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Contrast Effects in Sensory Acceptability Testing

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March 9, 2011

This study demonstrates that even fully balanced designs do not entirely prevent a contrast effect from occurring and causing a significance bias in judgments of food acceptability.

Background

Acceptance testing often involves two or more product flavour variants being tested by the same respondents. Concerns exist that product perception may be influenced by carryover or contrast effects. A contrast effect occurs when presentation of a sample of high flavour intensity or good quality just before one of weak flavour intensity (or poor quality) causes the second sample to receive a lower rating than if it has been rated alone. Preceding products may change perception of subsequent products physically e.g. a lingering flavour, and cognitively e.g. influence on attitudes. Designs which are balanced have been recommended to minimize these effects. Contrast effects in food acceptability assessment were examined for consumers evaluating soy beverages. Users of both vanilla flavoured and unflavoured (plain) soy beverages assessed paired, two vanilla and two unflavoured soy beverages for overall acceptability and specific attribute acceptability. Presentation of the products was fully balanced over the two flavours and within each of the two flavours to prevent occurrence of carryover effects.

Results

Based on the results, the position of the vanilla flavoured beverage, before or after the unflavoured beverage, impacted the overall acceptability of the unflavoured soy beverage. The unflavoured beverage was deemed to be significantly less likeable when it was presented after the more palatable vanilla beverage than when the unflavoured beverage was presented first. Contrast effects were stronger (i.e. reduction in the overall liking values for the unflavoured beverage) when unflavoured variants followed vanilla than when the unflavoured preceded vanilla (i.e. increase in overall liking values for vanilla flavoured beverage). A practical implication for multi-flavour studies, with an unbalanced flavour presentation, would be to present unflavoured and plain variants prior to highly flavoured variants. Further research is needed to confirm contrast effects in other food products and/or flavours. 

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