Performing Department
Nutrition Science
Non Technical Summary
"Good medicine tastes bitter," is a saying that dates perhaps all the way to Confucius. The idea is that things that are good for your health are unpleasant to consume. This phenomenon is actually more than psychology, as many of the chemical compounds in both drugs and foods that are "good for you," also have unpleasant flavors. Indeed, the same properties that make these chemicals unpleasant are also the properties that may drive their contributions to health. In foods, for examples, many of the bitter compounds in vegetables are the exact same chemical compounds that could fight cancer, reduce risk of diabetes, or protect against obesity.This results in a fundamental problem for human nutrition: the foods we should eat are the same foods our mouths tell us are unacceptable. However, there are potential solutions to this dilemma. Research indicates that repeatedly consuming a food, even bitter vegetables, increases its palatability. Some of this is due to simple familiarization with food product; as it becomes more familiar, it becomes more acceptable. However, there may also be actual biological components to this improvement in flavor. Studies in rodents indicate that changing an animal's diet will change its saliva in ways that can make bitter or astringent sensations less aversive3. This seems to be due to the animal being less sensitive to the unpleasant sensations, making the food more acceptable.While research is progressing in rodent studies demonstrating these saliva, diet, and palatability interactions, data are not available in humans. Thus, we propose to study the characteristics of human saliva that may be influencing flavor perception, and how dietary changes could alter the experience of those flavors. We will test fatty, spicy, and bitter compounds in food that could be bound by specific proteins in saliva that are likely to alter their potential as flavor compounds. The compounds responsible for these flavors (unsaturated fatty acids, capsaicin, and polyphenols) all have potential health benefits, such as reducing inflammation, protecting against diabetes and obesity, or reducing cancer risk. Additionally, we will develop a database to collect salivary protein profiles of individuals participating in dietary intervention studies. The database will provide knowledge of new potential target proteins in saliva that may change in response to specific dietary behaviors.The outcomes of this work will be foundational data on how diet influences human saliva, and how that saliva influences flavor perception. If specific proteins in saliva are identified that make unpalatable healthy foods more appealing, then we may be able to intentionally change saliva or foods to mimic that binding of unpleasant flavor compounds. These data may allow us to design functional foods that would bind unpleasant flavors in healthy foods, or to make oral rinses that could be used to enhance a person's salivary profile to block unpleasant flavors from healthy food.Additionally, the patterns of salivary changes in response to diet will allow new opportunities for monitoring human food intake. This could be a valuable tool for verifying dietary compliance. Personal reports of dietary intake are notorious for their variability, as well as for their inaccuracy. We hope that the database we are establishing will one day lead to clear patterns in salivary profiles that link to dietary intake of foods, which could be used to verify dietary self-reports or to estimate of dietary intake of particular food items across a population.
Animal Health Component
0%
Research Effort Categories
Basic
(N/A)
Applied
100%
Developmental
(N/A)
Goals / Objectives
What people eat and what they should eat are often very different. A principle for this is that many individuals prefer the flavor of less healthy foods. Thus, our overarching goal is to find ways to improve healthy food flavor. One unexplored avenue of this may be through modification of saliva. Preliminary data already indicate that saliva influences flavor perception for specific, potentially healthy food compounds (unsaturated fat, spicy compounds, polyphenols), and may be useful for making unpleasant sensations less intense. Thus, our objectives are to:Determine salivary proteomic changes before and after dietary addition of target bioactive flavor compounds (unsaturated fat, spicy compounds, polyphenols). Determine whether flavor perception is altered by changes in salivary proteome.Secondary objective: Some food compounds are structurally similar to salivary proteins that influence flavor. We will also determine whether such food constituents interrupt changes in salivary proteome and flavor perception.Determine changes in the salivary proteome during broader dietary interventions. Such interventions (e.g., low sodium diets, non-nutritive sweetener diets, etc.) are ongoing for multiple other projects in the Purdue Nutrition Science Department, and we will collaborate with the principle investigators for those projects on adding collection of saliva both before and after the dietary intervention. These data will be used to start a database on human salivary proteome and dietary behaviors, which will provide the basis for future work.
Project Methods
Objective 1: Determine how dietary exposure to influences salivary composition and flavorThis objective will be addressed through 3 experiments, one for each bioactive flavor type (unsaturated fat, spicy compounds, bitter polyphenols). Each experiment will be a counter-balanced crossover design with three interventions: 1) beverage containing bioactive flavor, 2) beverage containing bioactive flavor and food-based analog, and 3) control beverage (no bioactive flavor, no salivary analog). Each experiment will begin with preliminary sensory tests and salivary collection, then move into a dietary intervention stage.Preliminary sensory tests: Participants will attend a single visit where they will taste the three types of intervention beverages ("Flavor": bioactive flavor, "Analog": bioactive flavor with food-based analog, "Control": no bioactive flavor nor analog). Participants will first provide baseline saliva: unstimulated (spit into collection tube), and stimulated (chew on 1g piece of wax and spit into collection tube) for 60 seconds each. Then, they will taste the Flavor, Analog, and Control beverages in duplicate, presented in counterbalanced order. For each beverage, participants will first taste and expectorate one sip of the beverages. We will keep this expectorate sample for salivary analysis. Then, they will taste and swallow the rest of the sample. Samples will be rated for the flavors of interest as well as overall liking. We will test 3 different bioactive flavors: Polyunsaturated fatty acids (stimulate oleogustus/fatty acid taste and may interact with salivary lipocalin-1 [LCN1]or β-lactoglobulin [β-Lg]); capsaicin (stimulates spiciness and may interact with LCN1 or β-Lg); and polyphenols (stimulates bitterness and astringency and may interact with salivary proline rich proteins or milk casein).Using data collected during the preliminary sensory tests, we will identify groups of participants with: 1) high and low sensitivity to the flavor of interest and 2) high and low expression of the salivary protein of interest. We hypothesize that these groups will overlap, with those who have high expression of the salivary protein giving lower ratings for the flavor intensity. We also hypothesize that the presence of the analog will reduce the variability in the flavor ratings, resulting in lower correlation of the flavor intensity with the salivary protein of interest.Dietary intervention: For this portion of the experiments, participants from the groups identified in the sensory tests (high/low flavor sensitivity, high/low expression of salivary proteins of interest) will be invited back for a 6-week study. The first week will be a washout week, where participants avoid foods containing the bioactive ingredient. The next week, the participant will drink three 12 oz. beverages per day. This will be repeated for each beverages type (Flavor, Analog, Control), in counterbalanced order. At the end of each week (including both washout and beverages weeks), saliva and sensory ratings will be collected.We hypothesize that intensity of the flavors will decrease and salivary proteins of interest will increase during the Flavor beverage week, but that during the Analog beverage week these changes will not occur. We expect no changes in either flavor or salivary proteins during the control week. We also expect that changes will be larger for participants who initially rate the intensity of the flavors as high, or who initially had low expression of the salivary proteins of interest. The control beverage week will help us control for psychological confounders and novelty of the beverages. By comparing data on the control beverages at the beginning and end of the control week to data from the test beverage weeks, we can establish how much of the changes are due to the psychological exposure and how much do to the actual flavor.Salivary analysis: Saliva will be frozen at -80°C until subjected to proteomic analysis. We will collaborate with the Purdue Proteomics Facility to perform global analysis of saliva proteome by quantitative label-free protein abundance profiling by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Reproducibility of LC/MS platform will be evaluated by determining the coefficient of variation (CV) of peptide intensities and retention time (RT) using 3 technical replicates. From this information we will be able to precisely identify all the proteins expressed in the saliva, and their relative abundances. Further, we will compare the outcomes of proteomics to outcomes from western blots to verify our targeted proteins. However, using the proteomic approach will allow us to explore other potential protein targets, yet unidentified in current literature.Data analysis: We will use mixed models to analyze data from sensory ratings and compare them to salivary profiles. This approach allows for repeated measures analysis of variance with additional consideration for repeated samples or treatments.Participants and sample size: Participants will be healthy adults, age 18-45, with no food allergies. We will aim for 96 participants in the preliminary sensory tests, and 32 participants in the intervention tests (equal proportions of males/females). This will allow for 80% power to find: a 5pt difference in sensory ratings (SD=10), or a 41mg/mL or ng/mL difference for sPRP or LCN1 respectively (SD=50mg/mL or ng/mL).Objective 2: Develop a database of proteomic data on saliva and dietary behaviors.This aim will be addressed by a prospective, hypothesis generating study. The aim is to collect saliva and dietary data during screening visits for studies in the PI's lab and to facilitate saliva collection and analysis in conjunction with dietary intervention studies ongoing at Purdue University. As this database expands, it may allow us to uncover more relationships between dietary behaviors and salivary profile. In addition to our primary goals of identifying new flavor/diet/saliva interactions, analyzing patterns of salivary profiles and diet records may identify new relationships between diet and saliva. If these patters between saliva and diet can be defined, then salivary profiles may be useful in verifying diet records or dietary compliance in future studies in the field of nutrition. Knowing current projects at Purdue system, we expect we will be able to collect data on changes in saliva: with low-calorie sweetener consumption, during low-salt diets, and during high protein diets. These are only some examples based on current work, and we will consider other dietary patterns as the studies are established.Participants: Anyone may participate in this study, pending IRB and (for studies under the purview of other investigators) principle investigator approval. Data will be collected on each individual's health status and dietary habits. The goal is to include as diverse a population of race, ethnicity, health status, age, and sex as possible.Saliva collection: Saliva will be collected after rinsing with water. Both unstimulated (passive drool) and stimulated (chewing wax) saliva will be collected, each for 60 seconds. Tongue scrapings will also be collected. This will allow for analysis of both "free" saliva as well as adsorbed proteins on the surface of the tongue.Analysis: Saliva will be stored and analyzed as described in Objective 1.Expected outcomes: This is an exploratory objective based on preliminary data in animals that indicate salivary expression changes with dietary interventions (personal communications Dr. Ann-Marie Torregrossa, SUNY Buffalo). We expect salivary proteins are modifiable by diet, but this has yet to be established in humans. By starting a database on dietary behavior and salivary proteomes, we can uncover correlations in these factors for future studies on saliva as a tool to predict flavor sensations or to monitor dietary intake of certain foods.