Carbohydrates are perhaps one of the largest family of compounds in organic chemistry. As the name implies, carbohydrates are simply hydrated carbon molecules with complex structure. Of course, the most common carbohydrate is that of sucrose, or table sugar, but there are literally thousands of molecules in this branch of chemistry.
In green coffee, carbohydrates represent a significant portion of its structural matter making up approximately 50% of coffee's total dry basis. The composition is made up of a complex mixture of both soluble and insoluble matter including mono, oligo and polysaccharides.
In the case of Arabica, there is almost double the concentration of sugars than that of Robusta. Table 1 below outlines the basic differences in carbohydrates within each species.
Table 1: Carbohydrate Content in Green Coffee (% dry base):
As expected, the sucrose concentration varies with degree of ripening and should always be considered when making analytic comparisons. This is particularly true for defective beans where differences between sucrose concentration can vary significantly. See Table 2 below. 
Carbohydrate
Table 2: Monosaccharide Content in Green Coffee:
During roasting, sugars play a critical role with many of them participating in the Maillard reaction – a reaction, that is of prime importance to cooking/roasting. During coffee roasting a vast portion of these molecules decompose to form water, carbon dioxide (CO2), aroma, brown color, as well as smaller organic acids.