Alas, poor Twinkies! We knew them.
From How Twinkies Work:
Monoglycerides and diglycerides, which replace eggs in the Twinkie recipe, are chemicals that act as emulsifiers. They stabilize the cake batter, enhance flavor and extend shelf life [source: Ettlinger]. A very small amount of egg is used to leaven the cake. Polysorbate 60 serves a similar function to the glycerides, keeping the cream filling creamy without the use of real fat. Hydrogenated shortening replaces butter, giving the cake some of its texture and flavor and prolonging shelf life.
Taste tests by flavor experts have revealed that artificial butter flavoring is used in the cake and artificial vanilla flavoring goes into the cream filling [source: Ettlinger]. Both flavorings are chemicals derived from petroleum.
Despite the Twinkie’s reputation, only one ingredient is an actual preservative: sorbic acid. Other ingredients have preservative functions, but sorbic acid has one primary purpose — it stops the formation of mold [source: Ettlinger].
Finally, cellulose gum replaces fat in the filling. This ingredient can absorb 15 to 20 times its own weight in water. It keeps the filling smooth and creamy.