High-fructose corn syrup (HFCS) is a liquid sweetener derived from corn starch. It consists primarily of fructose and glucose, similar to table sugar, and is used widely in processed foods and beverages. This article explores how HFCS is made from corn.
Extracting Corn Starch
HFCS production begins with the wet milling of corn to separate its components. Shelled corn is first cleaned to remove impurities. The cleaned corn then steeps in water for 30 to 50 hours at around 50°C. This steeping softens the kernels, releasing starch, protein, oil, and fiber.
After steeping, the corn is coarsely ground to separate the germ, which contains corn oil and floats for removal. The remaining mixture of fiber, starch, and protein undergoes further fine grinding and screening. This isolates the starch, which is then washed multiple times using hydrocyclones to achieve high purity.
Converting Starch to Glucose
The purified corn starch, a long chain of glucose molecules, is broken down into individual glucose units. This is a two-step enzymatic hydrolysis. First, the starch slurry is mixed with water and adjusted to a specific pH.
An enzyme called alpha-amylase is introduced. Alpha-amylase breaks starch chains into shorter dextrins. This liquefaction process involves heating the mixture to temperatures around 100°C, then cooling it to about 90°C, where the enzyme continues to act for one to three hours.
After liquefaction, the pH is lowered to between 4.2 and 4.5, and the solution is cooled to approximately 60°C. Glucoamylase, another enzyme, is then added. This enzyme further hydrolyzes the dextrins into individual glucose molecules, forming a glucose syrup.
The Glucose-Fructose Transformation
The glucose syrup then undergoes a crucial step to become high-fructose corn syrup: isomerization. This process converts a portion of the glucose into fructose, which is significantly sweeter than glucose. The glucose syrup is purified and concentrated before entering the isomerization stage.
The key enzyme responsible for this conversion is glucose isomerase. This enzyme catalyzes the reversible isomerization of glucose to fructose, rearranging glucose’s molecular structure into fructose. The glucose isomerase is typically immobilized on a solid support, allowing for its reuse and continuous operation in fixed-bed reactors.
The isomerization reaction typically achieves an equilibrium where about 42% of the glucose is converted to fructose, resulting in HFCS 42. This concentration provides a sweetness profile similar to that of sucrose (table sugar). The process is carefully controlled, often at temperatures between 55-60°C and a pH of 7.5-8.0, with magnesium sulfate added to maintain enzyme activity.
Final Product and Variations
After the isomerization step, the resulting high-fructose corn syrup undergoes several purification and concentration stages. The syrup is first filtered to remove protein and then demineralized using ion-exchange resins to remove impurities. Activated carbon treatment is also used to decolorize the syrup for a clear final product.
The purified syrup is then concentrated through evaporation to reach the desired dry solids content. Different types of HFCS are produced by adjusting the fructose concentration. HFCS 42, containing approximately 42% fructose, is commonly used in processed foods, cereals, and baked goods.
To create HFCS 55, which is predominantly used in soft drinks, the HFCS 42 syrup is further processed. This involves a chromatographic separation step to isolate a high-fructose stream, sometimes reaching 90% fructose (HFCS 90). This HFCS 90 is then blended back with HFCS 42 in specific ratios to achieve a final product with about 55% fructose and 45% glucose.