Isomaltase is an enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 that breaks the bonds linking saccharides, which cannot be broken by amylase

Amylase

Amylase is an enzyme that catalyses the breakdown of starch into sugars. Amylase is present in human saliva, where it begins the chemical process of digestion. Food that contains much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns...

 or maltase

Maltase

Maltase is an enzyme that breaks down the disaccharide maltose. Maltase is an enzyme that catalyzes the hydrolysis of the disaccharide maltose to the simple sugar glucose. This enzyme is found in plants, bacteria, and yeast. Then there is what is called Acid maltase deficiency...

. It digests polysaccharides at the alpha 1-6 linkages. Its substrate, alpha-limit dextrin, is a product of amylose digestion that retains its 1-6 linkage (its alpha 1-4 linkages having already been broken down by amylase). The product of the enzymatic digestion of alpha-limit dextrin

Dextrin

Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch or glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α- or α- glycosidic bonds....

 by isomaltase is maltose

Maltose

Maltose , or malt sugar, is a disaccharide formed from two units of glucose joined with an αbond, formed from a condensation reaction. The isomer "isomaltose" has two glucose molecules linked through an α bond. Maltose is the second member of an important biochemical series of glucose chains....

.

Isomaltase helps amylase to digest alpha-limit dextrin to produce maltose.