A Hypothesis for the Chemical Basis for Perception of Sour Taste

Comparison of sensitivity to taste and astringency stimuli among vegans and omnivores

Taste perception plays a crucial role in determining food choices. It has been described in literature a relationship between diet composition and taste perception. Nowadays, with the rising concern in climate change and animal welfare, the number of people following a vegan diet is increasing to become a real trend. Research about differences in taste perception between vegan and omnivore is lacking. The aim of the study was to compare detection threshold for bitter, sour, umami and astringency stimuli (quinine monohydrochloride dihydrate, citric acid anhydrous, monosodium glutamate and tannic acid, respectively) participants following a vegan diet (n=24) and participants following an omnivore diet (n=30). Participants reported their consumption frequency for main food categories. The mean detection thresholds between the two groups narrowly missed significance with p-values of 0.07, 0.08, 0.06, for bitter, umami and astringency perception, respectively. No differences were found for sour taste (p-value=0.33). Further research is required to validate such findings and to understand the origin of the relationship between diet style and taste sensitivity.

Fruit Characteristics of Citrus Trees Grown under Different Soil Cu Levels

The effects of the increased soil copper (Cu) on fruit quality due to the overuse of Cu agents have been a hot social issue. Seven representative citrus orchards in Guangxi province, China, were investigated to explore the fruit quality characteristics under different soil Cu levels and the relationship between soil-tree Cu and fruit quality. These results showed that pericarp color a value, titratable acid (TA), and vitamin C (Vc) were higher by 90.0, 166.6, and 22.4% in high Cu orchards and by 50.5, 204.2, and 55.3% in excess Cu orchards, compared with optimum Cu orchards. However, the ratio of total soluble solids (TSS)/TA was lower by 68.7% in high Cu orchards and by 61.6% in excess Cu orchards. With the increase of soil Cu concentrations, pericarp color a value and Vc were improved, TA with a trend of rising first then falling, and TSS/TA with a trend of falling first then rising were recorded. As fruit Cu increased, pericarp color a value and TSS reduced and as leaf Cu increased, TSS/TA decreased while Vc was improved. Moreover, a rise in soil Cu enhanced leaf Cu accumulation, and a rise in leaf Cu improved fruit Cu accumulation. Fruit Cu accumulation reduced fruit quality by direct effects, leaf Cu improved fruit quality by direct and indirect effects. Soil Cu affected fruit quality by indirect effects by regulating leaf Cu and fruit Cu. Therefore, reasonable regulation and control of soil Cu concentrations can effectively increase pericarp color, sugar, and acid accumulation in citrus fruit.

Effect of the homogenization process on the sensory and rheological properties in model system

High pressure homogenization has been used for preparation and stabilization of emulsions and suspensions, promoting physical changes in products, such as viscosity change. However, its use in model systems for fruit nectar is innovative. This study aimed to evaluate the effect of the processing in high pressure homogenizer on the rheological behavior and the sensory attributes in model system of gellan gum. Gellan gum (0.05%), organic acids (0.3%), and sucrose (10%) were used to prepare the solutions, which were subsequently homogenized (0-control, 25 and 50 MPa) at 25°C. Rheological and sensory analyses were performed. The samples presented pseudoplastic behavior without residual stress and were characterized by the Ostwald-de-Waele model. The homogenization pressure (P_H ) altered the viscosity of the model systems, reduced the consistency index and apparent viscosity, and increased the flow behavior index. The stimuli sour taste and viscosity differed among the parameters evaluated in the time-intensity analysis. No differences were observed for the maximum intensity of viscosity between the treated samples (25 and 50 MPa), which exhibited a similar temporal profile. Therefore, studies on the rheological and sensory behavior are fundamental to product development and process optimization. The present study shows new trends on the use of the high pressure homogenizer and the sensory profile in model systems that can be used for fruit nectar. This study evaluated the sensory attributes through the time-intensity analysis. The sensory data indicate that the homogenization pressure altered the viscosity perception, but did not alter the perception of the acid taste for the same organic acid used. Sensory as well as rheological data present new alternatives for product development. These findings are interesting for future research, equipment design, and process optimization.

Application of time–intensity analysis in model system submitted to homogenization

The use of the high pressure homogenizer has been studied in fruit juices, but researches in model system for application in fruit nectar are scarce. Therefore, it is necessary to evaluate the application of these technologies and how the homogenization pressure (PH) can interfere in the sensorial profile of the samples. To prepare the solutions we used guar gum (0.1%), organic acids (0.3%), and sucrose (10%), which were later homogenized (0—control, 25 and 50 MPa) at 25 ℃. The rheological behavior and the temporal profile of the samples were evaluated. The model systems presented pseudoplastic behavior without residual tension and were fitted to the Ostwald–de Waele model. The consistency index reduced and the flow behavior index increased with processing. Apparent viscosity also decreased due to homogenization. In the time–intensity sensorial analysis, it was observed that the samples differed among the evaluated parameters, demonstrating that the samples with tartaric acid presented higher intensity for the sour taste. However, for sweetness, no change was observed. In the viscosity attribute, the model systems presented similar temporal profiles. Therefore, it was noted that the homogenization process favored a greater temporal profile of sour taste, making sensory perception more lasting in a model system for fruit nectar.

Use of JAR-Based Analysis for Improvement of Product Acceptance: A Case Study on Flavored Kefirs

A common question of dairy product developments is the possible success of the new product. Several publications reported successful results using just-about-right (JAR) scales; although there is some debate about their advantages/disadvantages. This study highlights the limitations and opportunities of JAR scales and penalty analysis of fruit flavored kefirs. The first question is whether penalty analysis results help to improve the product and thus its overall liking (OAL)? The second question is what happens to those who rated the products "ideal" (JAR) before product development when evaluating the new products? Fruit flavored live-flora stirred-type kefir samples were formulated and evaluated by 92 consumers before and after the JAR-based product development. The OAL of two products significantly increased after product development. A new visualization tool is introduced, which shows what happens to those who rated the attribute as JAR but the attribute has been modified. A general product development scheme is also introduced for JAR-based kefir product development.

Effect of Sucrose Stearate on the Sensory-Related Quality of the Broth and Porridge of Ready-To-Eat Ginseng Chicken Soup Samgyetang

The objective of this study was to assess the sensory-related characteristics of the broth and porridge of ready-to-eat (RTE) ginseng chicken soup (Samgyetang) with sucrose stearate added at various concentrations (0.1%, 0.2%, and 0.3%) during storage at 25°C for 12 mon. Scores indicating the lightness and size of fat droplets in the broth increased during storage as the sucrose stearate concentration increased, while the clarity scores decreased until 9 mon and the taste scores decreased throughout the storage period (p<0.05). The porridge lightness increased as the concentration of sucrose stearate increased after 6 mon (p<0.05), while scores indicating the softness and vividness were higher for treated samples with sucrose stearate than for the control group after 3 mon, despite a lack of significant differences among treatment groups (p >0.05). The taste scores were lower for treated porridge samples than for the control group (p<0.05), even though no significant differences were observed among the treatment groups (p >0.05). The addition of sucrose stearate to the RTE Samgyetang broth improved the lightness (CIE L*) value of the broth and various sensory palatability parameters, including the color and fat droplet size of the broth and the softness and vividness of the porridge, despite reductions in broth clarity and taste scores for the broth and porridge during storage.

Impact of Prior Consumption on Sour, Sweet, Salty, and Bitter Tastes

Food sensory tests generally require panelists to abstain from food or beverage consumption 30 min to an hour before a tasting session. However, investigators do not have a complete control over panelists' intentional or unintentional consumption prior to a tasting session. Currently, it is unclear how prior consumption impacts the results of the tasting session. The aim of this study was to determine the effects of temporary and lingering mouth irritation caused by the consumption of coffee, orange juice, and gum within 1, 15, or 30 min prior to the tasting session on the perception of 4 basic tastes: sweet, salty, sour, and bitter. Fifty-two panelists were served a beverage (orange juice, coffee, and water) or were asked to chew a piece of gum, and then, remained in the waiting room for 1, 15, or 30 min. They were then asked to report taste intensities using 15-cm unstructured line scales. Mean intensities of all tastes were not significantly different when orange juice was a primer at 1, 15, and 30 min when compared to water. Mean intensities of bitter were significantly lower when coffee was a primer at 1, 15, and 30 min than when water was a primer. Mean intensities of sweet were significantly lower when gum was a primer at 1 and 15 min than when water was a primer. The findings showed that it is necessary for 30 min or more waiting period of no food or beverage consumption prior to sensory testing.

The chemistry of sour taste and the strategy to reduce the sour taste of beer

The contributions of free hydrogen ions, undissociated hydrogen ions in protonated acid species, and anionic acid species to sour taste were studied through sensory experiments. According to tasting results, it can be inferred that the basic substance producing a sour taste is the hydrogen ion, including free hydrogen ions and undissociated hydrogen ions. The intensity of a sour taste is determined by the total concentration of free hydrogen ions and undissociated hydrogen ions. The anionic acid species (without hydrogen ions) does not produce a sour taste but can intensify or weaken the intensity of a sour taste. It seems that hydroxyl or conjugated groups in anionic acid species can intensify the sour taste produced by hydrogen ions. The following strategy to reduce the sensory sourness is advanced: not only reduce free hydrogen ions, namely elevate pH value, but also reduce the undissociated hydrogen ions contained in protonated acid species.

A chemical basis for sour taste perception of acid solutions and fresh-pack dill pickles

Sour taste is influenced by pH and acids present in foods. It is not currently possible, however, to accurately predict and modify sour taste intensity in foods containing organic acids. The objective of this study was to investigate the roles of protonated (undissociated) organic acid species and hydrogen ions in evoking sour taste. Sour taste intensity increased linearly with hydrogen ion concentration (R(2)= 0.995), and with the concentration of protonated organic acid species at pH 3.5 (R(2)= 0.884), 4.0 (R(2)= 0.929), and 4.5 (R(2)= 0.975). The structures of organic acid molecules did not affect sour taste after adjusting for the effects of protonated organic acid species and hydrogen ions. Sour taste intensity was also linearly related to the total concentration of protonated organic acid species in fresh-pack dill pickles (R(2)= 0.957). This study showed that the sour taste of organic acids was directly related to the number of molecules with at least 1 protonated carboxyl group plus the hydrogen ions in solution. Conclusions from these results are that all protonated organic acids are equally sour on a molar basis, that all protonated species of a given organic acid are equally sour, and that hydrogen ions and protonated organic acids are approximately equal in sour taste on a molar basis. This study provides a new understanding of the chemical species that are able to elicit sour taste and reveals a basis for predicting sour taste intensity in the formulation of acidified foods.

The chemistry and physiology of sour taste--a review

Sour taste is the key element in the flavor profile of food acidulants. Understanding the chemistry and physiology of sour taste is critical for efficient control of flavor in the formulation of acid and acidified foods. After a brief introduction to the main applications of food acidulants, several chemical parameters associated with sour taste are discussed. Special emphasis is given to hydrogen ions, protonated (undissociated) acid species, titratable acidity, anions, molar concentration, and physical and chemical properties of organic acids. This article also presents an overview of the physiology of sour taste and proposed theories for the transduction mechanisms for sour taste. The physiology of sour taste perception remains controversial and significant diversity exists among species with regard to cellular schemes used for detection of stimuli. The variety of mechanisms proposed, even within individual species, highlights the complexity of elucidating sour taste transduction. However, recent evidence suggests that at least one specific sour taste receptor protein has been identified.

Signal transduction and information processing in mammalian taste buds

The molecular machinery for chemosensory transduction in taste buds has received considerable attention within the last decade. Consequently, we now know a great deal about sweet, bitter, and umami taste mechanisms and are gaining ground rapidly on salty and sour transduction. Sweet, bitter, and umami tastes are transduced by G-protein-coupled receptors. Salty taste may be transduced by epithelial Na channels similar to those found in renal tissues. Sour transduction appears to be initiated by intracellular acidification acting on acid-sensitive membrane proteins. Once a taste signal is generated in a taste cell, the subsequent steps involve secretion of neurotransmitters, including ATP and serotonin. It is now recognized that the cells responding to sweet, bitter, and umami taste stimuli do not possess synapses and instead secrete the neurotransmitter ATP via a novel mechanism not involving conventional vesicular exocytosis. ATP is believed to excite primary sensory afferent fibers that convey gustatory signals to the brain. In contrast, taste cells that do have synapses release serotonin in response to gustatory stimulation. The postsynaptic targets of serotonin have not yet been identified. Finally, ATP secreted from receptor cells also acts on neighboring taste cells to stimulate their release of serotonin. This suggests that there is important information processing and signal coding taking place in the mammalian taste bud after gustatory stimulation.