By: Richard D. Cummings
Sugar alcohols are a reduced form of a sugar in which the aldehyde or ketone is replaced with an -OH, and sometimes referred to as polyols. Strictly speaking, the definition of an alcohol is an organic compound with one or more hydroxyl groups (-OH) attached to a carbon, so in that sense most sugars are alcohols. But here we are thinking of a specific type of alcohol – sugar alcohol – in which, unlike monosaccharides, the sugar alcohols cannot assume ring forms as they lack aldehydo or keto features and are straight chain polyols. [But some polyols, such as inositol, occur in ring form but are not sugars]. The simplest sugar alcohol is glycerol, a reduced form of glyceraldehyde, the simplest aldo-sugar. A well-known type of sugar alcohol is sorbitol, discussed below. Sugar alcohols are not building blocks for glycans, as only reducing sugars can be metabolized into complex carbohydrates.
Most commercial polyols are made by hydrogenation of the parent sugar, but many sugar alcohols occur naturally (1-3). Four of the most notable and naturally occurring sugar alcohols are mannitol- reduced form of mannose in many plants and seaweed - its name arises from the manna ash tree, Flaxinus ornus, whose sap contains mannose and mannitol (4, 5); erythritol- reduced form of erythrose that occurs naturally in some fruits and fermented foods (6); sorbitol- reduced form of glucose, also termed glucitol, that occurs naturally in many berries and fruits, e.g., apples and blackberries (7); and xylitol- reduced form of xylose that is found in many fruits, vegetables, mushrooms and fibers (8, 9). Two famous sugar alcohols derived from disaccharides include maltitol (4-O-α-glucopyranosyl-D-sorbitol), and lactitol (derived from lactose). Many of these sugar alcohols are sweet and are often used as sweeteners and sugar substitutes, but in regard to some of them there are concerns about their side effects (10). However, sugar alcohols are not quite as sweet as normal sugars, e.g., compared to sucrose sugar alcohols have ~50% of the sweetness, along with a few less calories per gram (glucose is 4 calories per gram whereas sorbitol is 2.6 calories per gram.) Nevertheless, sugar alcohols are being considered for their health benefits in treating diabetes (2), as many of the sugar alcohols cannot be fully digested nor readily absorbed, yet provide sweetening to foods. (Of course, some of these have undesirable side effects and can cause gastrointestinal problems.) Xylitol has been studied because it can cause a significant reduction in the incidence of caries and aid in tooth remineralization (11). Interestingly, mannitol has a history of being used in as a chemical permeation enhancer and a blood-brain barrier permeabilizer (12, 13). Finally, many different sugar alcohols are used in cosmetics where they are generally thought to be safe (14).
References:
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2. Msomi, N. Z., Erukainure, O. L., and Islam, M. S. (2021) Suitability of sugar alcohols as antidiabetic supplements: A review J Food Drug Anal 29, 1-14
3. Benucci, I., Lombardelli, C., and Esti, M. (2024) A comprehensive review on natural sweeteners: impact on sensory properties, food structure, and new frontiers for their application Crit Rev Food Sci Nutr 10.1080/10408398.2024.23932041-19
4. Martinez-Miranda, J. G., Chairez, I., and Duran-Paramo, E. (2022) Mannitol Production by Heterofermentative Lactic Acid Bacteria: a Review Appl Biochem Biotechnol 194, 2762-2795
5. Oddo, E., Saiano, F., Alonzo, G., and Bellini, E. (2002) An investigation of the seasonal pattern of mannitol content in deciduous and evergreen species of the oleaceae growing in northern Sicily Ann Bot 90, 239-243
6. Mazi, T. A., and Stanhope, K. L. (2023) Erythritol: An In-Depth Discussion of Its Potential to Be a Beneficial Dietary Component Nutrients 15,
7. Liang, P., Cao, M., Li, J., Wang, Q., and Dai, Z. (2023) Expanding sugar alcohol industry: Microbial production of sugar alcohols and associated chemocatalytic derivatives Biotechnol Adv 64, 108105
8. Makinen, K. K., and Scheinin, A. (1982) Xylitol and dental caries Annu Rev Nutr 2, 133-150
9. Muller, A., Meng, J., Kuijpers, R., Makela, M. R., and de Vries, R. P. (2024) Exploring the complexity of xylitol production in the fungal cell factory Aspergillus niger Enzyme Microb Technol 183, 110550
10. Makinen, K. K. (2016) Gastrointestinal Disturbances Associated with the Consumption of Sugar Alcohols with Special Consideration of Xylitol: Scientific Review and Instructions for Dentists and Other Health-Care Professionals Int J Dent 2016, 5967907
11. Makinen, K. K. (2010) Sugar alcohols, caries incidence, and remineralization of caries lesions: a literature review Int J Dent 2010, 981072
12. Chu, C., Liu, G., Janowski, M., Bulte, J. W. M., Li, S., Pearl, M. et al. (2018) Real-Time MRI Guidance for Reproducible Hyperosmolar Opening of the Blood-Brain Barrier in Mice Front Neurol 9, 921
13. Chu, C., Jablonska, A., Gao, Y., Lan, X., Lesniak, W. G., Liang, Y. et al. (2022) Hyperosmolar blood-brain barrier opening using intra-arterial injection of hyperosmotic mannitol in mice under real-time MRI guidance Nat Protoc17, 76-94
14. Cherian, P., Bergfeld, W. F., Belsito, D. V., Klaassen, C. D., Liebler, D. C., Marks, J. G., Jr. et al. (2024) Safety Assessment of Mannitol, Sorbitol, and Xylitol as Used in Cosmetics Int J Toxicol 10.1177/1091581824129709710915818241297097