Starch a-amylase

Wheat <Dairy products> starch, protein, moisture, ash, hardness, damaged starch, a-amylase activity, amino add, color value, ratio of contaminated bran, bread making quality, discrimination of cultivar... 

The difference in structure between amylose and amyiopectin is important when selecting the appropriate starch substrate for amylase determinations (see Chapter 21). The rate of hydrolysis is affected by structural differences in the starch. a-Amylase from the pancreas hydrolyzes internal a-l,4 glycosidic linkages. This hydrolysis results initially in the production of some maltose and a mixture of dextrins, which are subsequently hydrolyzed to maltose. The -1,6-... 

The enz5mie generally used for hydrolysis of starch, a-amylase, is rather inexpensive at US 0.04 per gallon of ethanol produced (McAloon et al., 2000). Com market value in August 2012 was close to US 338/t, leading to the production of 400 to 450 L of ethanol, depending on the process efficiency. Moreover, the by-products value, like post-distillation spent grain used for livestock feed, is a net asset for the whole economical balance of the process (Lee and Lavoie, 2013). 

Approximately 95% of the malt produced is used to make beet while small amounts are used as distillers and food malts. Distillers malt, which is used to convert starch-containing grains into fermentable sugars, is prepared almost exclusively for its enzymes, especially a-amylase (see Beverage SPIRITS, distilled). Food malts are sold for their davor and/or enzyme contribution to food products. 

The qua si-crystalline stmcture of natural starch granules causes them to be insoluble in water at normal room temperature and gives them relative resistance to carbohydrases other than a-amylase and glucoamylase unless the granules become swollen. Three-dimensional arrangements of crystalline and amorphous zones in starch granules have been suggested (2). 

Of particular importance for modifications of starch are the enzyme degradation products such as glucose symps, cyclodextrins, maltodextrins, and high fmctose com symps (HFCS). Production of such hydrolysis products requites use of selected starch-degrading enzymes such as a-amylase,... 

Another likely commercial starch is that from amaranth seed, an expanding crop for food use, particularly its flour. Amaranth starch granules (1—3 micrometers dia) have potential for numerous food appHcations, one of which is as a fat replacer because of their small size and especially after minor surface hydrolysis with a-amylase or glucoamylase to produce a fluffy surface (see Fat replacers). 

Enzyme—Heat—Enzyme Process. The enzyme—heat—enzyme (EHE) process was the first industrial enzymatic Hquefaction procedure developed and utilizes a B. subtilis, also referred to as B. amjloliquefaciens, a-amylase for hydrolysis. The enzyme can be used at temperatures up to about 90°C before a significant loss in activity occurs. After an initial hydrolysis step a high temperature heat treatment step is needed to solubilize residual starch present as a fatty acid/amylose complex. The heat treatment inactivates the a-amylase, thus a second addition of enzyme is required to complete the reaction. 

ThermalLkjucfaction Process. In the thermal Hquefaction process (see Eig. 1), a starch slurry containing no enzyme or added calcium is heated for several minutes. The slurry is slightly acidic and sufficient acid Hquefaction is achieved to reduce viscosity. The hydrolyzate (at essentially zero DE) is flash-cooled to 95—100°C, a-amylase is added, and the pH is adjusted. The reaction then goes to completion. 

Cooking. Cooking is the gelatinization by heat treatment and a-amylase Hquification of raw material starch (qv). 

Enzymatic Gravimetric Methods for TDF, SDF, and IDF. These methods use an a-amylase and protease to remove starch and reduce protein. They differ from each other in the conditions for gelatinization of starch. Elimination of detergent permits recovery of soluble fiber, which is not possible with the detergent methods. 

Urea Enzymatic Dialysis Method. This method (16) uses 8 M urea [57-13-6] to gelatinize and facUitate removal of starch and promote extraction of the soluble fiber at mild (50°C) temperatures. EoUowing digestion with heat-stable a-amylase and protease, IDE is isolated by filtration or I DE is obtained after ethanol precipitation. Values for I DE are comparable to those obtained by the methods described eadier, and this method is less time-consuming than are the two AO AC-approved methods. Corrections for protein are required as in the AO AC methods. 

A slurry of the starch is cooked in the presence of a heat-stable bacterial endo-a-amylase. The enzyme hydrolyzes the a-l,4-glycosidic bonds in pregelatinized starch, the viscosity of the gel rapidly decreases, and maltodextrins are produced. The process may be terrninated at this point. The solution is purified and dried, and the maltodextrins are utilized as blandtasting functional ingredients in dry soup mixes, infant foods, sauces and gravy mixes, etc. 

Starch A polymeric substance of glucose molecules and a component of many terrestrial and aquatic plants used by some organisms as a means of energy storage starch is broken down by enzymes (amylases) to yield glucose, which can be used as a feedstock for chemical or energy production. 

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