In chemistry, disaccharides are carbohydrates consisting of two monosaccharide units.
The units are joined via a condensation reaction. The bond can be between the 1, 4 or 6 carbon on each component monosaccharide. Even when both component sugars are the same (eg glucose) the different combinations of bond give disaacharides with different chemical and physical properties.
Like monosaccharides, they are crystalline, water soluble, and sweet tasting. A number occur in nature. The most common are sucrose(known as "table" "cane sugar" or "beet sugar"), lactose (milk sugar) and maltose producing during the malting of barley.
Trehalose is present in fungi and insects, and has been successfully produced at an industrial scale by enzymatic treatment of starch as a food ingredient.
Maltose and cellobiose are hydrolysis products of the polysaccharides starch and cellulose respectively.