Starch-processing enzymes – emphasis on thermostable 4-α-glucanotransferases

Starch is a major storage product of several economically important crops and the most common carbohydrate in human diets. A variety of enzymes are capable of starch hydrolysis and a large-scale starch processing industry has emerged in the last century. Enzymatic production of dextrose/glucose, maltose and high fructose syrups is increasing day by day as we have seen a shift from the use of traditional cane sugar to these sweeteners all over the world. The best known starch-processing enzymes are α-amylase, β-amylase and glucoamylase. Among starch-processing enzymes, a group whose functions are comparatively less well understood, are 4-α-glucanotransferases. In this review, we report on the classification of starch-processing enzymes based on the amino acid sequence and structural similarity as well as substrate specificity and reaction mechanism with emphasis on 4-α-glucanotransferases. Furthermore, applications of thermostable starch-processing enzymes are discussed.