The invertase enzyme, formally known as beta-fructofuranosidase, is a protein biocatalyst classified as a hydrolase. It is generally a glycoprotein, meaning it has carbohydrate molecules attached to its protein structure. This structure allows it to precisely interact with a specific substrate to accelerate a chemical reaction without being consumed. Its specialized action is central to numerous biological processes and industrial applications, especially in the preparation of specialized sugar products.
The Chemical Reaction
The specific function of invertase is to catalyze the hydrolysis of sucrose, a disaccharide made of glucose and fructose joined by a glycosidic bond. The enzyme uses a water molecule to cleave this bond, splitting the sucrose molecule into its two constituent sugars. Invertase is highly specific, targeting and breaking the $\beta$-D-fructofuranoside bond within the sucrose molecule.
The resulting product is an equimolar mixture of $\text{D}$-glucose and $\text{D}$-fructose, known as invert sugar or invert syrup. This name derives from the change in the solution’s optical rotation. Sucrose is naturally dextrorotatory, rotating plane-polarized light to the right (positive direction). The product mixture, however, results in a net rotation to the left (negative direction) because it contains strongly levorotatory fructose. This reversal of light rotation is the phenomenon of “inversion,” which names the enzyme and the resulting syrup.
Natural Sources and Biological Roles
Invertase is synthesized by organisms across multiple kingdoms, including plants, animals, and microorganisms. The primary source for large-scale industrial production is baker’s yeast, Saccharomyces cerevisiae. In yeast, the enzyme is typically found outside the cell membrane, breaking down external sucrose into smaller sugars the cell can absorb for fermentation.
In higher plants, invertase plays a significant role in carbohydrate management, regulating the storage and transport of sugars. For example, in sugar cane, the enzyme manages the sucrose concentration gradient needed to move energy throughout the plant structure. It is also found in animals, such as bees, which use invertase to convert nectar into honey. Trace amounts are present in the human digestive system, assisting in the initial breakdown of complex sugars.
Primary Commercial Applications
Invertase is highly valuable in food manufacturing, particularly in the confectionery industry. It is used to create soft or liquid centers in molded candies, such as chocolate cordials and soft-centered mints. A hard fondant made primarily of sucrose is prepared, and invertase is added before the candy is coated.
During storage, the enzyme slowly catalyzes the inversion reaction, converting the solid sucrose matrix into liquid invert sugar within the shell. This conversion happens gradually, resulting in the desired smooth, flowing center. The enzymatic method is preferred over harsh acid hydrolysis because it yields a cleaner product, avoiding unwanted byproducts, off-flavors, or color changes.
Beyond confectionery, invertase is employed in the preparation of fermentable sugars for the brewing and ethanol industries. By ensuring a rapid breakdown of sucrose into glucose and fructose, the enzyme provides a readily available food source for fermenting microorganisms. It is also used to produce purified invert syrup from beet or cane sugar for use in fruit juices and jams.
Properties of Inverted Sugar
Invert syrup possesses several practical properties that distinguish it from sucrose. One difference is its increased sweetness; because fructose is inherently sweeter than sucrose, the final equimolar mixture has a higher sweetness index than the original sugar.
Invert sugar is also highly hygroscopic, meaning it retains moisture. This property is useful in baking and food storage, helping to keep products soft and moist, thereby extending shelf life. The mixture also resists crystallization, preventing the formation of grainy textures in confections, syrups, and ice creams.