Sour taste preferences of children relate to preference for novel and intense stimuli

Previous research has suggested that some children have a preference for sour tastes. The origin of this preference remains unclear. We investigated whether preference for sour tastes is related to a difference in rated sour intensity due to physiological properties of saliva, or to an overall preference for intense and new stimuli. Eighty-nine children 7-12 years old carried out a rank-order procedure for preference and category scale for perceived intensity for four gelatins (i.e. 0.0 M, 0.02 M, 0.08 M, 0.25 M added citric acid) and four yellow cards that differed in brightness. In addition, we measured their willingness to try a novel candy and their flow and buffering capacity of their saliva. Fifty-eight percent of the children tested preferred one of the two most sour gelatins. These children had a higher preference for the brightest color (P < 0.05) and were more likely to try the candy with the unknown flavor (P < 0.001) than children who did not prefer the most sour gelatins. Preference for sour taste was not related with differences in rated sour intensity, however those who preferred sour taste had a higher salivary flow (P < 0.05). These findings show that a substantial proportion of young children have a preference for extreme sour taste. This appears to be related to the willingness to try unknown foods and preference for intense visual stimuli. Further research is needed to investigate how these findings can be implemented in the promotion of sour-tasting food such as fruit.     

Molecular mechanisms underlying the reception and transmission of sour taste information

Taste enables organisms to determine the properties of ingested substances by conveying information regarding the five basic taste modalities: sweet, salty, sour, bitter, and umami. The sweet, salty, and umami taste modalities convey the carbohydrate, electrolyte, and glutamate content of food, indicating its desirability and stimulating appetitive responses. The sour and bitter modalities convey the acidity of food and the presence of potential toxins, respectively, stimulating aversive responses to such tastes. In recent years, the receptors mediating sweet, bitter, and umami tastes have been identified as members of the T1R and T2R G-protein-coupled receptor families; however, the molecular mechanisms underlying sour taste detection have yet to be clearly elucidated. This review covers the molecular mechanisms proposed to mediate the detection and transmission of sour stimuli, focusing on polycystic kidney disease 1-like 3 (Pkd1l3), Pkd2l1, and carbonic anhydrase 4 (Car4).     

Understanding the basic biology underlying the flavor world of children

Health organizations worldwide recommend that adults and children minimize intakes of excess energy and salty, sweet, and fatty foods (all of which are highly preferred tastes) and eat diets richer in whole grains, low- and non- fat dairy products, legumes, fish, lean meat, fruits, and vegetables (many of which taste bitter). Despite such recommendations and the well-established benefits of these foods to human health, adults are not complying, nor are their children. A primary reason for this difficulty is...     

Evaluation of the Monell forced-choice, paired-comparison tracking procedure for determining sweet taste preferences across the lifespan

Lack of methodology to assess taste in children limits its measurement in research studies that include pediatric populations. We used the Monell 2-series, forced-choice tracking method to measure sucrose preferences of a racially/ethnically diverse sample (n = 949) of children, adolescents, and adults. Reliability was assessed by comparing the results of the first series with the second series. Validity was assessed by relating participants' sucrose preferences to their preferences for foods varying in sweetness. The task required, on average, 7 presentations of aqueous sucrose solution pairs. Children and adolescents preferred more concentrated sweetness than adults (P < 0.001). Black children/adolescents preferred a more concentrated sucrose solution than did White children/adolescents even when gender, parental education level, and family income were used as covariates. Data from a single series were sufficient to detect age-related differences but insufficient to detect racial/ethnic differences in sweet preferences. Level of sweetness preferred significantly correlated with the sugar content of favorite cereals (P < 0.001) and beverages (P < 0.02). This method is brief and has evidence of reliability and external validity. Although a single series will yield useful information about age-related differences in taste preferences, the 2-series version should be considered when differences in race/ethnicity are of interest.     

Genetic variation in taste and its influence on food selection

Abstract Taste perception plays a key role in determining individual food preferences and dietary habits. Individual differences in bitter, sweet, umami, sour, or salty taste perception may influence dietary habits, affecting nutritional status and nutrition-related chronic disease risk. In addition to these traditional taste modalities there is growing evidence that "fat taste" may represent a sixth modality. Several taste receptors have been identified within taste cell membranes on the surface of the tongue, and they include the T2R family of bitter taste receptors, the T1R receptors associated with sweet and umami taste perception, the ion channels PKD1L3 and PKD2L1 linked to sour taste, and the integral membrane protein CD36, which is a putative "fat taste" receptor. Additionally, epithelial sodium channels and a vanilloid receptor, TRPV1, may account for salty taste perception. Common polymorphisms in genes involved in taste perception may account for some of the interindividual differences in food preferences and dietary habits within and between populations. This variability could affect food choices and dietary habits, which may influence nutritional and health status and the risk of chronic disease. This review will summarize the present state of knowledge of the genetic variation in taste, and how such variation might influence food intake behaviors.     

Differences in the desire to eat in children and adults in the presence of an obese eater

Previous research has shown that the desire to eat foods decreases in adults in the presence of an obese eater compared to a normal-weight eater. This study investigated whether or not this decrease in eating desire was observed in younger children in the same way as in adults. Children aged 5 and 8 years old, as well as adults, were presented with photographs of liked and disliked foods presented either alone or with normal-weight and obese eaters expressing three different emotions--pleasure, disgust, and neutrality--toward these food products. The results showed that the eater's weight status had a greater effect on the adults' desire to eat than on that of the children. Adults were influenced by the eater's weight status, regardless of the facial expression or the food category. Compared to adults, the impact of the eater's weight status on the children's desire to eat depended on the emotional facial expression and the children's food preferences. Thus, when children did not like the foods, their eating desire was negatively influenced by the eater's obese status, as was that of adults. On the other hand, when children liked the food products, the eater's weight status had no effect on their eating desire. They were more influenced by the eater's facial expressions. Thus, an expression of pleasure increased the desire to eat the liked foods in the younger children, whereas an expression of disgust decreased it. These results are discussed in terms of the high sensitivity of young children to emotional facial expressions.     

DIFFERENTIATION OF ACTIVITY PATTERNS IN THE SUPRAHYOID MUSCLES DURING SWALLOWING OF FOODS WITH FIVE TASTE QUALITIES

Activity patterns of the suprahyoid muscles were examined using a new analytical technique. The suprahyoid activities were recorded during swallowing of tasteless foods and foods with taste qualities (sweet, salty, sour, bitter and umami). The technique involved: (1) division of cumulative integrated suprahyoid activities from each swallow into 10 equal sections and (2) assignment of individually sectioned activities to a standardized timescale as T_P (from T₁₀To T₁₀₀; relative time for P% of the cumulative electromyogram) to enable comparison of data from different trials. Three significant differences were found in T _p between the following foods: tasteless and sour, tasteless and bitter, and sour and umami. However, the differences were not repeatedly confirmed. These results suggest that gustatory signals from food tastes affect differentially the activity patterns of the suprahyoid muscles during pharyngeal swallowing, although the effect is not permanent. This method may be used to measure taste impressions in infants and in certain disabled subjects.     

Autonomic nervous system responses associated with primary tastes

The hedonic dimension of the taste sensation plays a crucial role in the control of many taste-mediated responses related to food ingestion or rejection. The purpose of this study was to evaluate the emotional reactivity associated with each primary taste (sweet, salty, sour and bitter) through analysis of the variations of autonomic nervous system (ANS) parameters. Thirty-four healthy non-smoker volunteer subjects (17 males and 17 females, mean age = 28 years) participated in the experiment. Taste stimuli were solutions of 0.3 M sucrose (sweet), 0.15 M NaCl (salty), 0.02 M citric acid (sour) and 0.00015 M quinine sulfate (bitter). Evian mineral water was used as the diluent and control (neutral taste). Throughout the test, five ANS parameters (skin potential and skin resistance, skin blood flow and skin temperature, and instantaneous heart rate) were simultaneously and continuously recorded. Results of the ANOVA evidenced a significant effect of primary taste on skin resistance amplitude (P: < 0.001) and duration (P: < 0.0001), skin temperature amplitude (P: < 0.001), skin blood flow amplitude (vasoconstriction) (P: < 0.0001) and instantaneous heart rate increase (P: < 0.0001). Skin resistance and cardiac responses were the most relevant ANS parameters to distinguish among the taste solutions. The four primary tastes could be associated with significantly different ANS responses in relation to their hedonic valence: the pleasantly connoted and innate-accepted sweet taste induced the weakest ANS responses whereas the unpleasant connoted tastes (salty, sour and bitter) induced stronger ANS responses, the innate-rejected bitter taste inducing the strongest ones. Such a neurovegetative characterization of each primary taste could provide references for the hedonic analysis of the more complex gustative sensation attached to foods.     

Integration of QSAR modelling and QM/MM analysis to investigate functional food peptides with antihypertensive activity

Antihypertensive peptides derived from dietary proteins have long been recognised as an important source of developing functional foods with blood pressure-lowering effect. However, most of such peptides exhibit diverse tastes, such as sweet, bitter, sour and salty, which is a non-negligible aspect considered in the food development process. In the present study, several predictive quantitative structure–activity relationship (QSAR) models that correlate peptide's structural features with their multi-bioactivities and bitter taste are established at both sequence and structure levels, and the models are then used to conduct extrapolation on thousands of randomly generated, structurally diverse peptides with chain lengths ranging from two to six amino acid residues. Based on the statistical results gained from QSAR modelling, the relationship between the antihypertensive activity and bitter taste of peptides at different sequence lengths is investigated in detail. Moreover, the structural basis, energetic property and biological implication underlying peptide interactions with angiotensin-converting enzyme (ACE), a key target of antihypertensive therapy, are analysed at a complex three-dimensional structure level by using a high-level hybrid quantum mechanics/molecular mechanics scheme. It is found that (a) bitter taste is highly dependent on peptide length, whereas ACE inhibitory potency has only a modest correlation with the length, (b) dipeptides and tripeptides perform a moderate relationship between their ACE inhibition and bitterness, but the relationship could not be observed for those peptides of more than three amino acid residues and (c) the increase in sequence length does not cause peptides to exhibit substantial enhancement of antihypertensive activity; this is particularly significant for longer peptides such as pentapeptides and hexapeptides.     

RELATIONSHIP OF PROP (6-N-PROPYLTHIOURACIL) TASTER STATUS WITH THE BODY MASS INDEX AND FOOD PREFERENCES OF FILIPINO ADULTS

The study determined the 6-n-propylthiouracil (PROP) status of Filipino adults and how it relates to their body mass indices (BMI) and food preferences. Self-reported food preference checklists were administered to 100 male and female adults aged 18–60, classified according to BMI. Increasing concentrations of PROP and NaCl solutions were rated in labeled magnitude scale to establish the PROP taster status of the selected respondents. The Filipino adult respondents were composed of 12% nontasters, 45% medium tasters and 43% supertasters. No association ( P >  0.05) between BMI and PROP taster status was found. Sweet-tasting foods were the most preferred and bitter-tasting foods were the least preferred within each taster status. Furthermore, medium tasters and supertasters had the highest acceptance for meats, fish and poultry, and least acceptance for beverages, which were mostly bitter. Decreased preferences for fats and oils, sugars and confectionery, and beverages were correlated ( P <  0.05) with responsiveness to PROP.

PRACTICAL APPLICATIONS

The research provides a general baseline data of the PROP taster status of Filipino adults. The findings from this study can be used as a reference and can be compared to similar studies conducted in other countries. Likewise, the information from the study can add to the scarce data for taste genetics specifically for the Asian population. The relationship of PROP taster status with body mass index and food preferences can be a guide in the design of products and dietary plans. Likewise, the study would be a means to understand why people vary in liking for particular food items and how these can be reflected in their food consumption and nutritional status.     

Relationships between and among selected measures of sweet-taste preference and dietary intake

The extent to which the sensory properties of foods influencedietary practices remains poorly characterized. Hedonic attributesappear to exert the predominant role among sensory factors.Therefore a parametric study to ascertain the relationshipsbetween measures of sweet-taste preferences and selected relevantdietary measures was undertaken. Twenty-five healthy, normalweight adults kept 7-day diet records and provided hedonic responsesto (i) lists of foods on questionnaires, (ii) prepared coffeeand oatmeal samples on category and visual analog scales, and(iii) water and coffee via an adjustment task. Ratings wereobtained under conditions where samples were swallowed versusexpectorated and viewed as ‘normal foods’ versus‘test samples’. Correlations were then sought betweendietary variables and both individual and aggregate profilesof preference measures. Either analytic approach revealed significantassociations with estimates of preferred tastes of the diet,but only taste profiles comprised of several taste preferencemeasures together were significantly related to nutrient intake(i.e. carbohydrate and alcohol calories). This observation,as well as findings obtained from the different testing proceduresand contexts, are considered from a methodologic perspective(i.e. what are the optimal conditions for examining diet–tasterelationships).     

Responsiveness of the cortical taste area neurons to a mixture of the four basic tastants in rats

The taste coding mechanism in the cortical taste area was investigated by analyzing the responses of 59 neurons in the cortical taste area of the anesthetized rat to a mixture of the four basic tastants in both absence and presence of bicuculline methiodide, a specific antagonist to the GABA(A) receptors. The mixture caused response suppression more frequently than response facilitation, both in the control state and during bicuculline application. Cluster analysis revealed that only a group of the neurons with the best response to both NaCl and HCl (group NH) showed the best response to the mixture in the control state, whereas during bicuculline application, in addition to group NH, two other groups of neurons responding to sucrose, or to HCl and quinine responded vigorously to the mixture. Multidimensional scaling located the mixture outside the space of the four basic tastants facing an NaCl-HCl line in both states. GABAergic inhibition caused the group NH to represent the taste of the mixture in the control state. Thus, the mixture probably tastes salty and sour to rats. No cortical neuron was found which specifically responded to the mixture.     

The taste system in fishes and the effects of environmental variables

The adaptability of the taste system in fish has led to a large variety in taste bud morphology, abundance and distribution, as well as in taste physiology characteristics in closely related species with different modes of life and feeding ecology. However, the modifications evoked in the sense of taste, or gustation, particularly during ontogeny when fishes are subject to different environmental variables, remain poorly studied. This review paper focusses on current knowledge to show how plastic and resistant the taste system in fishes is to various external factors, linked to other sensory inputs and shifts in physiological state of individuals. Ambient water temperature is fundamental to many aspects of fish biology and taste preferences are stable to many substances, however, the taste-cell turnover rate strongly depends on water temperature. Taste preferences are stable within water salinity, which gives rise to the possibility that the taste system in anadromous and catadromous fishes will only change minimally after their migration to a new environment. Food-taste selectivity is linked to fish diet and to individual feeding experience as well as the motivation to feed evoked by attractive (water extracts of food) and repellent (alarm pheromone) odours. In contrast, starvation leads to loss of aversion to many deterrent substances, which explains the consumption by starving fishes of new objects, previously refused or just occasionally consumed. Food hardness can significantly modify the final feeding decision to swallow or to reject a grasped and highly palatable food item. Heavy metals, detergents, aromatic hydrocarbons and other water contaminants have the strongest and quickest negative effects on structure and function of taste system in fish and depress taste perception and ability of fishes to respond adequately to taste stimuli after short exposures. Owing to phenotypic plasticity, the taste system can proliferate and partially restore the ability of fishes to respond to food odour after a complete loss of olfaction. In general, the taste system, especially its functionality, is regarded as stable over the life of a fish despite any alteration in their environment and such resistance is vital for maintaining physiological homeostasis.     

Genetic variation in the hTAS2R38 taste receptor and food consumption among Finnish adults

Genetic variation in bitter taste receptors, such as hTAS2R38, may affect food preferences and intake. The aim of the present study was to investigate the association between bitter taste receptor haplotypes and the consumption of vegetables, fruits, berries and sweet foods among an adult Finnish population. A cross-sectional design utilizing data from the Cardiovascular Risk in Young Finns cohort from 2007, which consisted of 1,903 men and women who were 30–45 years of age from five different regions in Finland, was employed. DNA was extracted from blood samples, and hTAS2R38 polymorphisms were determined based on three SNPs (rs713598, rs1726866 and rs10246939). Food consumption was assessed with a validated food frequency questionnaire. The prevalence of the bitter taste-sensitive (PAV/PAV) haplotype was 11.3 % and that of the insensitive (AVI/AVI) haplotype was 39.5 % among this Finnish population. PAV homozygotic women consumed fewer vegetables than did the AVI homozygotic women, 269 g/day (SD 131) versus 301 g/day (SD 187), respectively, p = 0.03 (multivariate ANOVA). Furthermore, the intake of sweet foods was higher among the PAV homozygotes of both genders. Fruit and berry consumption did not differ significantly between the haplotypes in either gender. Individuals perceive foods differently, and this may influence their patterns of food consumption. This study showed that the hTAS2R38 taste receptor gene variation was associated with vegetable and sweet food consumption among adults in a Finnish population.     

The good taste of peptides

The taste of peptides is seldom one of the most relevant issues when one considers the many important biological functions of this class of molecules. However, peptides generally do have a taste, covering essentially the entire range of established taste modalities: sweet, bitter, umami, sour and salty. The last two modalities cannot be attributed to peptides as such because they are due to the presence of charged terminals and/or charged side chains, thus reflecting only the zwitterionic nature of these compounds and/or the nature of some side chains but not the electronic and/or conformational features of a specific peptide. The other three tastes, that is, sweet, umami and bitter, are represented by different families of peptides. This review describes the main peptides with a sweet, umami or bitter taste and their relationship with food acceptance or rejection. Particular emphasis will be given to the sweet taste modality, owing to the practical and scientific relevance of aspartame, the well‐known sweetener, and to the theoretical importance of sweet proteins, the most potent peptide sweet molecules. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Physiological responses to taste signals of functional food components

The functions of food have three categories: nutrition, palatability, and bioregulation. As the onset of lifestyle-related diseases has increased, many people have shown interest in functional foods that are beneficial to bioregulation. We believe that functional foods should be highly palatable for increased acceptance from consumers. In order to design functional foods with a high palatability, we have investigated about the palatability, especially in relation to the taste of food. In this review, we discuss (1) the identification of taste receptors that respond to functional food components; (2) an analysis of the peripheral taste transduction system; and (3) the investigation of the relationship between physiological functions and taste signals.     

One man's meat is another man's poison. Science & Society series on food and science

Why does one person like cucumber while another hates it? Understanding the causes of our innate and idiosyncratic food preferences has real implications for encouraging children and adults to eat a healthy diet.

“Nothing would be more tiresome than eating and drinking if God had not made them a pleasure as well as a necessity.” Voltaire

Humans, like many other mammalian omnivores, have strong food-related biases. We tend to like sweet things and dislike bitter tastes; we are suspicious of new foods (neophobia); and we learn what to like and dislike from our experiences with food and the influence of those around us (Rozin & Vollmecke, 1986). These universal characteristics of food preference and avoidance are likely to have evolved to ensure that our diets are nutritionally adequate and to help us avoid toxins. Nevertheless, it is unclear whether and how food preferences are encoded in our genomes and what role the environment plays in shaping our preferences for particular foods. This question is not only intriguing for researchers, but also has implications for nutrition and health, particularly in the light of the abundance of food available in affluent nations that is feeding an epidemic of obesity, and the ensuing need to teach children how to choose a healthy and balanced diet.These universal characteristics of food preference and avoidance are likely to have evolved to ensure that our diets are nutritionally adequate and to help us to avoid toxinsAcross the world, humans eat an extraordinary variety of animals and plants; one country''s delicacy is sometimes regarded with disgust elsewhere. Nevertheless, there are dietary themes across cultures and nations: almost every cuisine has a basic form of carbohydrate—such as potato or rice—and sweet treats. Most diets also feature high-value protein-based foods that indicate social status or are used for celebrations, and many cuisines have different foods for children. Within local cuisines there is further variation, as individuals express their preferences for certain foods. This presents a puzzle for scientists: why does one person love cucumber and another hate it? Is it due to genes, experience, or both? If we are able to answer these questions, how can we use such knowledge to help young children choose a healthy diet that is rich in fruit and vegetables, with less fat and carbohydrate?Sweetness is an indicator of sugar content and therefore calories; a signal that has only lost its meaning somewhat since the invention of low-calorie sweeteners. Unsurprisingly, a preference for sweet tastes seems to be innate in humans. Almost all newborn infants react more positively to sugar solutions than to water, as measured by their facial expressions (Fig 1; Beauchamp & Moran, 1982). Most infants also show a strong dislike of bitter and sour tastes (Steiner, 1979). A liking for salty tastes is also common, and emerges slightly later in life at around four months of age (Beauchamp et al, 1986). Even infants who are exclusively breast-fed show a preference for salted over unsalted cereals at 16–25 weeks of age, despite the fact that breast milk has a low sodium content. This liking for salt persists through early childhood (Beauchamp & Cowart, 1990) along with the liking for sweetness: infants and children prefer higher concentrations of sugar and salt than adults.Within local cuisines there is further variation, as individuals express their preferences for certain foodsOpen in a separate windowFigure 1Reactions of a two-week old baby to different tastes.People also avoid foods that they have not encountered before, a trait that is known as ‘food neophobia''. It is common in omnivores and has been observed in a diverse range of species including warblers and capuchin monkeys (Greenberg, 1983; Visalberghi & Addessi, 2000). The adaptive value of avoiding new substances is obvious: it reduces the possibility of poisoning from toxic plants or animals. Interestingly, neophobia is minimal during infancy—when the child''s food intake is largely dictated by adults—but it increases rapidly as the child''s independence and autonomy increase—perhaps as a protective mechanism once the parents'' control of the child''s diet decreases. Humans and animals are more likely to accept an unfamiliar food when they observe other members of their species or family eating it and suffering no adverse effects, but new foods are often eaten sparingly at first—again, to minimize potential danger.Another interesting finding is that the tendency to like a food is associated with the energy density of that food (Birch et al, 1990). Even in food groups that have generally low energy density—such as fruits and vegetables—children prefer those containing more calories per gram, choosing carrots and peas over spinach and courgettes (Gibson & Wardle, 2003). As energy density is not a taste per se, such preferences must be learned through experience of the consequences of eating particular foods. This is supported by experiments in which the energy density of soups were modified by the addition of a tasteless starch. Each individual was given high- and low-calorie versions of the soup, and flavour–energy pairings were randomized across individuals. After several days, participants developed a preference for the flavour of the high-energy soup (Booth et al, 1982). A similar effect has been observed in children; after several exposures, they prefer flavours that are associated with higher energy density (Johnson et al, 1991). The adaptive value of this type of ‘flavour–consequence learning'' in impoverished food environments is clear, as it encourages foraging for foods with higher energy density.Overall, the evidence from twin studies indicates that genetic differences do not fully account for individual differences in food preferencesThe opposite of learning to like foods with positive nutritional effects is learning to dislike foods that have adverse effects. If animals or humans eat a food—especially a new food—and shortly afterwards experience negative consequences such as nausea or diarrhoea, they often develop a dislike for this particular food. This can persist even if they later learn that the illness was not caused by the food. Seligman called this ‘sauce béarnaise syndrome'' after a personal experience (Seligman & Hager, 1972). Studies in rats have shown that learning is associated with taste and not appearance (Wilcoxon et al, 1971). Aversions also seem to be learnt more quickly and overcome less easily than likes, and may persist for decades.Culture—as a shared experience—and genetics also influence our food preferences. Culture is a source of similarities within groups, as well as differences between them. Children develop dietary habits in accordance with their culture in terms of individual food preferences, combinations of ingredients, preparation methods, and times at which to eat particular meals. Distinctive and traditional spices and seasoning combinations can also facilitate the acceptance of new foods if these signal familiar and well-liked flavours (Pliner & Stallberg-White, 2000). Even flavours that are often innately disliked, such as chilli, or potentially disgusting items, such as insects, might be liked if they are part of the cuisine of the culture in which a child is growing up (Rozin & Schiller, 1980).Globalization of the food supply creates an increasing homogeneity of food across countries. High-fat foods, such as pizza and French fries, and sweet foods, such as chocolate or cookies, are in the top ten favourite foods of children in the UK, France, Spain, Germany and the USA (Cooke & Wardle, 2005). Few studies have investigated food preferences in populations outside Europe and North America, but the spread of fast-food chains globally suggests that this homogenization of tastes might expand elsewhere.Although it is clear that many cross-cultural differences are learnt from exposure and familiarity, there might also be genetic variations—such as those between different ethnic groups—that affect the acceptance and/or use of certain foods. One well-known example is lactose intolerance. After weaning, the gene that encodes the enzyme lactase—which breaks down lactose—is often ‘switched off'', impairing the digestion of lactose-containing, fresh dairy products. Some genetic variants, however, allow lactase production to continue, and these adults can therefore still digest milk or milk products. Lactase-persistence genetic variations are common in Europe and East Africa, but less so in China and Japan, countries where dairy consumption has traditionally been low.Despite the universal nature of food preferences, there is individual variation in favourite foods and, even more so, in foods that are disliked. Jack Spratt and his wife from the traditional English nursery rhyme are by no means an exception:“Jack Spratt would eat no fat, his wife would eat no lean, and so betwixt the two of them, they licked the platter clean.”Only a proportion of food dislikes seem to originate from specific and memorable aversive experiences, many of which occur early in life. The early development and stability over time of these preferences, along with the absence of obvious environmental causes, implicates genetic differences in their causation.Taste receptors for sweet, sour, bitter, salty, umami (savoury) and possibly fat, in combination with nasal and retronasal olfactory receptors create the complex tastes of foods (Fig 2). Genetic differences in taste receptors are therefore obvious candidates for causing differences in food preferences, although associations between receptors and hedonic responses to food have not been well mapped so far.Open in a separate windowFigure 2The combination of taste and olfactory receptors determine how we taste food.Quantitative genetics provides a methodology with which to assess the ‘bottom line'' of genetic influence. If certain traits—in this case, food preferences—are assorted according to the degree of genetic-relatedness between individuals, it would support the notion that genes explain differences in taste preferences. Heritability, therefore, is a factor that can be used to identify candidate genes; if heritability is low, the cause of individual differences in food preference is likely to be environmental.The results of studies of family food preferences have, in general, provided little support for genetic explanations. Although parents and their children share 50% of their genes, correlations between their food preferences are modest (Rozin, 1991). This is similar to the level of correlation found between spouses. Parents and children are different ages and have had different rearing experiences, which might partly explain the differences in their food preferences.Twin studies are more accurate measures of genetic influence, as monozygotic (MZ) twins are genetically identical and dizygotic (DZ) twins share on average 50% of their genes. Heritability is estimated from the extent to which the similarity between MZ pairs is greater than that between DZ pairs. Many twin studies have failed to provide evidence for a genetic contribution to food preferences (Faust, 1974), whereas others have found positive effects in only one or two foods (Falciglia & Norton, 1994). However, most of these studies have had small sample sizes and assessed only small numbers of foods. One large study used a sample of 428 young twins and an extensive list of foods, which were grouped into four categories based on the similarity of preferences within groups (Breen et al, 2006). The results found low heritability of preferences for sweet dessert foods (0.20) and vegetables (0.37), moderate heritability for fruits (0.51) and high heritability for protein foods (0.78). These differences are intriguing, but they are yet to be replicated so conclusions must be drawn tentatively. The low heritability of preferences for sweet foods is unsurprising as liking for sweets is widespread. More surprising was the high heritability of preferences for protein foods such as meat and fish, which had not been reported before. Genetic influences might be influential here through umami responsiveness. Overall, the evidence from twin studies indicates that genetic differences do not fully account for individual differences in food preferences.Another possible contributor to taste preferences is neophobia. Neophobic children are less likely to accept certain foods than their more-adventurous peers (Nicklaus et al, 2005). A large pediatric twin study estimated the heritability of neophobia as 78% (Cooke et al, 2007). It is possible that heritable differences in neophobia influence the number of foods that a person dislikes, by controlling their willingness to eat unfamiliar foods.Although humans are sensitive to bitter tastes from birth, there is variation in bitterness perception, especially as the ability to taste the compounds phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP) is inherited. A specific genetic locus has been identified—taste receptor, type 2, member 38; TAS2R38—that is associated with the number of fungiform papillae and taste buds on the anterior tongue. Although there are ethnic variations, approximately 30% of the global population are nontasters and 70% are tasters, of whom just over one-third are ‘supertasters''—individuals who are extremely sensitive to these compounds.It is assumed that PROP tasters are more sensitive than nontasters to bitterness. Cruciferous vegetables, such as broccoli, have attracted attention because they contain high levels of bitter-tasting glucosinolate compounds, but research findings in this area have been equivocal. Although Drewnowski et al (1999) found that young supertaster women had a lower liking for several cruciferous vegetables, studies in elderly women and college students found no differences (Mattes & Labov, 1989). In child PROP tasters, lower acceptance of raw but not cooked broccoli was observed in one comparison (Keller et al, 2002). Another study found a higher intake and liking of bitter-tasting foods—such as olives and broccoli—in nontasters in a free-choice test (Bell & Tepper, 2006). However, other studies have found no differences in vegetable intake or preference between PROP tasters and nontasters (Anliker et al, 1991).It seems clear that an individual''s experience with food is capable of overriding innate predispositionsIt is possible that research focusing on cruciferous vegetables—which most children dislike—has obscured other differences in preference. PROP taster status has been linked with acceptance of a variety of other foods including citrus fruit, alcohol, coffee, dark chocolate, milk and dairy foods, green tea and soy products, as well as sweet or salty tastes and fats (Anliker et al, 1991), although the explanation for this in terms of taste properties is yet to be identified.Efforts to identify genes that are related to food preferences have generally been unsuccessful, although variation in sensitivity to umami has recently been linked to polymorphisms on the TAS1R1 and TAS1R3 genes (Chen et al, 2009). Umami has been associated with monosodium-glutamate sensitivity specifically, but it might be linked with the liking of other savoury foods, which has been shown to be highly heritable.It seems clear that an individual''s experience with food is capable of overriding any innate predispositions. These experiences are the what, where, how often and with whom of food consumption. Twin studies are used not only to determine heritability, but also to distinguish between ‘shared environment'' effects—which tend to cause individuals who grew up in the same household to behave like one another—and ‘non-shared environment'' effects. Shared environment effects are implicated when twins—MZ or DZ—are more phenotypically similar than the heritability of the trait in question can account for. Yet, it requires large studies to reliably determine the extent of the environmental influence. Breen and colleagues (2006) have indicated that shared environment effects are important; being reared in the same home contributed significantly to the similarity between children. Just as the evidence of heritability provides an impetus for identifying the relevant genes, evidence for shared environment effects provides an impetus for identifying the environmental features that influence shared behaviour or preferences.One of the strongest environmental influences on food preference is taste. This can affect an individual''s likes and dislikes from the earliest stages of life; the maternal diet can influence the child in utero. In a series of studies at the Monell Chemical Senses Center, USA, Julie Mennella and her colleagues demonstrated this phenomenon by assigning pregnant women who were planning to breastfeed to one of three groups. Women were asked to drink carrot juice regularly either in the last trimester of pregnancy, while breastfeeding, or not at all. Babies born to the mothers in either of the carrot juice groups had less negative responses to carrots during weaning, and were perceived to like them more by their mothers than babies of mothers in the control group (Mennella et al, 2001). Similar results have been documented in rats, dogs, sheep, rabbits and piglets.Evidence for the ability of exposure to promote liking for certain foods has been building over the past three decades. Surveys in children of food consumption and preferences have linked early taste experiences to subsequent food acceptance (Cooke et al, 2004), which is consistent with an exposure effect. Experimental studies have also shown that exposure increases liking and acceptance in animals, children (Sullivan & Birch, 1990) and adults (Pliner et al, 1993). One study that compared children''s acceptance of three varieties of a new food—plain, salted or sugared tofu—showed that children preferred whichever variety they had been exposed to earlier (Sullivan & Birch, 1990).These findings have been replicated in the outside world. In one study, school children were randomly divided into three groups: exposure to the food (red pepper), exposure plus reward, or no exposure. After eight days, the children exposed to red pepper had significantly increased their liking and intake of it, compared with the control group (Wardle et al, 2003b). The same effects were achieved when the intervention was delivered by mothers who had been taught exposure feeding techniques. When offered a vegetable that they had initially disliked, children in the experimental group showed a greater increase in liking and intake after 14 days than those in the control groups, who had received no treatment or had been given leaflets about healthy eating (Wardle et al, 2003a).In animals, food preferences are thought to be socially transmitted: the sight of members of their own species eating, or even the smell of food on their breath can encourage consumption. In one study, lambs were exposed to three treatments: they ate a new food with their mother, observed her doing so but were unable to eat it themselves, or the mother ate the food out of their sight. Lambs that were with their mother while she was eating showed a stronger preference for the food in a subsequent test, even if they had not eaten the food themselves (Saint-Dizier et al, 2007).These modelling effects have also been observed in humans. In one study, children drank different flavours of new drinks while watching a video of a model expressing a like or dislike of the same drink (Baeyens et al, 1996). The children were found to prefer the flavour that the model had liked. This suggests that in the home, if parents, or better still peers, show that they like a food the child will be more inclined to taste and accept it.…serving new or less-liked foods in a happy mealtime atmosphere will increase the likelihood of a positive appreciation of those foods in the futureObservational and experimental studies indicate that modelling is an effective tool for influencing preferences. In one study, the ‘target'' children were seated with peers who had opposite preferences to them. On the first day, the target children had to choose between a preferred and non-preferred vegetable. On the next three consecutive days, the peers chose their preferred vegetable first. The target children were more likely to eat a vegetable that they did not like after observing another child eating it (Birch, 1980). Conversely, it is likely that food aversions can also be learnt through observation. Although there have been no studies demonstrating this in humans, it has been seen in animals. Mason and colleagues (1984) found that blackbirds that had observed others becoming ill after consuming food from a yellow cup avoided eating from yellow cups thereafter. Social learning presumably operates as a demonstration of safety and reassurance when a food is harmless, or notification of potential danger when a food should be avoided.Of course, preference is only an issue when there is something to prefer. Being choosy is a luxury born of plentyThe context of an individual''s first experience with a new food could contribute to their willingness to eat it in future. A negative physiological state such as tiredness, illness or negative mood by parents are thought to impair children''s enjoyment of eating (Wardle et al, 2001) and might also adversely affect hedonic reactions to new foods. Being hungry at the time of first exposure might result in a more-positive evaluation, although this might be more important when the food is energy-dense (Gibson & Wardle, 2001). Coercive feeding practices, which create a tense and negative atmosphere at mealtimes, might therefore impair the enjoyment of food (Galloway et al, 2006). The reverse is also true: giving food as a reward or linking eating with attention from adults has been shown to increase children''s liking, compared with nonsocial eating (Birch et al, 1980).The take-home message seems to be that serving new or less-liked foods in a happy mealtime atmosphere will increase the likelihood of a positive appreciation of those foods in the future. The determinants of food preferences, however, are not fully understood and although genetic factors are widely thought to be involved, the extent of their influence remains unknown. What follows is therefore speculation, rather than science.Since taste preferences are malleable and change through experience, it is easy to imagine how individual and sometimes eccentric food preferences develop. If the family''s principal food provider dislikes bananas, they will be bought and served infrequently, if at all. A child in this hypothetical family would be relatively unfamiliar with bananas, which, when combined with an inherited tendency to dislike fruit and the knowledge that bananas are not highly rated by their parent or caregiver, may give the impression that they are not good to eat. However, if this child is placed in an environment in which bananas are frequently and enthusiastically consumed, acceptance is likely to develop. Thus, genes are expressed in different environments to produce different food preference phenotypes.Even when the food provider likes the food that they are offering, the child may express surprise when given a new flavour, and this might be interpreted as rejection or dislike by the parent. A negative reaction to an unfamiliar food in infants—with the possible exception of very soft, sweet foods—is to be expected, irrespective of the innate palatability of the food being offered (Forestell & Mennella, 2007). Some research suggests that children need to taste a new food at least ten times before they change their preference (Wardle et al, 2003a), especially if its initial palatability is low. Mothers typically cease to offer foods that have been rejected on three or more occasions (Carruth et al, 2004) and as a result the necessary level of exposure required to create acceptance might not be reached. A child''s ‘dislike'' of bananas might become family lore, internalized by parents and child and never tested again.We might celebrate our idiosyncratic food likes and dislikes as evidence that we are original and special; meeting another person who shares an idiosyncratic dislike for a particular food creates a bond, especially on a first date. When the dislike is for a popular food, such as chocolate, rather than for a commonly rejected food, such as green vegetables, the effects are even stronger. This extends to our offspring; we might view our child''s rejection of sweets or liking for black olives as pleasing indications of their sophisticated palate and reflections of our enlightened parenting.Of course, preference is only an issue when there is something to prefer. Being choosy is a luxury born of plenty. In today''s food environment, you can like bananas and I can choose not to because I can always eat something else. Not long ago, this choice did not exist, which may have been advantageous from a health point of view. Now, when there is always a palatable alternative, making healthy choices is harder than ever and we might evaluate healthy foods more negatively simply because of this. Another issue concerns the expectation of pleasure from food. This was once the preserve of only the most prosperous, but is now normal in Western societies. What was once merely fuel to enable us to stay alive has become a source of enjoyment, comfort and even entertainment.The reason that fruit is sometimes consumed less frequently than recommended might be less to do with dislike—since we know that children rate fruit highly—and more to do with the alternatives on offer. Few children would choose an apple as a dessert when they know that a chocolate mousse lurks in the fridge. In light of the obesity epidemic that is ongoing in developed and many developing nations—which is, at least partly, caused by a diet rich in carbohydrates, fat and protein—knowledge about how we acquire and modify food preferences is crucial. It could be used to develop programmes to teach people, particularly children, to eat more healthily.Few children would choose an apple as a dessert when they know that a chocolate mousse lurks in the fridgeThe sheer quantity and variety of food that is available to us enables us to waste perfectly edible and nutritious parts of the foods that we eat. This might be simply because we are too squeamish to eat certain foodstuffs or parts of animals, or because we prefer not to eat the skin of fruit or vegetables. In the future, if we want to conserve the planet''s resources we might have to adapt and eat different, sometimes less attractive foods. It is therefore a good thing that food preferences seem to be more malleable and less hard-wired than has been previously assumed.? Open in a separate windowJane WardleOpen in a separate windowLucy J. Cooke

Science & Society Series on Food and Science

This article is part of the EMBO reports Science & Society series on ‘food and science'' to highlight the role of natural and social sciences in understanding our relationship with food. We hope that the series serves a delightful menu of interesting articles for our readers.     

The taste, odor and hedonic quality of polyglycerols

Twenty subjects judged the taste and odor intensity and thetaste and odor pleasantness/unpleasantness of five concentrationsof sucrose, glycerol, a commercial triglycerol, a syntheticlinear diglycerol and a synthetic linear triglycerol. Judgmentsof intensity were made using the method of magnitude estimation;judgments of pleasantness/unpleasantness were made using a graphicline scale. Only the two linear polyglycerols had appreciableodor intensity. Both were described as having an ‘acrid’or ‘burnt caramel’ quality. The odor exponent forthe linear triglycerol was extremely high (1.44) and may beattributed to its intensely unpleasant quality. Sucrose wascharacterized solely by sweet taste, glycerol and the commercialtriglycerol by sweet and bitter tastes, the linear diglycerolby sweet, bitter and sour tastes, and the linear triglycerolby bitter and sour tastes. The relationships between perceivedtaste intensity and concentration were well described by powerfunctions, although the slope of the psychophysical functionfor the linear triglycerol was markedly lower than that forthe other compounds. The relative order of taste intensitieswas: linear triglycerol > sucrose > glycerol = lineardiglycerol > commercial triglycerol. Judgments of taste (andodor) pleasantness/unpleasantness showed only sucrose and glycerolto have positive hedonic qualities. All the polyglycerols werejudged unpleasant at all concentrations. Differences in thetaste and odor characteristics of the commercial and synthetictriglycerols were attributed to the commercial product beinga mixture of over 20 compounds. Although the synthetic lineardi- and triglycerols are effective in lowering water activity,these data suggest that more purified crystalline forms mustbe synthesized before they can be used effectively as humectantsfor intermediate moisture foods.     

TASTE INTENSITIES OF OIL-IN-WATER EMULSIONS WITH VARYING FAT CONTENT

The objective of this study was to determine the effect fat has on the intensity of sweet, salty, sour, bitter and umami tastes in oil-in-water emulsions. The first experiment used two levels of fat (9% and 17% in oil-in-water emulsions) and two intensities of each taste (high and low). We compared the taste intensities of these emulsions to the intensities of oil-free samples with equal total volume, and to oil free samples of the same aqueous taste compound concentrations. Because of potential confusion between taste intensity and viscosity, we repeated the experiment, having panelists rate both thickness and taste intensity. Diluting with oil, compared to diluting with water, decreased bitterness, but increased the intensity of salty, sweet, sour and umami tastes. When compared to samples with equal aqueous taste compound concentrations, fat suppressed bitterness, but had no effect on the other tastes.