Galactose is a monosaccharide. It contains six carbons and an aldehyde group and is classified as an aldose and a hexose. Both the D and L forms are found in nature. The structure depicted at the right is the D isomer. D-Galactose is commonly found in milk as part of the disaccharide lactose. L-Galactose is present in polysaccharides, such as agar.