Harry T. Lawless - US grants

Individual differences in sensitivity and responsiveness are striking characteristics of the chemosensory modality of olfaction. Specific anosmia describes a selective deficit to a specific class of closely related chemical compounds among individuals with otherwise normal olfactory acuity. Specific anosmia has proven to be a promising tool for the study of the genetic basis of olfactory function, as well as the interplay of genetics with environmental and developmental influences. In spite of a growing literature on this potentially important chemosensory phenomenon, few if any studies have examined the responses of specific anosmics to stimuli above threshold or in physically complex mixtures. Such extension of psychophysical findings is necessary if the phenomenon of specific anosmia is to be shown to have relevance to real-life olfactory functioning of humans since most odor-guided behaviors involve stimulation above threshold or with chemical mixtures. Many compounds which are known to show strong individual differences in olfactory sensitivity (and thus are either candidates for or already-documented cases of specific anosmia may influence food flavor perception and thus food choice and food rejection and ultimately play a part in the interaction of the chemical senses with nutritional status and the quality of life. The proposed research will explore the psychophysical responses of individuals with specific anosmia to a number of important aroma and flavor components of foods, with respect to odor intensity and quality perceptions in mixtures. Methods will include psychophysical scaling of perceived intensity in perceptually separable odor mixtures and multidimensional scaling of odor similarities among more blended (i.e. less perceptually divisible) stimuli. Special emphasis will be placed on examining judgements of intensity of other mixture components in addition to those to which the person is anosmic, since second order effects such as mixture inhibition among odor components may also change when one or more mixture components are reduced in their sensory impact. The proposed research will provide a quantitative assessment of these changes in controlled psychophysical studies, as a first step toward bridging the gap between threshold studies of specific anosmia and everyday perception of odors and volatile flavors.

Adequate sensory function in the oral cavity is important to the overall appreciation of foods and to maintenance of good nutritional status. Increasingly, chemosensory scientists have attended to the contribution of sensations besides the four classical taste qualities in oral chemical perception. The broad goals of this work are to describe and quantify human reactions to one important class of trigeminally-mediated oral sensations, namely those of astringent materials. Astringent sensations produced by single compounds have received little attention from the chemosensory community in spite of their importance in foods. This work is designed to remedy that deficiency by controlled psychophysical evaluations of simple aqueous solutions of single compounds and two-component mixtures. Particular attention will be paid to the time-course and different qualities of sensations evoked by astringent stimuli. Three experiments are planned: 1) quantitative and qualitative assessments of perceived astringency from different chemical stimuli over time, 2) structure- activity studies of selected series of tannin compounds previously shown in vitro to vary in phenol-protein binding and are thus predicted to vary in perceptual astringency in vivo, and 3) a study of mixtures of astringent materials, to bridge the gap between single-compound studies and more complex food systems as well as provide information on interactions (synergy, masking) that have implications for the number of underlying mechanisms. Finally, since salivary flow rate is highly variable among individuals, and since salivary flow could affect astringent sensations by a number of mechanisms, flow rate will be assessed as a potentially important covariate of perceptual reactions to astringent materials in the first and second experiments in this plan. While the primary focus of this work is to provide a rich source of descriptive and hypothesis-generating information on a poorly understood class of oral chemical stimuli, the proposed research will have also have implications for understanding the mechanisms underlying astringency and individual differences in reactions to astringent compounds.

This project is a continuation of an effort to better understand an important class of chemical induced oral sensations, namely those associated with astringency from tannins, acids and complex salts. These sensations are poorly understood, yet are important components of food flavor. Furthermore, since the interactions of astringent substances with saliva impart a kind of "artificial xerostomia," understanding of astringency and its influences on other oral chemosensory stimuli may provide insights into the oral chemosensory function of patients suffering from dry mouth. The present application proposes fundamental psychophysical research into quantitative and qualitative specification of human perceptions derived from astringent stimulation. Previous work has shown the potential importance of astringent subqualities of oral drying, roughing and tightening, and individual assessment of these three attributes is a unique approach in this project. The proposed experiments include 1) studies of effects or stimulus volume, duration and buffering on perception of astringency, 2) assessment of qualitative descriptors used by individuals to describe these sensations via multidimensional scaling, 3) investigation of mixtures of astringent materials and their perceptual additivity, 4) studies of additional compounds and structure-activity assessment of polymeric tannins, and 5) specification of interactions of astringents with tastes and with irritative oral trigeminal stimuli in model systems. The research will provide basic information about the relationship of perceived astringency to fundamental physical variables. In broader terms, it should further clarify the interplay between oral chemical and tactile sensations and provide insights into the role of saliva in oral protection, lubrication and the modulation of flavor sensations.

DESCRIPTION: (Adapted From The Applicant's Abstract) The overall goal of the current proposal is to examine the relationship between salivary composition and the perception of astringency. Astringency is a class of oral sensations, induced by chemical stimuli, that are described as sensations of dryness and tightening of oral tissues. Astringency involves de-lubrication of the salivary coating in the oral cavity A critical step in the development of astringency is the association of tannin molecules with salivary proteins. The literature on chemical interaction of polyphenols and proteins has recently shown how binding can be assessed using turbidity measures. Animal models have also established a connection between tannins in the diet and the expression of salivary proline-rich proteins, effective binding agents for dietary tannins. Therefore, individual difference in salivary composition, astringency response and dietary intake of tannins will also be studied. Due to the fact that many astringent substances are also bitter, this approach is extended to examine individual differences in bitter taste responses. A new model is proposed for the prediction of bitterness and astringency based on a variance-component approach. This model attempts to supplement the traditional between-groups analysis (i.e., comparison of different PROP tasting groups) with a correlational approach to estimate the degree of association or common variance among predictor variables. Overall, the research will help explain individual differences in taste and chemo-tactile oral sensations through the study of an important and complex peri-receptor medium, saliva, its composition, and perceptual influences .

DESCRIPTION (provided by applicant): Sensory properties of divalent salts such as those of calcium and iron have received scant attention in the literature on the chemical senses. Given the aging of the US population and the prevalence of osteoporosis, dietary calcium insufficiency is a growing concern and is being addressed by an increasing number of calcium fortified food products. Iron deficiency is a continuing problem in the third world, affecting billions of people worldwide. Understanding the sensory properties of divalent salts such as those of calcium and iron will add to the knowledge base in the senses of taste and smell and may help the engineering of foods and supplements with acceptable sensory properties. A program of research is proposed here in two main sections. First, psychophysical characterization of divalent salts will address the qualitative and intensive properties of Group II of the period table including calcium, an active participant in various steps of taste transduction, as well as magnesium and barium. In preliminary research with calcium and magnesium, a frequent taste descriptor was the term "metallic." This property of multivalent halides has received little attention but qualitative work suggests that it results from the production of a volatile substance that is perceived retronasally. That is, metallic taste may be a smell and not a true taste. This is consistent with literature from food chemistry suggesting that metallic ions such as iron and copper can catalyze the production of very potent odor compounds from oxidation of lipids. The second program of research aims to characterize the sensory properties of iron and copper salts, which produce complex sensations in the oral cavity. Instrumental-sensory correlations will be brought to bear on the identification and characterization of volatile compounds produced from mixing ferrous sulfate with human saliva, and comparison of these compounds to known lipid oxidation products known to smell "metallic" as identified in the food chemistry literature. A parallel to the reports of metallic sensations from electric taste will be investigated. A primary question of interest is whether metallic taste is olfactory, gustatory or tactile in nature or some combination of the three.