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Synthesis of dodecenyl succinic anhydride (DDSA) corn starch
Food Research International 40 (2007) 232–238 www.elsevier.com/locate/foodres
Synthesis of dodecenyl succinic anhydride (DDSA) corn starch Hui Chi a, Kun Xu b, Donghua Xue a, Chunlei Song b, Wende Zhang b, Pixin Wang b
b,*
a Changchun University of Technology, School of Biological Engineering, Changchun 130012, China Polymer Engineering Laboratory, Changchun Institute of Applied Chemistry, Chinese Academy of Science, Changhun, Jilin 130022, PR China
Received 19 July 2006; accepted 21 September 2006
Abstract Dodecenly succinic anhydride (DDSA) starches were prepared commercially by the base catalyzed reaction of DDSA in pre-emulsion with starch granular in aqueous slurry. The results indicated that the degree of substitution and reaction efficiency were 0.0256% and 42.7%, respectively, at the parameters for the preparation of DDSA starches in starch slurry 30%, DDSA/starch radio 10% (wt/wt), pH 8.5–9.0, reaction temperature 313 K. After modification, product surface chemical composite had been changed which was prone to migrate into less polar solution. The chemical structural characteristics were investigated by methods of FTIR and 1H NMR. The results of X-ray diffraction showed the native A-type crystalline pattern, indicating that reaction of corn starch with DDSA caused no change in the crystalline structure. Compared to native starch, the hydrophobic performance of esters was greatly increased. With the DS increasing, contact angles were gradually increased, however, the adhesion works were decreased. The maximum contact angle of DDSA starch could attend to 123°, and the corresponding adhesion work was 33.2 mJ m2. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Corn starch; Dodecenly succinic anhydride; Emulsion; Starch ester
1. Introduction Starch is an important renewable occurring polymer which has found wide application in diverse areas of polymer science. Frequently starch is chemically modified by chemical reaction with hydroxyl groups in the starch molecule to confer additional properties such as hydrophobicity, porosity, functionality, formability and mechanical integrity (Zhang, 2003). Modified starch derivatives are provided with physicochemical properties that differ significantly from native starch, thus widening their applications in food manufacturing and other industrial processes. One of the common chemical modifications of starch is esterification (Zhang, 2003). Modification of starch with alkanoates like acetate and succinate imparts water resistance to the products. In contrast, the formation of starch alkenyl
*
Corresponding author. Tel./fax: +86 431 5262629. E-mail address: [email protected] (P. Wang).
0963-9969/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2006.09.013
succinates increases the hydrophilicity of modified starches (Jeon, Viswanathan, & Gross, 1999). Modification of starch with alkenyl succinic anhydrides (ASAs) results in highly versatile starch products with amphiphilic side-chains. The length of the alkenyl group and the degree of substitution ultimately determine the extent of hydrophobic character of the modified starch. Clearly, the alkenyl succinates are a family of highly versatile derivatives (Jeon et al., 1999). In 1953, Caldwell and Wurzburg patented the modification of starch with Octenyl succinic anhydride (OSA) (Caldwell & Wurzburg, 1953). In recent years, studies had been reported on preparation conditions of starches with succinates (Betancur-Ancona, Garcia-Cervera, Canizares-Hernandez, & Chel-Guerrero, 2002; Praful & Rekha, 2002) and alkenyl succinates (Jeon et al., 1999; Song, He, Ruan, & Chen, 2006), distribution of OSA groups (Shogren, Viswanathan, Felker, & Gross, 2000), the properties of succinate starches (Rudnik, Matuschek, Milanov, & Kettrup, 2005) and OSA starches (Angellier, Molina-Boisseau, Belagcem, & Dufresne, 2005; Bao, Xing, Phillips, &
H. Chi et al. / Food Research International 40 (2007) 232–238
Corke, 2003). In place of OSA, DDSA may be used to create a wider diversity of modified starch products. Certainly, an increase in the length of the alkenyl group provides a route to increase hydrophobic character at similar degree of substitution ranges. In addition, in a low degree of starch substitution, it may then be possible to better retain the biodegradability of the modified product. Furthermore, starch esterification in aqueous suspension system is environmental friendly (Jeon et al., 1999). The general method for reaction of DDSA with starch is by adding DDSA directly into the starch slurry system, using a sodium hydroxide solution to maintain the constant pH range. Because DDSA has a long side-chain, its solubility in water is very low. During the esterification, it is harder to react with the starch under the conditions. Also, starch is insoluble in water, so esterification in aqueous slurry systems is a heterogeneous reaction. As a result, both degree of substitution and reaction efficiency are very low (Jeon et al., 1999). Compared to the traditional method, anhydride in pre-emulsion form can improve the solubility of DDSA in water, and increase the opportunities to touch with starch granule, enhance obviously the level of degree of substitution and reaction efficiency. In this study, DDSA starches were prepared from corn starch in aqueous suspension system (Fig. 1). The main factors affecting the reaction including DDSA/starch ratio, reaction temperature and pH range of the system were investigated systematically. The native starch and different DS starches were characterized by wettability experiment, FTIR, 1H NMR, X-ray diffraction and contact angle measurement. 2. Materials and methods 2.1. Materials Corn starch was a commercial product obtained from Changchun Dacheng Industrial Group Co., Ltd (China). High purity dodecenyl succinic anhydride (DDSA) was obtained from Sinopharm Chemical Reagent Co., Ltd (China). Nonyl phenol polyethenoxy ether succinate sodium salt (MES) was obtained from Henan Tongxin Technology Co., Ltd (China). The other chemicals used in the study were of analytical grade.
2.2. Preparation of DDSA starch An emulsion of DDSA was prepared by mixing 28 parts of DDSA and 2 parts of MES in a conical flask (2 min, 298 K) with 70 parts of water. Corn starch (30.00 g, dry weight) was suspended in distill water (30%) with agitation. The pH was adjusted to 8.5 with 3% NaOH solution. 10.72 g emulsion of DDSA prepared as described above was added to the starch slurry. The pH range of the system was maintained at a given level with 3% NaOH solution until the reaction was completed. After reaction, the pH was brought to 6.5–7.0 using 5% HCl solution. The mixture was centrifuged, washed with excess acetone and distilled water. The solid was dried at 323 K for 12 h in vacuum oven. 2.3. Determination of the degree of substitution The degree of substitution (DS) was the average number of hydroxyl groups substituted per anhyglucose unit. The DS of DDSA starch was determined by titration (Zhang & Han, 2001). 5.00 g starch derivative was accurately weighted into a 50 mL beaker. Then 10 mL of ethanol was added to the beaker and was allowed to stir. 25 mL of 0.1 N HCl ethanol solution was added and the entire solution was allowed to stir for 30 min. The slurry was filtered and the wet cake was washed with deionized water until no Cl1 could be detected any longer (using 0.1 N AgNO3 solution). The wet cake was quantitatively transferred to a 900 mL beaker, 100 mL deionized water was added, and then 200 mL of boiling deionized water was added. The solution was placed into a boiling water bath and cooked for 30 min.Immediately, after the solution was cooked, 6–10 drops of 1% thymolphthalein indicator were added and the solution was immediately titrated with 0.1 N sodium hydroxide to the thymolphthalein endpoint. The DS was calculated by the following equation: DS ¼
162 C V 103 W 266 C V 103
Where: C is the molarity of the NaOH solution used during the titration; V is the consuming volume of NaOH solution; W is the weight of sample analyzed. 162 is the molecular weight of anhyglucose unit; 266 is molecular weight of dodecenly succinic anhydride.
H OH
H
H H
H
O
O
OH
OH
H
H O
233
OH O
+
C
CH 2
O C
CH
O
R
O
O
NaOH
H
H H
OH
O
O O
CH 2 CH CO ON a R
R:
CH2CH=CH(CH2)8CH 3
Fig. 1. Chemical reaction formula of starch and DDSA.
H. Chi et al. / Food Research International 40 (2007) 232–238
The reaction efficiency (RE) was calculated as follows: Actual DS 100% Theoretical DS
The theoretical DS was calculated assuming that all of the added anhydride reacted with starch to form the esters derivative. 2.4. Characterization FTIR analysis was performed using a Bruker Vertex 70 FTIR spectrometer (Germany). The starch and esters were mixed with analytical grade KBr. FTIR spectra were recorded with a resolution of 4 cm1 and with a total of 32 scans, and wave number ranged between 400 and 4000 cm1. The starch and DS 0.0256 ester were dried at 323 K for 12 h before analysis to avoid the interference of moisture. 1 H NMR spectra were recorded on a Bruker 400 MHz Fourier transform spectrometer (Germany). All spectra of starch and DS 0.0256 ester were taken in deuterated dimethyl sulfoxide solution (DMSO-d6) at 343 K. X-ray diffraction was obtained from a D/max 2500 Xray diffraction meter, a conventional copper target X-ray tube was set to 40 kV and 200 mA. The X-ray source was Cu Ka radiation. Data were collected from 2h of 5.00°– 35.00° (h being the angle of diffraction) with a step width of 0.02° and step time of 0.4 s. The native starch and different DS DDSA starches were equilibrated at 323 K for 12 h prior to the analysis. The contact angle was the angle between a liquid droplet and the surface over which it spread. The measurement of the contact angle gave an indication of the nature of the surface. Contact angles were measured at room temperature using a Drop Shape Analysis System G 10/DSA 10 (Kruess, Germany). Water droplets were dropped carefully onto the films. The average contact angle range was obtained by measuring at ten different positions of the same sample. A video camera attached to the computer was used to project an image of the drop onto a screen, from which measurements of the contact angle were obtained. According to the Young–Dupre’ equation, the adhesion work is also given by
3.1. Effect of DDSA/starch radio on esterification Fig. 2 shows the effects of relative percentage of DDSA to starch on DS and RE. The increase in DDSA/starch radio, DS improved due to the opportunities of collisions of anhydride with starch granule. However, because of DDSA derived long side-chains and its more steric inhibition, even increasing the DDSA/starch radio to 15%, DS only increased a little. With the addition of DDSA from 3% to 15%, RE decreased obviously from 71.1% to 28.6%. This might result in the reaction systems dilution by large alkaline reagents usages when using higher amounts of anhydrides. When DDSA/starch radio was 10%, the DS and RE were 0.0256% and 42.7%, respectively. Hence, considerations of DS and RE, 10% DDSA/ starch radio was preferred for the preparation starch esters in water and used in subsequent studies described below. Compared with the literature reported by Jeon et al. (1999), DDSA/starch radio was similar, but DS in our work was a little higher. 3.2. Effect of pH range on esterification It was also very important to control the pH range in this system. Fig. 3 shows that pH in the range of 8.5–9.0 was very effective to the esterification and DS was 0.0256, RE was 42.7%. With pH increasing, DS and RE were firstly increased and then decreased. In pH range of 7.0–8.5, DS and RE were increased from 0.012 to 0.0256 and from 20.0% to 42.7%, respectively. In pH of 9.0–10.0, they were decreased from 0.0256 to 0.0162 and from 42.7% to 27.0%, respectively. These results indicated that DS and RE could
80 70 60
ð1Þ
Where Wa and cL are the adhesion work and surface tension of water (72.8 mJ m2), respectively. After heating at 343 K in DMSO solution, starch and different DDSA samples (0.01 g/mL) were cooled at room temperature, then added onto the silicon substance dropwise and dried at 353 K for 2 h in a vacuum oven. 2.5. Statistics
50 40 30 20 10 0
DD 15 SA /
)
W a ¼ cL ðcos h þ 1Þ
3. Results and discussion
(%
RE ¼
multiple range tests to compare treatments means. Significance was defined at P < 0.05.
sta 10 rch (
R E
234
3
0 *1 DS
5
wt
/w
t, %
)
All measurements were made in triplicate. Analysis of variance (ANOVA) was performed using the Duncan’s
Fig. 2. Effects of DDSA/starch ratio on DS and RE. Conditions: starch slurry 30%, pH 8.5–9.0, reaction temperature 313 K.
H. Chi et al. / Food Research International 40 (2007) 232–238
40 30 20
235
the reaction temperature was above 318 K, the viscosity of system might increase due to the gelatinization of starch in alkali condition, resulting in difficulty of product filtration. Thus, reaction temperature of 313 K was concluded to be the most appropriate temperature for DDSA modification of corn starch in this aqueous slurry system. 3.4. Wettability experiments
10
5
E
-9. 9.0
pH
(% )
0
.5-
R
9.
0.0 5-1
9.0
3
5 ra 8 ng 8.0-8. e
0
-8.
7.5
DS
0 *1
Fig. 3. Effects of pH on DS and RE. Conditions: starch slurry 30%, DDSA/starch 10% (wt/wt), reaction temperature 313 K.
get optimal values in pH 8.5–9.0. It is well known that there are three hydroxyl groups in every glucose unit. When the pH < 8.5, it did not sufficiently activate hydroxyl groups of starch for nucleophilic attack of the anhydride moieties. However, when the pH > 9.0, the anhydride was favor to hydrolysis, it was adverse to esterification process. Hence, the pH range of 8.5–9.0 was very appropriate for the reaction and was applied in the subsequent experiments. 3.3. Effect of reaction temperature on esterification Fig. 4 shows the results of variation in reaction temperature on DS and RE. Temperature varied from 293 K to 313 K, both DS and RE increased. An increase in the reaction temperature would result in enhancing the solubility of DDSA in the aqueous phase and a higher temperature would also be expected to enhance DDSA diffusion into the starch granules as well as the swelling of starch granules that increased esterification reaction rates. However when
50
In general, the introduction of hydrophobic alkenyl succinic anhydride groups into the molecular structure of starch would alter its surface properties. A simple and valuable experiment was to mix the native or modified materials with two immiscible solvents having different polarities and to observe the affinity between these two substances. In our experiments, the distilled water and chloroform were used as the solvent system giving rise to two phases, the upper one corresponding to water (q = 1) and lower one to chloroform (q = 1.47). The reference experiment consisted of putting the same amount of unmodified starch and DS 0.0256 DDSA starch in the mixture. Obviously, native starch was not able to migrate into chloroform and remained in water medium due to its higher affinity with water. Even after shaking the container, we observed that starch still remained in the aqueous medium (Fig. 5A). Therefore, it was concluded that unmodified starch displayed a higher affinity for a polar solvent such as water. By adding DDSA starch to the mixture and shaking it, we clearly noticed that they migrated toward the chloroform (Fig. 5B), suggesting the lower polar nature after chemical modification. 3.5. FTIR To detect if the esterification existed, the FTIR spectra were measured and the spectra of native starch and DS 0.0256 DDSA starch are shown in Fig. 6. IR spectrum for native starch (Fig. 6A), at 3421 cm1 related to the OH group (Fang, Fowler, Tomkinso, & Hill, 2002) and at 1159, 1082, 1014 cm1 in the fingerprint region corresponding to –C–O–C– stretching vibration in glucose bonds (Fang, Fowler, Sayers, & Williams, 2004). The bonds at 992, 929, 861, 765, 575 cm1 were attributed to
40 30 20 10
(%
)
0
RE
15 re 3 10 ac tio 3 nt 05 em 3 0 pe 30 ra tur 95 e( 2 K)
3
DS
0 *1
Fig. 4. Effects of reaction temperature on DS and RE. Conditions: starch slurry 30%, DDSA/starch 10% (wt/wt), pH 8.5–9.0.
Fig. 5. Wettability tests of native starch and DDSA starch. (A) native starch in distilled water, (B) DS 0.0256 DDSA starch in chloroform.
236
H. Chi et al. / Food Research International 40 (2007) 232–238 Table 1 Chemical shifts and assignments for DS 0.0256 DDSA starch 861
575
929
765
1159 1082 1014 992
1724
1571
3421
Transmission (%)
2931
1648
A
Chemical shifts (ppm)
Assignment
5.11–5.22 4.34 3.33–3.66 1.52 1.26 0.85
OH-3,2 H-1 (starch) OH-6 (starch) H-2,3,4,5,6 (starch) CH (DDSA) CH2 (DDSA) CH3 (DDSA)
B
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Fig. 6. FTIR spectra for (A) native starch and (B) DS 0.0256 DDSA starch.
the whole glucose ring stretching vibrations. The band at 1648 cm1 presumably originates from tightly bound water present in the starch (Kacurakova & Wilson, 2001).The band at 2923 cm1 was the characteristic vibration of C– H stretches. In DDSA starch spectrum (Fig. 6B), some characteristics peaks of DDSA were found which were located at 1724 cm1 corresponding to the stretch ester carbonyl group (Marcazzan, Vianello, Scarpa, & Rigo, 1999), and 1571 cm1 relating to the asymmetric stretch of vibration of carboxylate RCOO (Zhang, Jin, & Liu, 2004; Nagaoka, Tobata, & Satoh, 2005). All these results confirmed that DDSA had been reacted into the starch backbone. 3.6. 1H NMR On the other hand, we used 1H NMR spectrum to detect the structure of DS 0.0256 DDSA starch (Fig. 7), and the assignments of spectrum peak are given in Table 1. In the condition of heating at 343 K, the resonances of proton signals (OH-6, OH-3, OH-2) were shifted upfield compared with the room temperature spectrum (be not shown), with the latter two coincident with that of H-1. This was similar with the 1H NMR of native starch at higher temperature (Peng & Perlin, 1987). The proton signals at 3.33–
3.66 ppm were very broad and complex, which were attributed to the protons of anhyglucose unit except H-1. The proton signals at 0.85–1.52 ppm were assigned to the methyl, methylene and methenyl groups of DDSA starch. The results further indicated that the esterification certainly proceeded. 3.7. X-ray diffraction X-ray diffraction measurements were performed to check if the chemical modification altered the crystallinity of starch. X-ray diffraction power patterns of unmodified and DDSA starches are displayed in Fig. 8. Starch was composed of amylose and amylopectin. Amylose is located mainly in the amorphous domain of starch granule. In contrast, amylopectin makes up the framework of the crystalline lamellae, branching points are located in the disordered amorphous domains between the crystallites, which leads to the crystal diffractions. Corn starch is a kind of cereals starch exhibiting an A-type pattern, with strong reflection at 15°, 17°, 18°, 23° (Zobel, 1988). It was observed DDSA starch displayed similar reflections, leading to the conclusion that the initial crystallinity was retained up to the DS 0.0256 DDSA starch. This observation showed that esterification mainly occurred primarily in amorphous domain. It did not react with the hydroxyl groups in the crystalline domain, and did not change the crystalline pattern of the starch. Similarly, Shogren et al. (2000), Angellier et al. (2005), Song et al. (2006) reported similar X-ray patterns in modified OSA starches.
Fig. 7. 400 M 1H NMR of DS 0.0256 DDSA starch in DMSO-d6 at 343K.
H. Chi et al. / Food Research International 40 (2007) 232–238
237
ing the lower wettabilities between water and esters. The contact angle and adhesion work of DS 0.0256 DDSA starch reached to 123° and 33.2 mJ m2, respectively. The DS of DDSA starches were very low, but they greatly improved the hydrophobicity performance of starch materials. Intensity
D
4. Conclusion
C B A
5
50
15
20
25
30
35
2θ (°)
Fig. 8. X-ray diffraction spectra for (A) native starch and (B) DS 0.0132 (C) DS 0.0180 (D) 0.0256 DDSA starches.
3.8. Contact angle measurements The dynamic behavior of the contact angle for a drop of distilled water on the surface of materials studies is shown in Fig. 9. When adding a drop of distilled water, it quickly spread out on the starch surface, giving the lowest contact angle valve and highest adhesion work (Table 2). Because the unmodified starch surface was of OH-rich macromolecules, it had the capability to establish hydrogen bond in water. The contact angles of modified substances were all about 3 times higher than that of unmodified starch (Table 2), indicating that chemical treatments induced dramatic changes in surface polarity of starch. With DS increasing, the contact angle of the esters had an improvement, however, the adhesion works were decreased (Table 2), indicat-
Fig. 9. Dynamic contact angles (h) of water drop on the surface of (A) native starch and (B) DS 0.0256 DDSA starch.
Table 2 Contact angles and adhesion worksof native starch and DDSA starches Native starch
Contact angles (°) Adhesion work (mJ m2)
43.1 126.0
DDSA starches DS 0.0132
DS 0.0180
DS 0.0256
110.5 47.9
116.2 40.9
123.4 33.2
Adhesion work was calculated according to Eq. (1).
DDSA starches were prepared in aqueous medium with DDSA in pre-emulsion. Optimal values of degree of substitution (0.0256) and reaction efficiency (42.7%) were obtained by the amount of DDSA 10% (in proportion to starch, wt/wt), reaction temperature 313 K, at pH 8.5– 9.0. FTIR and 1H NMR showed that the characteristic peaks at 1724 cm1 and 1571 cm1 and 0.85–1.52 ppm, respectively. X-ray diffraction indicated that modification caused no change in the crystalline pattern up to DS 0.0256. DDSA starches were hydrophobic derivatives confirmed by contact angle measurement. The contact angle of DS 0.0256 ester was up to 123°. Acknowledgment The financial support from Nation Science Foundation of Jilin Province of China (Grant No. 20050502) is gratefully acknowledged. References Angellier, H., Molina-Boisseau, S., Belagcem, M. N., & Dufresne, A. (2005). Surface chemical modification of waxy maize starch nanocrystals. Langmuir, 21, 2425–2433. Bao, J. S., Xing, J., Phillips, D. L., & Corke, H. (2003). Physical properties of octenyl succinic anhydride modified Rice, wheat, and potato starches. Journal of Agricultural and Food Chemistry, 51, 2283–2287. Betancur-Ancona, D., Garcia-Cervera, E., Canizares-Hernandez, E., & Chel-Guerrero, L. (2002). Chemical modification of Jack Bean starch by succinylation. Starch/Sta¨rke, 54, 540–546. Caldwell, C. G., & Wurzburg, O. D. (1953). National starch products Inc. US 2,661,349. Fang, J. M., Fowler, P. A., Sayers, C., & Williams, P. A. (2004). The chemical modification of a range of starches under aqueous reaction condition. Carbohydrate Polymers, 55, 283–289. Fang, J. M., Fowler, P. A., Tomkinso, J., & Hill, C. A. S. (2002). The preparation and characterization of a series of chemically modified potato starches. Carbohydrate Polymers, 47, 245–252. Jeon, Y. S., Viswanathan, A., & Gross, R. (1999). Studies of starch esterification: reactions with alkenylsuccinates in aqueous slurry systems. Starch/Sta¨rke, 51, 90–93. Kacurakova, M., & Wilson, R. H. (2001). Developments in mid-infrared FTIR spectroscopy of selected carbohydrates. Carbohydrate Polymers, 44, 291–303. Marcazzan, M., Vianello, F., Scarpa, M., & Rigo, A. (1999). An ESR assay for a-amylase activity toward succinylated starch, amylose and amylopectin. Journal of Biochemical and Biophysical Methods 38, 191–202. Nagaoka, S., Tobata, H., & Satoh, T. (2005). Characterization of cellulose microbeads prepared by a viscose phase-separation method and their chemical modification with acid anhydride. Journal of Applied Polymer Science, 97, 149–157.
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Peng, Q. J., & Perlin, A. S. (1987). Observations on NMR spectra of starches in dimethylsulfoxide, iodine-complexing, and salvation in water-dimethyl sulfoxide. Carbohydrate Research, 160, 57–72. Praful, N. B., & Rekha, S. S. (2002). Studies on the optimization of preparation of succinate derivatives from corn and amaranth starches. Carbohydrate Polymer, 47, 277–283. Rudnik, E., Matuschek, G., Milanov, N., & Kettrup, A. (2005). Thermal properties of starch succinates. Thermochimica Acta, 427, 163–166. Shogren, R. L., Viswanathan, A., Felker, F., & Gross, R. (2000). Distribution of octenyl succinate groups in octenyl succinic anhydride modified waxy maize starch. Starch/Sta¨rke, 52, 196–204.
Song, X. Y., He, G. Q., Ruan, H., & Chen, Q. (2006). Preparation and properties of octenyl succinic anhydride modified early Indica rice starch. Starch/Sta¨rke, 58, 109–117. Zhang, Y. P. (2003). Production and application of modified starch. Beijing: Chemical Industry Press, p. 269. Zhang, J., & Han, X. Z. (2001). Preparation of hydrophobic starch derivatives. Chinese Journal of Applied Chemistry, 18, 749–751. Zhang, Y., Jin, R. G., & Liu, M. H. (2004). Growth of CaCO3 in the templated Langmuie–Blodgett film of a bolaamphiphilic diacid. New Journal of Chemistry, 28, 614–617. Zobel, H. F. (1988). Starch crystal transformations and their industrial importance. Starch/Sta¨rke, 40, 1–7.
Synthesis of dodecenyl succinic anhydride (DDSA) corn starch Hui Chi a, Kun Xu b, Donghua Xue a, Chunlei Song b, Wende Zhang b, Pixin Wang b
b,*
a Changchun University of Technology, School of Biological Engineering, Changchun 130012, China Polymer Engineering Laboratory, Changchun Institute of Applied Chemistry, Chinese Academy of Science, Changhun, Jilin 130022, PR China
Received 19 July 2006; accepted 21 September 2006
Abstract Dodecenly succinic anhydride (DDSA) starches were prepared commercially by the base catalyzed reaction of DDSA in pre-emulsion with starch granular in aqueous slurry. The results indicated that the degree of substitution and reaction efficiency were 0.0256% and 42.7%, respectively, at the parameters for the preparation of DDSA starches in starch slurry 30%, DDSA/starch radio 10% (wt/wt), pH 8.5–9.0, reaction temperature 313 K. After modification, product surface chemical composite had been changed which was prone to migrate into less polar solution. The chemical structural characteristics were investigated by methods of FTIR and 1H NMR. The results of X-ray diffraction showed the native A-type crystalline pattern, indicating that reaction of corn starch with DDSA caused no change in the crystalline structure. Compared to native starch, the hydrophobic performance of esters was greatly increased. With the DS increasing, contact angles were gradually increased, however, the adhesion works were decreased. The maximum contact angle of DDSA starch could attend to 123°, and the corresponding adhesion work was 33.2 mJ m2. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Corn starch; Dodecenly succinic anhydride; Emulsion; Starch ester
1. Introduction Starch is an important renewable occurring polymer which has found wide application in diverse areas of polymer science. Frequently starch is chemically modified by chemical reaction with hydroxyl groups in the starch molecule to confer additional properties such as hydrophobicity, porosity, functionality, formability and mechanical integrity (Zhang, 2003). Modified starch derivatives are provided with physicochemical properties that differ significantly from native starch, thus widening their applications in food manufacturing and other industrial processes. One of the common chemical modifications of starch is esterification (Zhang, 2003). Modification of starch with alkanoates like acetate and succinate imparts water resistance to the products. In contrast, the formation of starch alkenyl
*
Corresponding author. Tel./fax: +86 431 5262629. E-mail address: [email protected] (P. Wang).
0963-9969/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2006.09.013
succinates increases the hydrophilicity of modified starches (Jeon, Viswanathan, & Gross, 1999). Modification of starch with alkenyl succinic anhydrides (ASAs) results in highly versatile starch products with amphiphilic side-chains. The length of the alkenyl group and the degree of substitution ultimately determine the extent of hydrophobic character of the modified starch. Clearly, the alkenyl succinates are a family of highly versatile derivatives (Jeon et al., 1999). In 1953, Caldwell and Wurzburg patented the modification of starch with Octenyl succinic anhydride (OSA) (Caldwell & Wurzburg, 1953). In recent years, studies had been reported on preparation conditions of starches with succinates (Betancur-Ancona, Garcia-Cervera, Canizares-Hernandez, & Chel-Guerrero, 2002; Praful & Rekha, 2002) and alkenyl succinates (Jeon et al., 1999; Song, He, Ruan, & Chen, 2006), distribution of OSA groups (Shogren, Viswanathan, Felker, & Gross, 2000), the properties of succinate starches (Rudnik, Matuschek, Milanov, & Kettrup, 2005) and OSA starches (Angellier, Molina-Boisseau, Belagcem, & Dufresne, 2005; Bao, Xing, Phillips, &
H. Chi et al. / Food Research International 40 (2007) 232–238
Corke, 2003). In place of OSA, DDSA may be used to create a wider diversity of modified starch products. Certainly, an increase in the length of the alkenyl group provides a route to increase hydrophobic character at similar degree of substitution ranges. In addition, in a low degree of starch substitution, it may then be possible to better retain the biodegradability of the modified product. Furthermore, starch esterification in aqueous suspension system is environmental friendly (Jeon et al., 1999). The general method for reaction of DDSA with starch is by adding DDSA directly into the starch slurry system, using a sodium hydroxide solution to maintain the constant pH range. Because DDSA has a long side-chain, its solubility in water is very low. During the esterification, it is harder to react with the starch under the conditions. Also, starch is insoluble in water, so esterification in aqueous slurry systems is a heterogeneous reaction. As a result, both degree of substitution and reaction efficiency are very low (Jeon et al., 1999). Compared to the traditional method, anhydride in pre-emulsion form can improve the solubility of DDSA in water, and increase the opportunities to touch with starch granule, enhance obviously the level of degree of substitution and reaction efficiency. In this study, DDSA starches were prepared from corn starch in aqueous suspension system (Fig. 1). The main factors affecting the reaction including DDSA/starch ratio, reaction temperature and pH range of the system were investigated systematically. The native starch and different DS starches were characterized by wettability experiment, FTIR, 1H NMR, X-ray diffraction and contact angle measurement. 2. Materials and methods 2.1. Materials Corn starch was a commercial product obtained from Changchun Dacheng Industrial Group Co., Ltd (China). High purity dodecenyl succinic anhydride (DDSA) was obtained from Sinopharm Chemical Reagent Co., Ltd (China). Nonyl phenol polyethenoxy ether succinate sodium salt (MES) was obtained from Henan Tongxin Technology Co., Ltd (China). The other chemicals used in the study were of analytical grade.
2.2. Preparation of DDSA starch An emulsion of DDSA was prepared by mixing 28 parts of DDSA and 2 parts of MES in a conical flask (2 min, 298 K) with 70 parts of water. Corn starch (30.00 g, dry weight) was suspended in distill water (30%) with agitation. The pH was adjusted to 8.5 with 3% NaOH solution. 10.72 g emulsion of DDSA prepared as described above was added to the starch slurry. The pH range of the system was maintained at a given level with 3% NaOH solution until the reaction was completed. After reaction, the pH was brought to 6.5–7.0 using 5% HCl solution. The mixture was centrifuged, washed with excess acetone and distilled water. The solid was dried at 323 K for 12 h in vacuum oven. 2.3. Determination of the degree of substitution The degree of substitution (DS) was the average number of hydroxyl groups substituted per anhyglucose unit. The DS of DDSA starch was determined by titration (Zhang & Han, 2001). 5.00 g starch derivative was accurately weighted into a 50 mL beaker. Then 10 mL of ethanol was added to the beaker and was allowed to stir. 25 mL of 0.1 N HCl ethanol solution was added and the entire solution was allowed to stir for 30 min. The slurry was filtered and the wet cake was washed with deionized water until no Cl1 could be detected any longer (using 0.1 N AgNO3 solution). The wet cake was quantitatively transferred to a 900 mL beaker, 100 mL deionized water was added, and then 200 mL of boiling deionized water was added. The solution was placed into a boiling water bath and cooked for 30 min.Immediately, after the solution was cooked, 6–10 drops of 1% thymolphthalein indicator were added and the solution was immediately titrated with 0.1 N sodium hydroxide to the thymolphthalein endpoint. The DS was calculated by the following equation: DS ¼
162 C V 103 W 266 C V 103
Where: C is the molarity of the NaOH solution used during the titration; V is the consuming volume of NaOH solution; W is the weight of sample analyzed. 162 is the molecular weight of anhyglucose unit; 266 is molecular weight of dodecenly succinic anhydride.
H OH
H
H H
H
O
O
OH
OH
H
H O
233
OH O
+
C
CH 2
O C
CH
O
R
O
O
NaOH
H
H H
OH
O
O O
CH 2 CH CO ON a R
R:
CH2CH=CH(CH2)8CH 3
Fig. 1. Chemical reaction formula of starch and DDSA.
H. Chi et al. / Food Research International 40 (2007) 232–238
The reaction efficiency (RE) was calculated as follows: Actual DS 100% Theoretical DS
The theoretical DS was calculated assuming that all of the added anhydride reacted with starch to form the esters derivative. 2.4. Characterization FTIR analysis was performed using a Bruker Vertex 70 FTIR spectrometer (Germany). The starch and esters were mixed with analytical grade KBr. FTIR spectra were recorded with a resolution of 4 cm1 and with a total of 32 scans, and wave number ranged between 400 and 4000 cm1. The starch and DS 0.0256 ester were dried at 323 K for 12 h before analysis to avoid the interference of moisture. 1 H NMR spectra were recorded on a Bruker 400 MHz Fourier transform spectrometer (Germany). All spectra of starch and DS 0.0256 ester were taken in deuterated dimethyl sulfoxide solution (DMSO-d6) at 343 K. X-ray diffraction was obtained from a D/max 2500 Xray diffraction meter, a conventional copper target X-ray tube was set to 40 kV and 200 mA. The X-ray source was Cu Ka radiation. Data were collected from 2h of 5.00°– 35.00° (h being the angle of diffraction) with a step width of 0.02° and step time of 0.4 s. The native starch and different DS DDSA starches were equilibrated at 323 K for 12 h prior to the analysis. The contact angle was the angle between a liquid droplet and the surface over which it spread. The measurement of the contact angle gave an indication of the nature of the surface. Contact angles were measured at room temperature using a Drop Shape Analysis System G 10/DSA 10 (Kruess, Germany). Water droplets were dropped carefully onto the films. The average contact angle range was obtained by measuring at ten different positions of the same sample. A video camera attached to the computer was used to project an image of the drop onto a screen, from which measurements of the contact angle were obtained. According to the Young–Dupre’ equation, the adhesion work is also given by
3.1. Effect of DDSA/starch radio on esterification Fig. 2 shows the effects of relative percentage of DDSA to starch on DS and RE. The increase in DDSA/starch radio, DS improved due to the opportunities of collisions of anhydride with starch granule. However, because of DDSA derived long side-chains and its more steric inhibition, even increasing the DDSA/starch radio to 15%, DS only increased a little. With the addition of DDSA from 3% to 15%, RE decreased obviously from 71.1% to 28.6%. This might result in the reaction systems dilution by large alkaline reagents usages when using higher amounts of anhydrides. When DDSA/starch radio was 10%, the DS and RE were 0.0256% and 42.7%, respectively. Hence, considerations of DS and RE, 10% DDSA/ starch radio was preferred for the preparation starch esters in water and used in subsequent studies described below. Compared with the literature reported by Jeon et al. (1999), DDSA/starch radio was similar, but DS in our work was a little higher. 3.2. Effect of pH range on esterification It was also very important to control the pH range in this system. Fig. 3 shows that pH in the range of 8.5–9.0 was very effective to the esterification and DS was 0.0256, RE was 42.7%. With pH increasing, DS and RE were firstly increased and then decreased. In pH range of 7.0–8.5, DS and RE were increased from 0.012 to 0.0256 and from 20.0% to 42.7%, respectively. In pH of 9.0–10.0, they were decreased from 0.0256 to 0.0162 and from 42.7% to 27.0%, respectively. These results indicated that DS and RE could
80 70 60
ð1Þ
Where Wa and cL are the adhesion work and surface tension of water (72.8 mJ m2), respectively. After heating at 343 K in DMSO solution, starch and different DDSA samples (0.01 g/mL) were cooled at room temperature, then added onto the silicon substance dropwise and dried at 353 K for 2 h in a vacuum oven. 2.5. Statistics
50 40 30 20 10 0
DD 15 SA /
)
W a ¼ cL ðcos h þ 1Þ
3. Results and discussion
(%
RE ¼
multiple range tests to compare treatments means. Significance was defined at P < 0.05.
sta 10 rch (
R E
234
3
0 *1 DS
5
wt
/w
t, %
)
All measurements were made in triplicate. Analysis of variance (ANOVA) was performed using the Duncan’s
Fig. 2. Effects of DDSA/starch ratio on DS and RE. Conditions: starch slurry 30%, pH 8.5–9.0, reaction temperature 313 K.
H. Chi et al. / Food Research International 40 (2007) 232–238
40 30 20
235
the reaction temperature was above 318 K, the viscosity of system might increase due to the gelatinization of starch in alkali condition, resulting in difficulty of product filtration. Thus, reaction temperature of 313 K was concluded to be the most appropriate temperature for DDSA modification of corn starch in this aqueous slurry system. 3.4. Wettability experiments
10
5
E
-9. 9.0
pH
(% )
0
.5-
R
9.
0.0 5-1
9.0
3
5 ra 8 ng 8.0-8. e
0
-8.
7.5
DS
0 *1
Fig. 3. Effects of pH on DS and RE. Conditions: starch slurry 30%, DDSA/starch 10% (wt/wt), reaction temperature 313 K.
get optimal values in pH 8.5–9.0. It is well known that there are three hydroxyl groups in every glucose unit. When the pH < 8.5, it did not sufficiently activate hydroxyl groups of starch for nucleophilic attack of the anhydride moieties. However, when the pH > 9.0, the anhydride was favor to hydrolysis, it was adverse to esterification process. Hence, the pH range of 8.5–9.0 was very appropriate for the reaction and was applied in the subsequent experiments. 3.3. Effect of reaction temperature on esterification Fig. 4 shows the results of variation in reaction temperature on DS and RE. Temperature varied from 293 K to 313 K, both DS and RE increased. An increase in the reaction temperature would result in enhancing the solubility of DDSA in the aqueous phase and a higher temperature would also be expected to enhance DDSA diffusion into the starch granules as well as the swelling of starch granules that increased esterification reaction rates. However when
50
In general, the introduction of hydrophobic alkenyl succinic anhydride groups into the molecular structure of starch would alter its surface properties. A simple and valuable experiment was to mix the native or modified materials with two immiscible solvents having different polarities and to observe the affinity between these two substances. In our experiments, the distilled water and chloroform were used as the solvent system giving rise to two phases, the upper one corresponding to water (q = 1) and lower one to chloroform (q = 1.47). The reference experiment consisted of putting the same amount of unmodified starch and DS 0.0256 DDSA starch in the mixture. Obviously, native starch was not able to migrate into chloroform and remained in water medium due to its higher affinity with water. Even after shaking the container, we observed that starch still remained in the aqueous medium (Fig. 5A). Therefore, it was concluded that unmodified starch displayed a higher affinity for a polar solvent such as water. By adding DDSA starch to the mixture and shaking it, we clearly noticed that they migrated toward the chloroform (Fig. 5B), suggesting the lower polar nature after chemical modification. 3.5. FTIR To detect if the esterification existed, the FTIR spectra were measured and the spectra of native starch and DS 0.0256 DDSA starch are shown in Fig. 6. IR spectrum for native starch (Fig. 6A), at 3421 cm1 related to the OH group (Fang, Fowler, Tomkinso, & Hill, 2002) and at 1159, 1082, 1014 cm1 in the fingerprint region corresponding to –C–O–C– stretching vibration in glucose bonds (Fang, Fowler, Sayers, & Williams, 2004). The bonds at 992, 929, 861, 765, 575 cm1 were attributed to
40 30 20 10
(%
)
0
RE
15 re 3 10 ac tio 3 nt 05 em 3 0 pe 30 ra tur 95 e( 2 K)
3
DS
0 *1
Fig. 4. Effects of reaction temperature on DS and RE. Conditions: starch slurry 30%, DDSA/starch 10% (wt/wt), pH 8.5–9.0.
Fig. 5. Wettability tests of native starch and DDSA starch. (A) native starch in distilled water, (B) DS 0.0256 DDSA starch in chloroform.
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H. Chi et al. / Food Research International 40 (2007) 232–238 Table 1 Chemical shifts and assignments for DS 0.0256 DDSA starch 861
575
929
765
1159 1082 1014 992
1724
1571
3421
Transmission (%)
2931
1648
A
Chemical shifts (ppm)
Assignment
5.11–5.22 4.34 3.33–3.66 1.52 1.26 0.85
OH-3,2 H-1 (starch) OH-6 (starch) H-2,3,4,5,6 (starch) CH (DDSA) CH2 (DDSA) CH3 (DDSA)
B
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Fig. 6. FTIR spectra for (A) native starch and (B) DS 0.0256 DDSA starch.
the whole glucose ring stretching vibrations. The band at 1648 cm1 presumably originates from tightly bound water present in the starch (Kacurakova & Wilson, 2001).The band at 2923 cm1 was the characteristic vibration of C– H stretches. In DDSA starch spectrum (Fig. 6B), some characteristics peaks of DDSA were found which were located at 1724 cm1 corresponding to the stretch ester carbonyl group (Marcazzan, Vianello, Scarpa, & Rigo, 1999), and 1571 cm1 relating to the asymmetric stretch of vibration of carboxylate RCOO (Zhang, Jin, & Liu, 2004; Nagaoka, Tobata, & Satoh, 2005). All these results confirmed that DDSA had been reacted into the starch backbone. 3.6. 1H NMR On the other hand, we used 1H NMR spectrum to detect the structure of DS 0.0256 DDSA starch (Fig. 7), and the assignments of spectrum peak are given in Table 1. In the condition of heating at 343 K, the resonances of proton signals (OH-6, OH-3, OH-2) were shifted upfield compared with the room temperature spectrum (be not shown), with the latter two coincident with that of H-1. This was similar with the 1H NMR of native starch at higher temperature (Peng & Perlin, 1987). The proton signals at 3.33–
3.66 ppm were very broad and complex, which were attributed to the protons of anhyglucose unit except H-1. The proton signals at 0.85–1.52 ppm were assigned to the methyl, methylene and methenyl groups of DDSA starch. The results further indicated that the esterification certainly proceeded. 3.7. X-ray diffraction X-ray diffraction measurements were performed to check if the chemical modification altered the crystallinity of starch. X-ray diffraction power patterns of unmodified and DDSA starches are displayed in Fig. 8. Starch was composed of amylose and amylopectin. Amylose is located mainly in the amorphous domain of starch granule. In contrast, amylopectin makes up the framework of the crystalline lamellae, branching points are located in the disordered amorphous domains between the crystallites, which leads to the crystal diffractions. Corn starch is a kind of cereals starch exhibiting an A-type pattern, with strong reflection at 15°, 17°, 18°, 23° (Zobel, 1988). It was observed DDSA starch displayed similar reflections, leading to the conclusion that the initial crystallinity was retained up to the DS 0.0256 DDSA starch. This observation showed that esterification mainly occurred primarily in amorphous domain. It did not react with the hydroxyl groups in the crystalline domain, and did not change the crystalline pattern of the starch. Similarly, Shogren et al. (2000), Angellier et al. (2005), Song et al. (2006) reported similar X-ray patterns in modified OSA starches.
Fig. 7. 400 M 1H NMR of DS 0.0256 DDSA starch in DMSO-d6 at 343K.
H. Chi et al. / Food Research International 40 (2007) 232–238
237
ing the lower wettabilities between water and esters. The contact angle and adhesion work of DS 0.0256 DDSA starch reached to 123° and 33.2 mJ m2, respectively. The DS of DDSA starches were very low, but they greatly improved the hydrophobicity performance of starch materials. Intensity
D
4. Conclusion
C B A
5
50
15
20
25
30
35
2θ (°)
Fig. 8. X-ray diffraction spectra for (A) native starch and (B) DS 0.0132 (C) DS 0.0180 (D) 0.0256 DDSA starches.
3.8. Contact angle measurements The dynamic behavior of the contact angle for a drop of distilled water on the surface of materials studies is shown in Fig. 9. When adding a drop of distilled water, it quickly spread out on the starch surface, giving the lowest contact angle valve and highest adhesion work (Table 2). Because the unmodified starch surface was of OH-rich macromolecules, it had the capability to establish hydrogen bond in water. The contact angles of modified substances were all about 3 times higher than that of unmodified starch (Table 2), indicating that chemical treatments induced dramatic changes in surface polarity of starch. With DS increasing, the contact angle of the esters had an improvement, however, the adhesion works were decreased (Table 2), indicat-
Fig. 9. Dynamic contact angles (h) of water drop on the surface of (A) native starch and (B) DS 0.0256 DDSA starch.
Table 2 Contact angles and adhesion worksof native starch and DDSA starches Native starch
Contact angles (°) Adhesion work (mJ m2)
43.1 126.0
DDSA starches DS 0.0132
DS 0.0180
DS 0.0256
110.5 47.9
116.2 40.9
123.4 33.2
Adhesion work was calculated according to Eq. (1).
DDSA starches were prepared in aqueous medium with DDSA in pre-emulsion. Optimal values of degree of substitution (0.0256) and reaction efficiency (42.7%) were obtained by the amount of DDSA 10% (in proportion to starch, wt/wt), reaction temperature 313 K, at pH 8.5– 9.0. FTIR and 1H NMR showed that the characteristic peaks at 1724 cm1 and 1571 cm1 and 0.85–1.52 ppm, respectively. X-ray diffraction indicated that modification caused no change in the crystalline pattern up to DS 0.0256. DDSA starches were hydrophobic derivatives confirmed by contact angle measurement. The contact angle of DS 0.0256 ester was up to 123°. Acknowledgment The financial support from Nation Science Foundation of Jilin Province of China (Grant No. 20050502) is gratefully acknowledged. References Angellier, H., Molina-Boisseau, S., Belagcem, M. N., & Dufresne, A. (2005). Surface chemical modification of waxy maize starch nanocrystals. Langmuir, 21, 2425–2433. Bao, J. S., Xing, J., Phillips, D. L., & Corke, H. (2003). Physical properties of octenyl succinic anhydride modified Rice, wheat, and potato starches. Journal of Agricultural and Food Chemistry, 51, 2283–2287. Betancur-Ancona, D., Garcia-Cervera, E., Canizares-Hernandez, E., & Chel-Guerrero, L. (2002). Chemical modification of Jack Bean starch by succinylation. Starch/Sta¨rke, 54, 540–546. Caldwell, C. G., & Wurzburg, O. D. (1953). National starch products Inc. US 2,661,349. Fang, J. M., Fowler, P. A., Sayers, C., & Williams, P. A. (2004). The chemical modification of a range of starches under aqueous reaction condition. Carbohydrate Polymers, 55, 283–289. Fang, J. M., Fowler, P. A., Tomkinso, J., & Hill, C. A. S. (2002). The preparation and characterization of a series of chemically modified potato starches. Carbohydrate Polymers, 47, 245–252. Jeon, Y. S., Viswanathan, A., & Gross, R. (1999). Studies of starch esterification: reactions with alkenylsuccinates in aqueous slurry systems. Starch/Sta¨rke, 51, 90–93. Kacurakova, M., & Wilson, R. H. (2001). Developments in mid-infrared FTIR spectroscopy of selected carbohydrates. Carbohydrate Polymers, 44, 291–303. Marcazzan, M., Vianello, F., Scarpa, M., & Rigo, A. (1999). An ESR assay for a-amylase activity toward succinylated starch, amylose and amylopectin. Journal of Biochemical and Biophysical Methods 38, 191–202. Nagaoka, S., Tobata, H., & Satoh, T. (2005). Characterization of cellulose microbeads prepared by a viscose phase-separation method and their chemical modification with acid anhydride. Journal of Applied Polymer Science, 97, 149–157.
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