GALACTOOLIGOSACCHARIDE PRODUCTION BY TRANSFER-REACTION OF AN EXOGALACTANASE

An exo-beta-1,4-galactanase was previously purified from Aspergillus n iger. It catalyzed the hydrolysis of potato galactan and several galac tooligosaccharides to produce galactose. In the present work, HPLC ana lysis of the reaction products showed intermediate oligomers with high er degrees of polymerization (dp) than initial oligomers. The exogalac tanase was shown to transfer galactose residues to galactooligosacchar ides. The influence of several parameters has been studied, such as th e nature and concentration of donor (galactan or galactose), the effec t of pH and temperature, and the amount of enzyme. Transgalactosylatio n, which was studied as the yield in reformed oligomers, was found to be most efficient when acceptor was used at a ID mM final concentratio n and galactan (1.5% w/v) was donor with 5 nkat ml(-1) exogalactanase at pH 7 and 40 degrees C. When the dimer was incubated under these con ditions, the yield in reformed oligomers was 30.9%.Transfer reactions were analyzed using oligomer with dp 2-5 as acceptor Each incubation p arameter was shown to influence the transglycosylation in the same way despite the dp of the initial oligomer. Transfer products were move s table at pH 7 than at pH 3.5 but were finally rehydrolyzed in galactos e. From experimental results,the enzymatic mechanism involving hydroly sis and transglycosylation is proposed.