Starch liquefaction

In the metagenomic approach, DNA was directly extracted from uncultured samples followed by cloning and expression [3]. For example, by combination of directed evolution with the metagenome approach, an a-amylase mutant with optimal activity at pH 4.5 and optimal thermostability at 105 °C was discovered for starch liquefaction and EtOH production [4]. 

Starch liquefaction, 10 287-288 Starch molecule, techniques for characterizing, 20 562 Starch phosphates, 4 724t Starch sodium phosphate monoesters, 4 721... 

Starch Liquefaction with a Highly Thermostable Cyclodextrin Glycosyl Transferase from Thermoanaerobacter Species... 

Alpha-amylases (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1) have conventionally been employed in starch liquefaction. Alpha-amylases hydrolyze the alpha-1,4-glucosidic linkages of the starch, producing maltodextrins. The alpha-amylases... 

Known producers of CGTase include Bacillus mascerans (7), Bacillus megaterium (8), Bacillus ohbensis (9), alkalophilic Bacillus sp. (lO M), Bacillus amyloliquefacien (15), Bacillus subtilis (16), Klebsiella oxytoca (17), and Micrococcus sp. (18), However, none of these CGTase enzymes are sufficiently thermostable for use in industrial starch liquefaction. 

Thermostability of Thermoanaerohacter sp. CGTase. The addition of 40ppm Ca+ + to the CGTase preparation during incubation at high temperatures in the absence or presence of starch substrate provided no enhancement of the thermostability of the enzyme. A comparison of the thermostable CGTase was made to other thermostable enzymes used in starch liquefaction including Termamyl Bacillus licheniformis) and Bacillus stearothermophilus alpha-amylase. 

Starch Liquefaction. Starch in its natural state is only degraded slowly by CC-amylases. To make the starch susceptible to enzymatic breakdown, it is necessary to gelatinize and liquefy a slurry with a 30—40% dry matter content. Gelatinization temperature depends on the type of starch (67) com is the most common source of industrial starches followed by wheat, tapioca, and potatoes. Liquefaction is achieved by adding a heat-stable a-amylase to the starch slurry. The equipment used for liquefaction may be stirred tank reactors, continuous stirred tank reactors (CSTR), or a jet cooker. Most starch processing plants liquefy the starch with a single enzyme dose in a process using a jet cooker (Fig. 9). 

Fig. 9. Starch liquefaction process, 35% dry substance at pH 6.3, 40 ppm Ca2+. Single enzyme dose of 0.5 kg a-amylase/120 L starch slurry, at 105°C for 5...

Getting ethanol from corn consists of five steps grain grinding, mash cooking, starch liquefaction, saccharification and fermentation, followed by ethanol separation and dehydration. Before fermentation, the starch has to be converted to soluble dextrin by liquefaction in the presence of specific enzymes, such as a-amylase. This process takes place at temperatures above 100 °C at suitable pH and residence time. Then, another enzyme glucoamylase is added that transforms the... 

Enzyme-enzyme conversion employs heat and an enzyme for starch liquefaction in place of acid. This is the most common form of com processing today Subsequent hydrolysis is by enzymes, as above. The choice of hydrolytic system depends upon economics and the kind of endproduct desired. Enzymes are usually inactivated by heating the symp to 75-80°C, with the exception of the heat-stable a-amylases that have come on the market in the last 10 to 15 years. 

Since CD production without the application of solvents may lead to microbial contamination, the process should be conducted at increased reaction temperature. A heat-resistant cyclomaltodextrin glucanotransferase, stable at temperatures above 100 °C, was isolated from Thermococcus species. The enzyme possesses also a-amylase activity and the production of CD is possible without the addition of a-amylase for the preliminary starch liquefaction [48]. 

Spezyme. [Genencor IntT.] Amylase enzyme for textile desizing, food processing, starch liquefaction. 

Taka-Therm . [Solvay Enzymes] Alpha-amylase emzyme for starch liquefaction and textile desizing. 

T rmamyl . [Novo Nordisk] Alpha-amylase heat-stable enzyme for starch liquefaction, for laundry and dishwash detergents, alcohol, brewing, and textile industries. 

The many circumstances leading to the Henri equation for enzyme conversion of soluble substrates are first noted, followed by some kinetic forms for particulate and polymer hydrolysis. Effects common to immobilized enzyme systems are summarized. Illustrative applications discussed Include metabolic kinetics, lipid hydrolysis, enzymatic cell lysis, starch liquefaction, microenvironment influences, colloidal forces, and enzyme deactivation, all topics of interest to the larger themes of kinetics and thermodynamics of microbial systems. 

Starch granule as well as with recrystallized states caused by retrogradation. In order to properly describe enzymatic starch liquefaction, these crystalline states must be accounted for. 

The amylopullulanases behave likes a-amylase in their action pattern. As mentioned before, some of these enzymes are hi y active tuid stable at 90-95 C and pH 5.0-6.0, and do not require calcium fior activity. These enzymes may be used in starch liquefaction processes in place of a-amylase at low pH and low Ca. They may be a superior alternative to the conventional a-an lase that is now used for starch liquefactitm if a more highly diermostable and dieimoactive amylopullulanase can be discovered by a screening program. These enzymes may also be usefril for making various specialty maltodextrin syrups because of thdr unique product specificity. 

The viscosity of a starch solution rapidly decreases on hydrolysis by a-amylase (starch liquefaction) and the iodine color disappears. The dextrins formed at first are further degraded on longer incubation, reducing sugars appear and, finally, a- maltose is formed. The activity of the enz)me decreases rapidly with decreasing degree of pol)merization of the substrate. 

In enzymatic processes, a-amylases, P-amylases, glucoamylases, and pullulanases are used. First, starch liquefaction is conducted with acid, with a-amylase, or with a combination acid/enzyme process. 

---