Towards an optimal process for gelatinisation and hydrolysis of highly concentrated starch-water mixtures with alpha-amylase from B. licheniformis
Baks, T. ; Kappen, F.H.J. ; Janssen, A.E.M. ; Boom, R.M. - \ 2008
Journal of Cereal Science 47 (2008)2. - ISSN 0733-5210 - p. 214 - 225.
twin-screw extruder - wheat-starch - enzymatic-hydrolysis - extrusion-cooking - corn starch - sago starch - model - liquefaction - degradation - kinetics
The enzymatic hydrolysis of starch is usually carried out with 30¿35 w/w% starch in water. Higher substrate concentrations (50¿70 w/w%) were reached by using a twin-screw extruder for gelatinisation and for mixing enzyme with gelatinised starch prior to enzymatic hydrolysis in a batch reactor. The aim of this study was to determine which parameters are important for gelatinisation of wheat starch and to investigate the effects of different extrusion conditions on the enzymatic hydrolysis. After extrusion, the degree of gelatinisation was measured. During hydrolysis, the carbohydrate composition, the dextrose equivalent (DE) and the alpha-amylase activity were measured. Gelatinisation measurements showed that mechanical forces lowered the temperature required for complete gelatinisation. During hydrolysis experiments, high DEs were observed even if starch was not completely gelatinised during extrusion. Due to high substrate concentrations, the residual alpha-amylase activity remained high throughout enzymatic hydrolysis, although high temperatures were used. Increased substrate concentrations did not affect the carbohydrate composition of the product. Furthermore, the time required for the batch hydrolysis step could be varied by choosing a different enzyme-to-substrate ratio. This article provides a basis for detailed optimisation of this process to develop an industrial-scale process at high substrate concentrations.
Starch hydrolysis under low water conditions: a conceptual process design
Veen, M.E. van der; Veelaert, S. ; Goot, A.J. van der; Boom, R.M. - \ 2006
Journal of Food Engineering 75 (2006)2. - ISSN 0260-8774 - p. 178 - 186.
thermostable alpha-amylase - niger glucoamylase-i - twin-screw extruder - enzymatic-hydrolysis - extrusion-cooking - corn starch - reactor - kinetics - glucose - liquefaction
A process concept is presented for the hydrolysis of starch to glucose in highly concentrated systems. Depending on the moisture content, the process consists of two or three stages. The two-stage process comprises combined thermal and enzymatic liquefaction, followed by enzymatic saccharification. The three-stage process starts with shear induced melting of starch, followed by enzymatic liquefaction and saccharification. At a low moisture content, the shear stress needed to completely melt corn starch is so high that significant enzyme inactivation cannot be avoided, which leads to a need for separating starch melting and liquefaction in two separate processing steps. Assuming the use of currently available enzymes, the final product composition was estimated to contain 69-93% glucose, starting with respectively 65% and 35% dry starch. These results showed that the formation of side-products, mainly isomaltose and isomaltotriose, increased with increasing dry matter content. Increasing the dry matter content from 35% to 65% resulted in increasing reactor productivity of 17%, while the amount of water that should be removed from the system was reduced by 87%. (c) 2005 Elsevier Ltd. All rights reserved.
Shear induced inactivation of a-amylase in a plain shear field
Veen, M.E. van der; Iersel, D.G. van; Goot, A.J. van der; Boom, R.M. - \ 2004
Biotechnology Progress 20 (2004)4. - ISSN 8756-7938 - p. 1140 - 1145.
twin-screw extruder - enzymatic-hydrolysis - starch - deactivation - cellulase - reactor - transglutaminase - kinetics - enzymes - beta
A newly developed shearing device was used to study shear-induced inactivation of thermostable alpha-amylase in a plain shear field, under conditions comparable to extrusion. The results show that the inactivation can be described well with a first-order process, in which the inactivation energy largely depends on the shear stress, instead of specific mechanical energy or strain history. The resulting dependency of the rate of inactivation on the shear stress is very strong and nonlinear, which leads to the conclusion that in many cases the maximally applied shear stress determines the inactivation. Quantification of the inactivation rates gives design criteria for the application of enzymes in more viscous systems than conventionally used, provided that the reactor is designed such that no peak shear stresses occur.
Understanding molecular weight reduction of starch during heating-shearing processes
Einde, R.M. van den; Goot, A.J. van der; Boom, R.M. - \ 2003
Journal of Food Science 68 (2003)8. - ISSN 0022-1147 - p. 2396 - 2404.
twin-screw extruder - plasticized wheat-starch - waxy-maize starch - extrusion-cooking - corn meal - in-line - extensional viscosity - functional-properties - rheological behavior - potato starch
Recent understanding of the mechanisms underlying the changes in molecular weight of starch as a function of process parameters during thermomechanical treatment, for example extrusion, holds promise towards more effective optimization of thermomechanical processes according to the desired modification of molecular weight. This paper summarizes recent advances in theoretical understanding and experimental methods. Empirical observations from extruder experiments can be better understood on this basis. The current status in this field has opened up potential for developing new equipment in which the main process parameters, which normally occur simultaneously, can be separated and optimized. This will create a much wider window for product-oriented process design and for new products.