Process for isomerizing glucose to fructose

DETAILED DESCRIPTION OF THE INVENTION Glucose-containing solutions are usually produced by treating starch by one of three methods.
In the first method an acid is utilized at relatively high temperatures to hydrolyze the starch; in the second, starch is first liquefied by an acid treatment and then saccharification is effected by enzymatic means; in the third method both liquefaction and saccharification are effected by enzymatic means.
The acid-enzyme and enzyme-enzyme processes are most widely practiced in the industry.
The stability or effective life of immobilized glucose isomerase is probably influenced to the greatest extent by the quality of the substrate.
The quality of glucose-containing liquors produced in the corn wet milling industry may be highly variable.
Generally, these liquors are refined by conventional methods prior to isomerization and U.
S.
Pat.
No.
Re.
28,885 teaches additionally that the presence of small amounts of SO.
sub.
2 in glucose-containing liquors during isomerization reduces denaturation of soluble or intracellular glucose isomerase as well as inhibiting color formation in the finished syrup.
Although the prior art methods have proven to be beneficial to a degree, continuous isomerization processes utilizing immobilized glucose isomerase have not hitherto been as efficient as desired due to the fact that the enzyme becomes inactivated after a relatively short period of use.
It has now been found that when glucose-containing liquors, which have been treated with carbon and ion exchange material in a conventional manner, are contacted with an ion exchange material in the bisulfite/sulfite form and the contacted liquors subsequently isomerized with immobilized glucose isomerase, the stability or effective life of the immobilized enzyme is substantially increased over that attained by prior art processes.
This finding is surprising in view of the fact that the concentration of SO.
sub.
2 in the resin-contacted liquors is similar to that taught by the prior art to be effective in reducing denaturation of soluble or intracellular glucose isomerase