The principal diastatic enzyme is the amylase or diastase of malt - that is, of germinated barley. It was the first enzyme to be isolated. Persoz and Payen4 effected the separation so far back as the year 1832, though the diastase obtained was only a very impure product.

Barley which has not germinated contains a different form of amylase ("barley diastase"), termed by Brown and Morris "translocation diastase," since its function appears to be the conversion of starch deposited in one part of the plant into sugar for transference to another part, where it is again deposited as starch. The ordinary malt amylase was termed "diastase of secretion," as it is chiefly formed during the germinating process by secretion from the scutellum of the embryo. (See under "Malt," p. 38).

Malt amylase quickly dissolves starch, converting it first into dextrins and then into maltose. It acts best at a temperature of about 50 - 55° (122 - 131° F:). At about 80° (176° F.) it becomes inactive, and begins to coagulate.

Enzymes of the amylase or diastase class, however, are by no means confined to barley. They are found widely distributed through the vegetable kingdom, in foliage leaves and ungerminated seeds, particularly in the aleurone layers of the seed-coats. In some small Continental distilleries, for instance, alcohol is made from raw rye, without malt of any kind, whether barley-malt or other. The diastase present in the raw grain suffices to saccharify the starch during the mashing operation. Similarly, it has been found that the bran of wheat has a high diastatic power, sufficient to allow of bran being employed technically as a saccharifying agent of starchy materials in fermentation operations.1

1 Trans. Chem. Soc, 1902, 81, 388.

2 Ibid., 1890, 57, 865.

3 Compt. rend., 1880, 91, 787.

4 Ann. Chim. Phys., 1833, [ii], 53, 73.

Persoz and Payen obtained their diastase by heating a cold-water extract of malt to 70°, filtering from coagulated proteins, and precipitating the diastase by adding a large quantity of absolute alcohol to the filtrate. The diastase was then further purified by re-solution in water and re-precipitation with alcohol: after drying at 40 - 50°, it was obtained as a white, tasteless powder.

A much better preparation is obtained by Lintner's method. This consists in concentrating a strong water-extract of malt by freezing, and pressing out the extract from the ice through a filter-cloth; the injurious effects of heat upon the enzyme are thus avoided. The diastase is precipitated from the concentrated extract by addition of ammonium sulphate.

J. B. Osborne2 has carried out an investigation in which the diastase was prepared by an elaborate method involving repeated dialysis, "salting out" with ammonium sulphate, and several precipitations by alcohol. The purest sample thus obtained had the following elementary composition: -

This composition agrees closely with that of a protein body. Naturally, the exact composition depends upon the degree of purity reached in the diastase prepared; thus one of Lintner's preparations showed much less nitrogen and much more oxygen than the foregoing, namely, nitrogen 10.4 per cent., and oxygen 34.5 per cent. Osborne's purest diastase had a diastatic power of 600, expressed in terms of Lintner's scale, or six times that of the most active preparation obtained by Lintner himself.

1 U.S. P. 1178039; see J. Inst. Brewing, 1918, 24, 26.

2 J. Amer. Chem. Soc, 1895, 17, 587-603.

Purified malt amylase (diastase) with a much higher diastatic power than Osborne's has, however, been obtained by Sherman and Schlesinger,1 working as follows.

Ground malt was extracted with two and a half times its weight of cold water, dilute alcohol, or a very dilute solution of sodium monophosphate, for one and a half to two hours at a temperature of about 10°. The extract was then decanted or filtered, and dialysed in collodion bags against ten times its volume of cold water (temperature 7-15°) for 25 to 42 hours, with two or three changes of the dialysate; next it was filtered, and an equal volume of alcohol or acetone added. The precipitate produced was discarded, and further alcohol or acetone added in quantity sufficient to bring the final concentration up to 65 or 70 per cent. The precipitate thus obtained was separated and dried in a partial vacuum over sulphuric acid at about 10°. So far as practicable, this temperature was maintained throughout the operations, and in any case the temperature was not allowed to rise above 20°.

Of a number of specimens thus prepared, 13 had diastatic powers equivalent to 1200-1800 on Lintner's scale, and seven gave values corresponding with 1800-2300. Even these values, though the highest yet recorded for malt amylase, were lower than those obtained by the authors with pancreatic amylase. The product (from malt) was a yellowish-white substance giving the typical protein reactions, and under the ultramicroscope it had the appearance of a colloid. It coagulated when heated in aqueous solution; the coagulum gave a violet-blue, and the solution a rose-red, biuret reaction. The most active specimen contained about 14 per cent, of nitrogen.

Diastase when quite dry can withstand a temperature of 150°, becoming inactive at about 158°.

Solutions of amylase for keeping are best prepared, according to Chrzaszcz and Joscht2 by extracting malt, not with the usual solvents (water, alcohol, acetone, chloroform), but with aqueous glycerin, aqueous pyridine (3-6 per cent.) or quinoline water The glycerin is preferably used at a concentration of about 50 per cent., but any strength between 20 and 90 per cent, can be employed.

Extracts prepared with these media, and containing 5 to 8 per cent, of diastase, have been tested as regards their starch-liquefying power, saccharifying power, and dextrin-forming power. The results show that there is no definite relation between the liquefying power of amylase and its saccharifying power; this suggests that these two functions may be due to different enzymes. The dextrin-forming power varies mainly in accordance with change of liquefying power, but the results are not conclusive as to the relationship between the two functions.