Alcoholysis reactions from starch with alpha-amylases

The ability of alpha-amylases from different sources to carry out reactions of alcoholysis was studied using methanol as substrate, It was found that while the enzymes from Aspergillus niger and Aspergillus oryzae, two well-s tudied saccharifying amylases, are capable of alcoholysis reactions, the cl assical bacterial liquefying cl-amylases from Baccillus licheniformis and B acillus stearothermophilus are not. The effect of starch and methanol conce ntration, temperature and pH on the synthesis of glucosides with alpha-amyl ase from A. niger was studied. Although methanol may inactivate alpha-amyla se, a 90% substrate relative conversion can be obtained in 20% methanol at a high starch concentration (15% w/v) due to a stabilizing effect of starch on the enzyme. As the products of alcoholysis are a series of methyl-oligo saccharides, from methyl-glucoside to methyl-hexomaltoside, alcoholysis was indirectly quantified by high performance liquid chromatography analysis o f the total methyl-glucoside produced after the addition of glucoamylase to the a-amylase reaction products, More alcoholysis was obtained from intact soluble starch than with maltodextrins or pre-hydrolyzed starch. The biote chnological implications of using starch as substrate for the production of alkyl-glucosides is analyzed in the contest of these results. (C) 1999 Fed eration of European Biochemical Societies.