CONVERSION OF STARCH INTO DEXTRIN. 97 



was heated in a closed vessel under a pressure of 3 or 4 atmospheres, the starch-substance 

 is dissolved entirely. From the solution on cooling there separated a gelatinous mass 

 that is insoluble in cold water and not acted upon by diastase. On heating, this mass 

 is again dissolved. If this heating and cooling process be repeated a number of times, 

 a stage is finallj^ reached when not all of the gelatinous mass is redissoh-ed on heating. 

 Repeated heating and cooling has therefore altered the constitution of that portion of 

 the starch which has thus been rendered insoluble. 



The results of various experiments show that the molecular condition of colloids, 

 such as gelatin, is very sensitive. For instance, Moore and Roaf (Biochem. Jour., 1906, 

 II, 34) found that a solution of gelatin kept for some time at 70 to 80, and cooled to room 

 temperature has its osmotic pressure considerably increased, which increase gi-adually 

 disappears upon keeping the solution for some days. The explanation for these changes 

 may lie in changes in the sizes of the molecular aggregates heat reducing them and cold 

 favoring their rebuilding. Pauli (Physical Chemistry in the Ser\'ice of Medicine, trans, 

 b}' Fischer, New York, 1907, 61) states that if a gelatin having a temperature which lies 

 between the melting-point and gelation-point be carefully warmed back to the melting- 

 point pre^^ously recorded, the gelatin remains solid. If, moreover, the gelatin is heated 

 beyond the pre^^[ously recorded melting-point, and is then carefully cooled to the starting 

 temperature, it remains liquid. By repeated heating and coohng both gelatin and melt- 

 ing temperatures are therefore altered, showing that the gelatin has undergone changes in 

 constitution. Tliis is paralleled in starch. Furthermore, granules of dry gelatin behave 

 towards water at different temperatures in all essential respects like crushed starch-grains, 

 undergoing swelling, gradually liquefying, becoming limpid, becoming insoluble, etc. The 

 conversion of raw starch into soluble starch can therefore be accounted for on jihysico- 

 chemical grounds, while there is neither satisfactory evidence nor good reason for the 

 assumption that there occurs a hydration in a strictly chemical sense. 



THE PROCESS IN THE CONVERSION OF STARCH INTO DEXTRIN. 



The conversion of starch into dextrin is likewise regarded as being due to hydrolysis, 

 but this rests merely upon assumption. This conception had its origin in the early work 

 of Musculus, in which it was recorded that dextrin and sugar are formed in definite ratio, 

 and that the reaction could be worked out theoretically on the basis of the taking uj) of 

 molecules of water which constitute an integral part of the product; but it has since been 

 shown that such ratios are determined by the laws governing the equilibrium of solution, 

 and not by the nature of the process, and that the chemical processes involved are merely 

 incidental in determining the direction of the reaction, synthetic or analytic, in order to 

 bring about this equilibrium. Dextrin is classed as a polysaccharose but of lower molecular 

 weight than starch, and while there is no clear evidence whatsoever from the chemical point 

 of ^'iew of its being a derivative that is formed through the agency of extra-molecular water, 

 it is logical to assume that it may arise through a process of atomic rearrangement and 

 sphttuig. If dextrin is a derivative of starch in the form of a hydrate, the molecules 

 of water concerned in the reaction must, it seems, have an intramolecular source. Thus, 

 in the formation of torref action dextrin it is justifiable to assume that starch must be 

 absolutely dehydrated before the temperature is reached at which the conversion occurs; 

 hence, the water taking part in the hydration must have been derived from mtra- 

 molecular disorganization. 



Furthermore, that dextrin is not formed conjointly in association with sugar by a 

 process of hydrolysis by which water becomes a part of the product, and that it is formed 

 entirely independently, has been rendered obvious by the results recorded by a number 

 of investigators in studies of the products of the actions of enzymes, dilute acid, and other 

 agents. As previously stated, Payen and Persoz (Ann. de chim. et phys., 1834, liii, 73) 



7 



