PHENOMENA OF DIGESTIBILITY — RAW STARCHES. 177 



the preparation. Wlicat and corn starches did not attain tlicir maximum stiffness until 

 after boilinjr for some miiuites; on the otlier hand, potato starch had its maxiniuiii stiff- 

 ness when the boihng-point was readied, and lost in power very considerably by further 

 lieating. 



The non-homogeneity of starch-paste was particularly refen-ed to by Pottevin (Ann. 

 d. Inst. Pasteur, 1899, xiii, 728) (see page 134). Ling (Jour. Fed. Inst. Brew., 1903, ix, 

 44(3) found considerable difference in the conversions of starch-pastes and also of raw starch 

 at temperatures below the point of gelatinization. 



The relative stiffening strength of starches prepared under tlie same conditions is, 

 according to the Scientific American Cyclopedia of Receipts, taking 100 as the standard 

 of comparison: Pure dry rice starch, 100; rice starch No. 1, 95; rice starch No. 2, 91; pure 

 dry corn starch, 87; corn starch, 85; rye starch, 81; oat starch, 80; acorn starch, 80; wheat 

 starch, 80; barley starch, 78; Bermuda arrowi-oot, 75; Natal arrowroot, 73; pure potato 

 starch, 08; and potato farina, 05. 



PHENOMENA OF DIGESTIHIUTY. 

 RAW STARCHES. 



It has long been established that starch-grains are in the nature of a reserve food 

 of the plant and that they undergo ready solution in situ (presumably by the action of 

 enzymes) when their derivatives are required for nutritive purposes. While such dissolution 

 takes place with ease in the plant, in seeds, in bulbs, etc., such is not the case in vitro, 

 even though presumably the same enzymes are present, unless the outer protective coat- 

 ings of the grains are injured so as to expose the starch-substance, especially the innermost 

 part. It is true that there are many records to indicate that various kinds of -raw starch 

 are digestible in vitro with various degrees of ease or difficulty, but it is quite clear that 

 when bacterial action has been prevented, and when tlie grains are uninjured, absolutely 

 no digestion occurs. If, however, the grains have been eroded by bacterial or other action, 

 or if the grains be fissured or broken so as to permit contact of the enzymes with the intra- 

 capsular part of the grain, digestion proceeds with variable degrees of rapidity according 

 to attendant conditions. So long as the grains are perfect, the coating, which varies in 

 resistiveness in starches of different kinds, and also in grains of the same starch, serves 

 as a perfect protective against the influences of diastatic enzymes in vitro, if bacterial action 

 is prevented. The writer has subjected various kinds of starches to the actions of ptyalin, 

 pancreatin, Taka-diastase, and malt diastase in a 1 per cent chloroform solution for over 

 12 months at optimal temperatures, without evidence of erosion or digestion of the grains, 

 except in the case of injured grains; yet similar solutions of the same enzymes caused a 

 practically complete saccharification of the boiled starches in 6 hours. It seems that the 

 virtually absolute indigestibility of perfect starch-grains in vitro in the presence of enzymes 

 is owing to the absence of some factor in the plant that in some way gets rid of the barrier 

 presented by the coating. 



The non-digestibility of raw starch by enzymes was recorded as far back as 1835. 

 Gucrin-Varry (Ann. d. chim. e. phys., 1835, lx, 32) set aside a preparation of potato starch 

 and malt extract in a sealed tube, at room temperature, for 63 days. At the end of this 

 period there was not a trace of sugar, nor did the grains show any microscoi^ic changes. 

 Dubrunfaut (Ann. d. chim. e. phys., 1847, xxi, 178) noted that while raw potato starch 

 is unaffected by malt diastase, wheat, barley, and rice starches arc affected. C. Nageli 

 (Die Starkekorner, loc. cit.), in liis digestion experiments with saliva, by which he differ- 

 entiated the so-called amylose and cellulose, found that the amylose was digested, leaving 

 the skeleton cellulose. In fact, as the author has found, saliva becomes absolutely inert 

 before any such action can take place. Hence it was not the saliva, but some otlier agent, 

 that caused the effects noted. The influences of saliva on raw starch were also studied 



12 



