The fractionation of wheat starch. VII. Retrogradation of starch solutions

Abstract

crcnses with dccrensiiig tempernt.urc.~* ~2 1 Stnudiiiger niitl Huseiiiniiii22 linre coiicluded tlint t.lie proportion of starch sepnrntii~g from nn aqueous solutioii ilecrcnses nitli dccrensing iiioleculnr wiglit of the starch, arid IIeyer et crl.3 linre slio\vii that the rntc of prccipitntioii is grenter for frnctioiis of Iiiglicr iiiolcculnr weight thnii' for t.liose of lower iiioleculnr weight. Further, it lins bceii slio\vn thnt lientiiig dry stnrclm to teiiipcrnturcs nl~ore 100" 6.21 resulted in the gradual disnppcnrniice of tlie property of sclrnrntiiig out, of solutioii 011 keeping, ~irobiibly bccnusc of the fnr-reaching depolynierisntion cniisetl by this Iient-trentiiieiit.Early iiirestigntorsJs 5 slioired thnt tlic proportion of tlic stnrcli selinrntiiig out froiii solut,ioii oii ngeiiig is soiiiea h n t liiglier iii very dilute solutioiis of acids and bases tlinii iii \rntcr ; Iiiglicr coiiceiit.rutioiis of ulknli nt first pnrtly inliiljit t.lw sepiirntioii froill soliit.ioii niid fiiially arrest it nltogether. Acid snlts niiil basic salts hnvc the sniiic cffect ns ncids niid I)nscs rcspectirely.a ihltlitioii of etliyl nlcohol, etliyl ether, or etliyl ncetntc fnrours the selrnrnt,ioii of sturcli froiu solution, wliercns wen, ncetniiiitlc, plieiiol, polypliciiols, or niiiiiies returd it ; snturntcd fiitty ncitls, foriunltleliytle, nntl ncetultleliyde liurc no cfl'ect? Jlore rccciitly, Biiiiicc niitl Beiikovic2u linw shoivii thnt the seprntion of stnrcli froiii solution is portly iiiliibited by tlie nclditioii of niiimoiiiuiit thiocyunnte, niiiiiioiiiuiii chloride, pliosplintes, borns, glucose, nnd glycerol, but is fnroured try tliendtlitioiiof niiiiiioiiiuiii iiulplinte. 111 gciicrnl, it niny IJC said tliiit,, as would Ire espected, t.lic scpnrntioii of st.nrcli from solutioii oii ngeiiig will be either retnrded or prevented by thc presence of rerigelits wliieli nre able to pcptisc stnrcli niitl will be iiicrensed by tlie preseiicc of rengimts wliicli congulnte siiirch.'j. 2oe Zi Sturch pustesChniiges oii ngcing Iiuve rilso becii observed iii starch pnstes of vnrious coiicciitrutioiis ; liere, tlic obserriitioii aid e\ucic\atioii of tlic agciiig chiinges nre coiiiplicotcd by the preseiice both of geliitiiiised srrolleii granules e i i d of uiidissolred griiiiule residues. For stnrcli pustes of low couceiitrntioiis,'* J * 5, " tlic results obtniiicd nre iii gciicrnl siiiiilnr to tliosc o1)tniiicd with sturcli solut,ioiis, but nt liiglicr stnrcli colicentrntioi)s tlic stnrcli pnstcs first set to ii gel oii cooliiig, niitl the gel Iutcr esliibitu the pheiiomciioii of syiicresis't 3 (sepnrntioii of w t c r from t.lic gel). At still liiglier stnrcli concentrntioiis, t h o process of synercsis is 110 longer oltsermblc but otlicr hydrntioii cliiiiiges still tnkc pliice.1~ 3 111 rccciit yeiirs I h t z hiis slioaii tlint tlic X-ray * It is of soiiiu iiitcrcst tlint other colloids besides starch nlso eupnrato out froin solution 011 ogciiig iiutler auitublu coiiditioiia of tumperuturo niid coiiccntrutioii. Thus, u...