13.2.1.3: Sugar Substitutes
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Sugar Substitutes
Sugar Alcohols (Polyols, Sugar Replacers)
Sugar(s) can provide a lot of calories and contribute to tooth decay. Thus there are many other compounds that are used as alternatives to sugar that have been developed or discovered. We will first consider sugar alcohols and then the alternative sweeteners in subsequent sections.
Below you can see the structure of three common sugar alcohols: xylitol, sorbitol, and mannitol.
Sugar alcohols are also known as "sugar replacers", because some in the public might get confused by the name sugar alcohol. Some might think a sugar alcohol is a sweet alcoholic beverage. Another name for them is nutritive sweeteners, which indicates that they do provide calories. Sugar alcohols are less sweet and provide about half the calories of sucrose as shown below. The name polyols also seems to be increasingly used to describe these compounds. It should be noted that consuming a large amount of sugar alcohols has a laxative effect.
| Sweetener | Relative Sweetness | Energy (kcal/g) |
|---|---|---|
| Lactose | 0.2 | 4* |
| Maltose | 0.4 | 4 |
| Glucose | 0.7 | 4 |
| Sucrose | 1.0 | 4 |
| Fructose | 1.2-1.8 | 4 |
| Erythritol | 0.7 | 0.4 |
| Isomalt | 0.5 | 2.0 |
| Lactitol | 0.4 | 2.0 |
*Differs based on a person’s lactase activity
Sugars are fermented by bacteria on the surfaces of teeth. Acid is a product of this fermentation, which results in decreased pH (higher acidity) that leads to tooth decay and, potentially, cavity formation. The major advantage of sugar alcohols over sugars is that sugar alcohols are not fermented by bacteria on the tooth surface. There is a nice picture of this process in the link below as well as a video explaining the process of tooth decay.
Tagatose
While not a sugar alcohol, tagatose is very similar to sugar alcohols. Tagatose is an isomer of fructose, that provides a small amount of energy (1.5 kcal/g). 80% of tagatose reaches the large intestine, where it is fermented by bacteria, meaning it has a prebiotic-type effect6. Notice the similarity in structure of tagatose to sugar alcohols, the only difference being a ketone instead of an alcohol group.
Alternative Sweeteners
Alternative sweeteners are simply alternatives to sucrose and other mono- and disaccharides that provide sweetness. Many have been developed to provide zero-calorie or low calorie sweetening for foods and drinks.
Because many of these provide little to no calories, these sweeteners are also referred to as non-nutritive sweeteners (FDA is using high-intensity sweeteners to describe these products10). Aside from tagatose (described in the sugar alcohol section), all sweeteners on the list below meet this criteria. Aspartame does provide calories, but because it is far sweeter than sugar, the small amount used does not contribute meaningful calories to a person's diet. Until the FDA allowed the use of Stevia, this collection of sweeteners were commonly referred to as artificial sweeteners because they were synthetically or artificially produced. However, with Stevia, the descriptor artificial can no longer be used to describe these sweeteners. More recently, Luo Han Guo Fruit extracts have also been allowed to be used as another high-intensity sweetener that is not synthesized or artificially produced. The table in the link below summarizes the characteristics of the FDA approved high-intensity sweeteners.
Saccharin
Saccharin is the oldest of the artificial sweeteners. However, it should be noted that both sweet and bitter taste receptors are triggered by it, so for some people it has an aftertaste that is off-putting11,12. It has been found that this bitter or metallic flavor can sometimes be masked by mixing alternative sweeteners13. It is a heat-stable alternative sweetener.
Aspartame
Aspartame is made up of 2 amino acids (phenylalanine and aspartate) and a methyl (\(\ce{-CH3}\)) group. The compound is broken down during digestion into the individual amino acids. This is why it provides 4 kcal/g, just like protein11. However, it is still considered noncaloric because it is so sweet that we use very small amounts that don’t provide any meaningful caloric value. Because it can be broken down to phenylalanine, products that contain aspartame contain the following message: "Phenylketonurics: Contains phenylalanine." Phenylketonuria (PKU) will be covered in greater detail in the protein section. When heated, aspartame breaks down and loses its sweet flavor7.
Neotame
Neotame is like aspartame version 2.0. Neotame is structurally identical to aspartame except that it contains an additional side group (bottom of the figure below, which is flipped backwards to make it easier to compare their structures). While this looks like a minor difference, it has profound effects on the properties of neotame. Neotame is much sweeter than aspartame and is heat-stable. It can still be broken down to phenylalanine, but such small amounts are used that it is not a concern for those with PKU7,11.
Advantame
The newest, sweetest alternative sweetener approved by the FDA in 2014 is advantame. It is heat-stable and does not have a trade name yet10. Notice it also has a similar structure to aspartame and neotame. Like Neotame, it can be broken down to phenylalanine, but such small amounts are used that it is not a concern for those with PKU. However, it has a much higher acceptable daily intake than Neotame11, meaning there is less concern about adverse effects from consuming too much.
Acesulfame-Potassium (K)
Acesulfame-potassium is not digested or absorbed, therefore it provides no energy or potassium to the body7. It is a heat-stable alternative sweetener.
Sucralose
Sucralose is structurally identical to sucrose except that 3 of the hydroxyl groups are replaced by chlorine molecules. This small change causes sucralose to not be digested and as such is excreted in feces7,11. It is a heat-stable alternative sweetener.
Stevia
Stevia is derived from a South American shrub, with the leaves being the sweet part. The components responsible for this sweet taste are a group of compounds known as steviol glycosides. The structure of steviol is shown below.
The term glycoside means that there are sugar molecules bonded to steviol. The two predominant steviol glycosides are stevioside and rebaudioside A. The structure of these two steviol glycosides are very similar21. The structure of stevioside is shown below as an example.
The common name for a sweetener containing primarily rebaudioside A is rebiana. Stevia sweeteners are heat-stable and have been marketed as a natural alternative sweeteners, something that has been challenged by lawsuits as described in the following link.
Stevia is a heat-stable alternative sweetener.
Luo Han Guo Fruit Extracts
Luo Han Guo (aka Siraitia grosvenrii Swingle, monk) fruit extracts are a newer, natural heat-stable alternative sweetener option derived from a native Chinese fruit. These extracts are sweet because of the mogrosides that they contain10. The structure of a mogroside is shown below.
We must be careful when replacing sugar (sucrose) with these sugar substitutes in recipes. Even though the sweetness comparison levels may be similar (or less), it is generally not possible to do straight 1-for-1 substitution. Sugar (sucrose) plays many roles in a recipe:
- It is a bulking agent.
- It absorbs moisture.
- It is a tenderizer.
- It adds moisture and extends shelf life.
- It adds color (caramelization).
Sugar substitutes may not work in a recipe in the same way.
More information on sugar substitutes and their relative sweetness can be found online.