To satisfy budgetary requirements there is often a need to test multiple flavored products at the same time, thereby inducing contrast effects to the research results. This paper discusses the results of a series of hedonic tests carried out at ACCE International, each involving multi-flavored product evaluations with a sequential monadic design, and representing five different food categories: soy beverages, cereals, potato chip snacks, dessert puddings and salad dressings. In order to investigate the hedonic contrast effect, products representing different levels and character of flavoring were tested together in one test in two possible configurations: plain with flavored products and flavored with flavored products. The authors found a negative contrast effect on sensory acceptability testing when plain and flavored products were tested in one session. Specifically, when a plain product was presented after a flavored product, the plain product received significantly lower acceptability ratings than when it was presented before the flavored product. A positive contrast effect was observed for the flavored product when it was presented after the plain product, resulting in an increased acceptability score for the flavored product however, the effect was small. When two flavored products were tested together the results were less consistent. One category (puddings) showed no contrast effect, whereas two other categories (chips and salad dressing) both displayed a negative contrast effect.
Emphasis is placed on the practical aspects of dealing with multi-flavor product testing including recommendations for test design optimization in commercial studies.