Starch hydrolysis isoamylase

Special products similar to maltose syrups are maltooligosaccharides containing 2-7 glucose units linked to each other by a-D-(1 4) bonds. They are obtained by enzymatic hydrolysis of starch with isoamylase or pullulanase and by hydrolysis of the obtained products using a-amylase. Maltooligosaccharides are fully utihsable sugars, which are used similarly to maltose syrups. 

An identical mechanism can be postulated for hydrolysis of the a-(l—>6) branch linkage by isoamylases and for cyclomaltodextrin glucanosyltransferase. For the latter enzyme, the water molecule is replaced by the C-4 hydroxyl group on the nonreducing end glucosyl unit of the starch chain (Figure 7.6). 

Pullulanase Enzyme degrading pnUnlan, a branched starch pullulanase catalyzes the hydrolysis of the a-l,6-glncosidic linkage in a-glucans. Pullulanase preferentially hydrolyzes pnUnlan while isoamylase has a preference for glycogen and amylopectin. See WaUenfels, K Bender, H and Rached, J.R., Pnllnlanase from Aerobacter aerogenes production in a cell-bound state. Pnrification and properties of the enzymes, Biochem. Biophys. Res. 

Two of the three starches that were quite resistant to glucoamylase hydrolysis, amylomaize-7 and shod starches, gave the highest percent reacdon with the a-(1 6) debranching enzyme, Ps. amyloderamosa isoamylase of 11.9 and 11.5%, respecdvely [109]. Waxy maize, maize, and barley starches were intermediate in their suscepdbility to isoamylase hydrolysis, giving 7.8, 7.3, and 6.2%, respectively. 

When gelatinized waxy maize starch was hydrolyzed 36% with isoamylase, only 16% of the hydrolyzed chains remained inside the granule. When 40% (v/v) ethanol was added to the waxy maize reacdon digest, however, 44% of the isoamylase hydrolyzed chains remained inside the granule, and when 80% (v/v) ethanol was added, 100% of the hydrolyzed chains remained inside the granule [109]. With an 80% ethanol concentration, 100% of the isoamylase hydrolyzed chains also remained inside the granules for potato and shoti starches, and 98% of the isoamylase hydrolyzed chains remained inside the granules for amylomaize-7 starch for a total percent isoamylase hydrolysis of 41, 10, and 13%, respectively [109]. 

The enzymatic activity of isoamylase is determined by measuring the rate of hydrolysis of high-amylopectin starch and is expressed in isoamylase units (lAU). The isoamylase enzyme preparations contain at least 1.25 x 10 lAU/g and have the following composition total organic solids (TOS), approximately 4% water, approximately 58% maltose and glucose, approximately 37% and glycerol fatty acids, approximately 0.1%. 

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