Associations between the perception of different oils, sensory detection thresholds for oleic acid and taste intensity ratings for sucrose and sodium chloride

In this study, detection thresholds of different sensory attributes including canola oil (triglyceride-rich), paraffin oil (triglyceride-rich), oleic acid (free fatty acid-rich) and canola oil + oleic acid (triglyceride- and free fatty acid-rich) will be determined in a repeated measure design to examine test-retest reliability and to compare detection thresholds of the four stimuli. Each of the four stimuli will be tested on 3 separate days. Hence, in total there will be 12 non-consecutive measuring days with one testing session of approximately 1 hour per day for each subject. All sessions will be held in the Deakin University Centre for Advanced Sensory Science laboratories. To determine detection thresholds for fat and fatty acids, concentrations of canola oil (9.90, 32.69, 46.09, 65.37, 92.18, 130.10, 183.70, 259.54, 366.75, 518.10, 731.87, 1033.58, 1634.37 mM), paraffin oil (5.41, 17.88, 25.21, 35.76, 50.42, 71.15, 100.47, 141.95, 200.59, 283.37, 400.29, 565.30, 893.90 mM), oleic acid (0.02, 0.06, 1.00, 1.40, 2.00, 2.80, 3.80, 5.00, 6.40, 8.00, 9.80, 12.00, 20.00 mM) and canola oil + oleic acid (9.90+3.80, 32.69+3.80, 46.09+3.80, 65.37+3.80, 92.18+3.80, 130.10+3.80, 183.70+3.80, 259.54+3.80, 366.75+3.80, 518.10+3.80, 731.87+3.80, 1033.58+3.80, 1634.37+3.80 mM) will be prepared in a non-fat milk emulsion, Detection thresholds will be determined using the 3-alternative forced choice method. In this method, subjects receive a set of 3 samples, one test sample containing the stimulus and two control samples. Subjects are instructed to taste and expectorate each sample and to identify the odd one out. Since samples are expectorated and the test stimuli are present in the daily diet, no washout phase is included. Concentrations are presented in ascending order. Whenever a subject’s answer is incorrect, the concentration of the test sample is increased until a concentration is reached, that can be detected by the subject. Following a correct identification of the test sample, the subject receives a new set of samples with the same concentration as correctly identified before. Whenever the subject identifies the same concentration three consecutive times in succession, this concentration is documented as detection threshold. To mask visual cues, the sensory testing is conducted under red light. To mask olfactory cues, subjects are instructed to wear a nose clip during testing. On each of the 12 study appointments, a detection threshold for one of the four stimuli is determined. Additionally, anthropometric measurements (body weight and height) will be measured during the first study appointment to determine the subjects’ body mass index. On the second study appointment, taste intenstiy testing for sucrose (100, 200, 300 mM) and sodium chloride (100, 200, 300 mM) will take place after the measurement of the detection threshold. To control for normal taste function, subjects will recieve three different concentrations of the stimulus (sucrose/sodium chloride in randomized order). After introducing the subject to a labelled magnitude scale, they have to taste each sample and rate its intensity on this scale. Saliva samples will also be collected after the first detection threshold for canola oil is assessed to determine the level of the saliva enzyme lingual lipase which is responsible for hydrolyzing triglycerides into free fatty acids which can evoke sensory signals by interacting with fat-specific receptors. Each testing day, subjects will report what they have eaten from the time they awoke in the morning. By evaluating these food diaries and additional questionnaires (Food Frequency Questionnaire, Food Like-Dislike Questionnaire, Visual Analogue Scales on physiological conditions such as hunger, appetite, etc.), the subjects’ eating behavior can be assessed. Additionally, conclusions about the influence of the food composition on sensory sensitivity can be drawn.