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The present study explored the possibility of generating a novel sensory evaluation instrument for describing comprehensive food palatability via its subdomains (rewarding, cultural, and informational) while keeping physiological factors constant. Seventy-five Japanese participants were asked to taste cheese samples and to respond to a questionnaire that was developed to dissect the distinct subdomains of palatability. The subsequent factor analyses revealed that three major factors may serve as distinct subdomains of palatability: rewarding, cultural, and informational, although the informational factor was not sufficiently robust. Multivariate regression analysis on cheese samples with exactly the same ingredients but sold in different packages led to different comprehensive palatability ratings due to the contribution of the cultural, but not the rewarding, factor. These results suggest that palatability is not merely determined by the physical and chemical properties that are intrinsic to a food product itself, but also depends on psychological properties that can arise through interaction between humans and the food product. The current study presents the first experimental demonstration that palatability could be dissociated to its subdomains.
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In research on human food intake and acceptance, the term “palatability” has been used in its colloquial sense that reflects a positive hedonic evaluation under a given set of conditions, but its usage has not always been clear and consistent (Ramirez 1990). For example, in meat studies, consumers are often asked to evaluate meat-related products (e.g., steaks) using hedonic scales for tenderness, juiciness, flavor, and palatability, which is often substituted with overall liking and pleasantness (Mehaffey et al. 2009). Considering this ambiguity in terminology, in this article, we use the term palatability to represent the positive hedonic reward provided by foods. However, as past literature often uses compatible terms, including “liking” and “pleasantness,” to refer to palatability, we sometimes incorporate such inferences to discuss palatability (Fig. 1).
Figure 1. Hypothesized structure of palatability. Palatability is related to liking and preference. Among the putative subdomains of palatability, the most influential physiological factor is kept constant to focus on the effects of other factors. Informational, rewarding, and cultural factors are assessed in the current study.
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We should also note that palatability could either be a measure of food or of a person unless the source is specified. Ramirez (1990) pointed out three different views on palatability. The first classical view proposes that palatability is an objective property of foods (e.g., Kissileff 1986). This is consistent with our colloquial usage of the term that a certain food is more palatable than another: a palatable chocolate would be palatable to everybody. Conversely, in the second view, as far as food intake evokes the hedonic response of a human to sensory stimuli, the palatability should be regarded as a measure of the human (e.g., Le Magnen 1987). Accordingly, instead of saying that a food is palatable, we should specify that a food is palatable to any individual under certain defined conditions. In a sense, this is just a different side of the same coin: the former view focuses on the stimulus while the latter on the response. The third more holistic view involves the effects of learning and experiences (Ramirez 1990). Namely, the same chocolate would taste more palatable to one person than to another because they had undergone different chocolate experiences. From this perspective, palatability should not be regarded as a fixed food property intrinsic to a given food or an automatic physiological response, but rather as the context-dependent evaluation of a food by an individual (Blundell and Rogers 1991), which is largely influenced by experience (Mela 2006).
Although no individual has the same experiences with specific foods, some common factors affecting palatability seem present. If so, palatability may be dissected into componential subdomains, which in turn may allow its reconstruction with explicit descriptions of the contribution of each subdomain. To explore this possibility, we developed a questionnaire that would reflect the composite nature of palatability and explore major factors that represent distinct aspects of palatability. In our subsequent analysis of the questionnaire responses, we ascribed comprehensive food palatability to its subdomains using multivariate regression analyses. We will hereafter describe the theoretical background for this strategy.
Referring to a wealth of research on palatability and related food properties, we infer four factors: physiological, rewarding, cultural, and informational (Fig. 1). First, the physiological factor plays a pivotal role in determining palatability. Five basic tastes, sweetness, sourness, saltiness, bitterness, and umami (savoriness), elicit relatively fixed hedonic responses (Prescott 2001, 2004). For example, humans prefer sweetness and are averse to bitterness. These responses appear as early as from birth, and thereafter last throughout the lifetime (Steiner et al. 2001). Additionally, nutritional deficit affects palatability through a homeostatically driven motivational system. It has been shown that physical exercise that necessitates calorie consumption increases preference for sucrose (Horio and Kawamura 1998). When animals, including humans, detect deficient or imbalanced protein intake, a sparing of protein and a search for the deficient materials are initiated to maintain the necessary level of dietary protein intake (Mori et al. 1991). Thus, the alteration in the physiological state due to nutritional deficit, fatigue, and/or hunger can affect food palatability.
The second factor is the reward elicited by the intake of high-calorie foods. This has been well evidenced by studies on food craving, a strong desire to eat a particular food that may lead people to go out of their way to satisfy it (Zellner et al. 1999). Although the intake of high-fat content foods, sweets, carbohydrates/starches, and fat-containing fast foods (White et al. 2002) often induces excessive caloric consumption and leads to obesity, they are frequently preferred. Underlying the over consumption of high-calorie foods, animal studies have revealed the role of the reward system involving the dopaminergic and opiate systems in the brain (Imaizumi et al. 2001; Bello et al. 2011). Hence, the activation of the reward system by high-calorie foods may be the dominant factor that underlies food palatability.
Third, food is influenced by cultural factors established as part of the acquisition of culture, including beliefs, culinary traditions, and special occasions (Rozin 1996). For example, a recent implicit association experiment revealed that positive attitudes toward traditional diets relate to the type of breakfast eaten in childhood in young Japanese (Kimura et al. 2010). Also, elderly Italians' favorite foods are not only based on the sensory aspects of dishes but also on tradition and familiarity from youth (Laureati et al. 2006). A subject's current vegetable consumption is known to be predicted by their previous vegetable intake at home (Uglem et al. 2007), and another study demonstrated that the intake frequency of fruits and vegetables at home was positively associated with the intake of fruits and vegetables 5 years later (Larson et al. 2008). This evidence collectively suggests that food palatability is influenced by cultural factors, and past eating habits seem to be the most effective predictors.
Fourth, taste expectations formed based upon information can dramatically bias the sensory perception of food. Information such as the name of the item, its shape, and how it is packaged would have a great impact on forming expectations, which can either raise or lower liking ratings (Cardello et al. 1985; Rozin et al. 1998). Indeed, a series of experimental studies about the effects of information on food intake performed by Wansink and colleagues clearly demonstrated the importance of informational factors. For example, environmental cues including ambience, lighting, and sounds can create expectations and generate an intake bias. It is believed that expectations may lead a person to focus on particular aspects of taste that strengthen their initial expectations (Wansink and Park 2002; Wansink 2004). Environmental cues of food quality can take many forms, including price, labels, appearance, or names (Wansink et al. 2005). Moreover, it has been revealed that specific colors influence the perception of specific tastes, liking, and intensity ratings (Maga 1974; Johnson and Clydesdale 1982; Johnson et al. 1982; Zellner and Durlach 2003). Even names can influence the perception of unimodal basic tastes (Okamoto et al. 2009).
Among the four factors presented above, physiological is considered the most influential. However, this poses a serious experimental problem: individuals tend to attribute their own food intake to a highly influential physiological state such as hunger ignoring other important but less influential factors (Vartanian et al. 2008). Alteration in the physiological state due to nutritional deficit, fatigue, or hunger may lead to individual differences regardless of food. Thus, we decided not to pursue the obvious effects of physiological factors. Rather, we controlled to minimize the effect of physiological variance by making the time of day for the experiment and the temperature invariant. The remaining three factors were psychometrically assessed in reference to the overall palatability of a food sample.
Thus, we aimed to assess the feasibility of dissecting comprehensive palatability into the three componential subdomains. We developed a questionnaire that reflected the composite nature of palatability, and explored major factors representing its distinct aspects. In our subsequent analysis of the questionnaire responses, we ascribed comprehensive food palatability to its subdomains using multivariate regression analyses. Combining these, we explored the possibility of generating a novel analysis instrument for sensory evaluation.