Sugar does more than just add calories - it adds important sensory properties to beverages. That is why full-sugar products remain popular despite the caloric impact they have. Sugar adds body, mouthfeel or weight to a beverage and makes the flavour more pleasant. It also has a positive effect on reducing the aftertaste sometimes associated with the high-intensity sweeteners.
Formulators have tried to work around these problems with changes in flavours and different combinations of high-intensity sweeteners. And yet there still has been something missing in the consumer's sensory experience. By using hydrocolloids, or gums, a beverage can be formulated that comes closer to the ideal represented by full-sugar products. Gums can enhance the mouthfeel, make the flavour more pleasant and reduce the aftertaste. The use levels are very low and the idea is to not make the product thick and heavy, but to make it more similar to the full-sugar product - only with far fewer calories.
Test results with hydrocolloids
CP Kelco has researched the effect of different hydrocolloids using a model beverage. The same flavour and acid levels were used in all beverages and a control was sweetened with sucrose. Eighteen drinks were formulated and tested with detailed sensory and physical analysis. The result shows the nuances of how gums and high-intensity sweeteners can work together to come closer to full-sugar-drink properties.
A total of 37 sensory attributes were evaluated by 12 panelists. These covered the broad categories of aroma, flavour, texture (mouthfeel), and aftertaste.
We tested a broad range of gums - pectin, cellulose gum, xanthan gum, gellan and more. Prior to the study the popular opinion was that gums could enhance beverages in one of two ways. The most obvious one was that the added viscosity would duplicate the viscosity enhancement found when sugar is added to water. A 12 percent solution of sucrose is approximately 35 percent more viscous than pure water. The other theory regarding gum function in beverages was less defined. It was based on the observation that for some fruit beverages the addition of pectin had little effect on the measured viscosity but, nevertheless, the body of the beverage was enhanced. Our aim in selecting gums was to look at many different gums with a broad range of viscosity values to try to understand what effect they had.
In order to understand more about the beverages, we also collected instrumental data. Viscosity was measured at a wide range of shear rates, and the density of the specific gravity or density was accurately determined. When these data were combined with the extensive sensory data set using statistical analysis, a clear picture of how gums affect beverages emerged.
Beginning with the aroma profile for three of the samples, one can reach a useful conclusion. For nearly every aroma parameter, the difference between sugar and artificial sweetener was not suppression of aroma but the fact that the profile was changed. In fact, most of the aroma attributes scored lower with sugar than without.
The choice of the gum used had a substantial effect on orange aroma. The positive control with sugar did not have the most aroma, but matching that aroma will make the product seem more like sugar to the consumer. Notice that some gum choices can actually enhance the orange aroma but others suppress it. Again, the ideal choice is not the maximum orange aroma but the one most like sugar. In this case that would be the Cekol 300 cellulose gum at 4 mPa*s viscosity or the Genu Vis pectin at 0.2 percent.
Aroma, of course, is not the only sensory characteristic influenced by gums. In this study, the flavour profile was changed when we used Keltrol xanthan gum or Kelcogel HAB gellan gum. Each of these gum choices made the flavour profile more like the sugar beverage.
Aroma and flavour are key factors in determining acceptability, but for many consumers the problem with artificially sweetened beverages lies with the aftertaste. The sugar beverage had a substantially reduced aftertaste profile. It is also clear that the addition of Keltrol SFT xanthan gum reduced the aftertaste and made the artificially sweetened product more like sugar.
The influence of gum addition on aroma, flavour and aftertaste is clear. Equally significant is the effect these ingredients have on the body or mouthfeel. A common misconception about adding gums to beverages is that the product will become "slimy" or have some other negative effect. Our work focused on the characteristics that provide body, as well as understanding other mouthfeel attribute changes.
Hydrocolloids and mouthfeel
There is a relationship between thick mouthfeel and the instrumental measures of viscosity and density. When these two instrumental measures are combined, a good prediction of the sensory property results. This shows that perceived thickness or body can come from two different physical characteristics provided by gums. The first and most obvious is the increase in viscosity; "thick mouthfeel" can obviously come from making the product higher in viscosity. Moreover, "thick mouthfeel" can also come from increasing the density of the beverage. Using a fairly high level of a low-viscosity gum such as pectin boosts the density of the beverage while leaving the viscosity relatively unchanged. The mouth senses the added density or weight, and the sensation of thickness results even with little actual viscosity change.
This finding is significant. When formulating a beverage, the food scientist has more than one strategy available to attain a given mouthfeel. Using either the viscosity or density approach can lead to enhanced body. Combined with the effect of different gums on aroma, flavour and aftertaste, there are many possibilities.
One final mouthfeel parameter remains to be addressed: sliminess. This is a difficult-to-define term that has been described variously as "thick and difficult to swallow" and "like egg whites." Whatever the definition, many food scientists unfortunately associate this somewhat negative term with the use of any gum in beverages. Our panel of nonfood scientists did not use this word but instead used the term "syrupy mouthfeel" to describe the sensation. Our study has shown a clear picture of what can enhance or diminish the sensory property called syrupy mouthfeel.
Two measurements predict the syrupy mouthfeel property very well. One is the viscosity at approximately 100 s-1 shear rate, and the other is the pseudoplasticity index from the power law relationship of shear stress and shear strain (shear stress=K * shear rate^n). The value of n is equal to 1 for Newtonian materials and becomes progressively lower as the pseudoplasticity of the sample increases.
Simply put, a syrupy product is one that has a fairly high viscosity in the mouth and is not very pseudoplastic. Knowing the cause of this characteristic allows it to be controlled. It is not something to avoid all of the time. For example, a nectar type of beverage could be enhanced by a higher degree of syrupy mouthfeel.
In conclusion, gums can have a profound effect on reduced-sugar beverages. The food scientist looking to enhance and improve products like this has many choices. One should consider more than just the viscosity that the gum contributes. The effects on aroma, flavour and the critical aftertaste attributes are equally important. Moreover, it is now much more clear how different gums provide body in different ways. This new knowledge will let formulators make important improvements as they introduce more reduced-sugar drinks.
Ross Clark is Distinguished Research Fellow at CP Kelco.