July 17, 2017 – Food scientists have available to them a range of high-potency sweeteners, but are they being used effectively? Maximizing the potential of these ingredients in foods and beverages is of paramount importance to product development. John Fry, Ph.D., of UK-based Connect Consulting, explained, however, that “rather than emphasize how these sweeteners work, I spend a great deal of time talking about how they don’t work and offering remedies.” As such, Fry helps food scientists use high-potency sweeteners effectively.
To know how to do this, one needs first to understand the physiology of sweetness receptors. Sweet taste receptors in the mouth are complex protein structures crossing the cell walls of sweet-sensing taste cells. The taste cells are contained within taste buds, distributed in the papillae of the tongue. The buds communicate with the exterior saliva via a taste “pore,” within which are tiny projections of the taste cells, called microvilli. The receptor proteins are on the microvilli and comprise four zones:
1) A “Venus fly trap” structure outside the taste cell and in contact with saliva;
2) an external, cysteine-rich protein chain connecting the Venus fly trap to:
3) a transmembrane zone of seven helical strands of protein, terminating in:
4) an intracellular protein thread that interacts with the taste cell contents and triggers a complex series of biochemical reactions, culminating in a nerve signal to the brain that signifies “sweet.”
The primary route for humans to sense sweetness requires two such receptors, T1R2 and T1R3, intertwined. This arrangement affords multiple points where the proteins can interact with the wide variety of substances we experience as sweet. A given high-potency sweetener generally interacts with only one or two such sites on the receptor complex.
There is, in addition, a secondary mechanism by which humans can also detect the sweetness of certain sugars, but this route does not respond to high-potency sweeteners.
Another aspect of so-called “high-intensity” sweeteners, continued Fry, is that they are actually “low-intensity.” Few can achieve even 10% sucrose equivalent (the approximate sweetness intensity of many fruit juices and soft drinks) on their own.
In contrast, sucrose itself can deliver much higher sweetness intensities. “This is why I prefer to refer to them as ‘high-potency,’ rather than high-intensity sweeteners,” Fry averred. Providing an example of a typical response curve, Fry indicated the maximum sweetening effect of Rebaudioside A (Reb A) occurs at about 5-800ppm concentration and exhibits a sweetness level roughly equivalent to an 8% sucrose solution.
All high-potency sweeteners have similarly shaped concentration-response curves that plateau at some relatively low sweetness intensity. Continued Fry, “So, if you double the concentration of a high-potency sweetener, you do not get double the sweetness. In contrast, sucrose has a linear response of sweetness to concentration.”
In addition, different high-potency sweeteners have different time-intensity relationships that can affect their taste profile. Fry noted that combining acesulfame-K (AceK), which exhibits a quick onset and rapid drop-off of sweetness, with slow-onset, more-lingering aspartame, more closely mimics the sweetness profile of sucrose.
This relationship is also “quantitatively synergistic.” That is, the combined sweetness from these two sweeteners exceeds that which would have been predicted based on the properties of each sweetener alone. (See chart “Synergies of Low-intensity/High-potency Sweeteners.”)
“This suggests that we can get synergistic enhancements of sweetness by combining high-potency sweeteners that react at different parts of the receptor structures,” concluded Fry. Nevertheless, while none of the available high-potency sweeteners alone generates sweetness intensities greater than that of about 15% sucrose solution, synergistic effects between different molecules also disappear around this level. Despite the fact that synergism will not furnish true high intensities, the effect is much used to maximize the effectiveness and taste quality of zero-calorie sweeteners in foods and beverages.
As Fry explained, use of high-potency sweeteners at levels approaching their sweetness plateau is a costly waste. In addition, at these elevated concentrations, many sweeteners exhibit intrinsic off-tastes (e.g., a bitter-metallic taste for saccharin). Blends allow product developers to keep individual sweeteners below the thresholds for off-taste development, while achieving quantitative synergies and, thus, minimizing cost.
Fry addressed other factors that can enhance the effectiveness of high-potency sweeteners, particularly in relation to typical issues of slow onset and lingering sweetness. Citing the “non-specific binding” hypothesis, he noted that increasing the osmotic pressure of food and beverage systems “compresses the time-intensity profiles of sweeteners,” thus speeding onset and reducing linger to produce more sucrose-like taste dynamics with almost any high-potency sweetener.
Hydrocolloids, sometimes used to remedy mouthfeel losses when sugars are removed, can also benefit the dynamics of sweetness perception by reducing the impact of non-specific binding. However, “perhaps the ultimate solution to the different taste qualities of high-potency sweeteners is not to use them at all,” suggested Fry. He pointed to a relatively new category of compounds, known as positive allosteric modulators (PAMs), that have no sweetness or flavor of their own but can greatly enhance the sweetness intensity of conventional sweeteners, such as sucrose.
Reduced-sugar formulations could thus be made that still deliver full sweetness and with all the taste qualities of the original sugar.
“How High-potency Sweeteners Work and What to Do about It,” John Fry, Ph.D., Director, Connect Consulting, j.fry@connectco.biz
The summary above is from the “2016 Sweetener Systems Conference Magazine.”
