Dextrins from Barley Starch

Limit Dextrins from Barley Starch. In one experiment, barley starch paste was treated with malt extract, in a second experiment with purified malt amylase (Table XVII). The purified enzyme has yielded limit dextrins with chain lengths greater than those given by the malt extract, possibly because certain carbohydrases capable of attacking the limit dextrins have been removed in the purification or because of a lower stability of the purified enzyme. 

Limit Dextrins from Barley Starch with Taka-amylase... 

Products Formed by Malted Barley Alpha Amylase from Beta Dextrine Formed from Arrowroot Starch by Beta Amylase (Data of Myrbiicku)... 

A Comparison of the Action of Purified Maltase-free Alpha Amylase from Malted Barley upon Corn Amylose, Corn Starch and upon Beta Dextrins Formed from Corn Starch by the Action of Beta Amylase (Data of Myrbdck and Thorsellu)... 

An interesting comparison is also given in Table XI86 of the action of malted barley alpha amylase upon corn starch, beta dextrins obtained from corn starch by the action of beta amylase, and upon corn amylose prepared according to the method of Meyer.6 90 These data show that, with equivalent amounts of enzyme, amylose was hydrolyzed much more rapidly and more extensively than unfractionated corn starch. Although the beta dextrins were hydrolyzed by this amylase, they were hydrolyzed much more slowly and less extensively than either of the other two substrates. These results are similar to those already considered for pancreatic amylase.41 64... 

Malt extract consists of soluble substances extracted from barley sprouts at 55 C. The obtained liquid is concentrated by heating at 55 °C to form a thick hrown viscous material which contains maltose, starch, dextrin, glucose, 5% proteins and protein breakdown products, minerals salts, growth factors and inositol. 

The mobility of malted-barley a-amylase on electrophoresis in polyacrylamide gels containing starch or amylose or the P-limit dextrin from amylopectin was retarded completely at low concentrations of the enzyme, but it was not affected at high concentrations. ... 

Early in the nineteenth century, human saliva was found to convert dissolved starch to sugars with dextrins as intermediate products, and in 1845 Louis Miahle isolated a ferment from saliva he called salivary diastase. The name, chosen by analogy with diastase, a ferment previously isolated from barley that had been dried after sprouting, is from the Greek diastasis, meaning separation. 

Preparation 76), Soluble starch, made from commercial starch by a mild treatment with acid, is hydrolyzed by the enzymes of barley flour to a mixture of maltose and dextrins (see under Maltotriose). These are separated by,fractional precipitation with alcohol, and the crude maltose is recrystallized from aqueous alcohol. Commercial maltose contains considerable quantities of dextrins which are removed by fractional precipitation of an aqueous solution with alcohol. 

The reacting mixtures of malted barley alpha amylase and starch exhibit alpha mutarotation.23,72 Myrback82 has presented evidence to show that this mutarotation is exhibited by the dextrins as well as by the sugars formed from starch by this enzyme. 

Studies of the rate of the hydrolysis of dextrins isolated from a reaction mixture after the extensive hydrolysis of starch by maltase-free malted barley alpha amylase, led Myrback11 to conclude that the flattening of the reaction curves with this amylase is not due to equilibrium between the amylase and the products of the hydrolysis. As indicated above, similar conclusions have been reached for pancreatic amylase and for the amylase of Aspergillus oryzae.41,7a... 

Fig. 5.—The Smallest, Resistant Dextrins Obtained on the a-Amylolysis of Starch, Using Enzymes from (a) Hog Pancreas, Human Saliva, and Aspergillus oryzae (b) Malted Barley and (c) Bacillus subtilus." [Q. a-D-glucose residue , reducing D-glucose residue —a-D-(l— 4) bond , a-D-(l- 6) bond.]...

In 1833, Payen (with Persoz) found that the transformation of starch into dextrin and sugar by malt (discovered by Kirchhoff) was due to a substance, diastase, extractable with water from germinated barley. They purified the material by repeated precipitation with ethanol and found that the activity was destroyed at lOO C (3, 39). 

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