Michael O’Mahony

Investigating more powerful discrimination tests with consumers: effects of memory and response bias

Abstract Two experiments were conducted to investigate the sensitivity of four discrimination methods when they were performed by consumers. In Experiment I, the influence of memory in the duo-trio method was studied. Three versions of the duo-trio method with different memory requirements were considered. Calculated d′ values indicated a higher sensitivity for the duo-trio with the reference tasted between the two test samples (DTM), illustrating the importance of memory in sensory discrimination testing. In Experiment 2, four discrimination tests were compared: the triangle, the DTM, the same–different and the dual-pair tests. The dual-pair test was predicted to increase the d′ value of the same–different test by eliminating the large response bias variations between consumers. Results indicated no significant differences in d′ among the protocols. Thus the dual-pair method was not able to improve the sample discrimination ability of the same–different test.

Comparison of d′ values for the 2-AFC (paired comparison) and 3-AFC discrimination methods: Thurstonian models, sequential sensitivity analysis and power

Abstract Using a model system comprising of low concentration NaCl vs water and a beverage system of varying strength apple juice, it was found that the 2-AFC (paired comparison) discrimination method yielded a higher d′ than the 3-AFC method. Although the 3-AFC method is theoretically more powerful than the 2-AFC, the higher d′ of the latter compensates for this, making it the more powerful of the two.

Are three-sample tasks less sensitive than two-sample tasks? Memory effects in the testing of taste discrimination

In order to provide insights into why discrimination protocols with three stimuli sometimes tend to be less sensitive than protocols with two stimuli, two experiments were conducted. In these experiments, the relative effects of memory decay and memory interference were investigated. Both experiments involved purified water and/or solutions of low NaCl concentration. In Experiment 1, three protocols were compared: the traditional same-different test (Protocol 1), the same protocol with a rinse between the two samples (Protocol 2), and Protocol 2 with an added time delay between the first sample and the intermediate rinse (Protocol 3.) The decrease in measuredd’ values as time delay increased indicated that memory decay might be a factor for tests with three stimuli, such as the triangle method, rendering it less sensitive than tests with two stimuli, such as the same-different method. In Experiment 2, four protocols were compared: the traditional same-different test, the two-rinse same-different test, the triangle test, and what will be called duo same-different test. The experimental design allowed the individual consideration of memory decay and interference effects. From this last experiment, the substantial effect of memory interference was uncovered. Further experimentation will be necessary to estimate the exact relative effects of memory interference and memory decay.

Rapid determination of total cholesterol in egg yolk using commercial diagnostic cholesterol reagent

Abstract A rapid and accurate method for cholesterol determination using a commercial diagnostic cholesterol reagent (‘enzyme method’) was developed and evaluated with four different yolk preparations. The cholesterol content of The National Institute of Standards and Technology (NIST) Standard Reference Material in whole egg powder, fresh, frozen, and dried egg yolk was determined using gas chromatography and the enzyme method. All samples were subjected to direct saponification and solubilization prior to analysis. No treatment was applied to control samples, which were analyzed by the enzyme method. Solubilization of samples was performed at 0.85, 2 and 5% (w/v) NaCl concentrations. Solubilization measured in terms of cholesterol value was best at 2 and 5% NaCl levels. For egg powder standard and fresh or frozen egg, the cholesterol values obtained by the enzyme method from saponified or solubilized samples were not significantly different from values obtained by gas chromatography. For solubilized dried egg yolk the enzyme method gave results indistinguishable from chromatography for saponified yolk. However, the results obtained by the enzyme method and gas chromatography from saponified dried egg yolk were significantly different. The simple and rapid procedure developed for sample preparation (solubilization) eliminates the need for saponification prior to cholesterol determination using the enzyme method, and provides an alternative to an expensive and time-consuming gas chromatographic method.

Fertilisation and pesticides affect mandarin orange nutrient composition

The effects of the application of foliar fertilisation and pesticide on nutritional quality of mandarin orange juices were evaluated using (1)H NMR metabolomics. Significant differences between the use of fertiliser and pesticides during fruit formation were observed, and included changes in sugar, amino acid and organic acid composition. To determine whether the difference in sugar concentration was enough for the consumer to detect, a sensory experiment was performed in which two orange juice samples were prepared to resemble the sweet/sour taste balance of juice from mandarin oranges in which foliar fertilisation was either applied or not. In a test using non-trained individuals, 68% could correctly identify which juice had a sourer, or less sweet, taste. The implications of this study could impact citrus growers, and ultimately aid in development of fruit with superior sensory quality.

Paired Preference Testing: False Preferences and Disruptive Protocols

This review introduces recent changes regarding measurement of preferences brought about by the discovery of false preferences that occur with paired preference testing. Testing protocols are examined critically. False preferences result from a response bias elicited by factors distinct from sensory properties of products being tested that can distort results. Statistical approaches to circumventing this problem are examined. Alternative methods are being developed to eliminate false preferences based on understanding information processing in the brain. This has led to development of disruptive experimental preference testing protocols based on hypothesized use of processing subroutines in the brain to protect the central processing system from overload. These disruptive protocols suppress response bias. Paired preference testing is designed to predict consumer behavior. A paucity of studies addressing whether they do is put into perspective.

Increased Taste Discrimination Ability by Flowing Stimuli over the Tongue

Flow presentation procedures have been used by several researchers for controlled taste stimulation to stabilize the environment of the taste receptors and to control adaptation effects. O’Mahony [1] has shown flow presentation to elicit remarkable taste sensitivity in subjects; they were able to disciminate between once and twice distilled water. O’Mahony et al. [2] later demonstrated that subjects showed more sensitivity for taste discrimination with the flow presentation than with a sip-and-spit presentation. This study was carried out to determine the reason for this phenomenon; we also used the flow presentation technique for discrimination testing with foodstuffs.