitter and astringent notes when preceded by a sample with a less intense flavour than when tasted in other positions. These results would appear to contradict the ideas presented by Poulton (1988).

These results indicate that the nature of a preceding sample may well be more influential than absolute position in the order within a session in determining perceived flavour. The second experiment was designed to enable this hypothesis to be investigated more thoroughly.

After obtaining the consensus configuration for the 48 units in Experiment 2 as described earlier, an analysis of variance with respect to sample, position and preceding

13 20 23

21 12 12

2&, 241 12 Ob, 2'

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11 I ' I2

I Vi 7 03

04

ofa;, 8. O4 04

FIG. 4. Two-dimensional projection plot for the main attributes used by the assessors in defining the first two consensus dimensions from Experiment 2. Numbers denotes attributes as listed in Table 4. The fitted projection for any attribute shown is given by a line joining the origin to that Point; the longer the line, the more important the attribute.

sample was carried out on scores on each of the first two principal axes. The results were summarised as means for each sample (A, B, C, D) in each position (1, 2,3 and 4) and for each preceding sample (denoted by a, b, c and d), there being no evidence of any interac- tion between position and preceding sample. The plot of these mean scores on the first two principal axes of the consensus configuration, which together account for 61% of the total variation, is shown in Fig. 3, with the most important fitted projections for interpreting these two dimensions shown in Fig. 4 (selected in a similar manner as for Experiment 1).

Using these fitted projections, the A samples appear to be separated from the other samples mainly in terms of their perception as much more dry, bitter, acid and much less sweet than the other samples. Also very clearly shown is the separation of each sample when assessed first in a session compared to any other position. When assessed first all samples appear to have much lower scores on the second principal axis, indicating a generally higher intensity of attributes such as raw and stewed apple, but with the intensity of attributes like dryness and bitterness building up during a session, particularly for sample A.

Al 61 D1

FIG. 3. Plot of the two-dimensional consensus scores for each sample-by-position mean and each sample-by-preceding-sample mean (Al, Ab, etc., where upper case letter denotes sample, digit denotes position and lower case letter denotes preceding sample) from Experiment 2. For a given sample, positions 2-4 are joined by dashed lines, preceding-sample means by full lines. An ellipse representing + SE for any mean in each dimension is shown in the left-hand comer.

106 Anthony A. Williams, Gillian M. Arnold

Considering the means for all samples except those assessed first in a session, the mean scores appear to be more diverse when preceding sample rather than position order is taken into accotmt. This is indicated by the triangle joining the points for preceding samples generally having a greater area than that joining the points for 2nd, 3rd and 4th position in a session. The significance of the effects of the known factors in the experimental design are shown in Table 5. The samples are clearly differenti- ated on both the first two dimensions, with order clearly significant for dimension 2 and interacting with sample for dimension 1. The significance of the order effects is due entirely to the differences between first and subsequent samples. The effect of preceding sample is highly significant in these first two dimensions, interacting with sample on the first dimension. As for Experiment 1, there is little evidence of effects of significance in the third dimension, so this two-dimension consensus is a good representation of the results obtained.

The quantitative effects of preceding samples for the first two dimensions are given in Table 6 and appear similar to those suggested by the results of Experiment 1. When preceded by A (the most dry, bitter and astringent sample), eiders B and D (and to a certain extent C) have higher scores on the first axis and appear to be perceived as having less bitterness and greater sweetness than when preceded by other samples. The cider with the least intense flavour is C, and when this is the preceding sample all other eiders have lower scores on the second axis, indicating a greater perception of apple flavours. Because of the nature of the design of this experiment with respect to position and preceding sample, these effects can be tested and attributed unambiguously as due to the preceding sample.

CONCLUSIONS

The patterns of the two-dimensional consensus configura- tions from each experiment are similar, as are the main attributes which appear to define them, giving greater confidence in these results. Effects of preceding samples suggested by the results of Experiment 1 were clarified and confirmed by the results of Experiment 2.

These results clearly demonstrate that both order of presentation and preceding sample can influence the perception of flavour characteristics in sensory profiling. The nature of the effects will to some extent depend on the particular characteristics of the samples being assessed, but the following conclusions can be drawn.

Order of presentation A sample will be assessed differently when it is presented as the first in a session compared with any other position in presentation order. Later order

effects are much less marked. There is an indication that dominant attributes, in particular bitterness and astringency, build up during a session. with more delicate characteristics, the change in perception may be more drastic, apple flavours, for example, being mainly noted when samples are assessed first.

Carry-over effects Carry-over effects appear to be greater than simple order effects. A preceding sample with strong flavour characteristics will tend to amplify opposite characteristics in following samples (e.g. intensifying sweetness when following a sample with strong bitterness), this being most marked for samples with least distinguishable characteristics.

The two experiments were not intended to establish a protocol for sensory evaluation per se; the results do, however, have implications both for how sensory profile experiments, whether conventional or free choice, are designed and in how results from them are interpreted. To overcome the effect of the first sample in a session being assessed differently, samples may be presented singly, with adequate time and palate cleansers between samples, or a warm-up sample may be presented before the assessments begin. The effects of order and particularly of preceding sample may well be of importance in explaining preferences in ‘real’ meal situations or why two components such as a particular wine and a food course complement each other. Prior eating of a particular food or drinki,ng of a particular beverage may well alter how one perceives the second component in a meal and hence affect its acceptability, in the ideal case toning down undesirable attributes or enhancing those which are desirable.

The conclusions from the experiments and analyses described in this paper will be of importance in the design of tasting experiments and their interpretation. The work will improve the understanding of percep tions of comestibles in general.

ACKNOWLEDGEMENTS

The authors wish to thank Mr G. A. Payne for his assistance in acquiring the data for the second main experiment described in this paper, and Dr A. J. Abbott for con- structive criticism of an earlier version of this paper and for assistance with graphical presentation of the results.

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Amerine, M. A., Pangborn, R. M. & Roessler, E. B. (1965). PrinciplRF of Sensoy Evaluatim of Food. Academic Press, New York, pp. 249-52,428.

The Injluence of Presentation Factors on the Sensory Assessment of Beverages 107

Arnold, G. M. & Collins, A. J. (1993). Interpretation of trans formed axes in multivariate analysis. Aj@!kd Statistics (in press).

Arnold, G. M. & Williams, A. A. (1986). The use of generalised Procrustes techniques in sensory analysis. In Statistical Procedures in Food Research, ed. J. R. Piggott. Elsevier Applied Science, London, pp. 233-53.

Cochran, W. G. & Cox, G. M. (1957). Experimental Designs, 2nd edn. John Wiley and Sons, New York.

Gower, J. C. (1975). Generalized Procrustes analysis. Psychomet&a, 40,33-51.

Guinard, J.-X., Pangbourn, R. M. & Lewis, M. J. (1986a). Effects of repeated ingestion on the temporal perception of bitterness in beer. Journal of the American Society of Brewing Chemistry, 44,28-32.

Guinard, J.-X., Pangbourn, R. M. & Lewis, M. J. (19866). The time course of astringency in wine upon repeated ingestion. American Journal ofEnoiogy and Viticulture, 37, 184-g.

Lea, A. G. H. & Arnold, G. M. (1978). The phenolics of eiders: bitterness and astringency. Jarnal of the Science of Food and Agriculture, 29,478-83.

Leach, E. F. & Noble, A. C. (1986). Comparison of bitterness of caffeine and quinine by a time intensity procedure. Chbmical Senses, 11, 339-45.

Lyman, B. J. & Green, B. G. (1990). Oral astringency; effects of repeated exposure and interactions with sweeteners. Chemical Senses, 15, 151-64.

MacFie, H. J., Bratchell, N., Greenhoff, K_ & Vallis, L. V. (1989). Designs to balance the effect of order of presentation and first-order carry-over effects in hall tests. Journal of Sensory Studies, 4, 129-48.

Noble, A. C. (1990). Bitterness and astringency in wines. In Bittenwss in Foods and Beverages: Developments in Food Science, ed. R. L. Roussett. Elsevier, New York, pp. 145-58.

O’Mahoney, M. (1986). Sensory Adaption. Journal of Sensq Studies, 1, 237-58.

O’Mahoney, M. & Goldstein, L. (1987). Tasting successive salt and water stimuli: the role of adaption, variability in physical signal strength, learning, supra- and s&adapting signal detectability. Chemical Senses, 12, 425-36.

O’Mahoney, M. & Odhert, N. (1985). A comparison of sensory difference testing procedures: sequential sensitivity analysis and aspects of taste and adaption. Jounzal ofFood science, 50,1055-8.

Poulton, E. C. (1988). Bias in QuantijjingJudgements. Laurence Erlbaum Associates, London, UIC

Williams, A. A. & Arnold, G. M. (1985). A new approach to the sensory analysis of foods and beverages. In Progress in Fluvour Research 1984, Proceedings of the 4th We-w-man Flavour Research Symposium, ed. J. Adda. Elsevier, Amsterdam, pp. 35-50.

Williams, A. A. & Langron, S. P. (1984). The use of freechoice profiling for the evaluation of commercial ports. Journal of the Science ofFood and Agrkulture, 35,558-68.

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Williams, E. J. (1949). Experimental designs for the estimation of residual effects of treatment. Australian Journal of Scientific Research, Series A, 2, 149-68.

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The influence of presentation factors on the sensory assessment of beverages