High fructose syrups: evaluation of a new glucose isomerase from Streptomyces sp
Gusek, T.W.; Sailaja, K.; Joseph, R.
Advances in Experimental Medicine and Biology 415: 17-25
1997
ISSN/ISBN: 0065-2598 PMID: 9131180 Document Number: 474415
Glucose isomerase from Streptomyces coelicolor A3(2) was immobilized onto activated alumina and onto granular DEAE-cellulose (GDC); each conjugate converted glucose to fructose. GDC proved to be the preferred support because the immobilization procedure (involving ion exchange) was simple and yielded higher enzyme loadings and increased reactor efficiency. Column reactors incorporating either support operated satisfactorily at various temperatures and flow rates. A syrup containing 23% fructose was prepared using the GDC reactor at 50 degrees C. Increased conversion of glucose to the industrial target of 45% should be possible if the high loading capacity of fibrous cellulose is exploited correctly. Immobilization onto activated alumina presumably involved the formation of covalent bonds between enzyme and carrier; a covalently coupled ligand should experience little to no leaching from the support. Data demonstrated that alumina provided a more stable conjugate than GDC (as measured by retention of isomerase activity during prolonged storage). This apparent benefit of alumina is outweighed by the high enzyme capacity and relative ease of preparing and regenerating GDC-based reactors; these features lead to lower processing costs, and GDC has become the favourite support for industrial production of high fructose syrup. The activity of S. coelicolor glucose isomerase is maximum at pH 7.0 (compared with 7.5-7.8 for typical industrial glucose isomerases), with >60% remaining at pH 6.0. Hence, using the new enzyme in the isomerization stage, less alkali is needed to neutralize the liquor from starch saccharification, and during isomerization there should less formation of impurities via alkaline degradation of monosaccharides.