An Overview of Chemical Reaction Analysis - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 88

which is drawn out in Eqn (3.2) (the fructose shown is D -fructofuranose):

OH

HO

1

O

O

HO 5

2

(3.2)

3

HO

HO

6

HO

4

OH

OH

OH

OH

The equilibrium in this isomerization reaction is 58% fructose (40.6% fructopyranose and
17.4% fructofuranose) and 42% glucose. An enzyme was discovered called glucose isomerase,
which isomerizes the molecules by exchanging the end aldehyde group with the neighboring
OH group to convert glucose into fructose. This enzyme cannot isomerize any other bonds in
these molecules.
The high-fructose corn syrup industry produces approximately 10 million tons of fructose
from glucose annually, making it the largest industrial bioengineering processes today, at
least in volume.
This process could not work without finding an effective and cheap way to run this bio-
logical reaction and to separate fructose from glucose (sucrose contains 50% glucose). These
were accomplished by finding improved strains of the enzyme, by finding ways to immobi-
lize and stabilize the enzyme on solid beads to keep them in the reactor and by finding adsor-
bents to separate fructose from glucose.
These are accomplished in large fermentors in chemical plants, mostly in the Midwest. The
cheapest feedstock is starch rather than sugar (other enzymes convert starch to glucose), and
corn from the Midwest is the cheapest source of starch.
Artificial sweeteners have also been developed to give the taste of sweetness without the
calories. These chemicals have sweetness many times that of sugar, so they sell for high prices
as low-calorie sweeteners. Many artificial flavors have also been developed to replace natural
biological flavors. In all cases, we search for processes that convert inexpensive rawmaterials
into chemicals that taste or smell like natural chemicals, either by producing the same chem-
ical synthetically or by producing a different chemical that can replace the natural chemical.
The glucose to fructose isomerization reaction can be written as

# (3.3)

A B

which is reversible. In other words, the reaction is both A A. When the reaction is

far away from equilibrium, e.g. if we start out from pure glucose and in the short time when
the reaction begins, we can regard the reaction as irreversible or
A

/ B and B /

/ B (3.4)

Consider the isomerization reaction of cyclopropane to propylene,
cyclo-C 3 H 6 / C 3 H 6 (3.5)

or in symbols

═ ⁄

(3.6)

∇⎯→