The terms monoglyceride and diglyceride are given to compounds composed of glycerol combined with one or two fatty acids respectively. Since the fatty acid used in these models is stearic acid (C17H35COOH, fully saturated), they may be called glyceryl monostearate and glyceryl distearate, or monostearin and distearin.
They are partial digestion products of triglycerides - neutral fats.
Monoglycerides can exist in 2 forms; one with the fatty acid chain attached to the central section of the glycerol residue (as shown here), and the other with the fatty acid attached to one of the outer sections. The form shown is less vulnerable to breakdown by the enzyme lipase, but the 2 forms can be intercoverted by isomerisation.
As food additives, monoglycerides and diglycerides are often used as emulsifying agents because of their contrasting components. They can interact with other lipids because of their hydrocarbon "tail"
and yet remain soluble in water by virtue of the exposed hydroxyl (-OH) groups
on the glycerol residue.