Abstract: Levulose-bearing syrups are produced by passing a dextrose solution through a column or bed of an immobilized dextrose isomerase enzyme preparation. The useful life of the enzyme preparation is extended by conducting the isomerization initially at a low operating temperature, then increasing the temperature of operation after an initial decrease in enzyme activity has been observed. Also disclosed is an improved immobilized xylose isomerase enzyme preparation which is prepared by contacting a solution of xylose isomerase with particulate basic magnesium carbonate. The novel immobilized enzyme preparation is useful in enzymatically isomerizing dextrose solutions to levulose-bearing syrups.