Corn syrup is a syrup, made using corn starch as a feedstock, and composed mainly of glucose. A series of two enzymatic reactions is used to convert the corn starch to corn syrup. Its major use is in commercially prepared foods as a thickener and for its moisture-retaining (humectant) properties which keep foods moist and helps to maintain freshness. It is widely used in products labeled "all natural" in the United States. Because of its mild sweetness, corn syrup may be used in conjunction with high intensity sweeteners.
The more general term glucose syrup is often used synonymously with corn syrup, since glucose syrup is most commonly made from corn starch. Technically though, glucose syrup is any liquid starch hydrolysate of mono, di, and higher saccharides and can be made from starch from any source, of which wheat, rice and potatoes are the most common sources.
High fructose corn syrup (HFCS) is a variant in which other enzymes are used to convert some of the glucose into fructose. The resulting syrup is sweeter and more soluble.
Until recently, corn syrup sold into the retail market, e.g. in supermarkets, was a high glucose version. HFCS is also appearing in retail products. The largest by market in the United States is Karo Syrup, a fructose/glucose syrup.
Some foods that commonly contain corn syrup are: baking and cooking ingredients, beverages, soft drinks, breads, breakfast cereals, breakfast pastries, candy bars, condiments, cookies and cakes, cough syrups, crackers, dairy, drink mixers, frozen foods, gummi bears, ice creams, infant formula, jams and jellies, syrups, meats, pastries, salad dressings, sauces, snacks, soda, and microwavable soup.