Mixed-mode resins: taking shortcut in downstream processing of raw-starch digesting α-amylases

Abstract

Bacillus licheniformis 9945a α-amylase (BliAmy) has been described as potent enzyme for raw starch hydrolysis. Starch represents an inexpensive source for production of glucose, maltose syrups and fructose which are widely used in food industries. Regarding energy costs, effective utilization of natural resources and viscosity problems, direct hydrolysis of raw starch below the gelatinization temperature by using raw-starch-digesting enzymes, such as α-amylase is desirable. In spite of the extensive studies concerning the structure and thermal properties of B. licheniformis amylase and the numerous reports in the literature referring to the molecular mechanism of irreversible thermoinactivation, little attention has been paid to its enzymological characterisation. Detailed knowledge about subsite architecture of B. licheniformis amylase is scarce. No report on kinetics and mode of action of this industrially important enzyme can be found in the literature especially when raw starch is used as a substrate. For mechanistic studies enzyme preparations of high purity are required and improving downstream processing is very beneficial. BliAmy was produced using optimized fed-batch approach in defined media and significant overexpression of 1.2 g L-1 was achieved. These amylases have exposed tyrosine and tryptophan residues as part of their surface binding sites. Mixed mode Nuvia cPrime™ resin is tested as improvement of the downstream processing of raw starch digesting amylases aiming at exploiting hydrophobic patches at their surface. This resin combines hydrophobic interactions with cation exchange groups. Presence of salt facilitates hydrophobic interactions while ionexchange groups enable proper selectivity. Surface response methodology was used to optimize binding and eluting conditions of BliAmy. This single step procedure enables simultaneous concentration, pigments removal and purification of amylase with a yield of 96% directly from fermentation broth.