Corn syrup is a food syrup, which is made from the starch of maize and composed mainly of glucose. Corn syrup is used in foods to soften texture, add volume, prevent crystallization of sugar, and enhance flavor. Corn syrup is distinct from high-fructose corn syrup, created when corn syrup undergoes enzymatic processing that produces a sweeter compound containing higher levels of fructose.
The more general term glucose syrup is often used synonymously with corn syrup, since glucose syrup is most commonly made from corn starch. Technically, glucose syrup is any liquid starch hydrolysate of mono-, di-, and higher-saccharides and can be made from any source of starch; wheat, rice and potatoes are the most common sources.
Glucose or dextrose syrup is produced from number 2 yellow dent corn. When wet milled, about 2.3 litres of corn are required to yield an average of 947g of starch, to produce 1 kg of glucose or dextrose syrup. A bushel (25 kg) of corn will yield an average of 31.5 pounds (14.3 kg) of starch, which in turn will yield about 33.3 pounds (15.1 kg) of syrup. Thus, it takes about 2,300 litres of corn to produce a tonne of glucose syrup, or 60 bushels (1524 kg) of corn to produce one short ton.
Formerly, corn syrup was produced by combining corn starch with dilute hydrochloric acid, and then heating the mixture under pressure. Currently, corn syrup is mainly produced by first adding the enzyme α-amylase to a mixture of corn starch and water. α-amylase is secreted by various species of the bacterium Bacillus; the enzyme is isolated from the liquid in which the bacteria are grown. The enzyme breaks the starch into oligosaccharides, which are then broken into glucose molecules by adding the enzyme glucoamylase, known also as "γ-amylase". Glucoamylase is secreted by various species of the fungus Aspergillus; the enzyme is isolated from the liquid in which the fungus is grown. The glucose can then be transformed into fructose by passing the glucose through a column that is loaded with the enzyme D-xylose isomerase, an enzyme that is isolated from the growth medium of any of several bacteria.
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