Starch and alpha-glucan acting enzymes, modulating their properties by directed evolution

Starch is the major food reserve in plants and forms a large part of the daily calorie intake in the human diet. Industrially, starch has become a major raw material in the production of various products including bio-ethanol, coating and anti-stating agents. The complexity and diversity of these starch based industries and the demand for high quality end products through extensive starch processing, can only be met through the use of a broad range of starch and alpha-glucan modifying enzymes. The economic importance of these enzymes is such that the starch industry has grown to be the largest market for enzymes after the detergent industry. However, as the starch based industries expand and develop the demand for more efficient enzymes leading to lower production cost and higher quality products increases. This in turn stimulates interest in modifying the properties of existing starch and alpha-glucan acting enzymes through a variety of molecular evolution strategies. Within this review we examine and discuss the directed evolution strategies applied in the modulation of specific properties of starch and alpha-glucan acting enzymes and highlight the recent developments in the field of directed evolution techniques which are likely to be implemented in the future engineering of these enzymes. (C) 2009 Elsevier B.V. All rights reserved