The Chemical Conversion of Sugars to Polyols
Sugar alcohols, also known as polyols, get their name from their unique chemical structure, which combines traits of both sugar molecules and alcohol molecules. Despite the name, they do not contain ethanol and will not cause intoxication. The core process for creating sugar alcohols is the chemical reduction of the aldehyde or ketone group found in a sugar molecule into a hydroxyl group. This process occurs in nature, but the majority of sugar alcohols used commercially are produced on an industrial scale to meet demand.
Industrial Production Methods
Commercial production of sugar alcohols primarily uses two methods: catalytic hydrogenation and fermentation.
- Catalytic Hydrogenation: In this process, a solution of a specific sugar (like glucose) is exposed to hydrogen gas at high temperature and pressure in the presence of a metal catalyst, often nickel. This adds hydrogen atoms to the sugar molecule, converting the aldehyde group into a hydroxyl group. For example, the catalytic hydrogenation of glucose produces sorbitol, and xylose yields xylitol.
- Fermentation: Certain sugar alcohols, such as erythritol, are produced through fermentation using specific bacteria or yeast. In this method, microorganisms consume a sugar source, like glucose or sucrose, and metabolize it into the desired polyol. This process is a biological conversion rather than a purely chemical one.
Natural Sources of Sugar Alcohols
While the bulk of sugar alcohols are manufactured, small amounts are found naturally in many plant-based foods. For example:
- Sorbitol: Found in fruits such as apples, pears, peaches, and berries.
- Mannitol: Occurs in pineapple, olives, asparagus, and carrots.
- Xylitol: Found in small quantities in fruits, vegetables, corncobs, and some cereals.
- Erythritol: Present in small amounts in some fruits like melons, as well as in fermented foods like soy sauce and wine.
Common Types of Sugar Alcohols and Their Origins
Different sugar alcohols are derived from various starting materials, leading to unique properties and uses. Their production often starts with common plant carbohydrates such as cornstarch, sugar cane, or even milk products.
- Xylitol: Often called "wood sugar," commercial xylitol is most often derived from xylose, which is sourced from corncobs or hardwood materials like birch.
- Erythritol: This polyol is created by fermenting glucose, typically derived from cornstarch, with a yeast. It is particularly popular because it is mostly excreted in urine rather than fermented in the gut, reducing potential digestive upset.
- Sorbitol: Commercially produced by the hydrogenation of glucose, which is typically extracted from corn syrup or other starches.
- Maltitol: Formed by the hydrogenation of maltose, a disaccharide derived from corn, potato, or wheat starch.
- Isomalt: Produced by chemically converting sucrose (table sugar) into isomaltulose and then hydrogenating it.
- Lactitol: Created by hydrogenating lactose, or milk sugar, which is sourced from whey.
How Sugar Alcohols Differ from Regular Sugar
Sugar alcohols differ from regular sugar in several key ways, largely due to their unique chemical structure and how the body metabolizes them.
- Lower Calorie Count: With their hydroxyl groups, sugar alcohols are not completely absorbed by the body. This incomplete absorption means they provide fewer calories per gram than regular sugar (4 kcal/g). For example, erythritol has nearly zero calories, while xylitol and sorbitol offer about 2.4 kcal/g and 2.6 kcal/g, respectively.
- Reduced Glycemic Impact: Due to their slow and incomplete absorption in the small intestine, sugar alcohols do not cause a sharp spike in blood glucose levels. This makes them a useful alternative for people with diabetes or those managing blood sugar.
- Dental Health: Oral bacteria cannot metabolize sugar alcohols, so they do not produce the acid that causes tooth decay. Xylitol, in particular, has been shown to actively inhibit the growth of cavity-causing bacteria.
- Digestive Effects: Because they are not fully digested, consuming large amounts of sugar alcohols can lead to gastrointestinal issues. They ferment in the large intestine, producing gas, bloating, and a potential laxative effect, especially for those with sensitive digestive systems.
Comparison of Common Sugar Alcohols
This table provides a quick overview of several widely used sugar alcohols, highlighting their origin and relative sweetness compared to sucrose.
| Name | Origin | Relative Sweetness (% of Sucrose) | Calories (kcal/g) | Common Uses |
|---|---|---|---|---|
| Erythritol | Fermented cornstarch or glucose | 60–80% | ~0.2 | Baked goods, beverages, keto products |
| Xylitol | Corncobs, birch wood, or other plant sources | ~100% | ~2.4 | Chewing gum, mints, toothpaste |
| Sorbitol | Hydrogenated glucose (corn syrup) | 50–70% | ~2.6 | Sugar-free candies, baked goods |
| Maltitol | Hydrogenated maltose (cornstarch) | ~90% | ~2.1 | Sugar-free chocolate, hard candies |
| Isomalt | Hydrogenated sucrose (beet sugar) | 45–65% | ~2.0 | Hard candies, toffee |
| Lactitol | Hydrogenated lactose (whey) | 30–40% | ~2.0 | Ice cream, chocolate, baked goods |
Benefits and Drawbacks of Sugar Alcohols
Sugar alcohols offer several advantages as low-calorie sweeteners, but consumers should also be aware of their potential downsides.
Benefits:
- Weight Management: Their lower calorie count can support reduced caloric intake for those aiming to lose or manage weight.
- Diabetes-Friendly: The slower absorption rate and lower glycemic impact make them a suitable sweetener for managing blood sugar levels.
- Cavity Prevention: They do not cause tooth decay and are often included in oral hygiene products like toothpaste and mouthwash.
- Cooling Sensation: Some polyols, like erythritol and xylitol, provide a desirable cooling effect in the mouth, often utilized in chewing gum and mints.
Drawbacks:
- Gastrointestinal Distress: For some individuals, especially those with sensitive digestive systems or IBS, overconsumption can cause gas, bloating, and diarrhea.
- Incomplete Sweetness Profile: Not all sugar alcohols match the taste and sweetness of regular sugar, and some have a noticeable aftertaste.
- Toxicity to Pets: Xylitol, while safe for humans, is highly toxic to dogs and can cause a dangerous drop in blood sugar and liver failure.
- Emerging Health Concerns: Recent observational studies have linked high circulating levels of erythritol and xylitol to an increased risk of cardiovascular events, particularly for those with pre-existing risk factors. More research is needed to confirm these findings and understand the long-term impact.
Conclusion
In essence, what is sugar alcohol made of comes down to the chemical modification of simple sugars and starches. Through processes like catalytic hydrogenation and fermentation, a variety of polyols like xylitol, erythritol, and sorbitol are produced for industrial use. While they occur naturally in small amounts, the bulk of the supply comes from manufacturing. These low-calorie sweeteners offer benefits for dental health and blood sugar management but can cause digestive upset if consumed in excess. Consumers should understand the specific type of polyol they are consuming and consider potential health implications, especially in high amounts. Overall, sugar alcohols remain a useful tool for reducing sugar intake when used in moderation as part of a balanced diet.
