Starch processing enzymes from extremophiles

Starch is massively produced in plants as a reserve carbohydrate and is the most common constituent of the human diet, providing the carbon and energy needed for life. Starch is also the starting material for numerous industrial applications (in the food, chemical, textile, pharmaceutical sectors), based on physical, chemical and biotechnological approaches. Among them, enzymatic modifications are gaining momentum due to their lower energy requirements, higher sustainability and specificity. In addition, the continuous development of –omics technologies is providing the way to open a treasure-chest of new starch-modifying enzymes from a variety of sources, including extreme environments. Extremophilic microorganisms are therefore extensively studied for the identification of novel enzymes capable of withstanding the sometimes harsh conditions of industrial processes. Characteristics of starch-processing enzymes of the main glycoside hydrolase families (GH13, GH57, GH70 and GH77) identified in extremophilic microorganisms will be discussed. A specific discussion will focus on amylomaltases from extremophiles. These enzymes can perform a double-step catalytic process, resulting in transglycosylation reactions. Amylomaltases are an interesting research topic thanks to their capacity to modify starch for biotechnological applications (e.g. production of low-digestible starch or synthesis of cycloamyloses to be used as encapsulating agent for hydrophobic molecules)