Oleomargarine differs from butter mainly in the fact that a smaller amount of butyrin is present.    From Wordnik.com.  [An Elementary Study of Chemistry] Reference

This fat is churned up with milk, or a small amount of butter is added, in order to furnish sufficient butyrin to impart the butter flavor.    From Wordnik.com.  [An Elementary Study of Chemistry] Reference

In addition to these three, there are also small amounts of other fats, as butyrin in butter, which give character or individuality to materials.    From Wordnik.com.  [Human Foods and Their Nutritive Value] Reference