To convert one isomer into another: molecules with the same chemical formula but different structural arrangements. In food chemistry, isomerisation is commercially important in the production of high-fructose corn syrup, where the enzyme glucose isomerase converts glucose into the sweeter fructose. Heat processing can also isomerise compounds: for example, the trans fats formed during partial hydrogenation of oils are geometric isomers of the original cis fatty acids, with different physical and health properties. Carotenoids and certain vitamins likewise exist as isomers with differing biological activity. Controlling isomerisation during processing helps manufacturers achieve desired sweetness, texture, colour, and nutritional value.