L. SAIR’ Corn Industries Research Foundation, New York (17), N. Y.
W. R. FETZERs Union Starch and R & b s
c
Cereal, root, tuber, and p i t h starches differ in their hygroscopicity or Zks amount of moisture vetention. Little attentienhebeen giwn tuthis aharactehtic and its possible correlation to other propertie$ of the starches. The present paper deals with thisproperty among the various starch vrieties of commerce; Sorption isotherms hooe been obtained for sewn starch varieties on samplessubjected to i*lbn&ae de-tion and ale0 on unheated controls. From these data the starch varieties can be divided in three #roup-
Company, Granite City, IU.
namely, cereal, pith or root, and tuber. The results indicate that the sorptim capacity of a starch may be a nwasve of its degree of association. The sorptim cupacity df tuber starchen can be reduced to vatws s i m l h t o thosefo~ndfor cereal starches l o i t b u t causing injury or $&atinisation of the granwk. This reduction has bpn accomplwhed treatment of air-dried potato starch f o r 3 hour- with steam at a pressure of 5 poundspersquareinch. Thisvapor tredtmentprofoundly alters theproperties of the tuber starches.
INDUSTRIAL A N D E m I# E B R I N 0 C H E M I S T R Y
Vol. 36, No. 3
The dsta.obtfdnedfor,~, arrowpot, and potato strahes S r e ’ u l i m in hqnre 1. For companaon, a c u m fOr-.ddow (cotton) is also gven (87). -ON
IsolgERMS
IBOTHEBY.
. h m o N he iritia~pcjint .on a e desorption c u m (Wper q n t rektive,humidity) is in realjQ an adenrption point sinm +&e experb6ent ww Sfarted at 92 per crot E:H.
.
ForeachlOpercent~Edeueaeefmm~to2oper.~t,wbsat, rice, and conii~tiwhealose Zcnl mg. of water per gam of d r ~ starch; Sapo, armand wpeat potata stamhes low !+23 mg., and potato st8mh.hea 21-30,mg: Thin constgnoy that watar is retainedby 20 and 90 perkant R H. in one form ody-&orMd watm. Below 20 per cent R. H., stamhea retain their water mpre t a a c i o d y . The M@ion iso-
themraformUdowareincontw3ttothmeof stamh, forat.higk humiditiea ( ~ P i U a r ywater) the moisture losa for eacb 10 csnt ~
RH.deoregssiemuchmoremsikedthanatth0l~erh~dit~. An 2 shows, the desur&n data plotteaby Freundlich’s aamrptson equption fieldtwo hearrels regioi1of25-36perasntR.H. Further atamh re+na ita .water below 90 per cent E. H. b y adsorptive fomps aloae is obtained by .reterenCa to heat at adsorp.ti (8, So). The amount of e t e r retainad by potato stglc per cent IL.H:appmaimetsS.O.3 gam per grsm.of s .isingOdagE%men . . t with Fresman’s bo&d water value,(?) for potato ntarch.
Figure 1. Sorption CWM for Various S e e s and Cotton
(20,Sf). Definite information concerning the forms in which waterisretained bystarchat90pere~ttativehumidityislacking. X-ray studies (S, 10) have d i s c l d that the pattern of c e d and tuber starches difler; theae pattern were designated A and B, respectively. Furthermore, water is easential in the observation of crystalline starch patterns. In the dry state (7) thepatternofwheatandpotatostarchiscloselyaimilar,hutshows increasing differences with increase in moistwe conteut. MATERIALS AND EXPERIMENTAL MKTHOD
Loo P
*m
2. Dew&tion EM- PlOttea ~ - ~ i n to g Freundlieh’s Ademption Epuation
Seven commercial starch varieti? were used in es+blishing somtion isotherma. I n m u c h w I t hss been rec0en1.d that ADSO~PTION ISGTEE~Y. At 30 per cent R. W.the starch products had adsorbed easentiauy the same quantities of water (within 3 mg.), an indication that their primary adsorptive powom are reaeonablysimilar (Figure 1). At 50 per cent R.H. the aorpgve capacityof theabove thraestarch groups &wsa dear divergence which becomes incmsingly marked with further humidity incme. A plot of the adsorption data by Freundlich’s equation gave a distinct break m u n d 26 per cent R H. In the region of 25-80 percent R H. thereisa tmitionperidindiOatingaomechange in the water dation8 of starch. It is of h h t to note that the theoretid amount of water required for a monohydrate is 111 mg., and this vdue cormponds closely to the amount of water held at 25-24 per cent R H. The sk.srch-water system could he wmidered an adsorptive p-, olosaly allied to a chemicalreaction (ff, 84). The water retained up to 80 per cent R. H. might be termed the “primary” adsorption, and that adsorbed from 85 to 90 per cent R. H., the “secondsry”. Potato, snowmot, and wmstglches which are typical of the seven varietiesstudied are p r a c t i d y the same with
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
a07
nysmmais
77 67 42.6 ~
.
18.3
216 189 la8 8a.6
ala 181 140
m
2ar 1oJ 162
Da
?MI
161
Da
98
a8a 24%
176
loo
275
244 174 loa
IQfollowing the moisture cycle of biological pmducta, it is easentisl that the r e m u t a t i v e pointa of the variom enmpka a h d be OQ either the standsrdndsnrpthm or the stghdard desmp tion cuwa at the test humidity (28). In the studies with starch the enmplea wem 6rat conditioned at high humidity, ead the & sorption h t h e n u was obtained. The extent af the hyotme8ia effect in the cantml $tar& prcduata is indimted by mfemt~mto the isothermsshown in Figure 1. The increase in hyetemh w%mh inmessingrelative humidity is shown in Figure 4, from WE& it la evident that the three starch puk vary in hbtereainbeliairior. At 60 per cent R. H., potato starch exhihita a diffemm of 60 mg. per grsm of dry starch in ita abihty to rebm water, d e
%TION M 8Tnaca PIJOPEBTIna. From the sorption data the atarch varieties studied may be divided into three gmup: cereal starchea (wheat, com,ead rice), pith or mot starches (sapo, armwnmt, and sweet potato), and tuher ~tarch(potato). If the hydmxyl group is the point of attachment for water (IS,.%),the reault.9 indicate that potato or tuber Btsrch has a higher percentage of free hydmxyl p u p av&ble for the attachment of water moleculee than has either pith or mot starch or cereal starch. In other words,the degree of aasociation of the st&h types follow the order: c e d > mot or pith > tuber. This association difference may he a factor in the explanation of the Werenoae in the gelation propertias of these starches. Studies are now underway to determine more closely the relation of the sorptive c&pacity of starches to their pro@ea.
BEAT TPEATMKNT
The results shown in Figure 3 indicate the subsequent desorp tive behavior of starches after severe desiccation in vacuo at 100' and 135' C. With one exception (meat potato), the reaulta are m harmony with the hypothesis previously prasented to explain the sorption ditlerenw h p m tuber, mat, and cereal Btsrches. Thm pmducts having the loweat dagree of association (tuber starches) ahow the grant& d t of dehydration. Denimtion reduces the ability of the stamhen to retain water, the grant& @%ct being on tuher starches at high tamperatm. The heatdesicc$d starches retain lese water than the control starches, and it is mfmnable to s u p p e &t thia multa from the mutual bohding of hydtmyl group on m d of water during severe desiccation (86). TABLE11. E m m
OF DESICCATION AT ROOM TEMP~RATUEE ON WATER R?=LATIONS OF 8 T M
iLr
Corn
whwt
Bioo
Arronwt
k b
8.2
11.1 8.8 16.2 18.6 28.2
4.4
a.8 +0.6
6.3 8.6 8.1
8.8 11.0 18.1
4.0
8.2
.
4.2
Heat-deaiccated atarohea show only a negligible change in ability to retain water when r8dried over conoentrated sulfuric acid at room temperature (final point OQ desorption m), while ~ppmciablybut not to the a h L of high-temperature desiccation. The bdeorpuon ourve includes the two seta of desiccated samples. The result. are given in TableI1,andare~~atsBpercdntR.H wherethesscond. qvaiencsfomes play a lsge d i n the sorptive pmcese. when starches of Werent origin are to be used for relative h-pp city studies, the b r p t i o n isotherm must be 0 b t a i i b . t . smw d'eaiccstion affects the mbsequmt sorptipa properties.
oontml6hhw =re
Figurn 3. E6-t of Desiccation on Sorption CapPCit, of starches
pending on whether the standard adsorption or desorption c m is used, m w m o t and corn exhibit a W e m c e of 33 and 25. mg., reapeetively. The hy8kmis eflact a h ~ # l y inbeyond 40 per cent R. H., levels off at Bo per cent R. H., and hegins to diminish beyond 70 per cent R. H. suggested that hysteresis results beuauea the adUrquhart aorhing surface is in a leas active condition during ad.orptionthan during desorption. He considem that desiccation & in a bonding of the free hydroxyl pups, and if the material l a b allowed to abeorb water, ad.orption will 6rst take place in the remaining free group; but subsequently hy ita &traction, the &bed water will tend to reatme the orlglnal odentstlon to the surface 80 that the number of .dive groups increaees. ThL4 mmeae, however, will not he ao grant as the originrJ demme, smca the tende.noy of mme of the bonded group to IEIUaiQ att m t e d t o one another will be greater than the tendenoy d the water to bring it back b i t e origiud capldition. The starch -plea deaiocsted at high tamperatwe exhihit a lower sorptive capacity than the conhle. Sinoe theae pioduota
I
i
i
Trea(meat of the potato aunh with water vapor at a p of 6 povnda per 8q" yleb leduosd ita mrpr1re eapaoity at e5 percent dative h w n i w by 68 mg. per gramdry atamb. This marked deanuvle u1 sorptive ospeelty wan a o o o m ~ e dby a change in the x-ray pattern of the stamb; the diflrseuon pattern (leat* treated potato mdrmdemblsd thw c d type ( A ) more olosely thao the mot type (BL A preliminary study of the eRect of vapor treatment on the pastins ahacterinties of potato &arch indicated that they hsd ixm completely altered. The pasted were short and opaque, their nsmsitie.?wen, markedly d u d , and they had lost their rubbery eharaoter. Additional studm are h e i i conduated to detemune the relation of aasoclation an in&cated by sorption data to the properties of starebea.
TABLE 111. MOI~TUR. . . M oCONTENT i .ox.WPfBw), ~ OF %rm .m . . (PEE . , -.
CBWT
TABLEN.
i !
m
ON 80-
OF WATER VAPOR AT 5 POUNDS l'wa9rmrS CAPACITY OF % l ' -
Roduot
!
!
E
EFFECP OF HEAT AND'hOISTVRE
To detemune what effect high p p a t u r e in the pressnce of moisture would have on sorptive capacity, t b e a k l r i d starches were heated in a pmsure cooker at 5 p u n & per squsre inch (la0 per cent R. H.). When tmat.4 over a 16hour period under these conditibns, the starche.? retained 15-20 per cent m o b ture and did not gelatinhe or exhibit granule damage. Results in Table IV show the eEect of Show treatment under thpse conditions.
i
1I . .
(1980).
,
~
, The wrptive capacity of the steam-heatdutade.? falls within *ngc (!in8 ta 323 me.) while Orioinsllv their w d v e aapscity Msied fmm 288 to 280 mg. Fiyraa shorn that beat in the m e a of moiatnm has a mu& more h t i c eE& than heat alone in ducing tim mrptive capaaitp of the stsuchea. 1 It waa -ted pmionaly tlmt t& wrption diEmncfa in starshasmayFeaultfmmdi6e18~~=inth&+of aesodstion. Im'one zaw (bher stsuchas) more bydmrJrl ~roups.me free to exert their seoon&y v h m i d than in the second case (analatarchen). The d t a In T a b Ey lead emue suppOrt tb flds hypo&e&. Tmatment of Btrchasspith heat in EOmMnation with moisture might be expmted to dtar the ratio of couplea to uncoupled hydroxyl @up and thus bIhE the stambeaM88r
* nM.*
aentielly the anme equilibrium d u e .
,
(11) Langmdr, I.. J.,Am. C h . S ' ' 'io,la61,(1918). (12) Meyer. K.E.. "Recent Ded&nta in S k o h , in "Adin colloid.Soienw". Vol. 1, New York. In& ucienes Pub., 1942. (13) ESWM. F. T.. snctlsurnst. ~ m .8 ., a (1929). (14) R s d b . J. A., "8teroh snd Ita Derisativas", New York, D. Van Nostrand Co.. 1940. (16) . . R h W d d , A,. KOUdd-2.. 9, 224 (1911); 10, 22 (1912); 11, a88 (mil). (16) Rundle, R. E..p6vste OommUnicsti0n. 4lQ. &&, L., .pdFetur,.W..IC,.Im.W-.CrmH.u, dlUL ED..14, 843 (194%. (18) Ekmeo. M..Tram. Fa& Soc.. SI,,?% (1936). (10) Bcbwb.'T.J.. Cered dhsm., 18.121'(1941). 0 S h e m b d , 8. E., and XVm~ome, T.,'Im.Em. ChX~16.
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e.
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