POV: date=December 2007

Fructose (also levulose or laevulose) is a simple reducing sugar (monosaccharide) found in many foods and is one of the three important dietary monosaccharides along with glucose and galactose. Honey, tree fruits, berries, melons, and some root vegetables, such as beets, sweet potatoes, parsnips, and onions, contain fructose, usually in combination with glucose in the form of sucrose. Fructose is also derived from the digestion of granulated table sugar (sucrose), a disaccharide consisting of glucose and fructose, and high-fructose corn syrup (HFCS).

Crystalline fructose and high-fructose corn syrup are often mistakenly confused as the same product. The former is simply pure (100%) fructose. The latter is composed of nearly equal amounts of fructose and glucose. Crystalline fructose is held to offer many unique benefits such as improved product texture, taste and stability. Specifically, when combined with other sweeteners and starches, crystalline fructose is said to boost cake height (in baked goods) and mouth-feel of foods and beverages and to produce a pleasing brown surface color and pleasant aroma when baking.

Classification and Structure

Fructose, also referred to as fruit sugar is a simple monosaccharide with a ketone functional group. Fructose is an isomer of glucose with the same molecular formula (C₆H₁₂O₆) but with a different structure. Fructose is a 6-carbon polyhydroxyketone. Like glucose, it forms ring structures when dissolved in solution. When fructose forms a 5-member ring, the OH group on the fifth carbon atom attaches to the carbonyl group that is on the second carbon atom (D-Fructofuranose). Alternatively, the OH group on the sixth carbon may attach to the carbonyl carbon to form a 6-member ring (D-Fructopyranose). Fructose may be found at equilibrium containing a mixture of 70% fructopyranose and 30% fructofuranose

Figure 1 Isomeric Forms of Fructose

Fructose and Maillard Reaction

Fructose undergoes the Maillard reaction, non-enzymatic browning, with amino acids. Because of fructose exists to a greater extent in the open-chain form than does glucose, the initial stages of the Maillard reaction occurs more rapidly than with glucose. Therefore, fructose potentially may contribute to changes in food palatability, as well as other nutritional effects, such as excessive browning, volume and tenderness reduction during cake preparation, and formation of mutagenic compounds.

Fructose and Fermentation