High Fructose Corn Syrup (HFCS) is a liquid sweetener produced from corn. The process transforms corn starch into a mixture of the simple sugars glucose and fructose, making it a common ingredient in many processed foods and beverages. Manufacturing advantages, including solubility and cost-effectiveness, have made it a widely used alternative to traditional sugar. HFCS production involves several distinct stages, starting with the physical preparation of the corn kernel and progressing through multiple enzymatic conversions.
Extracting Starch from Corn
The initial step in creating HFCS is isolating pure starch from the raw corn kernel. This process, known as wet milling, begins with steeping the corn kernels in warm water containing sulfur dioxide for 30 to 40 hours. Steeping softens the kernels and loosens the starch-protein bonds, allowing for easier separation of the components. The softened kernels are then coarsely ground, which liberates the germ containing the corn oil.
The remaining mixture, containing fiber, protein, and starch, is finely ground and passed through screens to separate the fiber. Next, the protein, called gluten, is separated from the starch through countercurrent washing or centrifugation, utilizing the difference in density. The final product is a purified, concentrated starch slurry, which is the starting material for the chemical conversions that follow.
Enzymatic Breakdown to Glucose
With a clean starch slurry prepared, the manufacturing process converts the complex starch molecules into simple glucose sugar. This conversion is a two-stage enzymatic hydrolysis process, beginning with liquefaction. In liquefaction, the starch slurry is heated and treated with the enzyme alpha-amylase, which breaks the long chains of starch into shorter sugar chains known as dextrins or oligosaccharides.
The resulting liquid is then cooled, and a second enzyme, glucoamylase, is introduced in the saccharification stage. Glucoamylase acts on the dextrins, clipping off individual glucose molecules from the ends. This reaction continues until the solution is predominantly composed of glucose, resulting in a glucose syrup that is nearly 95% pure glucose, also known as dextrose.
The Isomerization Process
The defining step in HFCS production is isomerization, which converts a portion of the glucose into the sweeter sugar, fructose. This stage uses the enzyme glucose isomerase, sometimes referred to as xylose isomerase, to chemically rearrange the molecular structure of the glucose. Isomerization transforms a molecule into an isomer, meaning it has the same chemical formula but a different arrangement of atoms.
The enzyme converts the six-carbon ring structure of glucose into the five-carbon ring structure of fructose. The glucose syrup is passed over columns containing immobilized glucose isomerase, which is bound to a support material for continuous reuse. This reversible reaction reaches a chemical equilibrium, yielding a syrup composed of about 42% fructose and 52% glucose. This resulting product is the initial commercial grade, known as High Fructose Corn Syrup 42 (HFCS 42).
Blending and Grading of Commercial HFCS
After the initial isomerization, the resulting HFCS 42 syrup is often refined or blended to create commercial grades. To produce more concentrated grades, the HFCS 42 undergoes chromatographic separation. This technique uses a material that preferentially binds to fructose, separating the fructose-rich stream from the glucose-rich stream.
The separated, high-fructose stream can reach concentrations of 90% fructose, marketed as HFCS 90. The most common commercial product, High Fructose Corn Syrup 55 (HFCS 55), is created by blending the concentrated HFCS 90 with the initial HFCS 42 syrup. HFCS 55 contains 55% fructose and 42% glucose, and its sweetness profile is similar to that of table sugar (sucrose), making it widely used in soft drinks.