Bitter Qualities Research Articles

Mashing Isothermally at High Temperature Compared to Infusion Mashing for the Production of Full-Bodied, Alcohol-Reduced Beer

The objective of this study was to investigate the influence of the mashing temperatures on alcohol content and taste of bottom-fermented Pilsner style beers and to ascertain whether these beers exhibit comparable sensorial properties. For this purpose, three beers brewed with three different mashing procedures were compared. The worts produced were sampled during mashing and after boiling, and subsequently analysed for their original gravity, fermentable sugars, and free amino nitrogen. The beers were analysed for their alcohol content, aroma compounds, apparent degree of fermentation, pH value, foam, and bitterness units as well as being evaluated sensorially according to DLG (= “Deutsche Landwirtschafts-Gesellschaft - German Agricultural Society”) grading in the categories: odour, purity of taste, body, carbonation, quality of bitterness. Overall it was shown, that the isothermal mashing procedure yielded less fermentable but more unfermentable sugars than the two more traditional mashing procedures, leading to a comparable original wort of 11.6°P in the final beer and lower alcohol content of 2.8% v/v in comparison to the more traditional mashing procedures (“high-short” and “simplified high-short” mashing procedure) with original worts of 12.1°P and alcohol contents of 4.5% v/v and 5.0% v/v, respectively. The DLG-rating showed that the beers derived from the different mashing procedures were all classified similarly with scores above 4.5 on average (out of 5.0) in all categories with no significant differences.

Impact of Hop Freshness on Dry Hopped Beer Quality

The hop plant is seasonal, but beer production continues throughout the whole year. The quality of hops begins to decrease immediately after harvesting; therefore, maintaining the highest possible quality is important. A good indicator of hop freshness is the hop storage index (HSI). In this study, three different varieties of hops with five different HSI values, from 0.3 to 0.7, were used for brewing with the dry hopping technique. The main goal was to evaluate the impact of the HSI value on beer quality in terms of hop aroma and bitterness. Alpha acids, iso-alpha acids, humulinones, bitterness units and hop aroma compounds were chemically analysed. Sensorial analysis was also conducted on all samples. Decreases in the intensity and quality of hop aroma were detected with increasing HSI. The quality of bitterness was also reduced. High HSI also led to undesirable gushing. Beers brewed with hops with HSI values greater than 0.4 had deviations in aroma and bitterness when compared with beers brewed with fresh hops.

Bitter Taste Stimuli Induce Differential Neural Codes in Mouse Brain

A growing literature suggests taste stimuli commonly classified as “bitter” induce heterogeneous neural and perceptual responses. Here, the central processing of bitter stimuli was studied in mice with genetically controlled bitter taste profiles. Using these mice removed genetic heterogeneity as a factor influencing gustatory neural codes for bitter stimuli. Electrophysiological activity (spikes) was recorded from single neurons in the nucleus tractus solitarius during oral delivery of taste solutions (26 total), including concentration series of the bitter tastants quinine, denatonium benzoate, cycloheximide, and sucrose octaacetate (SOA), presented to the whole mouth for 5 s. Seventy-nine neurons were sampled; in many cases multiple cells (2 to 5) were recorded from a mouse. Results showed bitter stimuli induced variable gustatory activity. For example, although some neurons responded robustly to quinine and cycloheximide, others displayed concentration-dependent activity (p<0.05) to quinine but not cycloheximide. Differential activity to bitter stimuli was observed across multiple neurons recorded from one animal in several mice. Across all cells, quinine and denatonium induced correlated spatial responses that differed (p<0.05) from those to cycloheximide and SOA. Modeling spatiotemporal neural ensemble activity revealed responses to quinine/denatonium and cycloheximide/SOA diverged during only an early, at least 1 s wide period of the taste response. Our findings highlight how temporal features of sensory processing contribute differences among bitter taste codes and build on data suggesting heterogeneity among “bitter” stimuli, data that challenge a strict monoguesia model for the bitter quality.

The Influence of Hop Harvest Date on Flavor Stability in Dry-hopped Beers

The aim of this work was to investigate the influence of hop harvest date on the flavor stability of a dry-hopped lager. The selected harvest dates encompassed a period of 24 days, from a very early (date 1) to a very late (date 5) harvest date. To assess flavor stability, beers brewed with hops harvested at an early date (date 2) and a very late date (date 5) were chosen. The flavor stability of beer is an important criteria of successful brands, and among these, dry-hopped craft beers are being distributed over ever-increasing distances. This is the first study to investigate whether hop harvest date influences the flavor stability of a dry-hopped lager. The results showed that in terms of acceptance ratings beers brewed with late-harvested hops had slightly better flavor stability. However, with increasing storage time and temperature, after 45 days differences in acceptance values decreased and leveled off. Flavor suffered most with increasing storage temperature and time. Also, aroma values decreased with increasing storage temperature and time and showed slightly better ratings for beers brewed with late-harvested hops compared with beers brewed with early-harvested hops when stored at temperatures lower than 28°C. Bitterness quality in stored beer samples was rated higher when beers were brewed with hops from date 5 but only when these were stored at cool temperatures. Consequently, hops that are harvested later seem to support flavor stability but only for a limited time, and this support is more evident when the beer is stored at low temperatures.

Degradation of Iso-α-Acids During Wort Boiling

A detailed study on the degradation of iso-α-acids was conducted. Because of the complexity of the wort matrix and interfering interactions during real wort boiling, the investigation of degradation kinetics was performed in an aqueous solution. Degradation was investigated as a function of time (0–90 min), temperature (80–110°C), pH value (4–7), original gravity (10–18°P) and ion content of the water (0–500 ppm Ca2+ and Mg2+). After 90 min of boiling, over 20% of the dosed iso-α-acids could no longer be detected. A strong dependence of degradation could be shown due to high temperature, low pH, high original gravity and a high Mg2+ content. The cis:trans ratio and co-iso-α-acid content did not change significantly. Losses of isohumulones could be lowered by reducing the temperature and original gravity, as well as by heightening the pH value. High amounts of Ca2+ and Mg2+ salts also led to an increase in degradation products. Solutions to decrease degradation and thereby possible improvements in sensory bitter quality are discussed.

Impact of Mashing-Off Temperature and Alternative Kettle-Hopping Regimes on Hop α-Acids Utilization upon Wort Boiling

In this study, the influence of the mashing-off temperature (78 versus 95°C) on α-acids behavior and isomerization during wort boiling at the 10-L scale was investigated. In addition, various kettle-hopping regimes were applied to determine their possible impact on the isomerization of α-acids into iso-α-acids. As determined by quantitative HPLC as a function of wort-boiling time, mashing-off at 95°C always resulted in significantly higher hop α-acids utilization at the end of wort boiling (approx. 58%) compared with conventional mashing-off at 78°C (approx. 42%). Moreover, with mashing-off at 95°C, iso-α-acid profiles obtained at the end of wort boiling were potentially favorable in view of a finer, less lingering beer bitterness (relatively less isocohumulone) and prolonged bitterness stability upon aging (proportionally less trans-isomers). In regard to alternative hopping regimes, dosed addition of hop material as a function of wort boiling time resulted in similar α-acids utilizations compared with full hopping at the onset of the boil. Our results point to the potential of alternative ways of kettle hopping, in particular when mashing-off at 95°C, for more economic hopping combined with enhanced bitterness quality and stability.

The Bitter Qualities of Reduced and Nonreduced Iso-α-acids

The temporal and qualitative bitterness of reduced and nonreduced iso-α-acids were measured in this study. A trained panel using a time-intensity protocol determined the temporal attributes of these compounds added to an unhopped lager beer. Principal components analysis and analysis of variance were applied at equibitter concentrations to determine differences among compounds (α = 0.10). Qualitative characteristics of the hop compounds, quinine sulfate, and caffeine were evaluated at equibitter concentrations using a free-choice profiling sensory protocol and were statistically separated through the application of generalized procrustes analysis (GPA). Caffeine and quinine were significantly harsher and less vegetative than the hop compounds. To further understand the differences among hop acids, the nonhop compounds were removed, and the qualitative data were reevaluated by GPA. Overall, tetrahydro-iso-α-acids were the most different in both temporal and qualitative aspects, with a longer duration and greater overall impact, and were described as harsher and more medicinal than the other hop acids. Hexahydro-iso-α-acids and iso-α-acids did not diverge significantly in time-dependant aspects but were qualitatively different, with hexahydro-iso-α-acids being more medicinal and metallic. Rho-iso-α-acids and iso-α-acids were similar temporally, except that rho had a greater initial intensity, whereas, qualitatively, rho-iso-α-acids and iso-α-acids were smoother and more vegetative than tetrahydro-iso-α-acids and hexahydro-iso-α-acids.

Quantitative Studies and Taste Re-engineering Experiments toward the Decoding of the Nonvolatile Sensometabolome of Gouda Cheese

The first comprehensive quantitative determination of 49 putative taste-active metabolites and mineral salts in 4- and 44-week-ripened Gouda cheese, respectively, has been performed; the ranking of these compounds in their sensory impact based on dose-over-threshold (DoT) factors, followed by the confirmation of their sensory relevance by taste reconstruction and omission experiments enabled the decoding of the nonvolatile sensometabolome of Gouda cheese. The bitterness of the cheese matured for 44 weeks was found to be induced by CaCl2 and MgCl2, as well as various bitter-tasting free amino acids, whereas bitter peptides were found to influence more the bitterness quality rather than the bitter intensity of the cheese. The DoT factors determined for the individual bitter peptides gave strong evidence that their sensory contribution is mainly due to the decapeptide YPFPGPIHNS and the nonapeptides YPFPGPIPN and YPFPGPIHN, assigned to the casein sequences beta-CN(60-69) and beta-CN(60-68), respectively, as well as the tetrapeptide LPQE released from alphas1-CN(11-14). Lactic acid and hydrogen phosphate were identified to play the key role for the sourness of Gouda cheese, whereas umami taste was found to be due to monosodium L-glutamate and sodium lactate. Moreover, saltiness was induced by sodium chloride and sodium phosphate and was demonstrated to be significantly enhanced by L-arginine.

The Relationship between PROP and Ethanol Preferences: An Evaluation of 4 Inbred Mouse Strains

Ethanol's taste attributes undoubtedly contribute to the development of drug preference. Ethanol's taste is both sweet and bitter. Taster status for bitter 6-n-propylthiouracil (PROP) has been proposed as a genetic marker for alcoholism; however, human results are conflicting. We collected preference scores for both tastants in 4 mouse strains selected on the basis of previously reported taste preference, with the generally accepted idea that inbred mice show minimal within-strain variation. Eighty-eight male mice (22 per strain) participated. The strains were as follows: C57BL/6J, ethanol preferring; BALB/cJ, ethanol avoiding; SWR/J, PROP avoiding; and C3HeB/FeJ, PROP neutral. Using a brief-access (1-min trials) 2-bottle preference test, we assessed the taste response of each strain to PROP and ethanol on separate days. Although PROP avoiding versus neutral mice could be segregated into significantly different populations, this was not the case for ethanol avoiding versus preferring mice, and all strains showed high variability. On average, only BALB/cJ, SWR/J, and C3HeB/FeJ mice conformed to their literature-reported preferences; nonetheless, there were a substantial number of discordant animals. C57BL/6J did not conform to previous results, indicating that they are ethanol preferring. Finally, we did not observe a significant relationship between PROP and ethanol preferences across strains. The high variability per strain and the number of animals in disagreement with their respective literature-reported preference raise concerns regarding their utility for investigations underlying mechanisms of taste-mediated ingestive responses. Absent postingestive consequences, the brief-access results suggest a possible degree of previously masked polymorphisms in taste preferences or a more recent drift in underlying genetic factors. The absence of a relationship between PROP and ethanol indicates that the bitter quality in ethanol may be more highly related to other bitter compounds that are mediated by different genetic influences.

Gustatory Function After Tonsillectomy

To assess taste function before and after tonsillectomy (TE). Prospective study. University hospital. Sixty-five patients (42 females, 23 males; mean age, 28 years). Taste function was investigated before TE with 4 concentrations each of sweet, sour, salty, and bitter quality, respectively, on both sides of the anterior and posterior areas of the tongue. Self-assessment of gustatory function was performed by visual analogue scales. Thirty-two patients were retested 64 to 173 days after TE. Thirty-three patients could not be retested after TE but were interviewed by telephone. Self-assessed taste function significantly decreased (P=.001). Yet, none of the subjects reported taste dysfunction. Tonsillectomy had no major effect on taste test scores (P>.27). Persisting taste dysfunction seems to be rare after TE.

Taste dysfunction in patients receiving radiotherapy

Taste loss is a major cause of morbidity in patients undergoing head and neck irradiation. In a prospective study, 51 patients undergoing radical head and neck irradiation at the Tokyo University Hospital were assessed for taste loss. Taste ability was measured by the taste threshold for the four basic tastes (sweet, sour, salt, and bitter qualities) plus another taste of "umami" quality using a filter-paper-disc method in patients before, during, and after radiotherapy (RT). All tastes declined on the fifth week after the start of RT and improved on the 11th week. Anatomic pathologic analyses in rats revealed that taste buds diminished completely on the sixth day after irradiation of 15 Gy in a single fraction, and the appearance of taste buds returned almost to the preirradiation state on the 28th day. The main cause of taste disorder resulting from RT was believed to be a disappearance of taste buds and not damage to the taste nerves.

Prediction of the Sensory Quality of Canned Beer as Determined by Oxygen Concentration, Physical Chemistry Contents, and Storage Conditions

ABSTRACT: The objective of this research was to predict any sensory characteristics of canned beer related to its oxygen concentration, composition, temperature, and time intervals of storage. The initial content of oxygen and content of carbon dioxide, pH, color, turbidity, thiobarbituric acid, and bitterness were instrumentally evaluated during 16 wk and 3 storage temperatures. Simultaneously, 8 trained panelists evaluated the degree of oxidation, quality of bitterness, and sensory stability. Principal components regression adjusted models explained the 85% to 86% (P &lt; 0.01) variability of the sensory characteristics. The results suggest that sensory characteristics of canned beer can be predicted by instrumental measures of its composition and storage conditions.

Effects of caloric deprivation and satiety on sensitivity of the gustatory system

BackgroundSensitivity of the gustatory system could be modulated by a number of short-term and long-term factors such as body mass, gender, age, local and systemic diseases and pathological processes, excessive alcohol drinking, drug dependence, smoking, composition of oral fluid, state of oral hygiene, consumption of some foods among many others. A few studies have demonstrated the effects of hunger and caloric satiety on sensitivity of the gustatory system in obese humans and animals. The aim of the present study was to assess the effects of short-term caloric deprivation and satiety on recognition taste thresholds of healthy, non-smoking, non-drinking, non-obese young male subjects. The two-alternative forced-choice technique was used to measure taste threshold.ResultsRecognition thresholds for sucrose and salt were significantly lower during fasting state than after a meal (t = 2.23, P < 0.05, and t = 2.86, P < 0.02, respectively) while the values of recognition thresholds for bitter substances in fasting state and after caloric loading did not differ significantly.ConclusionsShort-term caloric deprivation in our study model was associated with increased taste sensitivity to sweet and salty substances compared to satiated state while taste sensitivity to bitter substances was not affected by the conditions of measurements. Selective modulation of sensitivity of the gustatory system might reflect the different biological importance of salty, sweet and bitter qualities of taste.

Dual actions of caffeine on voltage-dependent currents and intracellular calcium in taste receptor cells.

Although the numerous stimuli representing the taste quality of bitterness are known to be transduced through multiple mechanisms, recent studies have suggested an unpredicted complexity of the transduction pathways for individual bitter stimuli. To investigate this notion more thoroughly, a single prototypic bitter stimulus, caffeine, was studied by using patch-clamp and ratiometric imaging techniques on dissociated rat taste receptor cells. At behaviorally relevant concentrations, caffeine produced strong inhibition of outwardly and inwardly rectifying potassium currents. Caffeine additionally inhibited calcium current, produced a weaker inhibition of sodium current, and was without effect on chloride current. Consistent with its effects on voltage-dependent currents, caffeine caused a broadening of the action potential and an increase of the input resistance. Caffeine was an effective stimulus for elevation of intracellular calcium. This elevation was concentration dependent, independent of extracellular calcium or ryanodine, and dependent on intracellular stores as evidenced by thapsigargin treatment. These dual actions on voltage-activated ionic currents and intracellular calcium levels suggest that a single taste stimulus, caffeine, utilizes multiple transduction mechanisms.

Sensory and Analytical Characterisation of Reduced, Isomerised Hop Extracts and Their Influence and Use in Beer

The use of reduced, isomerised hop extracts became very popular during the last decade in terms of achieving both better foam and light stability. Today the most common products are those with tetra-hydro-iso-α-acids (THIA) or rho-iso-α-acids (RHIA). There is still not clarity concerning the taste properties of these products in comparison with iso-α-acid Bitter Units (BU). The experiments conducted showed that the bitter conversion factors determined in previous work (1.6 for THIA and 0.7 for RHIA) represented only perceived bitterness when presented in tap water. In the test beers a bitter conversion factor of 1.0–1.1 for THIA was determined and the factor of 0.7 for RHIA in beer was confirmed. Photometric methods led to considerable deviations when used for the determination of THIA and RHIA, whereas the HPLC method, in combination with either Solid Phase Extraction (SPE) or Liquid Liquid Extraction (LLE), led to very good results. RHIA was found to have a foam stabilising effect and it was also shown that the foam stabilising effect of THIA in unhopped beer was higher than in hopped beer. The quality of bitterness decreased with an increase of THIA and RHIA. A dependency on the alcohol content in regard to the bitter intensity was ascertained.

Effects of chlorhexidine on human taste perception

Chlorhexidine, a bis-cationic biguanide antiseptic, greatly reduces the perceived intensity of the salty prototype sodium chloride and may prove to be an important probe of mechanisms that underlie the human salty taste quality. Chlorhexidine, which tastes bitter, also reduces quinine hydrochloride taste intensity, but neither sweet sucrose nor sour citric acid is affected. Perceptual intensity rating and quality identification were measured for human subjects before and for 30 min following treatment with 1.34 mM chlorhexidine gluconate. In one experiment, test stimuli were the taste-quality prototypes; in a second experiment, stimuli were series of sodium, halide and sulfate salts. Experiment 1 showed a single 3-min chlorhexidine treatment resulted in reductions in taste intensity that persisted for at least 30 min. Experiment 2 showed a single 2-min chlorhexidine treatment reduced perceptual intensities of halide and sulfate salts except those with divalent cations. Chlorhexidine impaired identification of the salty quality and produced a bitter quality in nonbitter salts and impaired identification of the bitter quality of quinine, but not bitter salts. The specific effect of chlorhexidine on the bitterness of quinine suggests it may bind to the same receptor as quinine. The ability of chlorhexidine to specifically disrupt saltiness of a wide range of salts is consistent with proposed peripheral transduction mechanisms for the salty quality that involve transepithelial ion transport.

Taste effects of antiretroviral drugs on chorda tympani responses in gerbil

In clinical reports, HIV-infected patients complain that antiretroviral drugs produce unpleasant tastes that affect compliance with their medication regimen. In this study, taste effects of seven antiretroviral drugs (protease inhibitors and nucleoside analogs) were investigated in a gerbil model. Electrophysiological recordings were obtained from the chorda tympani nerve after lingual application of HIV medications. The effect of adaptation of the tongue to HIV medications on other taste stimuli with salty, sweet, sour and bitter qualities was also determined to simulate the presence of drug in the saliva. Four drugs (ritonavir, lamivudine, indinavir and didanosine) produced taste responses in the chorda tympani nerve of the gerbil at 0.625 mM and higher. Zidovudine, saquinavir and stavudine gave no taste responses at concentrations below 10 mM. The protease inhibitors saquinavir (2 mM) and ritonavir (10 mM) suppressed most taste stimuli with the greatest effect on bitter and sweet qualities. The nucleoside analog lamivudine gave a taste response at 20 mM and produced the greatest suppression on sour tastes. Results show that protease inhibitors had a more potent effect on chorda tympani responses in gerbil than nucleoside analogs.

Gustatory neural coding in the cortex of the alert cynomolgus macaque: the quality of bitterness.

We sought to define the gustatory neural representation in primates for stimuli that humans describe as predominantly bitter. Thus we analyzed the responses of single neurons from the insular cortex of two alert, male cynomolgus macaques in response to the oral application of four basic taste stimuli (glucose, NaCl, HCl, and quinine HCl) and fruit juice, and to a series of 15 other chemicals to which humans ascribe a bitter component. Gustatory neurons occupied a volume of 109 mm3 across an area of 4.0 mm in the anterposterior plane, 4.4 mm in the mediolateral, and 6.2 mm in the dorsoventral. Taste cells represented 161 (8.6%) of the 1881 neurons tested for chemical sensitivity. Fifty of these could be monitored throughout the delivery of the entire stimulus series, and their responses constitute the data of this study. The mean spontaneous discharge rate of the cortical gustatory cells was 3.2 +/- 3.3 spikes/s (range = 0.2-17.7 spikes/s). The mean breadth-of-tuning coefficient was a moderate 0.77 +/- 0.15 (range = 0.25-0.99). Forty-eight neurons responded to taste stimuli with excitation, and two responded with inhibition. Forty-one of the 50 neurons were able to be classified into one of four functional types based on their responses to the four basic stimuli used here. These were sugar (n = 22), salt (n = 7), acid (n = 7), and quinine (n = 5). A two-dimensional space was generated from correlations among the response profiles elicited by the stimuli array. The 16 bitter chemicals formed a coherent group that was most closely related to HCl, moderately to NaCl, and bore no relationship with glucose. Within the bitter stimuli, six formed a subgroup that was most separated from all nonbitter chemicals: quinine HCl, phenlythiocarbamide, propylthiouracil, caffeine, theophylline, and phenylalanine. Humans describe these stimuli as rather purely bitter. Of the remaining 10 bitter compounds, 4 were on the fringe of the bitter group leading to NaCl: MgCl2, CaCl2, NH4Cl, and arginine. Humans characterize these as bitter-salty. Three were on the fringe leading to HCl: urea, cysteine and vitamin B1. Humans call these bitter-sour. The remaining three (nicotine, histidine, and vitamin B2) occupied the center of the bitter group. Taste quality, inferred from the position of each stimulus in the space, correlated well with human descriptions of the same stimuli, reinforcing the value of the macaque as a neural model for human gustation.

The effect of neonatal capsaicin treatment on gustatory behavior in the albino rat

Small-diameter fibers present in gustatory peripheral nerves have historically been suspected of relaying information about the bitter quality of a taste stimulus. Neonatally injected capsaicin irreversibly destroys a proportion of unmyelinated C- and some Aδ-fibers. Consummatory responses to increasing concentrations of quinine and other chemical solutions following neonatal capsaicin injection were compared to those of untreated and vehicle-injected control Sabra albino rats. Capsaicin-treated rats significantly increased their withdrawal thresholds to noxious, CO 2 laser-generated heat pulses verifying treatment effectiveness. Furthermore, neonatal capsaicin treatment diminished sensitivity to pungent capsaicin solutions in mature rats. However, there were no group differences in quinine intake, suggesting that the full array of unmyelinated fibers associated with taste buds is not essential for the transmission of bitter taste. Capsaicin-treated animals showed a significant reduction in intake of normally highly preferred sodium chloride and sucrose concentrations. These results were probably not due to loss of peripheral unmyelinated afferent fibers per se, but rather to secondary central changes.

Radiation-induced changes in taste acuity in cancer patients

Changes in taste acuity were measured in 27 patients with various forms of cancer who received radiation to the head and neck region. In 9 of these patients (group I) measurements of taste acuity were made more than 1 year after completion of radiation therapy. In the other 18 patients (group II) taste measurements were made before, during and approximately I month after radiation therapy. Taste acuity was measured for four taste qualities (salt, sweet, sour and bitter) by a forced choice-three stimulus drop technique which measured detection and recognition thresholds and by a forced scaling technique which measured taste intensity responsiveness. In group II patients impaired acuity, as indicated by elevated detection and recognition thresholds, was observed approximately 3 weeks after initiation of radiotherapy. The bitter and salt qualities showed the earliest and greatest impairment and the sweet quality the least. Taste intensity responsiveness also was impaired in group II patients. As for thresholds, scaling impairment was most severe for bitter and salt taste qualities. Scaling impairment occurred before changes in either detection or recognition thresholds. Detection and recognition thresholds determined in group I patients also showed salt and bitter qualities were affected more severely than either sweet or sour qualities. Zinc administration to group I patients in an uncontrolled study suggested that zinc therapy may be useful in ameliorating taste impairment in some patients. These results suggest that taste loss may be a factor in the anorexia and weight loss that is observed commonly in patients who have undergone radiation treatment. Correction of this abnormality may be useful in aiding the nutritional status of these patients.