R.A. de Wijk

The effect of viscosity on ad libitum food intake

Background:Energy-yielding liquids elicit weak suppressive appetite responses and weak compensatory responses, suggesting that liquid calories might lead to a positive energy balance. However, data is often derived from foods differing in many characteristics other than viscosity.Objective:To investigate the effect of viscosity on ad libitum food intake in real-life setting and to investigate whether a difference in ad libitum intake is related to eating rate and/or eating effort.Design:In real-life setting 108 nonrestrained subjects (26±7 years, BMI 22.7±2.4 kg m−2) received a chocolate flavored liquid, semi-liquid and semi-solid milk-based product, similar in palatability, macronutrient composition and energy density. In laboratory setting 49 nonrestrained subjects (24±6 years, BMI 22.2±2.3 kg m−2) received the liquid or semi-solid product. Effort and eating rate were controlled by means of a peristaltic pump.Results:In real-life setting the intake of the liquid (809±396 g) was respectively 14 and 30% higher compared to the semi-liquid (699±391 g) and semi-solid product (566±311 g; P<0.0001). In laboratory setting, removing eating effort, resulted in a 29% (P<0.0001) intake difference between liquid (319±176 g) and semi-solid (226±122 g). Standardizing eating rate resulted in 12% difference between liquid (200±106 g) and semi-solid (176±88 g; P=0.24). If not controlled, the difference in intake between liquid (419±216 g) and semi-solid (277±130 g) was comparable to the real-life setting (34%; P<0.0001).Conclusions:Products different in viscosity but similar in palatability, macronutrient composition and energy density lead to significant differences in intake. This difference is partially explained by the higher eating rate of liquids.

The effects of food viscosity on bite size, bite effort and food intake.

Two studies investigated the effect of a foods viscosity on bite size, bite effort and food intake using a standardized protocol in which subjects sipped through a straw every 20 s for a period of 15 min from one of two products, a chocolate-flavored dairy drink and a chocolate-flavored dairy semi-solid, matched for energy density. In the first study, subjects consumed 47% more from the liquid than from the semi-solid to reach the same degree of satiation, with larger bite sizes for the liquid throughout the 15 minute period (8.7+/-0.45 g) compared to the semi-solid (5.8+/-0.3 g, p<0.01). In the second study bite effort was eliminated by using a peristaltic pump to present the products every 20 s. Oral processing time before swallowing was set at 5 s (both products) or 8 s (semi-solid). With the elimination of bite effort and a standardized oral processing time, subjects consumed as much from the semi-solid as from the liquid to reach the same degree of satiation. Bite size for liquids started relatively small and grew gradually over successive bites, whereas the bite size for the semi-solid food started relatively large and became gradually smaller. The latter effect was even more pronounced when the oral processing time was increased from 5 to 8 s. In conclusion, semi-solids resulted in smaller bite sizes and lower intake than liquids, but these differences disappeared when differences in bite effort were eliminated.

Effect of viscosity on appetite and gastro-intestinal hormones

In previous studies we showed that higher viscosity resulted in lower ad libitum intake and that eating rate is an important factor. In this study we aimed to explore the effect of viscosity on the gastro-intestinal hormones ghrelin, CCK-8 and GLP-1. Thirty-two subjects (22+/-2 y, BMI 21.9+/-2.2 kg/m(2)) participated in this cross-over study. Subjects received a fixed amount of a chocolate flavored milk-based liquid or semi-solid product similar in energy density and macronutrient composition. Before intake and 15, 30, 60 and 90 min thereafter, appetite was rated and blood was drawn to determine glucose, CCK-8, active ghrelin, desacyl ghrelin and GLP-1 concentrations. After the last blood withdrawal, subjects were offered a chocolate cake meal to consume ad libitum. In the appetite ratings we observed a small effect showing that the semi-solid product is apparently considered as more satisfying than the liquid. There was a significant product effect for fullness (p 0.03), desire to eat (p 0.04), appetite something sweet (p 0.002) and prospective consumption (p 0.0009). We observed no clear effect of viscosity on gastro-intestinal hormones. Only for desacyl ghrelin there was a significant product effect (p 0.004). Concentrations were consistently higher after intake of the semi-solid product. Ad libitum intake of the chocolate cake was 102+/-55 g after the liquid and 96+/-46 g after the semi-solid product (ns). The results of our study show a similar response of the gastro-intestinal hormones CCK-8, ghrelin and GLP-1 after a fixed preload of a liquid and semi-solid product similar in energy- and macronutrient composition.

The effect of oral and product temperature on the perception of flavor and texture attributes of semi-solids

This study examined the effect of oral and product temperature on the perception of texture and flavor attributes. A trained panel assessed 21 texture and flavor attributes in one high-fat and one low-fat product of two semi-solids: custard dessert and mayonnaise. The products were evaluated at 10, 22 or 35 degrees C in combination with oral temperatures of 27, 35 and 43 degrees C. Results showed that modulation of product and oral temperature had significant effects on a number of attributes. Flavor intensities, melting mouth feel, and fat after feel increased, while subjective thickness decreased with increasing product temperature. Neither product- nor oral temperature had an effect on over-all creaminess. Oral temperature affected a number of mouth feel attributes: melting, heterogeneous and smooth. Furthermore, large differences existed in ratings between the high- and low-fat products of custard and mayonnaise, and they were more prominent in mayonnaise. We conclude that the effect of oral temperature on the perception of sensory attributes in semi-solids was small, but present, while the product temperatures influenced the ratings greatly.

Temporal integration and reaction times in human smell

A model description of intensity perception in human taste and smell developed earlier has now been verified experimentally to determine parameter values for odorants. The final objective is to quantify and understand odour-odour interaction phenomena in e.g., masking, deo-perfumes and flavour enhancement. Five types of olfactometer experiments were carried out, viz. determination of thresholds, determination of reaction times, scaling of perceived intensity after 5 sec stimulation, scaling of perceived intensity of a fixed concentration at variable duration, and measurement of intensity/time relationships. Four subjects were used and the odorants cineole, geraniol and hexane.

Learning to (dis)like: The effect of evaluative conditioning with tastes and faces on odor valence assessed by implicit and explicit measurements

Evaluative conditioning may be an important mechanism for learning food preferences and aversions; however, in both real life and experimental settings it has not been consistently successful. The current study aimed to gain more insight into which underlying factors may contribute to a successful outcome of olfactory evaluative conditioning. Two groups of 18 participants came in on three consecutive days, and were repeatedly exposed to four novel, neutral odors (CS) coupled to varying disliked, neutral, liked, or no stimuli (taste and/or pictures, US), following a 50% reinforcement schedule, leading to 40 odor presentations per session. Liking ratings, as well as changes in the autonomic nervous system were assessed before, during and after conditioning. We were able to induce negative, but not positive, affective changes by pairing neutral odors with tastes and pictures differing in valence. Negative as well as multimodal stimuli appear to be more potent US, since they may be considered more salient. Lastly, results of the current study imply that heart rate is responsive to changes in valence of olfactory stimuli, and perhaps even more sensitive than explicit ratings of liking.

Habituation and adaptation to odors in humans

Habituation, or decreased behavioral response, to odors is created by repeated exposure and several detailed characteristics, whereas adaptation relates to the neural processes that constitute this decrease in a behavioral response. As with all senses, the olfactory system continually encounters an enormous variety of odorants which is why mechanisms must exist to segment them and respond to changes. Although most olfactory habitation studies have focused on animal models, this non-systematic review provides an overview of olfactory habituation and adaptation in humans, and techniques that have been used to measure them. Thus far, psychophysics in combination with modern techniques of neural measurement indicate that habituation to odors, or decrease of intensity, is relatively fast with adaptation occurring more quickly at higher cerebral processes than peripheral adaptation. Similarly, it has been demonstrated that many of the characteristics of habitation apply to human olfaction; yet, evidence for some characteristics such as potentiation of habituation or habituation of dishabituation need more support. Additionally, standard experimental designs should be used to minimize variance across studies, and more research is needed to define peripheral-cerebral feedback loops involved in decreased responsiveness to environmental stimuli.

Behavioural and physiological responses to two food odours

Consumer food choice and intake are largely controlled by unconscious processes, which may be reflected better by implicit physiological and behavioural measures than by the more traditional explicit sensory tests. In this study, 26 human participants were exposed to an orange (pleasant) and a fish (unpleasant) odour presented in three different concentrations perceived as weak, medium and strong intensity, and five replications in a semi-random order via an olfactometer (Burghart OM2). Reactions to these odours were measured implicitly by means of facial expressions (automatically analysed with FaceReader), skin conductance responses and heart rate frequency (automatically analysed by Biolab), and explicitly with pleasantness ratings. Facial expressions reflected the odour’s valence (71% explained variance) and ranged from neutral (orange) to sadness/disgust/anger (fish) but showed additional differentiation with respect to odour intensity (15% explained variance). Skin conductance responses were largest for the unpleasant odour ( p p p

Effects of bread roll unit size on bread and energy intake in children

Background Bread choice • The average number of consumed bread rolls was 4.2 (SD=1.9). • White bread rolls were favourite: the first chosen bread roll was usually white (89%) regardless of size of offered rolls. 81% of total bread consumption was white. • Children ate more bread in grams when white rolls were larger-sized (Ps<0.001). Objective Although people tend to eat more when food is served in larger units (unit size effect), children often prefer food served in smaller units as they look more appealing. Whether unit size of bread rolls can be used to encourage children’s intake of whole wheat bread is unclear. Objective: To determine the effect of unit size of bread rolls on lunch energy and bread intake during a school lunch.

Evaluation of Segmentation Bases for the Heterogeneous Elderly Consumer Population: the Functional Food Market

It is beneficial for both the public health community and the food industry to meet nutritional needs of elderly consumers through product formats that they want. The heterogeneity of the elderly market poses a challenge, however, and calls for market segmentation. Although many researchers have proposed ways to segment the elderly consumer population, the elderly food market has received surprisingly little attention in this respect. Therefore, the present paper reviewed eight potential segmentation bases on their appropriateness in the context of functional foods aimed at the elderly: cognitive age, life course, time perspective, demographics, general food beliefs, food choice motives, product attributes and benefits sought, and past purchase. Each of the segmentation bases had strengths as well as weaknesses regarding seven evaluation criteria. Given that both product design and communication are useful tools to increase the appeal of functional foods, we argue that elderly consumers in this market may best be segmented using a preference-based segmentation base that is predictive of behaviour (for example, attributes and benefits sought), combined with a characteristics-based segmentation base that describes consumer characteristics (for example, demographics). In the end, the effectiveness of (combinations of) segmentation bases for elderly consumers in the functional food market remains an empirical matter. We hope that the present review stimulates further empirical research that substantiates the ideas presented in this paper.It is beneficial for both the public health community and the food industry to meet nutritional needs of elderly consumers through product formats that they want. The heterogeneity of the elderly market poses a challenge, however, and calls for market segmentation. Although many researchers have proposed ways to segment the elderly consumer population, the elderly food market has received surprisingly little attention in this respect. Therefore, the present paper reviewed eight potential segmentation bases on their appropriateness in the context of functional foods aimed at the elderly: cognitive age, life course, time perspective, demographics, general food beliefs, food choice motives, product attributes and benefits sought, and past purchase. Each of the segmentation bases had strengths as well as weaknesses regarding seven evaluation criteria. Given that both product design and communication are useful tools to increase the appeal of functional foods, we argue that elderly consumers in this market may best be segmented using a preference-based segmentation base that is predictive of behaviour (for example, attributes and benefits sought), combined with a characteristics-based segmentation base that describes consumer characteristics (for example, demographics). In the end, the effectiveness of (combinations of) segmentation bases for elderly consumers in the functional food market remains an empirical matter. We hope that the present review stimulates further empirical research that substantiates the ideas presented in this paper.It is beneficial for both the public health community and the food industry to meet nutritional needs of elderly consumers through product formats that they want. The heterogeneity of the elderly market poses a challenge, however, and calls for market segmentation. Although many researchers have proposed ways to segment the elderly consumer population, the elderly food market has received surprisingly little attention in this respect. Therefore, the present paper reviewed eight potential segmentation bases on their appropriateness in the context of functional foods aimed at the elderly: cognitive age, life course, time perspective, demographics, general food beliefs, food choice motives, product attributes and benefits sought, and past purchase. Each of the segmentation bases had strengths as well as weaknesses regarding seven evaluation criteria. Given that both product design and communication are useful tools to increase the appeal of functional foods, we argue that elderly consumers in this market may best be segmented using a preference-based segmentation base that is predictive of behaviour (for example, attributes and benefits sought), combined with a characteristics-based segmentation base that describes consumer characteristics (for example, demographics). In the end, the effectiveness of (combinations of) segmentation bases for elderly consumers in the functional food market remains an empirical matter. We hope that the present review stimulates further empirical research that substantiates the ideas presented in this paper.