Study of some factors affecting intensity/time characteristics of sweetness

A Pharmacological perspective on the temporal properties of sweeteners

Several non-caloric sweeteners exhibit a delay in sweetness onset and a sweetness linger after sampling. These temporal properties are thought to be the result of non-specific interactions with cell membranes and proteins in the oral cavity. Data and analysis presented in this report also support the potential involvement of receptor affinity and binding kinetics to this phenomenon. In general, affected sweeteners exhibit distinctly higher binding affinity compared to carbohydrate sweeteners, which do not have temporal issues. In addition, binding kinetic simulations illustrate much slower receptor binding association and dissociation kinetics for a set of non-caloric sweeteners presenting temporal issues, in comparison to carbohydrate sweeteners. So, the higher affinity of some non-caloric sweeteners, dictating lower use levels, and affecting binding kinetics, could contribute to their delay and linger in sweetness perception. Simple pharmacology principles could explain, at least in part, some of the temporal issues of sweeteners.

Sensory properties of Australian bunya nuts

Abstract

Bunya nuts are the seeds of Araucaria bidwillii, a conifer native to South‐East Queensland, Australia. They are one of the 19 species of Araucaria family found around the world, with the nuts from South America being the most commonly consumed. They are traditionally eaten boiled or roasted. This study aims to profile the sensory properties of bunya nuts with chestnut as a comparator. Since chestnuts do not come from a conifer tree, it is expected that there will be differences. Different methods of preparation are also expected to change the sensory attributes. Representative samples were collected from a variety of locations in South‐East Queensland, prepared and presented to a panel of 14 experienced tasters applying conventional sensory descriptive profiling.

Practical Application

There is an increase demand for local, sustainable, and natural foods. Bunya nuts are native to Australia and are part of the Araucaria family, which includes 19 species that can be found around the world. To the best of our knowledge there is no study characterizing Araucaria nuts in terms of sensory attributes. This study builds a lexicon for bunya nuts and compares to chestnuts. It also shows how different preparation methods affect its sensory attributes, as well as possible future uses in product development. The outcomes might provide information to support studies on Araucaria nuts in other countries.

Individual differences in perceived bitterness predict liking of sweeteners

Although recent molecular studies suggest that only one receptor and one signaling pathway are involved in the perception of sweetness, this seems to contradict everyday experience that people not only have different likes and dislikes of certain sweeteners but also perceive the sweeteners differently. One possible explanation is that variation in liking of sweeteners is due, in part, to variation across individuals in sensitivity to nonsweet tastes, such as bitterness, which are transduced by a variety of receptors. Fifty individuals were asked to rate intensities of several taste attributes of 10 sweeteners and to give hedonic assessments of each sweetener. Additionally, their sensitivity to 6-n-propyl-3-thiouracil (PROP) was determined. Results indicated that when matched for sweetness, the perception of bitterness and the sweetener compound were the 2 largest factors contributing to overall liking of a sweetener. Sensitivity to PROP did not contribute significantly to the model.

Measurement of the kinetics of protein unfolding in viscous systems and implications for protein stability in freeze-drying

PURPOSE

The aim of the study is to determine the degree of coupling between protein unfolding rate and system viscosity at low temperatures in systems relevant to freeze-drying.

METHODS

The cold denaturation of both phosphoglycerate kinase (PGK) and beta-lactoglobulin were chosen as models for the protein unfolding kinetics study. The system viscosity was enhanced by adding stabilizers (such as sucrose), and denaturant (guanidine hydrochloride or urea) was added to balance the stabilizing effect of sucrose to maintain the cold denaturation temperature roughly constant. The protein unfolding kinetics were studied by both temperature-controlled tryptophan emission fluorescence spectroscopy and isothermal high-sensitivity modulated differential scanning calorimetry (MDSC) (Tzero). Viscometers were used to determine the system viscosity. To verify the predictions of structure based on protein unfolding dynamics, protein formulations were freeze-dried above the glass transition temperatures, and the protein structures in dry products were determined by fluorescence spectroscopy of reconstituted solids by extrapolation of the solution data to the time of reconstitution.

RESULTS

Empirical equations describing the effect of sucrose and denaturant (urea and guanidine hydrochloride) on protein cold denaturation were developed based on DSC observations [X. C. Tang and M. J. Pikal. The Effects of Stabilizers and Denaturants on the Cold Denaturation Temperature of Proteins and Implications for Freeze-Drying. Pharm. Res. Submitted (2004)]. It was found that protein cold denaturation temperature can be maintained constant in system of increasing sucrose concentration by simultaneous addition of denaturants (urea and guanidine hydrochloride) using the empirical equations as a guide. System viscosities were found to increase dramatically with increasing sucrose concentration and decreasing temperature. The rate constants of protein unfolding (or the half-life of unfolding) below the cold denaturation temperature were determined by fitting the time dependence of either fluorescence spectroscopy peak position shift or DSC heat capacity increase to a first-order reversible kinetic model. The half-life of unfolding did slow considerably as system viscosity increased. The half-life of PGK unfolding, which was only 3.5 min in dilute buffer solution at -10 degrees C, was found to be about 200 min in 37% sucrose at the same temperature. Kinetics of protein unfolding are identical as measured by tryptophan fluorescence emission spectroscopy and by high-sensitivity modulated DSC. The coupling between protein unfolding kinetics and system viscosity for both proteins was significant with a stronger coupling with PGK than with beta-lactoglobulin. The half-lives of PGK and beta-lactoglobulin unfolding are estimated to be 5.5 x 10(11) and 2.2 years, respectively, even when they are freeze-dried in sucrose formulations 20 degrees C above Tg'. Thus, freeze-drying below Tg' should not be necessary to preserve the native conformation. In support of this conclusion, native PGK was obtained after the freeze-drying of PGK at a temperature more than 60 degrees C above the system Tg' in a thermodynamically unstable system during freeze-drying.

CONCLUSIONS

Protein unfolding kinetics is highly coupled with system viscosity in high viscosity systems, and the coupling coefficients are protein dependent. Protein unfolding is very slow on the time scale of freeze-drying, even when the system is freeze-dried well above Tg'. Thus, it is not always necessary to freeze-dry protein formulations at temperature below Tg' to avoid protein unfolding. That is, protein formulations could be freeze-dried at product temperature far above the Tg', thereby allowing much shorter freeze-drying cycle times, with dry cake structure being maintained by the simultaneous use of a bulking agent and a disaccharide stabilizer.

Release and Transport of Flavors In Vivo: Physicochemical, Physiological, and Perceptual Considerations

For flavor perception to occur, the chemicals responsible for flavor perception must be released from the food matrix and transported to the flavor receptors in the mouth and nose. The overall process is governed by the properties of the flavor compounds, the nature of the food matrix and the physiological conditions of the mouth, nose and throat during consumption of the food. These factors combine to determine the concentrations and rate at which the flavor chemicals reach the receptors, thus creating the characteristic flavor profile of a food. Physicochemical factors like partitioning, interfacial mass transport and diffusion are the typical mechanisms governing flavor release. Although the theory behind these factors is well understood, applying them to the situation in-mouth during eating is difficult. This is because key parameters like surface area and flavor concentrations in the gas and liquid phases change rapidly with time as a result of the physiological processes occurring during eating. Furthermore, individuals vary in their rate of breathing, swallowing and salivation, which affects the transport of flavors from the saliva phase to receptors on the tongue and in the nose. This review covers all aspects of flavor release from food matrices and the subsequent delivery of flavor to the olfactory and gustatory receptors.

Identification and characterization of human fructose or glucose taste variants with hypogeusia for one monosaccharide but not for the other

Human psychophysical functions for sweetness are similar for sucrose and fructose, but different for glucose, and suggest different mechanisms for fructose and glucose. Drosophila behavioral and electrophysiological data are similar to the human data and indicate separate receptor cell mechanisms for the monosaccharides. Moreover, fructose 'nontasters' (NTs) and glucose NTs have been identified in two Drosophila species. Identification of human NTs would confirm separate mechanisms and could lead to identification of proteins in human sweet taste by molecular genetic techniques. To identify human NTs, we first obtained responses for sucrose, fructose and glucose from 20 subjects. They tasted seven concentrations of each sugar (2-128 mM), paired with water, and indicated the sweeter of each pair. Functions for recognition indices (RIs) (proportion of subjects recognizing the sugar as sweeter) were similar for sucrose and fructose and different for glucose; this result agrees with the previous studies and supports different mechanisms for the monosaccharides. At 128 mM, RIs for all three sugars were 1.0; this result is consistent with the monogeusia reported by Breslin et al. for concentrations higher than those tested here. Eleven rising-phase concentrations (10-35 mM fructose, 10-90 mM glucose) then were tested on 32 subjects. A statistically significant interaction indicated different regression slopes and supported different monosaccharide mechanisms. From these data, positive identification values (PIDs) (lowest concentration at which the sugar always was judged sweeter than the water) were determined for each subject. The fructose log(PID) and glucose log(PID) data were not well correlated; thus separate mechanisms were supported further. Next, NT traits were defined by log(PID)s > or = 2 SD above the mean for one sugar, while the PID for the other remained within 1 SD of the population mean log(PID). Ninety-two subjects were screened to identify 12 glucose NTs and four fructose NTs. Two glucose NTs and three average subjects were tested in six additional sessions. The NTs showed an experience-induced change: there was a statistically significant reduction of glucose PIDs, but not of fructose PIDs. No change occurred in PIDs of the average subjects for either sugar.