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Double Sugars or Disaccharides

By Joelle DiTucci

You may not think that mushrooms and beer have much in common, but in reality, they are each made up of two monosaccharide glucose molecules joined together. While they clearly differ in other aspects of their composition, they are both examples of the disaccharide class of carbohydrates. There are four physiologically important types of disaccharides -- sucrose, trehalose, maltose and lactose.

Disaccharides Defined

A disaccharide, or a double sugar, is made up of two monosaccharides, or single sugars that cannot be broken down further -- and these carbohydrates are in the category of "simple carbohydrates." Your body can quickly convert simple carbohydrates into energy, and they are generally found among foods such as fruits, milk and milk products.

Sucrose: The Table Sugar

Sucrose is made up of the two monosaccharides glucose and fructose. The main source of sucrose in your diet is likely white sugar, which is made from processing sugar beet or sugar cane. This source of carbohydrates is also present in every fruit and vegetable as the product of photosynthesis, the process by which they transform energy from the sun into food. Sucrose is the sugar that all other sugars are compared to in ratings of sweetness, given an arbitrary sweetness value of 1.00, or 100 percent. However, fructose, the fruit sugar, and artificial sweeteners are markedly sweeter than sucrose.

Trehalose: The Mushroom Sugar

Trehalose comprises two glucose molecules and is present in yeast and stored instead of starch in mushrooms. Although trehalose is only 45 percent as sweet as sucrose, it is more stable and often used in processed foods like bakery products that require a long shelf life. Its stability also makes it an excellent sweetener for fruit products that would otherwise change color over time. Additionally, trehalose is added to ice creams to depress the freezing point and to frozen foods like meats to create greater water-holding capacity and prevent protein deterioration.

Maltose: The Malt Sugar

Maltose, or "malt sugar," is also made up of two glucose molecules and is the least common disaccharide in nature. It is less sweet than trehalose and only 33 percent as sweet as sucrose. This type of disaccharide is mainly present in germinating cereal or grain, in malt and in a small amount in corn syrup. Beer also involves maltose since beer's components are water, malted barley and hops. Once the barley is "malted," it is especially high in particular starches that can easily convert into maltose.

Lactose: The Milk Sugar

Lactose, well known as the "milk sugar," is broken down by acids and the enzyme lactase into a glucose and a galactose molecule. Lactose is found in milk and milk products and can be detected in trace amounts in the urine of pregnant women. Lactose is one of the more commonly discussed disaccharides because of the prevalence of lactose intolerance, a condition causing certain people to have bloating, diarrhea and gas after consuming milk products. Lactose is least sweet on the list of disaccharides, with a rating of 16 on the sweetness index.

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