TIME-INTENSITY SCALING WITH JUDGES TRAINED TO USE A CALIBRATED SCALE: ADAPTATION, SALTY AND UMAMI TASTES

Differences in dynamic perception of salty taste intensity between young and older adults

In super-aged societies, high salt intake substantially increases the risk of stroke and cardiovascular disease. Perceived low salty taste often prompts the addition of table salt to food. However, it remains unclear how older adults perceive the nature and intensity of salty taste in the mouth and brain. We compared the perceptions of salty taste intensities of older adults with those of young adults. Participants were 74 healthy adults: 31 older (age, 60–81 years [65.0 ± 5.5 SD]) and 43 young (age, 21–39 years [25.0 ± 3.6 SD]). Our research project comprises three sequential experiments. This article reports on the first two, which were (1) static and (2) dynamic sensory evaluations of taste perceptions in the mouth. Participants assessed the taste of 0.3 M and 0.5 M sodium chloride solutions in two types of sensory evaluations: (1) a cup tasting test, in which they sipped the solution from cups, spat it out, and rated static salty taste intensity, and (2) a time-intensity sensory evaluation, in which the solutions were delivered to participants’ tongues through a custom-made delivery system while they recorded dynamic taste intensities on a hand-held meter. Older adults perceived significantly lower taste intensities than young adults (p = 0.004 and p < 0.001 for 0.3 M and 0.5 M, respectively). Reaction timings for both solutions did not differ, but the slopes for both concentrations were significantly lower for older adults than for young adults (p < 0.001). Using a standardized system allowed us to evaluate and directly compare real-time feedback on taste intensities according to age. This study is the first to characterize the time-intensity profiles of salty taste intensity in older adults. Our findings show that older adults do not take longer to recognize a salty taste, but their perception of taste intensity slowly increases, and yet remains lower than that of young adults. This suggests that older adults should be aware of the tendency to add more salt to their food to compensate for their low perceptions of salty taste. We would like to suggest them to savor and chew sufficiently during eating to optimize the perceived salty taste. Furthermore, our results offer a reference for ordinary citizens’ taste-intensity perceptions; our standardized system could be usefully integrated into clinical follow-up examinations and treatments.

The 9-point hedonic scale and hedonic ranking in food science: some reappraisals and alternatives

The 9-point hedonic scale has been used routinely in food science, the same way for 60 years. Now, with advances in technology, data from the scale are being used for more and more complex programs for statistical analysis and modeling. Accordingly, it is worth reconsidering the presentation protocols and the analyses associated with the scale, as well as some alternatives. How the brain generates numbers and the types of numbers it generates has relevance for the choice of measurement protocols. There are alternatives to the generally used serial monadic protocol, which can be more suitable. Traditionally, the 'words' on the 9-point hedonic scale are reassigned as 'numbers', while other '9-point hedonic scales' are purely numerical; the two are not interchangeable. Parametric statistical analysis of scaling data is examined critically and alternatives discussed. The potential of a promising alternative to scaling itself, simple ranking with a hedonic R-Index signal detection analysis, is explored in comparison with the 9-point hedonic scale.

Taste Enhancement by Pulsatile Stimulation Is Receptor Based But Independent of Receptor Type

Effects of subjects' taste sensitivity (expressed as taste detection threshold), tastant quality and taste transduction mechanism on pulsation-induced taste enhancement were tested. Taste intensities of pulsatile MSG and NaCl stimuli at pulsation periods below, at and above individual taste fusion periods (TFP in seconds) were compared to taste intensities of a continuous reference of the same net tastant concentration and quality. In line with results previously reported for sucrose, pulsation-induced taste enhancement peaked around TFP for both MSG and NaCl and did not require perception of tastant pulsation. TFP and pulsation effects were independent of the taste transduction mechanism (G-protein-coupled receptor for MSG versus ion-channel for NaCl). The absence of a relation between TFP and taste sensitivity suggests that temporal gustatory resolution and taste sensitivity are not necessarily influenced by the same factors. The results support earlier findings that early stages of taste transduction are involved in pulsation-induced taste enhancement. Pulsation-induced taste enhancement is determined by the pulsation rate (i.e. TFP) which is longer for MSG than NaCl. This is probably due to the tastant-specific interaction with the receptor rather than the taste transduction mechanism (G-protein-coupled receptor versus ion-channel) involved.

Collecting, comparing, and computing sequences: the making of Margaret O. Dayhoff's Atlas of Protein Sequence and Structure, 1954-1965

Collecting, comparing, and computing molecular sequences are among the most prevalent practices in contemporary biological research. They represent a specific way of producing knowledge. This paper explores the historical development of these practices, focusing on the work of Margaret O. Dayhoff, Richard V. Eck, and Robert S. Ledley, who produced the first computer-based collection of protein sequences, published in book format in 1965 as the Atlas of Protein Sequence and Structure. While these practices are generally associated with the rise of molecular evolution in the 1960s, this paper shows that they grew out of research agendas from the previous decade, including the biochemical investigation of the relations between the structures and function of proteins and the theoretical attempt to decipher the genetic code. It also shows how computers became essential for the handling and analysis of sequence data. Finally, this paper reflects on the relationships between experimenting and collecting as two distinct "ways of knowing" that were essential for the transformation of the life sciences in the twentieth century.

Astringency: mechanisms and perception

Astringency plays an important role in the sensory experience of many foods and beverages, ranging from wine to nuts. Given the recent trend toward fortifying consumables with astringent compounds and the evidence regarding the health benefits of some astringents, the mechanisms and perceptual characteristics of astringency warrant further discussion and investigation. This paper reviews the current state of the literature, including consideration of new methods for describing and measuring astringency, and provides an overview of research concerned with elucidating the physical, physiological, and psychological factors that underlie and mediate perception of this sensation.

Timing of intensity perception of a polar vs nonpolar aroma compound in the presence of added vegetable fat in milk

Differences in timing of intensity perception of the retronasal aroma of a nonpolar (linalool) vs polar (diacetyl) compound when the matrix (milk) fat content was varied (0%, 1%, 5%, or 10% rapeseed oil) were studied using a time-intensity method. Aromas were also evaluated by orthonasal means and with static headspace gas chromatography (GC). With increasing fat content, linalool was considerably retained in the matrix, while the release of diacetyl was not affected. As little as 1% fat was sufficient to significantly reduce the volatility (GC results) of linalool and orthonasal, but not retronasal, intensity. No effect of fat was found on the rate of linalool release. The linalool perception of the sample containing the greatest amount of fat lasted a shorter time than that of the samples containing less fat; however, the decrease in intensity perception was steeper in lower fat samples. The observed temporal release of linalool partly challenges the often-repeated statement that reduction of fat results in a more rapid and shorter aroma release.

Umami and food palatability

Umami is the term that identifies the taste of substances such as L-glutamate salts, which were discovered by Ikeda in 1908. Umami is an important taste element in natural foods; it is the main taste in the Japanese stock "dashi," and in bouillon and other stocks in the West. The umami taste has characteristic qualities that differentiate it from other tastes, including a taste-enhancing synergism between two umami compounds, L-glutamate and 5'-ribonucleotides, and a prolonged aftertaste. The key qualitative and quantitative features of umami are reviewed in this paper. The continued study of the umami taste will help to further our general understanding of the taste process and improve our knowledge of how the taste properties of foods contribute to appropriate food selection and good nutrition.

Method of stimulation, mouth movements, concentration, and viscosity: effects on the degree of taste adaptation

Although sensory adaptation, the gradual loss of sensation during prolonged stimulation, has been demonstrated in laboratory taste experiments, a comparable loss of taste intensity is not experienced in real-life eating situations. This discrepancy may be due to differences in the proximal stimuli or to differences in the ways the taste receptors are stimulated. In two experiments, the effects of four potentially relevant variables were investigated: stimulus intensity, stimulus viscosity, mouth movements, and presentation method. During the initial seconds of stimulation, adaptation to the weakest of the two solutions was faster. Although more viscous stimuli were less sweet, viscosity as such did not affect adaptation rate, nor did mouth movements. Among the three presentation methods, a sucrose-soaked filter paper on the tongue produced more adaptation than either sipping the solution or flowing it over the tongue. This suggests that even mouth movements far more subtle than those still present in the no-movement condition of a sip-and-spit experiment can disrupt the adaptation process.

Taste adaptation during the eating of sweetened yogurt

Taste adaptation, a gradual decline of taste intensity with prolonged stimulation, is frequently observed in laboratory experiments. However, during normal eating the taste of food does not seem to decrease or disappear. During eating, the presence of saliva, the interactions between tastants and odorants, and mouth movements can influence the time course of taste intensity. Therefore, results from standard laboratory adaptation experiments about adaptation seem of limited relevance to the prediction of the time course of taste intensity when eating real foods. We studied whether taste adaptation occurs when subjects eat yogurt, sweetened with two concentrations of sucrose (3.75 and 7.5%). In addition, we examined whether this adaptation is related to taste adaptation measured with a filter paper method. During the eating of yogurt, sweetness intensity declined with time, whereas sourness intensity did not. As expected, taste adaptation in the "yogurt task" was only slightly correlated to adaptation measured with filter paper.

Relation between parotid saliva flow and composition and the perception of gustatory and trigeminal stimuli in foods

The objective of this study was to investigate whether and how parotid saliva flow and composition correlated with the perception of gustatory and/or trigeminal stimuli in foods. Thirty (15 male and 15 female) subjects tasted seven foods or beverages (lemonade, beer, wine, soup, methyl cellulose, peanut butter, and crackers) with three levels each of a gustatory or trigeminal stimulus and rated the perceived intensity of the corresponding sensation over time using the time-intensity (TI) method while their parotid saliva was being collected. Salivary flow rates of males were significantly higher than those of females for all stimuli (p < 0.001). That did not translate, however, into consistent differences in perception of sensory attributes between males and females. Significant positive correlations were found between saliva flow and (1) TI parameters for adhesiveness of peanut butter and cohesiveness of mass of crackers (p < 0.05 or lower) and (2) time from intake to swallowing of crackers and peanut butter (p < 0.05). No correlations were found between saliva composition (e.g., sodium and total protein) and TI parameters. These results indicate that parotid saliva flow may correlate with the perception of some texture and mouthfeel attributes (presumably through oral work and bolus formation) but not with that of the taste attributes examined in this study (at the concentrations studied).

Relation between saliva flow and flavor release from chewing gum

The objective of this study was to investigate whether or not parotid saliva flow is a significant determinant of flavor release from chewing gum. Cherry-flavored gum with 3 concentrations of citric acid (0.5, 1, and 2%) acting as a sialagogue was evaluated for sweetness and cherry flavor in duplicate by 13 subjects, using a computerized system for simultaneous time-intensity (TI) measurements and unilateral collection of parotid saliva. With increased acidity in the gum, maximum intensity of, and area under, the cherry flavor curve increased (p < 0.001), whereas total duration of sweetness decreased (p < 0.05). Large interindividual differences were found for parotid saliva flow in response to chewing gum. Mean unilateral parotid saliva flows in response to stimulation with water and gum with 0.5, 1, and 2% citric acid were 0.07, 0.30, 0.36, and 0.44 g/min, respectively. There was a significant positive correlation between saliva flow and time to reach maximum intensity of sweetness (p < 0.05) and of cherry flavor (p < 0.01), with "high-flow" subjects taking longer to reach maximum intensity than "low-flow" subjects for both attributes. We conclude that parotid saliva flow may affect the rate of flavor release, but not how much nor for how long flavor is released.

Time-quality tracking of monosodium glutamate, sodium saccharin, and a citric acid-saccharin mixture

The temporal patterns of taste-quality descriptors evoked by 1000-ms duration stimulus liquids flowed through a closed delivery system over the anterodorsal tongue tip region were indicated using touch-typing on a computer keyboard. Single keys corresponded to the taste words of a 23 item code. A computer monitor displayed for subjects the keys pressed and when they were pressed, starting at stimulus delivery. For 2 mM sodium saccharin (NaSac), 75% of the responses were "sweet," 6.5% "sugar"; for NaSac in 10 mM citric acid (ArtLem), 43% "sour," 20% "citrus," and 11% "sugar"; for 214 mM monosodium glutamate (MSG), 28% "salty," 14% "sour," and 10% 1st "soapy," then "no taste," and finally "bitter." Distilled water received "no taste" on all trials. Response durations were 657 ms for ArtLem, 594 ms for NaSac, 577 ms for MSG. MSG yielded multiple quality responses on 25.5% of the trials; ArtLem, 9%; and NaSac, 1%. These results are compared with temporal patterns for taste intensity and with unrestricted verbal descriptions of the solutions.