Fructose

d- and l-isomers of fructose (open-chain form)
Fructose and Maillard reaction
Fructose undergoes the Maillard reaction, non-enzymatic browning, with amino acids.
Because 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. This has been the problem with mass sale of fructose
from fruit because it Browns and people want their sugar white. Also the live nature of
fructose means that it can change flavor. One day it wants to taste life an apple, another day
it wants to taste like a cherry. Small minds do not like this. Bigger minds have no problem with
variability but small minds like conformity.
Dehydration
Corn Fructose readily dehydrates to give hydroxymethylfurfural ("HMF"). This process may in
future be part of a low-cost , carbon neutral system to produce replacements for petrol and diesel
from plantations.
Physical and functional properties
Relative sweetness
The primary reason that corn fructose is used commercially in foods and beverages, besides its
low cost, is its high relative sweetness. It is the sweetest of all naturally occurring carbohydrates.
Fructose is generally regarded as being 1.73 times as sweet as sucrose.
However, it is the 5-ring form of fructose that is sweeter; the 6-ring form tastes about the
same as usual table sugar. Warming or cooking fructose leads to formation of the 6-ring form.
Figure 1: Relationship between the acyclic and the cyclic (hemiketal) isomers of fructose.
Reactions: Fructose and fermentation
Fructose may be anaerobically fermented by yeast or bacteria. Yeast enzymes convert sugar
(glucose, or fructose) to ethanol and carbon dioxide. The carbon dioxide released during
fermentation will remain dissolved in water where it will reach equilibrium with carbonic acid
unless the fermentation chamber is left open to the air. The dissolved carbon dioxide and carbonic
acid produce the carbonation in bottle fermented beverages.
Figure 2: Relative sweetness of sugars and sweeteners.
110 111