PHENOMENA OF DIGESTIBILITY — RAW STARCHES. 179 



The effects of enzymic action on raw starch were studied by Meyer (Die Starkekorner, 

 loc. cit.), who records that diastase as well as saliva can penetrate the porous starch-grains, 

 as shown by tlie following observations: Fresh starch-grains from the endosperm of 

 Hordeum disiichum when placed in malt extract form many cracks which radiate from the 

 center of the grains. The presence of these cracks is explained upon the assumption that the 

 penetrating ferment causes a swelling of the grain. Starch-grains from Dieffenbachin, 

 treated for 3 weeks with malt extract, when compared with untreated grains, show a degree 

 of transparency which indicates that some of the substance has been lost, or that the grains 

 have undergone some internal change. Diastase, he states, has the capacity to dissolve 

 every layer of every starch-grain at ordinary room temperature if the action continues for 

 a sufficient length of time. At 40° the ferment action is more powerful on intact grains 

 than at 17°. At 40°, after 24 hours all the grains acted upon were dissolved. A pressure 

 of 3 atmospheres on a preparation consisting of wheat starch and a solution of diastase did 

 not accelerate the solution. In another place Meyer notes that perfect potato-starch grains 

 are dissolved away centripetally in successive layers, gradually fornung long, spindle-shaped 

 grains ; but grains having clefts or fissures were acted upon so as to give rise to channels, 

 pits, cavities, etc. Similar effects were recorded with the starch of Dieffenbachia seguine. 



The non-uniform composition of different starch-grains was pointed out by Pottevin 

 (Woch. f. Brau., 1899, xvi, 641) to be shown by the behavior of starch-grains acted upon 

 by diastase at ordinary temperature when the process is carefully observed under the 

 microscope. Wheat starch, he found, is attacked by diastase at ordinary temperature. 

 Pottevin observed that the thickest grains were less rapidly affected than the thinner 

 grains, and that the smallest polyhedral grains were not at all attacked. The outer layers 

 were not digested, remaining as residues. He also obtained a number of residues by digest- 

 ing starch-grains in the cold for an hour, obtaining the residues of undigested matter, 

 at specified periods, and subjecting these residues in turn to digestion. He thus obtained 

 a number of residues, each successive residue being more resistant than the preceding to 

 diastase. All of these residues were gelatinized with hot water, and in comparison with 

 whole starch yielded only little more than one-half the proportion of maltose. He believes 

 that the starch-grain is heterogeneous, and that therefore starch-paste is heterogeneous, 

 the part of the paste formed from the less dense parts of the grains being easily digested 

 and the denser parts digested with difficulty and after prolonged action, the dextrin from 

 the latter constituting the "residual dextrins." 

 x^ Effront (Enzymes and their Applications, trans, by Prescott, 1902, 128) states that a 

 \ granule of starch is irregularly attacked by diastase, corrosion occurring m very different 

 1 directions and places. The manner of corrosion, he found, arises from the inequality of 

 -resistance of the surface of the grains, so that the difference existing in the compactness 

 of the various parts of the grain is, on the whole, the initial cause of the variations in the 

 resistance to diastatic action. Potato and barley starch he writes are both composed of 

 non-homogeneous grains whose layers differ in degree of compactness; but in potato starch 

 more resisting layers are found than in barley starch. Gelatinization, he records, does not 

 change the properties of starch, which are owing to the variations in the compactness of 

 the layers; therefore the more coherent particles form a paste that is more difficult to 

 liquefy, and yield a dextrin of greater resistance than the less coherent particles. 



Ling (Brit. Assoc. Report, 1903; Jour. Soc. Chem. Ind., 1903, xxii, 1058) found in 

 his investigations of the action of diastase on starch-grains of raw and malted barley that 

 the starches of cereals differ from the starch of potato in being readily attacked by diastase 

 in an ungelatinized condition. He carried out a series of experiments with mashes of barley 

 and malt starches of various origin, the starches being mixed with the diastase preparation 

 in the dry state and mashed with water at various temperatures for 2 hours. The figures in 

 table 24 illustrate the results. 



