Starch-hydrolyzing enzymes from thermophiles

Abstract

Starch represents a ubiquitous molecule in plants and is composed of linear polymer amylose and branched polymer amylopectin. Due to its complex structure, it is insoluble in water and needs to be liquefied at high temperatures to make it a useable substrate for hydrolyzing biocatalysts. Hyper-/thermophilic microorganisms belonging to Archaea and Bacteria have been isolated from volcanically and geothermal-heated hydrothermal vent systems and were shown to be capable of utilizing natural polymeric compounds such as starch and cellulose as energy and carbon sources. During the last 25 years, considerable efforts have been made to shed light on structure-function relationships of starch-degrading thermoactive enzymes (extremozymes) and exploit these in various industrial processes. Mostly derived from Bacteria or Archaea, these biocatalysts are stable and highly active at temperatures up to 120ΰC even in the presence of high concentrations (99%) of organic solvents. A great portfolio of amylolytic enzymes enables these microorganisms to degrade polysaccharides into oligo- and monosaccharides. Such enzymes (e.g. amylases, glucoamylases, pullulanases and CGTases) have been employed in producing a series of valuable products. In this chapter, we will focus on starch-converting enzymes from thermophiles and their application in food, feed, textile, chemical, pharmaceutical and other industrial sectors.