KEACTION-INTKNSITIES WITH EACH AGENT A\l> REAGENT. 



11.-, 



the insoluble t<> the soluble non-gelatinizablc form is 

 apparently not in any way related to water, inasmuch 

 as it may be broughl about in anhydrous starch by 

 ilr. in- acetic acid, and is therefore an anhydrous pi 

 unli ss water is derived in some ob cut w i b intra- 

 molecular disorganization. Then' is at all events qo 

 inter molecular disorganization such as occurs antecedent 

 tii ami associated with obvious gelation. 



The foregoing changes in the starch molecules in 

 association with the more or less marke I differences 

 exhibited by a given starch in the reactions with diffi 

 reagents indicate clearly thai beneath and overshadowed 

 by the conspicuous phenomena of gelation there lay 

 processes or reactions that vary, within even wide limits, 

 in relation to the components of the reagents. More 

 inn-, raw starch presents certain very striking charac- 

 teristics in its relations to water, entirely apart from 

 the phenomena of hydration that is expressi d 3 gelation. 

 It has been found that raw starch is not only highly 

 hygroscopic and clings tenaceously to water, hut also 

 thai its behavior toward water is in certain respects 

 different from that of hydrated starch, the percentage of 

 water in the raw grains being influenced to a very limited 

 degree and that of hydrated starch to a maximum degree, 

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

 dried starches from different sources have been found 

 to contain from 9.0 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 standi to a 

 temperature of 120° or in vacuo 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 

 direct relationship to the degree of dehydration and the 

 kind and amount of starch. A preparation consisting of 

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

 showed an increase of temperature equal to 3° ; and a 

 similar 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 (set- 

 preceding memoir, page 1G7), bid it can satisfactorily 

 and better be accounted for upon the basis el' adsorption 

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



The level of aqueous saturation is maintained within 

 very narrow limits, and it is very much more influenced 

 by variations in external moisture than by changes in 

 temperature 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 

 level is, however, not only materially higher in hyd 

 starch, but 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, Zeitsch. physiol. Chem., 1!M:.. \, v. 104). 

 A- the temperature falls, even though in the pr 

 of an atmosphere saturated with moisture, there is - in 

 reversion of hydrated starch to raw or insolul 



Starch grains do not either g< or pas? into 



solution in their normal state because apparently of the 

 existence of some peculiar surface condition which, like 

 10 



an osmotic membra! rcvent a further inflow 



of water after a certain level of partial saturation has 



1 d. and which likewise tflow 



of water as long as external a ed 



chemical 

 equilibrium ;ards water within and without 



starch grain. That such a surface conditii 1 



t in the sudden >' level at 



temperature of gel at and I level 



in comminuted and otherwise injured grains in which 

 the starch molecules of the interior of the grain 



iosed to the water. The intracapsular starch 

 thus expo 1 similar but not identical sui 



condition, which is owing to differences in the intra- 

 capsular and capsular starches, as will I"' noted more 

 particularly later. Therefore, in studying the phe- 

 nomena of gelatinization and absorption of water both 

 nf these surface conditions must be considered, a- must 

 also be both forms of starch. 



When raw starch in water is subjected to Blowly ris- 

 ing temperature, at a certain temperature that va 

 for different starches and within narrow line:- for ■ 

 starch there occurs a loss of anisotropy (which ind 

 an intermolecular disorganize mediately 



followed by a rapid taking up of water attended by 

 swelling and gelatinization. This disappearance 1 f 

 anisotropy is taken to mean that immediately ante. 

 a modification or removal of the surface condition has 

 occurred. This surface condition may likewise be 

 affected by various gelatinizing reagents such as have 



I n used iu this research, and thus hydration of the 



starch grain permitted as in the case of gelation by 

 heat : or there may be tie- 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 been noted in the 

 study of certain other colloids, from which it seems that 

 heat and other gelatinizing agent- 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, hut it seems that it is to be 

 located directly or indirectly cither in a hypothetical 

 ; t on the surface of the grain by the cell-sap or in 

 the modified form of the starch that constitutes the 

 capsular part of the grain (the so-called starch 

 lose). This pai't 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 digi 

 resistance to decomposing agents, and in both qua 

 five and qualitative color reactions with iodine. The 

 degree of re aries in si from diff 



sources, and it is -0 marked in some i> in the 



initial stage of the 1 a- t" rendeT gelatiniz 



for a period varying from 1 to 10 minuti 

 be followed by gelatinization that varies in rapiditj 

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

 ('harts ]) l to D 691 that exhibit tin ' gela- 



tinization. Upon this assumption, any asrent wdiich 

 affects the physico-chemical condition of tie 

 part of the grain will modify the surface conditions or 



