Life is sweet…maybe too sweet!

Sugar substitutes are gaining more and more relevance due to the heath problems associated with the consumption of high amounts of sugar. Specifically, excess sugar consumption has been associated with obesity, type II diabetes, cardiovascular disease, certain cancers, and tooth decay. In the United States, it is estimated that the average person consumes more than 126 grams of sugar per day, in Canada around 89 grams per day. This is extremely high, according to the American Heart Association (AHA), someone of normal weight should not be consuming more than 38 and 25 grams per day for men and women respectively.[1] As a frame of reference, a 355 mL can of regular Coke contains 39 grams of sugar!

Figure 1. Sugar and fat consumption in several countries [2]  

Figure 1. Sugar and fat consumption in several countries [2]

 

In this blog entry I don’t want to discuss the relative pros and/or cons of sugar substitutes and sugar, but I thought it would be interesting to take a few of those substitutes and acquire their proton NMR spectrum in our NMReady. In figure 2, we see the stack spectra of several common sugar substitutes that I acquired from a nearby coffee shop. At the bottom I have also included the spectra of sucrose (table sugar) and glucose for comparison.

Figure 2. Stacked 1H NMR spectra of common sweeteners (in D2O)

Figure 2. Stacked 1H NMR spectra of common sweeteners (in D2O)

Table sugar, predictably, is pure sucrose, which is the most widely occurring disaccharide consisting of glucose and fructose. We clearly see that C&H sugar is mainly sucrose and we observe the characteristic doublet around 5.48 ppm corresponding to the glycosidic proton (in red in figure 3). Sucrose is found is all photosynthetic plants and is obtained commercially from sugar beet or sugar cane.

Figure 3. Left, sucrose. Right, glucose (dextrose)

Figure 3. Left, sucrose. Right, glucose (dextrose)

In figure 4, the proton NMR stacked plot of the sweeteners that aren’t based on sucrose. We see that Splenda, Equal and Sweet’N Low show the same peak around 5.3 ppm. If we look at the list of ingredients in each sweetener (figure 5) we see that all they have in common dextrose (glucose) and maltodextrin. These two compounds are added as ‘bulking agents’ and probably make up to 90 or 95 % of the total volume of each packet.[3] Most sugar substitutes are many, many times sweeter than sugar. Therefore, considerably less amount of sweetener is required and its energy contribution (calories) is often insignificant. For instance, aspartame is 200 times sweeter than sugar and sucralose is 600 times sweeter than sugar. Since less amount of sweetener is required most sugar substitutes need the presence of ‘bulking agents’ to increase their volume. Imagine how inconvenient it would be to add 12 milligrams of sucrose to your coffee, if by mistake you add twice that much your coffee would be disgusting! So, if we compare the spectra of those three sweeteners with the spectrum of pure glucose we see that the peak around 5.3 ppm comes from glucose…wait a minute! Isn’t glucose also a ‘sugar’? You are right, glucose is also a sugar or carbohydrate, but there is so little per serving that the calories are negligible, so companies can get away saying that their products are ‘sugar free’.

Figure 4. Proton NMR of Selected sweeteners

Figure 4. Proton NMR of Selected sweeteners

Figure 5. Ingredients in Splenda, Sweet’N Low and Equal

Figure 5. Ingredients in Splenda, Sweet’N Low and Equal

What about the other ingredients? Let discuss each sweetener separately now. Sweet’N Low also contains sodium cyclamate and silicon dioxide (SiO2). Sodium cyclamate (figure 6) is the least potent of the commercially used artificial sweetener (only 30–50 times sweeter than sugar) and for that reason roughly 34% of the packet is sodium cyclamate. In the proton spectrum, we can see sodium cyclamate in the alkyl region between 1.0 and 2.5 ppm in figure 4. In other countries Sweet’N Low contain saccharin as the artificial sweetener, but in Canada the use of saccharin as a food additive is not allowed since the 1970s.[4] I was a little bit surprised when I read silicon dioxide as an ingredient, but it turns out that silicon dioxide is commonly used as an ‘anticaking agent’ to reduce adhesion of particles and maintain the texture.

Figure 6. Several artificial sweeteners

Figure 6. Several artificial sweeteners

The artificial sweetener in Splenda is sucrose (figure 6), which is more or less 1,000 times sweeter than sugar. Unfortunately, in the proton NMR spectrum we cannot see the sucrose present in Splenda due to the small amount present and probably most of the signals are buried under the glucose peaks as well.

The main sweetener in Equal is aspartame, but it also contains acesulfame potassium (figure 6). Both sweeteners are roughly 200 times sweeter than sugar. Acesulfame potassium is blended with aspartame in order to improve the overall taste of the sugar substitute. The combination of these two compounds gives a more sugar-like taste. If you pay close attention to the spectrum of Equal, you will be able to see tiny peaks around 2.0, 2.5 and 7.4 ppm, which correspond to the aspartame and acesulfame potassium present in the sweetener!

Stevia is a sweetener extracted from the leaves of Stevia rebaudiana, which is native to the Amambay Cordillera in Northeast Paraguay.[5] When we think of stevia most of the time we think of a single component forming this natural sweetener, but this is wrong! There are actually several compounds that form stevia and they belong to a family called steviol glycosides. For that reason, most of the time the main ingredient listed for Stevia is “stevia leaf extract”. Some of the steviol glicosides extracted from Stevia rebaudiana are: stevioside, Rebaudioside A, Rebaudioside C, and Dulcoside A. However, stevioside is present in the highest weight percent. If we look at the Stevia spectrum in Figure 3, we can see a small bump around 5.50 ppm, which is very close to the chemical shift of the glycosidic proton of sucrose. If you thought there was sucrose present in stevia you were wrong, but not totally wrong. A glycoside unit is part of stevioside (figure 7) and its glycosidic proton shows at 5.50 ppm. Giving the similar chemical environments of the glycosidic proton of sucrose and glycoside unit in stevioside, it’s not surprising that their chemical shifts are so similar.

Figure 7. Stevioside structure

Figure 7. Stevioside structure

We have seen that’s possible to detect and identify several components in the most commonly used sweeteners using the NMReady. Feel free to contact us if you have any questions about our instruments or if you want to see whether our instrument will be suitable for your chemistry, food science or otherwise!


References
[1] American Heart Association (AHA). “Sugar 101” http://www.heart.org/HEARTORG/HealthyLiving/HealthyEating/Nutrition/Sugar-101_UCM_306024_Article.jsp#.WP4PDlPyvwc (accessed April 19, 2017)
[2] https://www.washingtonpost.com/news/wonk/wp/2015/02/05/where-people-around-the-world-eat-the-most-sugar-and-fat/?utm_term=.88082a1b9ec7
[3] Wikipedia. “Sugar substitute” https://en.wikipedia.org/wiki/Sugar_substitute (accessed April 19, 2017)
[4] Heath Canada. “Saccharin” http://www.hc-sc.gc.ca/fn-an/securit/addit/sweeten-edulcor/saccharin-eng.php (accessed April 19, 2017)
[5} Ceunen, S.; Geuns, J. M. C. J. Nat. Prod. 2013, 76, 1201.