Fructose Fructose, also called levulose, has exactly the same chemical formula as glucose, but the atoms are arranged in a different structure. Like glucose, fructose is found in fruits and honey, and certain corn syrups are treated with enzymes to convert
their glucose into fructose. It’s also sold in pure crystalline form. Fructose is the sweetest of the common sugars, the most soluble in water (4 parts will dissolve in 1 part room-temperature water), and absorbs and retains water most effectively. Our bodies metabolize fructose more slowly than glucose and sucrose, so it causes a slower rise in blood glucose levels, a quality
that makes it preferable to other sugars for diabetics. Fructose melts and begins to caramelize at a much lower temperature than the other sugars do, just above the boiling point of water at 220ºF/105ºC.
The fructose molecule exists in several different shapes when dissolved in water, and the different shapes have different effects on our sweet receptors. The sweetest
shape, a six-corner ring, predominates in cold, somewhat acid solutions; in warm or hot conditions, this shape shifts to less sweet five-corner rings. The apparent sweetness of fructose is cut nearly in half at 140ºF/60ºC. Neither glucose nor sucrose changes so drastically. Fructose is thus a useful substitute for table sugar in cold drinks, where it can provide the same sweetness with half the concentration and a calorie savings approaching 50%. In hot coffee, however, its sweetness drops to the level of table sugar.