An experimental study on the carboxymethylation of granular potato
starch in non-aqueous media
C.J.Tijn,H.J.Kolk,E.J.Stamhuis,A.A.C.M.Beenackers *
Department of Chemical Engineering,University of Groningen,Nijenborgh 4,9747AG Groningen,The Netherlands
Received 30November 1999;revid 1April 2000;accepted 4May 2000
Abstract
The optimal reaction conditions for the carboxymethylation of granular potato starch in mixtures of water and organic liquids were determined.The reaction was carried out with pellets of NaOH and sodium monochloro acetate (SMCA)powder as the carboxymethylation reagent.Different alcohols,from methyl alcohol up to the three isomers of butyl alcohol,and acetone were compared in terms of the degree of substitution,DS,and the reaction ef®ciency,RE.Gelatinisation of the starch granules was avoided at all times.For ethyl alcohol and isopropyl alcohol the effect of the water fraction was studied.The highest RE and the highest DS were obtained for isopropyl alcohol with 10
wt%water.For this system the effect of the temperature,the NaOH to SMCA molar ratio and the theoretical DS was studied in detail.The DS obtained in a single reaction step was limited to about 1.3,with an RE of 0.6.The modi®cation was also carried out in three concutive steps;resulting in granular carboxymethyl potato starch with a DS of 2.2.The results for the DS and the RE,obtained in this work,are considerably higher than the values reported in the literature.q 2001Elvier Science Ltd.All rights rerved.
Keywords :Starch;Carboxymethyl starch (CMS);Reaction conditions,Organic solvents
1.Introduction
Native starches are chemically modi®ed to improve speci®c properties.In order to provide easy ¯ow and hand-ling,and to avoid excessive drying and paration costs,it is advantageous to keep the granular structure of the starch intact.Starch becomes cold water soluble by substituting the hydroxyl groups with sodium monochloro acetate (SMCA)to give carboxymethyl starch (CMS).To prevent gelatinisation of the starch granules,the reaction should be carried out in an organic medium.In this paper an experi-mental study is discusd on the u of organic liquids as a reaction medium for the production of highly substituted granular carboxymethyl potato starch.
The sodium salt of CMS,also called CMS,is mainly ud as a thickening agent,with applications in both the food and non-food industry (Roberts,1967).CMS is ud as a disin-tegrant,called sodium starch glycolate,in the pharmaceuti-cal industry (Bolhuis,Zuurman &te Wierik,1997),and as a sizing and printing agent in the textile industry (Ragheb,El-Sayied &Hebeish,1997).
CMS is produced by etheri®cation of the hydroxyl groups
with monochloro acetic acid or SMCA in the prence of alkali.The method is bad on Williamson's ether synthesis (Ege,1989).The ®rst step in the carboxymethylation is an equilibrium reaction between NaOH and the hydroxyl groups of starch
ROH 1NaOH Y RONa 1H 2O
1
Here,R is the starch backbone.The cond step is the actual formation of the carboxymethyl group by the substitution of SMCA
RONa 1ClCH 2COONa !ROCH 2COONa 1NaCl
2
SMCA can also react,by an undesired side reaction,with NaOH to form sodium glycolate
NaOH 1ClCH 2COONa !HOCH 2COONa 1NaCl
3
Sodium glycolate can react with itlf or SMCA to give sodium diglycolate.
The amount of carboxymethyl groups formed is indicated by the degree of substitution,DS.The DS is de®ned as the average number of substituents per Anhydro Gluco Unit,AGU,the monomer unit of starch.Each AGU contains three hydroxyl groups,so the DS lies between zero and three.The reaction ef®ciency,RE,is a better parameter to optimi the reaction conditions.The RE is calculated by dividing the experimental DS by the theoretical DS.The theoretical
Carbohydrate Polymers 45(2001)219±226
0144-8617/01/$-e front matter q 2001Elvier Science Ltd.All rights rerved.PII:S0144-8617(00)00243-5
/locate/carbpol
天蝎座男星*Corresponding author.Tel.:131-50-3634486;fax:131-50-3634479.E-mail address:beenackers@chem.rug.nl (A.A.C.M.Beenack-ers).
DS,DS t,is the maximal DS obtained for complete conversion of the limiting reactant,either SMCA or NaOH,assuming that no side reaction occurs.The RE lies between zero and unity and is given by
RE DS
DS t
4a
with
DS t
n A;0
n AGU;0
4b
The initial amount of moles of the limiting reactant is given by n A,0,and n AGU,0is the initial amount of moles of starch. Numerous studies discuss the in¯uence of the reaction agent concentration,reaction medium and temperature,on the carboxymethylation of starch. Hebeish and Khalil(1988),Khalil,Hashem and Hebeish (1990),Mofti,Hassan,Salma and El-Sabbah(1982)and Ravel,Patel,Patel and Patel(1994)studied the effect of the reagent concentration in an aqueous reaction medium. In an organic reaction medium Bhattacharyya,Singhal and Kulkarni(1995)and Jingwu,Dongli,Yuquan,Xiaohong and Dahua(1993)investigated the in¯uence of the reagent concentrations.In all cas,an increa in the SMCA(or monochloro acetic acid)concentration resulted in an increa in the DS of the product,up to a constant value. While,an increa in the SMCA concentration decreas the RE and an increasing NaOH concentration gives an opti-mum in the DS and RE.In the studies the DS t and the NaOH to SMCA ratio were varied simultaneously by vary-ing either the NaOH or SMCA concentration.In our study the last two parameters are varied independently.
In the literature various organic liquids were ud. Schrodt(1942)tested methyl alcohol for the carboxymethylation of potato starch.Ethyl alcohol was ud by Sloan,Mehltretter and Senti(1962)for high amylo starch and by Thewlis(1969)for wheat starch. Mofti et al.(1982)also ud ethyl alcohol but did not specify the type of starch ud.Acetone was ud by CÏeh (1972)for the modi®cation of corn starch.The effect of the water content in the organic reaction medium was studied by Bhattacharyya et al.(1995),Hebeish and Khalil(1988),
恐龙的英文C.J.Tijn et al./Carbohydrate Polymers45(2001)219±226
220
Table1
Literature results for carboxymethylation of starch
References Starch Medium Water(wt%)DS(±)RE(±) Jingwu et al.(1993)Corn Isopropyl alcohol240.530.3 Jingwu et al.(1993)Potato Isopropyl alcohol120.9±
Corn Isopropyl alcohol22 1.15±Bhattacharyya et al.(1995)Corn Isopropyl alcohol200.220.13
Amaranth Isopropyl alcohol100.240.11
Corn Cyclohexane200.240.14
Amaranth Cyclohexane100.340.15
Jingwu et al.(1993),Khalil et al.(1990)and Suzuki,Tado-koro and Taketomi(1961).In Table1an overview is given of the optimal reaction media found in the literature.The DS reported in the literature was transformed into an RE using the DS t calculated from the reaction conditions.Unfortu-
nately,Jingwu et al.(1993)did not report the concentration of the reagents ud,so it is not possible to calculate the RE for their experiments.Most of the results reported have rather low DS and RE RE below0.3.Further-more,it is clear that the optimal amount of water in the system depends on the type of starch and organic liquid ud.
The results for the DS and the RE reported in the litera-ture for the production of granular CMS are rather low. Therefore,the initial aim of the prent rearch is to produce routinely granular CMS with DS value above1. The cond aim is to reali the high DS values with an RE signi®cantly above the low values known from the literature.To achieve this a systematic experimental program,for veral organic liquids and various reaction conditions,was carried out.
2.Experimental
2.1.Materials
Potato starch,food grade quality,was obtained from AVEBE(Veendam,The Netherlands).Before usage the starch was washed three times with demineralid water and dried in a vacuum oven at558C to a moisture content between10±15wt%.Technical grade powder sodium monochloro acetate(SMCA)was obtained from Akzo Nobel(Arnhem,The Netherlands).The NaOH pellets were of
analytical grade.Dehydrated isopropyl alcohol of a technical grade,purity higher than99%,was obtained from Acros Chemica(Geel,Belgium).Ethyl alcohol,96% pure,acetone and nitrogen were of technical grade.The other organic hyl alcohol,propyl alcohol, butyl alcohol,c-butyl alcohol and tert-butyl alcohol, were of analytical grade.
2.2.Carboxymethylation experiments
焦躁的意思The organic liquid was®rst mixed with a speci®c amount of water.Then the granular potato starch and the reaction medium were mixed in a1dm3jacketed reaction vesl, followed by¯ushing with nitrogen.During the experiments N2¯ushing continued to prevent any reaction of NaOH with CO2from the air.A re¯ux-cooler was ud to prevent the loss of organic liquid.Typically,after15min NaOH was added to the reaction mixture.Subquently,the vesl was heated to the reaction temperature and left overnight under stirring to assure equilibrium between the starch and the sodium hydroxide.Adding powder SMCA started the reac-tion.Periodically,a small sample was taken for analysis. The reaction was stopped by addition of sulphuric acid.
2.3.Analysis
The DS was determined with high-performance liquid chromatography,HPLC.This technique has bee
n described for carboxymethyl cellulo(Heinze,Erler,Nehls& Klemm,1994)and for carboxymethyl inulin(Verraest, Peters,Batelaan&van Bekkum,1995).The method is applicable over the whole substitution range,0#DS#3; and requires the hydrolysis of the carbohydrate polymer into modi®ed gluco units.About0.1g CMS was hydrolyd with18ml of0.75M sulphuric acid at1008C for4h.The sample was neutralid by barium hydroxide resulting in precipitation of barium sulphate.Glucos with zero,one, two or three carboxymethyl groups were parated on two Bio-Rad HPX-870HPLC columns in ries at658C,and were analyd with a refractive index detector.The¯ow rate of the eluent,1.5mM sulphuric acid,was0.5ml/min. Fig.1gives a typical HPLC chromatogram of the hydro-lyd CMS with a DS of0.6.Seven peaks,in arbitrary units, are identi®ed.The DS is calculated from the modi®ed gluco peaks indicated by2,3,4and5.Peak1consists of inorganic salts,mainly sulphate and chloride,peak6is sodium diglycolate and peak7is the unreacted SMCA and the side product sodium glycolate.The DS is calculated from
DS
X3
i 0家英语
泪雨纷纷
iA i
M w i
X
i 0
A i
M w i
5明辨是非的反义词
with A the relative peakarea and M w the molecular weight. For the various peaks,in Eq.(5),i is equal to0for gluco
C.J.Tijn et al./Carbohydrate Polymers45(2001)219±226
221
Fig.1.HPLC chromatogram of carboxymethyl starch in isopropyl alcohol±water after hydrolysis;degree of substitution equals0.6.1:inorganic salts, 2:tri-carboxymethyl gluco,3:di-carboxymethyl gluco,4:mono-carboxymethyl gluco,5:gluco,6:sodium diglycolate and7:sodium monochloro acetate and sodium glycolate.
(peak5),1for mono-(peak4),2for di-(peak3)and3for tri-carboxymethyl gluco(peak2).
3.Results and discussion
The effect of the reaction conditions on carboxymethyla-tion was studied by varying one parameter at a time,while the other parameters were kept constant at the standard conditions given in Table2.This in contrast to the statistical
approach ud in Tijn,Scherpenkate,Stamhuis and Beenackers(1999).There,the parameters were varied according to an experimental design,to investigate the para-meter interactions.The study prented here is required to obtain the optimal organic liquid as well as the relevant boundaries of the levels ud in the experimental design study of Tijn et al.(1999).
3.1.Comparison of organic media无法启动此程序
Organic liquids ud in the carboxymethylation of potato starch included:methyl alcohol,ethyl alcohol,propyl alcohol,isopropyl alcohol,butyl alcohol,c-butyl alcohol, tert-butyl alcohol and acetone,all diluted with10wt% water.In all the experiments the same DS t was applied, i.e.the DS is proportional to the RE.For the alcohols tested Fig.2shows the RE as a function of reaction time.Under the conditions studied isopropyl alcohol gave the highest RE and the highest DS.In isopropyl alcohol,after about 460min of reaction,an RE of0.80and a DS of0.90was obtained.For propyl alcohol and the three isomers of butyl alcohol,the RE was equal to0.70,after 13%lower than for isopropyl alcohol.The lowest RE,0.07 after450min,was obtained for methyl alcohol and ethyl alcohol.Reproducibility of the results appeared to be over 95%.
The good performance of isopropyl alcohol for the carboxymethylation of potato starch is in agreement with results reported for other types of starch,e Table1.A comparison between the performance of the various organic media obtained in this workand the performance reported in the literature is made in Fig.3.Table3gives an overview of the various reaction conditions applied.The quantities reported in the literature are bad on volume fractions, whereas mass fractions are ud in this study.From Fig.3 it can be concluded that for the different liquids applied,the highest RE is obt
ained for potato starch in isopropyl alcohol. With butyl alcohol and acetone,potato starch also appears to give the highest RE.In contrast,potato starch appeared to give the poorest results in methyl alcohol and ethyl alcohol. The signi®cant difference between the results for corn starch from Bhattacharyya et al.(1995)and Khalil et al.(1990)are most likely to be caud by the different reaction conditions and the experimental method ud.
Our experimental method to prepare CMS differs from procedures reported in the literature.Bhattacharyya et al. (1995)and Khalil et al.(1990)added aqueous NaOH drop-wi prior to the reaction.Jingwu et al.(1993)added a NaOH solution during the reaction.In our study all the NaOH was added as pellets at least12h before the carboxy-methylation reaction was started by addition of SMCA. Jingwu et al.(1993)suggested that the addition of aqueous NaOH in two steps incread the RE and reduced the forma-tion of sodium glycolate.Unfortunately,Jingwu et al. (1993)did not report the reagent concentration,so,it is not possible to compare their RE with our results.Further-more,a mixture of isopropyl alcohol,NaOH and water can
C.J.Tijn et al./Carbohydrate Polymers45(2001)219±226 222
Table2
Standard reaction conditions
Amount of liquid(kg)M l 1.0
Mass fraction water(kg/kg)W H
2O
0.1
Temperature(8C)T40 Mass fraction starch(kg/kg)W AGU0.04 NaOH/SMCA molar ratio(mol/mol)± 1.0 Theoretical DS(mol/mol)DS t
1.1
reportedly form a two-pha liquid system (Mills &Hughes,1957;Yokota,1985).Conquently,when an aqueous NaOH solution is added to a starch±isopropyl alcohol suspension,a two-pha liquid system can be formed with a localid high NaOH concentration.If so,SMCA may react with NaOH to form sodium glycolate before the main reaction proceeds.The formation of a two-pha liquid system ems to be avoided with our experimental method.3.2.Effect of water
The effect of the water fraction on the carboxymethyl-
ation was studied in more detail for isopropyl alcohol and ethyl alcohol.The moisture content of the starch granules was included in the total water fraction.Fig.4a shows the RE as a function of time for four isopropyl alcohol±water mixtures.In all the experiments the same DS t was he DS is proportional to the RE.The optimal water fraction for isopropyl alcohol appeared to be about 0.1.Fig.4b gives similar results for three ethyl alcohol±water systems.The highest DS in ethyl alcohol is obtained for a water fraction of 0.2.However,in the latter ca,after about 250min the starch gelatinid at a DS of about 0.26with an RE of 0.23.Apparently,with isopropyl alcohol it is possible to have a granular product with a high DS and a high RE,over a broad range of conditions.
From the results prented in Figs.3and 4it follows that the optimal amount of water in the organic re
action medium depends on the type of starch as well as on the type of alcohol.We found that for potato starch a water fraction of 0.1in isopropyl alcohol is optimal.Bhattacharyya et al.(1995)also found that for amaranth starch isopropyl alcohol with a water fraction of 0.1is optimal.For corn starch the optimal water fraction in isopropyl alcohol is about 0.2(Bhattacharyya et al.,1995;Khalil et al.,1990).For ethyl alcohol we found an optimal water fraction of 0.2for potato starch.In methyl alcohol the optimum water fraction is 0.24for corn starch (Khalil et al.,1990).The optimal amount of water appeared to increa with decreasing carbon number of the alcohol.This is con®rmed by Filbert (1952),who studied the carboxymethylation of various carbohydrates,including potato starch,gum and cellulo,and reported optimal water fractions of 0.28for ethyl alcohol and 0.22for propyl alcohol.The values are somewhat higher than our results.However,Filbert (1952)did not discuss a dependency of the optimal water fraction on the type of carbohydrate.
3.3.Reaction conditions for isopropyl alcohol
In this ction the other reaction conditions are optimid for the carboxymethylation reaction in the optimal liquid isopropyl alcohol with about 10wt%water.
C.J.Tijn et al./Carbohydrate Polymers 45(2001)219±226
223
Table 3
Overview of the experimental conditions,ud for the comparison of the reaction ef®ciency (RE)given in Fig.3
Khalil et al.(1990)
Bhattacharyya et al.(1995)This work Starch
Corn Corn Amaranth Potato T (8C)60653040DS t (±)
1.71 1.71
2.57 1.1NaOH/(S)MCA (mol/mol) 1.89
情声1.27 1.73 1.0W H 2O (kg/kg)0.21±0.240.20
0.10
0.10
V H 2O (m 3/m 3)0.20
0.16±0.1800.08±0.090.08±0.09W AGU (kg/kg)0.04±0.050.06250.120.04AGU (g)44440
V (dm 3)0.10.060.030.98±1.02t (min)
120
90
90
100
