RBACTIOS-IMKNSITIKS \\1I1I K \r|| A-.I.M AM) Kl.V.lAI 



II.-, 



the insoluble to the soluble non-gelatinizablu form is 

 apparently not in any way related to water, inaMinn h 

 it may be brought about in anhydrous starch l>y anliy- 

 .mi] i therefore nn anhydrous process 

 oolcM water : in some obscure way by intrs- 



Bolrcular disorganization There i* at all events no 



molecular disorganization such a* occurs antecedent 

 with obvious gelation. 

 rhanges in the starch niolivules in 

 association with the mr. or lew mark*"! differences 

 exhibited by a given starch in the nactions with different 

 rcag-ii(- inilirutc 1 1- .irl\ tii.it beneath niul overshadowed 

 rupiniou- phenomena of gelation there lay 

 pnxvsM- - that vary, within even wide limits, 



in relation to the OOapOMOii of the reagent*. More- 

 raw stan-h present* certain very striking charac- 

 :i it- relations to water, entirely apart from 



lenomcna of hydriition that is expressed by gelation. 

 It has been found that raw starch is not only highly 



scopic and clings tenaceously to water, but also 

 that its Miavior toward water is in certain respects 

 different from that of hydrated starch, the percentage of 

 water in the raw Drains being influenced to a rery limited 

 degree and that of hydrated starch to a maximum degree, 

 in the presence of water by changes in temperature. Air- 

 1 starches from different sources have been found 



ntain from 9.9 to 35 per cent of water, the figure 

 varying with the kind of starch, impurities, and per- 

 centage of moisture in the air. Freshly prepared starch 

 may contain as much as 45 per cent of water. Anhy- 

 drous starch is obtained by subjecting the starch to a 

 temperature of 120 or in racuo at 100. Starch that 

 has been partially or completely dehydrated and then 

 placed in water at room temperature takes up water very 

 rapidly with the evolution of heat, the amount being in 



relationship to the degree of dehydration ami the 

 kind and amount of starch. A preparation consisting of 

 20 grams of air-dried potato starch in 20 grams of water 

 chowcd an increase of temperature equal to 3 ; and a 

 Minilar preparation of anyhydrous starch, an increase of 

 13.8. The formation of heat has been ascribed to an 

 actual chemical combination of the starch and water (see 



ling memoir, page 167), but it can satisfactorily 

 and better be accounted for upon the basis of adsorption 

 (which, however, is in fact a form of chemical union). 

 The level of aqueous saturation is maintained within 



narrow limits, and it is very much more influenced 



i nations in external moisture than by changes in 



rature that occur below the temperature of gela- 

 tion; and it is reached before there is the least detectable 

 change in the starch grain or starch molecule. This 



;-, however, not only materially higher in hydrated 

 starch, hut also variable within wide degrees and in direct 

 relation to moisture and temperature, and it probably 

 reaches its highest level at the baking temperature of 

 bread (Katz, Zeits<h. physiol. Ch. m., HH.l. \rv. 104). 



.0 temperature falls, even though in the presence 



of an atmosphere saturated with moisture, there is some 



reversion of hydrated starch to raw or insoluble st.in-h. 



Starch grains do not either gelatinize or pass into 



solution in their normal state because apparently of the 



nee of some peculiar surface condition which, like 



10 



an osmotic membrane, serres to prevent a further inflow 

 of water after a certain level of partial saturation has 

 been reached, and which likewise prevents an outflow 

 of water as long as external conditions are unaltered 



T words, maintains a state of physico-chemical 

 equilibrium as regards water within and without the 

 starch grain. That such a surface condition exists seems 

 evident in the sudden dissipation of this level at the 

 tfiiijH-rature of gelation and in the absence of thu 

 in comminuted and otherwise injured grains in which 

 the starch molecules of the interior of the grain arc 

 freely exposed to the water. The intracapsular starch 

 thus exposed exhibits a similar but not identical surface 

 condition, which is owing to differences in the intra- 

 capsular and capsulnr starches, M will be noted more 

 particularly later. Therefore, in studying the phe- 

 nomena of gelntinization and absorption of water l>oth 

 of these surface conditions must be considered, as must 

 also be both forms of starch. 



When raw starch in water is subjected to slowly ris- 

 ing temperature, at a certain temperature that varies 

 for different starches and within narrow limits for each 

 starch there occurs a loss of anisotropy (which indicates 

 an intcrmolecular disorganization) that is immediately 

 followed by a rapid taking up of water attended by 

 swelling and gelatinization. This disappearance of 

 anisotropy is taken to mean that immediately antecedent 

 a modification or removal of the surface condition has 

 occurred. This surface condition may likewise be 

 affected by various gelatinizing reagents such as have 

 been used in this research, and thus hydration of the 

 starch grain permitted as in the case of gelation by 

 heat ; or there may be the opposite effect, as when there 

 is present a sufficient quantity of alcohol, acetone, 

 alcohol-ether, brine or other so-called dehydrating rea- 

 gent. Analogous phenomena have lx>en noted in the 

 study of certain other colloids, from which it seems that 

 heat and other gelatinizing agents are effective by affect- 

 ing primarily the surface condition, thus giving rise to 

 an alteration in the level of aqueous saturation. The 

 underlying cause of this peculiar surface condition is at 

 present problematical, but it seems that it is to be 

 located directly or indirectly either in a hypothetical 

 deposit on the surface of the grain by the cell-sap or in 

 the modified form of the starch that constitutes the 

 cap-ul a r part of the grain (the so-called starch cellu- 

 lose). This part of the grain is the last to be deposited, 

 and it differs from the inner part (or so-called starch 

 granulose) especially in density, solubility in cold and 

 hot water, digestibility, dextrin products of digestion, 



:... to decomposing agents, and in both quantita- 

 tive and qualitative color reactions with iodine. The 

 degree of resistance varies in starches from different 

 sources, and it is so marked in some instances in the 

 initial stage of the reaction as to render gelatinization 

 very slow for a period varying from 1 to 10 minutes, to 

 U- followed by gelatinization that varies in rapidity from 

 slow to very rapid, as will be seen by an examination of 

 Charts 1) i '1 that exhibit the velocities of gela- 



tinization. T'pon this assumption, any agent which 

 affects the physico-chemical condition of the capmlar 

 part of the grain will modify the surface conditions or 



