Amylases liquefying

In contrast to the /S-amylase, the malt a-amylase (and other liquefying amylases) very rapidly lower the viscosity of starch pastes. When the relative viscosity has dropped to half the original value, only about 0.1% of the D-glucosidic linkages in the starch have been hydrolyzed. The malt a-amylase is a typical liquefying enzyme. 

Although acid hydrolysis is most commonly used to prepare the starting sirup, the liquefying amylase from B. subtilis can be used to thin the initial starch paste without the need for add resistant tanks. The process then becomes an all-enzyme process. The all-enzyme process produces a smaller amount of reversion products than the acid-enzyme process. 

Methylamylose and 6-deoxyamylose have been studied as substrates for the crystalline liquefying amylase of Bacillus subtilis. The oligosaccharides obtained from the enzyme digests were separated by paper chromatography and some of the fractions identified after acetylation by electron-impact m.s. Neither... 

Figure 6. Relationship between reducing value and iodine stain during hydrolysis of amylopectin various amylases. BLA is BaciUus liquefying amylase and F—ZAmylase is the purified amylase.

Liquefaction - Lab-Scale. 35% DS com starch slurries were liquefied with the CGTase at a dose of 4.46 Phadebas units/gram DS starch at pHs 4.5-5.5 for 14 minutes at 105 C (primary liquefaction) and for 4 hours at 90 (secondary liquefaction) +/- 40 ppm calcium. Final volumes were 5-10 ml. Termamyl and Bacillus stearothermophilus alpha-amylase were run as controls at pHs 6.2 and 5.8, respectively in the presence of 40 ppm calcium. 

The results demonstrated that the CGTase is able to liquefy com starch at any pH in the range 4.5-5.5 (Table I). Liquefaaion was considered positive if the starch syrup was pourable. The starch was liquefied to a negligible dextrose equivalent (DE) i.e., without the formation of reducing sugars as expected with a CGTase. The presence of calcium was not required. The B, stearothermophilus amylase, on the other hand, provided suitable liquefaction only at pH 5.5 and calcium was required, but still not optimal as evidenced by the results obtained at pH 5.8. 

The viscosity achieved by the CGTase at pH 4.5 is very similar to the viscosities produced by Termamyl at pH 6.2 and B, stearothermophUus pha-amylase at pH 5.8 as measured at a drive speed of 32 (Table II). Reducing the CGTase dose to 2.23 Phad as units still yielded acceptable viscosity. These results establish that the CGTase can liquefy starch under simulated industrial conditions of high stardi but at a pH i.e., 4.5 where conventional alpha-amylases do not function. 

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). 

Since malt is used as a source of liquefying and saccharifying enzymes in whiskey and grain spirits fermentations, and gibberellic acid increases the a- and /3-amylase content of malt, it became desirable to determine gibberellin residues in a distiller s feed by-product. 

Starch is first liquefied and hydrolyzed to specific dextrose equivalents with hydrochloric acid. After evaporation to 60 percent solids, a saccharifying enzyme (fungal a-amylase) is added to continue hydrolysis to the desired level. By choosing two or more types of enzymes (such as a-amylase, -amylase, glu-coamylase, pullulanase) and adjusting the initial acid hydrolysis, syrups with different ratios of dextrose, maltose, and higher saccharides can be obtained.92... 

Fig. 4.—Composition of Corn-starch Hydrolyzates Prepared by Acid Catalysis (Curve a and b), and Idealizations of Compositions Attained by Action of Fungal Amylase on 50 d.e. Acid Hydrolyzate (Curve c and d), by Action of beta-Amylase on 20 d.e. Acid Hydrolyzate (Curve e and f), by Limited Action of beta-Amylase on a low d.e., aif)/ia-Amylase-liquefied Substrate (Curve g and h), and by Further Action of Fungal Amylase or Mixtures of beta-Amylase and Glucoamylase (Curve h and i). [A = 100% maltose, B = 100% D-glucose, C = 100% saccharides other than maltose or D-glucose, or both.]...

In enzymatic processes, a-amylases, 5-amylases, glucoamylases, and pullulanases are used. First, starch is liquefied and hydrolyzed with acid, with a-amylase, or with a combination acid or enzyme process. 

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