Recent advances in enzyme biotechnology on modifying gelatinized and granular starch

Enzymatic modification of foods is an important tool for enhancing starch functionality due to its safety, high efficiency, and specificity. Enzymatic modification of gelatinized starch systems is well reported in literature. However, to our knowledge, a review describing and comparing the effects of granular vs. gelatinized systems and enzyme-assisted modification of starch is both timely and lacking. We summarize, discuss and point at future aspects of the consequences of using various techniques of enzymatic treatment of granular and gelatinized starch for modifying their structure and physicochemical properties, including the crystalline and granular structure, and functional properties. For gelatinized starch systems, we generally discuss catalytic mechanism, substrate specificity and product molecular structures for different types of starch-acting enzymes with emphasis on the resulting molecular structures. We critically discuss the problems of enzyme attack on granular starch in relation to two common strategies for starch granular pretreatment, namely, the preparation of porous starch and cold water-swelling of granular starch, both aim at increasing the enzyme catalytic efficiency. Finally, we point out research directions to expand the applications of enzymatic treatments in starch modification. The catalytic efficiency of starch-acting enzymes is higher on amorphous gelatinized starch than on semi-crystalline granular starch. To enhance the catalytic efficacy on granular starch, granules can be engineered to allow for a more efficient enzyme binding on granular surfaces. Additionally, we in-depth describe efforts to increase the specific surface area of starch granules by I) generating pores and channels at the granular surface via treatment with hydrolases or by II) swelling granules via e.g., thermal pretreatment in the presence of ethanol. It is generally found that strategy I reduces the starch yield due to the hydrolytic effect, decreasing the pasting properties. Strategy II retains a high yield of the starch product and generates granular starch with high pasting stability.