Enzymatic synthesis of lactulose from lactose and fructose by commercial β_ Galactosidase from Klyveromyces lactis
Integration of life sciences & engineering
Integration of Life Sciences & Engineering - Poster (T5-P)
Keywords: lactulose, lactose,β_ Galactosidase
Lactulose (4-O-β-D-galactopyranosyl-D-fructose) is a synthetic ketose disaccharide that can be obtained from lactose by chemical synthesis. Lactulose cannot be decomposed by human digestive enzymes, so it is classified as an indigestible oligosaccharide. Lactulose specifically promotes the intestinal proliferation of Bifidobacterium, which is known to be a very important humanizing factor in infant formula and is added to commercial infant formula products and various milk products. Lactulose is used in pharmaceuticals as a gentle laxative and to treat hyperammonemia.
Lactulose is currently manufactured by chemical synthesis involving the alkaline isomerization of lactose. The process includes expensive separation and purification steps to remove by-products. The formation of a considerable percentage of hard-to-separate colored by-products leads to low lactulose yield. Lactulose is also produced by using complex reagents such as aluminate and borate; however, this process is unsatisfactory from an industrial point of view, due to the need to eliminate the aluminate and borate. To overcome the disadvantages of lactulose production by various types of chemical synthesis, an alternative method such as a biocatalytic process with clean production and easy purification should be developed.
In this research, a simple system for the enzymatic synthesis of lactulose by commercial β_ galactosidase from Klyveromyces lactis was developed. The reaction is catalyzed by β_ galactosidase in the presence of lactose as a galactosyl doner and fructose as an acceptor leads to the synthesis of transgalactosylation compound (lactulose) in addition to the hydrolysis products.
At first stage, the effect of the conditions such as reaction time and amount of enzyme for hydrolysis of lactose and lactulose was studied. More than 90% of lactose and 75% of lactulose were consumed with addition of 100 µl of enzyme stock solution (3000 U/ml) to the 100g of 5%( w/w) sugar solutions in 40ºC and pH=6.7 after 1 and 3hr respectively.
Then the effect of the reaction time, amount of enzyme and acceptor concentration on the lactulose synthesis reaction was investigated. The presence of fructose decreased the kinetics of lactose conversion, so more amount of enzyme solution (400µl) was used for 100g of reaction mixture at 40ºC and pH=6.7. While lactose concentration was kept constant in 10% (w/w), by varying fructose concentrations of 10, 20, 30%(w/w), maximum lactulose yield related to the initial lactose concentration was 8.7, 10.1 and 12.2% after 60, 100 and 120 minutes respectively.
Presented Wednesday 19, 13:30 to 15:00, in session Integration of Life Sciences & Engineering - Poster (T5-P).
