Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Process for o~iidising starch
The present im ention relates to a process for reducing the ~,iscosit~ of
pol~saccharides, especiall~ starch, b~ o~;idati~c degradation ~ithout meta~ catal~sts.
Starch is economicall~ relc~-ant both as a foodstuff and for non-food
applications. Worldwidc thc annual starch production is about ''6 million tons. One
of the largest non-food uscrs of starch deri~ati~es is the paper industr~. In this fie~d
starch solutions with high starch content ( '5 v~t.'~") and lo~ ~iscosities are much
desired. Important features of starch dcri~ati~es arc an impro~-cd initial wet strength
of the papcr sheet, a bettcr printabilit~, a bcttcr rctention of cationic additi~-es and
o applicabilit~ as glue. Thc dcmand for thcsc starch dcri~ati~es is sc~-eral million tons
a ~,~ear.
Starch has to be subjcctcd to a ~ iscosit~-rcducing treatment, before it can be
used on an industrial scalc. For this purpose. thc starch is gcnerall~ treated
oxidati~ el~ in an al~alinc medium at incrcascd tcmperaturc (40-60~C). This
treatment takes ~-15 hours at about 60~C, for e~;amplc in casc h~pochlorite is used
as an o~idisiDg agcnt togethcr ~ith sulphuric acid or phosphoric acid. Disad~antages
of this method are the amount of salt produccd in addition to chlorine-containing
deri~ ati~ es, and a high proportion of short chain starch moleculcs. Thcse dis-ad~antages are becoming morc and more important as thcre is an incrcasin~ demandfor chlorine-free product.
According to anothcr mcthod, h~ drogcll pcro~;idc is uscd togcthcr with a
transition metal as a catal) st. Ho~c~ cr. it is difficult to climinate the, oftcn
poisonous, catal~st aftcrwards, C~CIl ~rhcn USillg compounds such as EDTA. Another
disad~antage is the discoloration of the product.
2s US-A-5,36''.868 discloses a proccss ~hcrcill thc ~iscosit~ of (h!dro~eth~l)
starch is reduccd b~ o~idation using a peracid at pH's ranging from I to 6 and at 40-
50~C. For e~;amplc, pcrox~ sulphuric acid (H,SO ,) or pcracetic acid are used asperacid. Thc perox~sulphuric acid has to bc prcparccl in situ from h~drogcn pcro~;ide
and sulphuric acid~ or elsc a salt of thc acid has to be used, which has thc
disad~ antage of gcncrating salts as l ~ products. The reacti~ it~ of peracctic acid is
lo~er and results in longcr rcaction timcs. It is also dcscribcd in US-A-5,36'',868,
,! . . . . ~ .
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~0 U~
that the reactio~l with hy~og~ peroxide results in unacccpta~le reactio~ tlmes.
~rencll p~te~t 87814~ scs thc trC~ttncnt of sta~ch with pera~tic acid at 111~~C,vvhich gi~ves a bctt~r Yiscc~sity reduction than trcatm~nt wi~h sodium pero~Idc, but
results ~n thc starch to be simultancously p~Lst~d.
s Accordi~g to l~E-A-4035053, cellulosic rn~teri~ts su~h a~ ~ottOn caI~ bc
hC~;l b~ tr~ating th~ t~ri~l~ with pcrac~tic a~id without activators~ ~nd
simulta~cously subjecti~2~ th:m to a~ ultrasonic trsatmc~t (33 ~kHz).
~JS 5,342,542 ~licclosps thc us~ of sucrose l~ ct~s for i~creasiIIg thc
ble~chin~ cff;c y of perborate in tex~i1e w~sh".g.
~4 obje~t of thc inYen~On is ~o plo~d~ a proc~ss for re~lucing the viscosity
of st~rch and other polysaccha~ides with simpl¢ mcans, without thc us~ of hcavy
me~als a.~d sal~-produ~ ag~ts, and with~ut orgar~ by-pl~duct. It ~s also an
obj~t to providc a ~iscosity--rcducing pro~~~ss whicJ~ allows thc s~arc.h g~anu1c to
rcmai~ intact, for casicr workin~, dryin~ handli~g ~ 'hc pro~u~:t
This obj~ct i~ a¢hicvcd by means of a pr~c~ss wherein t~c polys~c~h~ri~ is
oxi~iscd u.,i~g hydrogcn pcroxid~ in thc prcs~c~ of an acylatcd polys~eh~nclc c~s a~
activator.
As a polysacchariclc which can ~e trcat~d u~hl~; thc proccss of thc i~cnti~n,
any wholl~ of pa~tially water--solublc polysac~har~dc can be used. I~scsc con~prise
2n firstly st~rch ~c.~. po~to, corn, wasy mai~c, tapIoca, wh~at, ricc and other starcllcs~
a~d fractions and d~,;va,ti-~,s thcrcof, such as amylosc5 floc ~els, ctho~ylated starrh
a~d carb~xymethyl starc~. Furthelmor~, thc solubility of ~el11rlase ~l~iv~liY~s a~d
inulin and de~ivatives th~co~ an~ p~nt~s~nc such as xylans call be i...yl~lv,_~ o~ th~ir
~~isco~ity can be recluccd with the proces~ s~f thc invcn~io~. CarbohydMte ~rivatnes,
~5 su~ N-~ylatc7~ lated, carboxymethylatcd, alXyIatcd, hydroxy~l}cSrlate~3,
u~ellated and dehy~ro~n~tcd de~ivati~es can also be treated accor~n~ to ~hc
i~entic~n.
The acylated carbohydrate use~l as a catalyst ~an be a~y palysacchaJide which
i~ wholly cr paI~ally acylated. It w~s found tllat only a small ~moun~ of a~ylated
30 carbohydrate is n~c~ h~y to ensur~ an ~ffl~i~nt rç~k~n- r~ ~s often sui~ficie~t if for
each 700 anhyd~lucose (or other lu~ f~2l~ide) ~t~, one aeyiated mnnl~s~rc~h~de
urut i~ prescr~t~ Preferably at lc~st one and e~pec~ally It least ~our monoacyl~t~d
Jno~ rh~ridc units are pr~se~t for ~ach laO uni~s. I~ particular an av~ra_e of
0.06~)2 acyl~ted m~losa~ dc ullits ~s pr~s&nt pcr m~ ch~ idc unit in th~
ElYL~Ei~ S.~cET
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total of non-ac~ lated and ac~ latcd pol~ saccharidc. Thc term "ac~lated" comprises
alkano~ lated (form~ lated acet~ latcd propion~ latcd~ etc.) benzo~-lated sulphatated
phosphor~latcd etc
The ac~lated carboh~drate Call sin~pl~ bc obtailled b~ treatment of a carbo-
h~drate with an ac~ lating a~cnt such as acctic anh~ dride USillg standard methods.
Some ac~-lated carboh~dratcs are commcrciall)~ a~.lilal71c such as acet~l starch having
a DS of about ''.5% or 8~.
An ad~antage of thc usc of an ac~latccl carhoh~drate is that the oxidation
reaction proceeds smoothl~ and no undesircd h! -products arc formed; the ac~ lated
0 pol~ saccharidc or its o~;idation product can bc part of the treatcd pol~saccharide
product without an~ incon~elliellce.
The ac~lated carboh~dratc can ad~antaleousl~ be a derivative of the same
carboh~ drate to be ~rcatcd. Thus thc trcatment of starch can suitablc bc pcrformed
using acet~lated starch as thc activator. Thc ac~ latcd carhoh~drate can be prepared in
situ e.g. b~ ac~lation ~ith ~he corre.sponding carl?o~51ic anh~dride at pH 8-9.5 in a
concentrated solution or SUSpcllSiOIl of thc calholl~dratc. Thc ac~lation ma~ then be
followed bs the oxidation but oxidation ma~ also l c startcd during ac!~lation.
The amount of h~dro_cn peroxidc to I c uscd is cntircl! depcndent Oll the
desired de~rec of oxidatioll. An amount of I w t.C~ is sufficicnt in general forachic~ ing an effecti~ c ~ iscosit~ clcgrcc. Acl~ antaPcouxl~ t.%~ in particular ~-
'~0 wt.~o of h~drogen pcroxidc is uscd. with rcfcrcllcc to thc total of pol!saccharide
and ac~lated carboh~drate. The h~dro~cll pcro~;idc can hc addcd at once but it has
been found that bctter products arc obtaincd ~hcll thc h~drogcn peroxide is addcd
graduall~ or in portions for cxamplc over a pcriod from 5 minutcs to 3 hours.
The reaction can bc pcrformccl at room tcmperaturc~ but prefcrabl~ at
incrcased temperaturc gencrall! from ~n to gnoe. in particular from 40~C to 5~C
below the pasting tempcraturc~ wllich pastin~ tcmpcrature is at about 6~~C for most
starch t~ pcs. This results in a ~ iscosit! -rcducccl product still having a granular
structure. The rcaction timc is from scvcral minutcs to se~ eral hours at that
temperaturc dcpcndin_ on thc palticular pol~ saccll.lride and thc desired dc_ree of
viscosit~ reduction.
Thc pol~saccharidc is prcfcral-l! trcatcci at a rclati~cl~ high conccntratio
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such as 10-55 wt.Yo, in particular 33-5(3 ~, b~ ci~ht. Thc treatmcnt is carried out
under neutral to alkaline conditions~ i.e. at a pH bct~eell S and 1~?, espcciall~
between 8 and 11, in particular bctweell ~ and 11. Thc treatment can ad~-antagcously
be carried out in two or morc sta~es! i.e. addition of pcro~;idc at neutral pH ~5--8.5)
s and subsequent reaction at all;alinc pH (8.:~-11). In casc of in situ ac~ lation, the
ac~lation can be performed undcr slightl~ alk.~ le conditions (pH 7.5-9.5~, during or
after ac~lation pcroxide is addcd ~ith somc pH dccrea~c (e.g. pH 6-8.5) and
oxidation is completed at hi~her pH (~.:~-11).
The product obtaincd b~ thc process of thc in~cntioll is esscntiall~ frce of
0 chlorinc (as salt or co~alcntl~ bound~ i.c. not al-o~c natural abundance (< ''0 ppm)
and of transition metals. Thc carbox~l contcnt is prcfcral~ls bctween 0,'? and 5,
especiall~ between 0.~ and 3 ~t.~. Thc ~ iscosit~ is prcfcrabl~ belo~ 4000
Brabender units (at ''~ ~.t% dr~ sul?stancc ancl at~O~C) and in particular bclo~ 1000
Brabender units.
Example 1
Oxidation of StQrc~z U'i~l H~()? it~ t~te prcsenc ~ of (lc(~ (Jf~d .~r~lrc~l
To a stirrcd suspension of nati~ c potato st.lrch (70() ~) and Pcrfectam) l AC
(commerciall~ a~ailablc acct~latcd starch. acct~lation DS ~", 3no g) in watcr (1 1)
at 4S~C and pH 7 ~A~aS addcd H O~ (3() ~t.~ () ml = ahout 0.3 mol.cq.). Thc pH
was slo~l~ raised to pH 10.5 usin~ n.s M sodiulll h!droxidc (v~ithin 30 minutes) and
was thcn held constant for thc rcmaindcr of thc rcaction time (total reaction time 3
hours). At the end of the rcaction thc pH of thc rcaction mi~;turc v~as slo~l) adjusted
to pH 6 ~ith concentratcd sulphuric acid (9~ ~t.~,). Thc rcaction mi~;turc was then
filtered and the modificd starch ~as ~ashcd witll ~atcr (. 1, room tempcraturc~, after
2s which it ~as dricd. Thc rhcological propcrtics ~cre dctcrmincd v.rith a Brabender
Viskograph E. Thc results arc gi~ en bclo~ in Bral?clldcr units at ~noc; V5 mcans
~iscosit~ at 5 ~t.~o.
V5top V5~alle~ V~cncl ~' V ~alle) V~~ end
75 < 5 70 1~)7()() ?~00 X
The end ~ iscosities could bc lo~-crcd solllc~ t 1~ a) incrcasin~ thc pH to 1 1 ; b)
increasing the amount of H~O: c) adding thc H,O gradu;~ in 7-1n minutcs at pH
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8. A strong further ~ iscosit~ reduction v.-as obtained b~ increasing the ratio of
acet~lated starch to native starch.
B ~ wa of comparison the expcrimcnt was rcpcatcd using 85 g of galactose-penta-
acetate instead of Pcrfectam~l u~hich resultcd in and end iscosit~ V5 of 11~0.
5 Example 2
To a stirred suspension of Pcrfcctam~rl AC (acct~ latcd starch acetylation DS 8%100~ g) in water (1 I) at 50~C and pH In.S was added H~O2 (30 wt.% 400 ml =
about 0.6 mol.eq.) in 70 portions o~er 1 hour using ~ M sodium h~droxide. After 3
hours another 0. mol.eq was addcd at con..tant pH of 1().5 (total reaction time 4
10 hours). The reaction mixturc was worl;cd-up a-.. in E~;amplc 1. The carbo~;~l contcnt
was dctermined b~! titration. Thc iscosit data arc giVCIl below:
V-Stop V allc! V~~end %COOH
0.6 cq H O 3 0 ~ 0~0 1.4
O.g eq H 0? 10t) ~0 180 1.6
Example 3
lS Oxi~tion of stQrc~ it~l H~O, ar~ sit~ ccttl~t~ .starc~l
To a stirred suspcnsion of nati e potato starch (~5() g) in v~atcr ( 50 ml) at 5~C and
pH 8-9.5 acetic anh dride (AA ~ g = ~7 molc 70 ().~1~ ml.min~~ as slowl v
added in 3 hours. 5 ml of 30 wt.~o H~O~ as acldcd during acet~lation. The DS foracet lation was 1 l~o. Subscqucntl~ thc tcmpcratul-c was raised to 50~C at pH 7.20 Threc portions of 5 ml H O~ wcrc thcn addcd in 1 hour (total amount about 0.6mol eq.). The pH was slowl~ raiscd to pH 1 n.s using 1 .t) M of sodium h~ droxide
(within 30 minutcs) and ~A~as thcn hcld constallt for thc remainder of the rcaction time
(total rcaction timc 3 hours). Thc rcaction mixtul-c ~as ~or~ied up as in Example 1.
The rcsults are gi en belov~-.
molc5o AA YoCOOH V~top V-~vallc~ V-~ end
7 1 .9 7: ~() 3 100
Comparative Example
To a slurr~ of starcll (7t) g dr ~cigllt in 13t3 g water: 35 ~t.%) g of
glucosc penta-acctate is addcd at ~t)~C. Thcll a solution of 10 ml h~dro~cn pcroxidc
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(30 wt.%) is addcd at once. Thc pH is lov~crcd to 1.~ using 1 N aqueous h~dro-
chloric acid. After a reaction timc bcl ~ecn I~ millutcs and 6 hours the reaction
mixture is neutralised and the o~idised starch is scparated b~ filtration washed with
watcr en dried ~A~ith acctone. Tl e iscosit~ of a suspcllsion of q0 g of product in 380
5 ml of water is dctermined USill~ a Brabcndcr -iscosimcter.
Table 1 summarises thc rcsults of thc product aftcr 3 hours and after 6
hours. Thc result of the trcatment using onl h!dro~cn pero~idc aftcr 3 hours is also
gi~-en for comparison.
Tal le l
Viscosit~ of starch at 5 ~t.~ drS su~?stance~ after oxidation
Oxidant Rcaction Initial Top Top End
time (h) tcmp. tcmp.~iscosit~~iscosit~
(~C~I (~C)q 71~ ~4
none (blanc) - ~)l 8() 3 00 1180
HqOq 3 ~~ 8-> 1560 500
H O~ + GluAc 3 6~ 7~ 5~ ?0
15HqO + GluAc~ >~)() 5()() ~0
1 Initial temperature of Brabcldcr cur~c
2 Temperature of the top of the Bral?clldcr cur c
3 Brabendcr units at top of Brabcndcr cur c: 7~ rpnl. tcmp. ~radicnt:
1.5~C/min. tSIa~ ~0~C t~ 9()~C hold: 3() mim: AVEB~ standard 0191
20 ~ Brabcnder units in ~allc of Brabcndcr cur c (as 3)
