G Model
ARTICLE IN PRESS
BIOMAC 4337 1–7
International Journal of Biological Macromolecules xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Effects of acid-hydrolysis and hydroxypropylation on functional properties of sago starch
1
2
3 4
Q1
Elham Fouladi, Abdorreza Mohammadi Nafchi ∗ Food Biopolymer Research Group, Food Science and Technology Department, Damghan Branch, Islamic Azad University, Damghan, Semnan, Iran
5
6 18
a r t i c l e
i n f o
a b s t r a c t
7 8 9 10 11 12
Article history: Received 6 April 2014 Received in revised form 29 April 2014 Accepted 5 May 2014 Available online xxx
13
17
Keywords: Sago starch Dual modification Thermal properties
19
1. Introduction
14 15 16
20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
In this study, sago starch was hydrolyzed by 0.14 M HCl for 6, 12, 18, and 24 h, and then modified by pro- Q2 pylene oxide at a concentration of 0–30% (v/w). The effects of hydrolysis and etherification on molecular weight distribution, physicochemical, rheological, and thermal properties of dually modified starch were estimated. Acid hydrolysis of starch decreased the molecular weight of starch especially amylopectin, but hydroxypropylation had no effect on the molecular weight distribution. The degree of Molar substitution (DS) of hydroxypropylated starch after acid hydrolysis ranged from 0.007 to 0.15. Dually modified starch with a DS higher than 0.1 was completely soluble in cold water at up to 25% concentration of the starch. This study shows that hydroxypropylation and hydrolysis have synergistic effects unlike individual modifications. Dually modified sago starch can be applied to dip-molding for food and pharmaceutical processing because of its high solubility and low tendency for retrogradation. © 2014 Published by Elsevier B.V.
Starch is an abundant polysaccharide, and its properties differ according to plant source. Applications of native starch in food products are based on these inherent properties. However, some inherent functional properties, such as insolubility in water, tendency for retrogradation, opacity of cooked paste, and low flow, have restricted the applicability of starch in their native forms [1,2]. Many attempts have been made to overcome the disadvantages of starches and to develop industrial scale applications [3]. Modification of starch can be carried out physically, chemically, enzymatically, and genetically. Chemical modification of starch is the most common because it can be readily controlled, and the principal actions of chemical modifications are well understood compared with those of other methods of starch modification [4]. Depolymerization (i.e., acid-thinned hydrolysis or oxidation) and derivatizations (i.e., etherification or esterification) using chemical reagents are typical modifications that have a wide range of application in the starch industry [5]. Chemical modification causes changes in the molecular structure or introduces functional groups, thus improving the applicability of plant-derived materials in food and non-food industries [6–8].
∗ Corresponding author. Tel.: +98 232 522 5045; fax: +98 232 522 5039. E-mail addresses: [email protected], [email protected] (A.M. Nafchi).
Starches can be stabilized through reaction with monofunctional reagents. In these reactions, hydroxyl groups of the starch are converted into larger ether or ester groups to block interchain associations. This process tends to stabilize pastes and gels by giving them a reduced tendency to undergo retrogradation [9]. Hydroxypropyl starch (HPS) is a popular modified starch that is widely used in food industry. Hydroxypropylation of starches can cause high paste clarity, low tendency for retrogradation, freeze–thaw stability, and high solubility in cold water after cooking [10,11]. Molar substitution (DS), molecular weight distribution, and distribution of functional groups are the factors that characterize the properties of HPS. HPS also has good film formation properties. The properties of HPS film, such as mechanical, water vapor, and aroma permeability, have been investigated previously [12–14]. Generally, native starches have a low degree of substitution because of their limited degree of reaction on the granule surface. Karim et al. [15] observed that enzymatic hydrolysis prior to the hydroxypropylation of corn starch could improve the yield in the etherification process. Whistler et al. [16] also reported similar improvements in the esterification of corn starch after enzymatic hydrolysis. Researchers assume that hydrolysis gives the substituent groups more access to the subsurface of granules where it can react efficiently, resulting in the increased degree of substitution. Acid-thinned hydrolysis changes the physicochemical properties of starch but does not alter its granular structure. Previous
http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013 0141-8130/© 2014 Published by Elsevier B.V.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
G Model
ARTICLE IN PRESS
BIOMAC 4337 1–7
E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
2 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88
studies show that the gelatinization parameters (i.e., gelatinization temperature and enthalpy) increase upon hydrolysis [17,18]. The tendency for retrogradation of acid-thinned starch also increases because of an increase in the concentration of linear chains. The viscosity and average molecular weight of hydrolyzed starch decreases, whereas the solubility and gel strength of acid-thinned starch increase relative to the untreated starch [19]. Hydroxypropylation introduces a hydrophilic bulky group to the starch chains and improves solubility. Hydroxypropylation also decreases the tendency for retrogradation and improves thermal properties [20]. Therefore, the combination acid-thinned hydrolysis and hydroxypropylation should increase solubility and overcome the disadvantages of native starch. The effect of two common methods of chemical modification on the solubility of sago starch was evaluated. Acid hydrolysis is an inexpensive and effective method for increasing sago starch solubility [18]. The etherification of sago starch in different substitution levels of propylene oxide was also examined [21]. In this study, sago starch was first hydrolyzed and then hydroxypropylated to evaluate the synergistic effect of dual modification on sago starch. Thermal properties, molecular weight distribution, solubility, and other functional properties were evaluated.
89
2. Materials and methods
90
2.1. Materials
94
Sago starch (13% moisture, 0.21% fiber, 0.18% fat, 0.12% ash, and 0.11% protein; 28% amylose, and 72% amylopectin) was purchased from SIM Company Sdn. Bhd. (Pulau Penang, Malaysia). All chemicals were of analytical grade.
95
2.2. Dual modification of sago starch
91 92 93
96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126
Acid-thinned hydrolysis: About 40% sago starch slurries were prepared by adding 400 g starch (db) with 0.14 N hydrochloric acid (HCl) solution at 50 ◦ C to a final weight of 1000 g according to the modified Wang and Wang [22] method [18]. The suspension was incubated at different times (6, 12, 18, and 24 h) at 50 ◦ C to prepare sago starch with different molecular weights. Preliminary experiments showed that incubation times lower than 6 h did not have significant effects on sago starch, and incubation for 24 h decreases the molecular weight, and the starch solution has not film formability. Suspensions were stirred at 200 rpm in an orbital incubator shaker (Jeio Tech SI-. 600R, Seoul, South Korea) to prevent sedimentation. After a specific length of time (6, 12, 18, and 24 h), the slurries were neutralized with NaOH (1%) to a pH 5.5, washed three times with two-fold volume of distilled water, and filtered by a Whatman filter paper 4. The starches were dried in an oven at 40 ◦ C overnight. Hydroxypropylation: Hydrolyzed hydroxypropylated sago starch (HHSS) was prepared using the method of Hjermstad [23] with some modifications [15,21]. Sodium sulfate (20%, w/v, based on the total solution) was added to the hydrolyzed starch slurry (20%, w/v) and stirred. The pH was adjusted above 10.5 with NaOH (5%). As an etherifying agent, propylene oxide was added to constitute 10%, 20%, and 30% of the dry weight of the hydrolyzed starch. For each concentration, the reaction flask was capped and the mixture was stirred at room temperature for 30 min. The suspension was then incubated for 24 h at 40 ◦ C. To prevent sedimentation, the mixture was stirred at 200 rpm in an orbital incubator shaker SI-600R (JEIOTech, Seoul, Korea). Next, using HCl (10%), the pH of the suspensions was neutralized and adjusted to 5.5. The samples were washed immediately with distilled water. The starch cakes obtained were washed with distilled water until the sulfate content was negative according to the BaCl2 test. The samples were
dried in an oven at 40 ◦ C until the moisture content was approximately 10%. The samples were ground using a hammer mill and sieved to the size of 250 m. HHSS was prepared in triplicate using different hydrolysis sago starches, and the mean of the values was determined. 2.3. Molecular weight distribution after dual modification by gel permeation chromatography (GPC) GPC measurements were taken by a chromatograph equipped with a PerkinElmer Series 200 pump, Knauer Smartline 2300 refractive index detector, Knauer Smartline column thermostat, Shodex Ohpak SB-G guard column, and Shodex OHpak SB-806MHQ column. Elution was carried out using a 5 mM LiBr in DMSO/DMF (75/25) solution as the mobile phase at a flow rate of 0.3 mL/min. The temperature of the columns was maintained at 60 ◦ C. A calibration curve was constructed using 12 pullulan standards (2560, 1660, 788, 404, 212, 112, 47.3, 22.8, 11.8, 5.9, 1.32, and 0.342 kDa). A starch concentration of 0.25% and a sampling volume 100 L were used. To obtain more reliable results, the starch samples were dissolved in the same solvent used as eluent in the GPC system. For better solubilization, the sols were heated in an oil bath at 120 ◦ C for 10 min. The warm (approximately 40 ◦ C) solution was filtered through a 0.45 m membrane (Whatman 25 mm GD/X, GMF), allowed to cool down, and then injected into the HPLC system [18]. For each samples three replicated using for GPC and the mean of the values was determined. 2.4. DS estimation of propylene oxide The hydroxypropyl content of the hydrolyzed starches was determined according to the method of Johnson [24] and expressed as DS [21]. The method involves the hydrolysis of the hydroxypropyl group to propylene glycol, which in turn is dehydrated to propionaldehyde and the enolic form of allyl alcohol. These products were measured spectrophotometrically at 590 nm after reacting with ninhydrin reagent (3% ninhydrin in 5% Na2 S2 O5 ) to form a purple color. MS was calculated as follows: DS =
162W 100 − (M − 1)W
where W is the equivalent hydroxypropyl group in 100 g of starch, and M is the molecular weight of C3 H6 O [11,25]. 2.5. Solubility and swelling power The method described by Liu et al. was used to determine the solubility and swelling power of the different dually modified sago starches [26]. Briefly, 0.5 g of dually modified starches (db) was weighed and placed in a centrifuge tube with 40 mL of distilled water. The tubes were heated at different temperatures (i.e., 30 ◦ C, 50 ◦ C, 70 ◦ C, and 90 ◦ C) in a shaking water bath for 30 min. The tubes were cooled down to room temperature and centrifuged at 1670 × g for 20 min. The supernatant was carefully poured out and dried overnight at 120 ◦ C. Solubility was determined as the ratio of dried supernatant to dry starch (%), and swelling power was calculated as the ratio of sediment weight to dry starch (g/g). Triplicate measurements were obtained for each starch at each temperature. To measurement the maximum solubility in cold water, different concentrations of dually modified sago starch (from 1% to 20%) were prepared with deionized water. Dispersions were heated up to 90 ◦ C for 30 min and cooled down to room temperature. The maximum concentration that shows liquidity after cooling was considered as the maximum solubility in cold water [18].
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
127 128 129 130 131
132 133
134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151
152
153 154 155 156 157 158 159 160
161
162 163
164
165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182
G Model BIOMAC 4337 1–7
ARTICLE IN PRESS E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
3
Fig. 1. Gel permeation chromatograms of dually modified sago starch.
183
184 185 186 187 188 189 190 191 192 193 194 195 196 197 198
199 200
201 202 203 204 205 206 207 208 209 210 211 212 213 214 215
2.6. Pasting properties by rapid visco analyzer (RVA) The slurry of dually modified sago starches was analyzed using the procedure described in Huijbrechts et al. [27] with minor modifications [21]. A Rapid ViscoTM Analyser (Model RVA-4, Newport Scientific Pvt. Ltd., Warriewood, NSW, Australia) was used to determine the pasting properties of the samples. In an RVA sample cup, 16% (db) dually modified sago starches were prepared by adding 4 g starch to 25 g of distilled water. A programmed heating and cooling cycle was used. The samples were stirred rapidly at 960 rpm for 10 s, and the shear input was decreased to 160 rpm and remained constant. The samples were equilibrated at 50 ◦ C for 1 min. In the succeeding steps, the samples were heated at 95 ◦ C for 2.7 min, placed at 95 ◦ C for 3.3 min, cooled to 50 ◦ C for 4 min, and then placed at 50 ◦ C for 2 min. Triplicate measurements were made for each starch. Peak viscosity, hot paste viscosity, breakdown, setback, and cold paste viscosity were determined from the RVA plots [28]. 2.7. Gelatinization parameters and evaluation of tendency to retrogradation by differential scanning calorimetry (DSC) The thermal characteristics of dually modified sago starches were studied using a differential scanning calorimeter (DSC-Q100, TA Instruments, New Castle, DE, USA) equipped with Thermal Analyst 2000 software. The instrument was calibrated using pure indium (melting point 156.4 ◦ C). Starch slurries (approximately 10 mg) were prepared at 1:2 dry starch/water ratios, hermetically sealed using a DuPont encapsulation press (DuPont Co., Wilmington, DE, USA), and left for at least 1 h for equilibration [29]. An empty pan was used as reference, and DSC was conducted from 10 ◦ C to 100 ◦ C at a heating rate of 10 ◦ C/min. Based on the DSC curve, onset temperature, peak temperature, completion temperature, and enthalpy of gelatinization were calculated. Enthalpies were calculated on a dry starch basis. After completion of the DSC run, the gelatinized starch samples were stored at 4 ◦ C in the original sealed pans for retrogradation studies. After 7 days, the samples
were removed and allowed to equilibrate for 1 h at room temperature. They were analyzed again by DSC using the same heating program. The ratio of the second gelatinization enthalpy (H2 ) to the first (H1 ) reflects the degree of retrogradation [30]. Each sample was run in triplicate to determine the mean value.
2.8. Intrinsic viscosity Intrinsic viscosity was determined based on the method described by Chan et al. [31] with minor modifications. Starch suspensions (0.5%) were prepared by dissolving starch in dimethylsulfoxide (DMSO 90%). Samples were homogenized using an orbital incubator shaker SI-600R (JEIOTech, Seoul, Korea) at 150 rpm for 16 h at room temperature. An Ubbelohde-type capillary viscometer (Poulten Selfe & Lee Ltd., Essex, United Kingdom; PSL ASTM IP IC, constant = 0.03009 [mm2 /s]/s) with a diameter of 0.75 mm was used to measure the intrinsic viscosity. The temperature was fixed using a temperature controlled water bath at 25.0 ± 0.1 ◦ C. Exactly 10 mL of starch solution was transferred to the viscometer and held for 5 min to equilibrate temperature. The samples were further diluted with 90% DMSO to yield four different concentrations within the range of 0.27–0.5% (w/w). By extrapolating the specific viscosity values measured for the successive dilutions, the intrinsic viscosity of the starch solution at an infinite dilution was obtained. Triplicate determinations were performed for each starch.
2.9. Statistical analysis ANOVA was performed using ANOVA of the IBM SPSS 21.0 statistical software for Windows (SPSS, Inc., Chicago, IL, USA). Duncan’s least significant test was used to compare the means at the 5% significance level.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
216 217 218 219 220
221
222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238
239
240 241 242 243
G Model
ARTICLE IN PRESS
BIOMAC 4337 1–7
E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
4
Table 1 Molar substitution of hydrolyzed sago starches at different ratio of propylene oxide. Propylene oxide ratio 10% 20% 30%
Native
AH6
AH12
AH18
AH24
0.007 ± 0.001bC 0.100 ± 0.005aB 0.150 ± 0.008aA
0.021 ± 0.001aC 0.080 ± 0.002aB 0.142 ± 0.004aA
0.019 ± 0.001aC 0.088 ± 0.002aB 0.148 ± 0.005aA
0.018 ± 0.001a 0.087 ± 0.004a 0.154 ± 0.010a
0.020 ± 0.001aC 0.088 ± 0.005aB 0.146 ± 0.007aA
The values are mean ± SE (n = 3). Different small letters show significant difference at 5% level of probability between values in same rows, and capital letters for same columns. The numbers after ‘AH’ represent the time (in hours) of acid hydrolysis.
244
3. Results and discussions
3.3. Pasting properties of dually modified sago starch
245
3.1. Structural characterization of dually modified sago starch
Pasting properties are mostly related to the properties of starch granules. The modification of starch affects the granules and consequently changes the pasting properties. Both hydrolysis and hydroxypropylation decrease the pasting properties, especially peak viscosity [32]. Fig. 2 compares one sample of acidhydrolyzed (AH12) sago starch with another sample of combined acid-hydrolysis (AH12) + hydroxypropylation (20% PO) sago starch; the peak viscosity of sago starch decreased more in the combined sample than that in hydrolysis only. The pasting temperature also shifted to a lower temperature by dual modification compared with that by acid-hydrolysis alone. The effects of hydroxypropylation on pasting properties for hydrolyzed starch are the same as those observed in native starch discussed in previous studies [18]. Upon gelatinization, dually modified sago starch differed from gels of native starches and gels of starches modified by hydrolysis alone. Although the concentration tests for hydrolyzed starch (14%) were lower than those for dually modified (16%) sago starch (as recommended in the use of RVA equipment for modified starch), the final viscosity (at 50 ◦ C) for hydrolyzed starch was very high (1460 cP). Conversely, the final viscosity of dually modified sago starch did not show changes, except for a small peak during gelatinization. These results show that dually modified sago starch is cold-water soluble, but hydrolyzed starch is not. Moreover, dual modification causes substantial loss of viscosity and gel forming capacity. Fig. 3 represents the pasting properties of hydrolyzed and hydroxypropylated sago starch. Starches were hydrolyzed at various times and substituted by propylene oxide at approximately 0.1 DS. Dual modification significantly altered the pasting properties of sago starch unlike in those of hydrolyzed starch [18]. The higher
246 247 248 249 250 251 252 253 254
255
256 257 258 259 260 261 262 263 264 265 266 267 268 269
Acid hydrolysis of starches reduces the molecular weight of starch components, especially amylopectin [15,18]. Fig. 1 compares the GPC chromatograms of acid-thinned sago starch at the 12 h reaction time (AH12) and dually modified sago starches hydrolyzed at 12 h and modified with 20% and 30% propylene oxide (AH12HP20, AH12HP30). The introduction of propylene oxide into the structure of the hydrolyzed starch did not significantly change the low molecular weight fraction, but it slightly increased the molecular weight of the high molecular weight fraction.
3.2. Effects of hydrolysis on the DS of sago starch Table 1 shows the DS of native and hydrolyzed sago starch with different hydrolysis reaction duration times. The results indicate a significant difference between native and hydrolyzed sago starch for DS at 10% propylene oxide. However, no significant difference was observed in the higher propylene oxide ratio. Karim et al. [15] reported that hydrolysis could improve hydroxypropylation at 10% of propylene oxide (per dried starch) because of the effects of hydrolysis on the surface of granules of sago starch that improves the penetration of propylene oxide. Our results are consistent with those of Karim et al. at 10% propylene oxide ratio. In higher ratios (20% and 30%) of propylene oxide, the effects of hydrolysis were negligible because the concentration of the reactant was high and the time was enough for the penetration of propylene oxide to occur.
Fig. 2. RVA pasting profiles of hydrolyzed sago starch before and after hydroxypropylation (20% propylene oxide).
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
270
271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300
G Model
ARTICLE IN PRESS
BIOMAC 4337 1–7
E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
5
Fig. 3. RVA pasting profiles of dual modified sago starch. The numbers after ‘AH’ represent the time (in hours) of acid hydrolysis. All samples hydroxypropylated by 20% propylene oxide.
301 302 303
304
305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321
degree of hydrolysis at the same degree of substitution effectively decreased the peak viscosity, but gelatinization viscosity did not change with decreasing temperature.
3.4. Solubility and swelling power Introducing a hydrophilic group to the starch structure increases the solubility of the starch. The increase in the DS level also improves the solubility of the starch in water. A 1.25% (w/w) solution of starch was used to evaluate its solubility and swelling power. The solubility of dually modified sago starches at this concentration (1.25%, w/w) was almost 100%, but no swelling was observed (Table 2). High concentrations of dually modified sago starches were prepared after gelatinization at 90 ◦ C, and the solubility of dually modified sago starches was determined. Starches hydrolyzed for more than 12 h and hydroxypropylated at a DS level of 0.08 and above were completely soluble in cold water up to 25% soluble solid concentration. These results are consistent with the data gathered from the evaluation of pasting properties. The high concentration and low viscosity of dually modified sago starch solutions makes them an ideal alternative for gelatin in certain applications such as dip-molding process.
3.5. Gelatinization and tendency for retrogradation
322
Fig. 4 shows the gelatinization of dually modified sago starches compared with that of hydrolyzed and native starches. As discussed in previous studies [18], hydrolysis increases the gelatinization temperature, but hydroxypropylation, as stated in another research [21], decreases the gelatinization temperature. The combination of these two modifications decreases the gelatinization temperature (Fig. 4). Results show (not shown) that in dual modification of sago starch, hydroxypropylation plays a basic role in thermal properties, and increasing the degree of hydrolysis has not significant effects on the gelatinization properties [18,21]. Retrogradation was investigated by immediately scanning the samples after preparation and then rescanning after 7 days of storage at 4 ◦ C. Although retrogradation was increased by hydrolysis, dual modification with hydroxypropylation overcame this disadvantage. Fig. 5 shows a peak for the hydrolyzed sago starch upon rescan, but no peak was observed for dually modified starch. One of the possible applications of this material is in dip-molding or coating process. Retrogradation significantly affects the functional properties and reduces the shelf-life of the starch films. Therefore, hydroxypropylation can improve the properties of starch so that it can be used as an alternative to gelatin in processes in which low viscous materials are needed as basic constituents.
Table 2 Solubility and Swelling power of dually modified sago starch compared to hydrolyzed, hydroxypropylated and native sago starch after gelatinization at 90 ◦ C. Native
AH6
AH12
AH18
AH24
Solubility (%)
Propylene oxide ratio 0% 10% 20% 30%
44.62 ± 1.83cD 66.62 ± 2.1cC 93.02 ± 1.2bB 97.64 ± 0.88bA
58.90 ± 2.41bD 88.46 ± 0.29bC 99.62 ± 0.18aB 100 ± 0.0aA
99.42 ± 0.42aB 99.84 ± 0.11aAB 100 ± 0.0aA 100 ± 0.0aA
99.45 ± 0.24aB 100 ± 0.00aA 100 ± 0.0aA 100 ± 0.0aA
99.60 ± 0.26aB 100 ± 0.00aA 100 ± 0.0aA 100 ± 0.0aA
Swelling power (g/g dried starch)
0% 10% 20% 30%
18.24 ± 1.54aA 15.66 ± 1.12aB 2.69 ± 0.44aC 1.99 ± 0.28aD
14.63 ± 0.98bA 8.26 ± 1.2bB 0.49 ± 0.15bC 0 ± 0.0bD
0.95 ± 0.24cA 0.37 ± 0.07cB 0 ± 0.0cC 0 ± 0.0bC
0.78 ± 0.26cA 0 ± 0.0 dB 0 ± 0.0cB 0 ± 0.0bB
0.60 ± 0.14cA 0 ± 0.0 dB 0 ± 0.0cB 0 ± 0.0bB
Values are means ±SE (n = 5). Mean within a row with different small letter or within a column with different capital letter are significantly different at 5% level of probability. The numbers after ‘AH’ represents the time (h) of hydrolysis.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345
G Model BIOMAC 4337 1–7
ARTICLE IN PRESS E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
6
Fig. 4. DSC thermograms of native, hydrolyzed (12 h) and dually modified sago starch (12 h hydrolysis and indicated molar substitutions).
346
347 348 349
3.6. Intrinsic viscosity The intrinsic viscosities of native, hydrolyzed, hydroxypropylated, and dually modified sago starches are listed in Table 3. In previous studies [18,21], researchers showed that both hydrolysis
and hydroxypropylation decreased intrinsic viscosity. Dual modification results in synergistic effects and decreased intrinsic viscosity, which are the reasons why dually modified sago starch readily dissolves in water. Statistical analysis showed that when hydrolyzed for more than 12 h and when molar substitution was
Fig. 5. DSC thermograms of hydrolyzed (12 h) and dually modified sago starches with 12 hr hydrolysis time and MS = 0.15 for scan and 7 days rescan.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
350 351 352 353 354
G Model
ARTICLE IN PRESS
BIOMAC 4337 1–7
E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
7
Table 3 Intrinsic viscosity of native and modified sago starch. Propylene oxide ratio (molar substitution) 0% 10% (MS = 0.02) 20% (MS = 0.10) 30% (MS = 0.15)
Intrinsic viscosity (mL/g)a Native
AH6
AH12
AH18
AH24
121.2 ± 5.1aA 98.3 ± 4.7aB 82.2 ± 2.1aC 79.6 ± 3.3aD
88.5 ± 4.2bA 73.2 ± 3.4bB 54.1 ± 2.1bC 42.7 ± 1.7bD
36.4 ± 3.4cA 17.4 ± 1.6cB 5.7 ± 0.1cC 4.3 ± 0.1cD
21.5 ± 4.1dA 8.3 ± 0.2 dB 3.8 ± 0.2cC 3.6 ± 0.1cC
14.4 ± 3.8dA 4.4 ± 0.1eB 3.5 ± 0.2cC 3.1 ± 0.2cC
a Values are means (n = 5) ± SE. Mean within a row with different small letter or within a column with different capital letter are significantly different at 5% level of probability. The numbers after ‘AH’ represents the time (h) of hydrolysis
357
equal to or greater than 0.1, the intrinsic viscosity was very low and did not change significantly with the change in hydrolysis time or extent of substitution.
358
4. Conclusion
355 356
369
Starch in native form cannot be used in most industrial applications because of low solubility and tendency to retrogradation. In this study, starch was first hydrolyzed into short chains and then propylene oxide, a hydrophilic group, was introduced to the structure. The hydrolysis and hydroxypropylation of sago starch improved solubility in water up to 25%. This study found that hydroxypropylation and hydrolysis have synergistic effects unlike in individual modifications. Dually modified sago starch was soluble in cold water at high concentration and had a low tendency to retrogradation. This dually modified sago starch is useful in food or pharmaceutical processes like dip-molding.
370
References
359 360 361 362 363 364 365 366 367 368
371 372 373 374 375 376 377 378 379 380 381
[1] K. Krogars, O. Antikainen, J. Heinämäki, N. Laitinen, J. Yliruusi, European Journal of Pharmaceutical Sciences 17 (2002) 23–30. [2] L. Nouri, A. Mohammadi Nafchi, International Journal of Biological Macromolecules 66 (2014) 254–259. [3] A.M. Nafchi, R. Nassiri, S. Sheibani, F. Ariffin, A.A. Karim, Carbohydrate Polymers 96 (2013) 233–239. [4] O. Wurzburg, Food Polysaccharides and Their Applications, CRC Press, 2006. [5] J. Huber, K. BeMiller, in: A.C. Bertolini (Ed.), Starches, CRC Press, 2010. [6] A.C. Bertolini, in: A.C. Bertolini (Ed.), Starches, CRC Press, 2009. [7] X. Xia, Z. Hu, M. Marquez, Journal of Controlled Release 103 (2005) 21–30. [8] A. Mohammadi Nafchi, R.H. Tabatabaei, B. Pashania, H.Z. Rajabi, A.A. Karim, International Journal of Biological Macromolecules 62 (2013) 397–404.
[9] J. Singh, L. Kaur, O.J. McCarthy, Food Hydrocolloids 21 (2007) 1–22. [10] A. Gunaratne, H. Corke, Cereal Chemistry 84 (2007) 30–37. [11] W. Liu, Z. Xie, B. Zhang, Q. Wang, W. Yao, X. Gao, L. Yu, Journal of Agricultural and Food Chemistry 58 (2010) 1615–1621. [12] I. Arvanitoyannis, A. Nakayama, S.-i. Aiba, Carbohydrate Polymers 36 (1998) 105–119. [13] N.M. Sereno, S.E. Hill, A.J. Taylor, J.R. Mitchell, S.J. Davies, Journal of Agricultural and Food Chemistry 57 (2009) 985–990. [14] W. Vorwerg, J. Dijksterhuis, J. Borghuis, S. Radosta, A. Kröger, Starch - Stärke 56 (2004) 297–306. [15] A.A. Karim, E.H. Sufha, I.S.M. Zaidul, Journal of Agricultural and Food Chemistry 56 (2008) 10901–10907. [16] R.L. Whistler, M.A. Madson, J. Zhao, J.R. Daniel, Cereal Chemistry 75 (1998) 72–74. [17] Y.-C. Shi, P.A. Seib, Carbohydrate Research 227 (1992) 131–145. [18] M.N. Abdorreza, M. Robal, L.H. Cheng, A.Y. Tajul, A.A. Karim, LWT - Food Science and Technology 46 (2012) 135–141. [19] D. Thirathumthavorn, S. Charoenrein, Starch - Stärke 57 (2005) 217–222. [20] R. Hoover, D. Hannouz, F.W. Sosulski, Starch - Stärke 40 (1988) 383–387. Q3 [21] M. Aminian, A.M. Nafchi, M. Bolandi, A.K. Alias, Starch - Stärke (2013). [22] L. Wang, Y.J. Wang, Starch - Stärke 53 (2001) 570–576. [23] E.T. Hjermstad, US Patent 3577407, 1971. [24] D.P. Johnson, Analytical Chemistry 41 (1969) 859–860. [25] O.S. Lawal, Food Hydrocolloids 23 (2009) 415–425. [26] H. Liu, L. Ramsden, H. Corke, Starch - Stärke 51 (1999) 249–252. [27] A.M.L. Huijbrechts, M. Desse, T. Budtova, M.C.R. Franssen, G.M. Visser, C.G. Boeriu, E.J.R. Sudhölter, Carbohydrate Polymers 74 (2008) 170–184. [28] A.A. Karim, M.Z. Nadiha, F.K. Chen, Y.P. Phuah, Y.M. Chui, A. Fazilah, Food Hydrocolloids 22 (2008) 1044–1053. [29] Z.A.N. Fadzlina, A.A. Karim, T.T. Teng, Journal of Food Science 70 (2005) C560–C567. [30] K. Morikawa, K. Nishinari, Food Hydrocolloids 14 (2000) 395–401. [31] H.T. Chan, R. Bhat, A.A. Karim, Journal of Agricultural and Food Chemistry 57 (2009) 5965–5970. [32] Q. Liu, S. Xie, Food Carbohydrates, CRC Press, 2005.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417
ARTICLE IN PRESS
BIOMAC 4337 1–7
International Journal of Biological Macromolecules xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Effects of acid-hydrolysis and hydroxypropylation on functional properties of sago starch
1
2
3 4
Q1
Elham Fouladi, Abdorreza Mohammadi Nafchi ∗ Food Biopolymer Research Group, Food Science and Technology Department, Damghan Branch, Islamic Azad University, Damghan, Semnan, Iran
5
6 18
a r t i c l e
i n f o
a b s t r a c t
7 8 9 10 11 12
Article history: Received 6 April 2014 Received in revised form 29 April 2014 Accepted 5 May 2014 Available online xxx
13
17
Keywords: Sago starch Dual modification Thermal properties
19
1. Introduction
14 15 16
20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
In this study, sago starch was hydrolyzed by 0.14 M HCl for 6, 12, 18, and 24 h, and then modified by pro- Q2 pylene oxide at a concentration of 0–30% (v/w). The effects of hydrolysis and etherification on molecular weight distribution, physicochemical, rheological, and thermal properties of dually modified starch were estimated. Acid hydrolysis of starch decreased the molecular weight of starch especially amylopectin, but hydroxypropylation had no effect on the molecular weight distribution. The degree of Molar substitution (DS) of hydroxypropylated starch after acid hydrolysis ranged from 0.007 to 0.15. Dually modified starch with a DS higher than 0.1 was completely soluble in cold water at up to 25% concentration of the starch. This study shows that hydroxypropylation and hydrolysis have synergistic effects unlike individual modifications. Dually modified sago starch can be applied to dip-molding for food and pharmaceutical processing because of its high solubility and low tendency for retrogradation. © 2014 Published by Elsevier B.V.
Starch is an abundant polysaccharide, and its properties differ according to plant source. Applications of native starch in food products are based on these inherent properties. However, some inherent functional properties, such as insolubility in water, tendency for retrogradation, opacity of cooked paste, and low flow, have restricted the applicability of starch in their native forms [1,2]. Many attempts have been made to overcome the disadvantages of starches and to develop industrial scale applications [3]. Modification of starch can be carried out physically, chemically, enzymatically, and genetically. Chemical modification of starch is the most common because it can be readily controlled, and the principal actions of chemical modifications are well understood compared with those of other methods of starch modification [4]. Depolymerization (i.e., acid-thinned hydrolysis or oxidation) and derivatizations (i.e., etherification or esterification) using chemical reagents are typical modifications that have a wide range of application in the starch industry [5]. Chemical modification causes changes in the molecular structure or introduces functional groups, thus improving the applicability of plant-derived materials in food and non-food industries [6–8].
∗ Corresponding author. Tel.: +98 232 522 5045; fax: +98 232 522 5039. E-mail addresses: [email protected], [email protected] (A.M. Nafchi).
Starches can be stabilized through reaction with monofunctional reagents. In these reactions, hydroxyl groups of the starch are converted into larger ether or ester groups to block interchain associations. This process tends to stabilize pastes and gels by giving them a reduced tendency to undergo retrogradation [9]. Hydroxypropyl starch (HPS) is a popular modified starch that is widely used in food industry. Hydroxypropylation of starches can cause high paste clarity, low tendency for retrogradation, freeze–thaw stability, and high solubility in cold water after cooking [10,11]. Molar substitution (DS), molecular weight distribution, and distribution of functional groups are the factors that characterize the properties of HPS. HPS also has good film formation properties. The properties of HPS film, such as mechanical, water vapor, and aroma permeability, have been investigated previously [12–14]. Generally, native starches have a low degree of substitution because of their limited degree of reaction on the granule surface. Karim et al. [15] observed that enzymatic hydrolysis prior to the hydroxypropylation of corn starch could improve the yield in the etherification process. Whistler et al. [16] also reported similar improvements in the esterification of corn starch after enzymatic hydrolysis. Researchers assume that hydrolysis gives the substituent groups more access to the subsurface of granules where it can react efficiently, resulting in the increased degree of substitution. Acid-thinned hydrolysis changes the physicochemical properties of starch but does not alter its granular structure. Previous
http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013 0141-8130/© 2014 Published by Elsevier B.V.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
G Model
ARTICLE IN PRESS
BIOMAC 4337 1–7
E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
2 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88
studies show that the gelatinization parameters (i.e., gelatinization temperature and enthalpy) increase upon hydrolysis [17,18]. The tendency for retrogradation of acid-thinned starch also increases because of an increase in the concentration of linear chains. The viscosity and average molecular weight of hydrolyzed starch decreases, whereas the solubility and gel strength of acid-thinned starch increase relative to the untreated starch [19]. Hydroxypropylation introduces a hydrophilic bulky group to the starch chains and improves solubility. Hydroxypropylation also decreases the tendency for retrogradation and improves thermal properties [20]. Therefore, the combination acid-thinned hydrolysis and hydroxypropylation should increase solubility and overcome the disadvantages of native starch. The effect of two common methods of chemical modification on the solubility of sago starch was evaluated. Acid hydrolysis is an inexpensive and effective method for increasing sago starch solubility [18]. The etherification of sago starch in different substitution levels of propylene oxide was also examined [21]. In this study, sago starch was first hydrolyzed and then hydroxypropylated to evaluate the synergistic effect of dual modification on sago starch. Thermal properties, molecular weight distribution, solubility, and other functional properties were evaluated.
89
2. Materials and methods
90
2.1. Materials
94
Sago starch (13% moisture, 0.21% fiber, 0.18% fat, 0.12% ash, and 0.11% protein; 28% amylose, and 72% amylopectin) was purchased from SIM Company Sdn. Bhd. (Pulau Penang, Malaysia). All chemicals were of analytical grade.
95
2.2. Dual modification of sago starch
91 92 93
96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126
Acid-thinned hydrolysis: About 40% sago starch slurries were prepared by adding 400 g starch (db) with 0.14 N hydrochloric acid (HCl) solution at 50 ◦ C to a final weight of 1000 g according to the modified Wang and Wang [22] method [18]. The suspension was incubated at different times (6, 12, 18, and 24 h) at 50 ◦ C to prepare sago starch with different molecular weights. Preliminary experiments showed that incubation times lower than 6 h did not have significant effects on sago starch, and incubation for 24 h decreases the molecular weight, and the starch solution has not film formability. Suspensions were stirred at 200 rpm in an orbital incubator shaker (Jeio Tech SI-. 600R, Seoul, South Korea) to prevent sedimentation. After a specific length of time (6, 12, 18, and 24 h), the slurries were neutralized with NaOH (1%) to a pH 5.5, washed three times with two-fold volume of distilled water, and filtered by a Whatman filter paper 4. The starches were dried in an oven at 40 ◦ C overnight. Hydroxypropylation: Hydrolyzed hydroxypropylated sago starch (HHSS) was prepared using the method of Hjermstad [23] with some modifications [15,21]. Sodium sulfate (20%, w/v, based on the total solution) was added to the hydrolyzed starch slurry (20%, w/v) and stirred. The pH was adjusted above 10.5 with NaOH (5%). As an etherifying agent, propylene oxide was added to constitute 10%, 20%, and 30% of the dry weight of the hydrolyzed starch. For each concentration, the reaction flask was capped and the mixture was stirred at room temperature for 30 min. The suspension was then incubated for 24 h at 40 ◦ C. To prevent sedimentation, the mixture was stirred at 200 rpm in an orbital incubator shaker SI-600R (JEIOTech, Seoul, Korea). Next, using HCl (10%), the pH of the suspensions was neutralized and adjusted to 5.5. The samples were washed immediately with distilled water. The starch cakes obtained were washed with distilled water until the sulfate content was negative according to the BaCl2 test. The samples were
dried in an oven at 40 ◦ C until the moisture content was approximately 10%. The samples were ground using a hammer mill and sieved to the size of 250 m. HHSS was prepared in triplicate using different hydrolysis sago starches, and the mean of the values was determined. 2.3. Molecular weight distribution after dual modification by gel permeation chromatography (GPC) GPC measurements were taken by a chromatograph equipped with a PerkinElmer Series 200 pump, Knauer Smartline 2300 refractive index detector, Knauer Smartline column thermostat, Shodex Ohpak SB-G guard column, and Shodex OHpak SB-806MHQ column. Elution was carried out using a 5 mM LiBr in DMSO/DMF (75/25) solution as the mobile phase at a flow rate of 0.3 mL/min. The temperature of the columns was maintained at 60 ◦ C. A calibration curve was constructed using 12 pullulan standards (2560, 1660, 788, 404, 212, 112, 47.3, 22.8, 11.8, 5.9, 1.32, and 0.342 kDa). A starch concentration of 0.25% and a sampling volume 100 L were used. To obtain more reliable results, the starch samples were dissolved in the same solvent used as eluent in the GPC system. For better solubilization, the sols were heated in an oil bath at 120 ◦ C for 10 min. The warm (approximately 40 ◦ C) solution was filtered through a 0.45 m membrane (Whatman 25 mm GD/X, GMF), allowed to cool down, and then injected into the HPLC system [18]. For each samples three replicated using for GPC and the mean of the values was determined. 2.4. DS estimation of propylene oxide The hydroxypropyl content of the hydrolyzed starches was determined according to the method of Johnson [24] and expressed as DS [21]. The method involves the hydrolysis of the hydroxypropyl group to propylene glycol, which in turn is dehydrated to propionaldehyde and the enolic form of allyl alcohol. These products were measured spectrophotometrically at 590 nm after reacting with ninhydrin reagent (3% ninhydrin in 5% Na2 S2 O5 ) to form a purple color. MS was calculated as follows: DS =
162W 100 − (M − 1)W
where W is the equivalent hydroxypropyl group in 100 g of starch, and M is the molecular weight of C3 H6 O [11,25]. 2.5. Solubility and swelling power The method described by Liu et al. was used to determine the solubility and swelling power of the different dually modified sago starches [26]. Briefly, 0.5 g of dually modified starches (db) was weighed and placed in a centrifuge tube with 40 mL of distilled water. The tubes were heated at different temperatures (i.e., 30 ◦ C, 50 ◦ C, 70 ◦ C, and 90 ◦ C) in a shaking water bath for 30 min. The tubes were cooled down to room temperature and centrifuged at 1670 × g for 20 min. The supernatant was carefully poured out and dried overnight at 120 ◦ C. Solubility was determined as the ratio of dried supernatant to dry starch (%), and swelling power was calculated as the ratio of sediment weight to dry starch (g/g). Triplicate measurements were obtained for each starch at each temperature. To measurement the maximum solubility in cold water, different concentrations of dually modified sago starch (from 1% to 20%) were prepared with deionized water. Dispersions were heated up to 90 ◦ C for 30 min and cooled down to room temperature. The maximum concentration that shows liquidity after cooling was considered as the maximum solubility in cold water [18].
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
127 128 129 130 131
132 133
134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151
152
153 154 155 156 157 158 159 160
161
162 163
164
165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182
G Model BIOMAC 4337 1–7
ARTICLE IN PRESS E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
3
Fig. 1. Gel permeation chromatograms of dually modified sago starch.
183
184 185 186 187 188 189 190 191 192 193 194 195 196 197 198
199 200
201 202 203 204 205 206 207 208 209 210 211 212 213 214 215
2.6. Pasting properties by rapid visco analyzer (RVA) The slurry of dually modified sago starches was analyzed using the procedure described in Huijbrechts et al. [27] with minor modifications [21]. A Rapid ViscoTM Analyser (Model RVA-4, Newport Scientific Pvt. Ltd., Warriewood, NSW, Australia) was used to determine the pasting properties of the samples. In an RVA sample cup, 16% (db) dually modified sago starches were prepared by adding 4 g starch to 25 g of distilled water. A programmed heating and cooling cycle was used. The samples were stirred rapidly at 960 rpm for 10 s, and the shear input was decreased to 160 rpm and remained constant. The samples were equilibrated at 50 ◦ C for 1 min. In the succeeding steps, the samples were heated at 95 ◦ C for 2.7 min, placed at 95 ◦ C for 3.3 min, cooled to 50 ◦ C for 4 min, and then placed at 50 ◦ C for 2 min. Triplicate measurements were made for each starch. Peak viscosity, hot paste viscosity, breakdown, setback, and cold paste viscosity were determined from the RVA plots [28]. 2.7. Gelatinization parameters and evaluation of tendency to retrogradation by differential scanning calorimetry (DSC) The thermal characteristics of dually modified sago starches were studied using a differential scanning calorimeter (DSC-Q100, TA Instruments, New Castle, DE, USA) equipped with Thermal Analyst 2000 software. The instrument was calibrated using pure indium (melting point 156.4 ◦ C). Starch slurries (approximately 10 mg) were prepared at 1:2 dry starch/water ratios, hermetically sealed using a DuPont encapsulation press (DuPont Co., Wilmington, DE, USA), and left for at least 1 h for equilibration [29]. An empty pan was used as reference, and DSC was conducted from 10 ◦ C to 100 ◦ C at a heating rate of 10 ◦ C/min. Based on the DSC curve, onset temperature, peak temperature, completion temperature, and enthalpy of gelatinization were calculated. Enthalpies were calculated on a dry starch basis. After completion of the DSC run, the gelatinized starch samples were stored at 4 ◦ C in the original sealed pans for retrogradation studies. After 7 days, the samples
were removed and allowed to equilibrate for 1 h at room temperature. They were analyzed again by DSC using the same heating program. The ratio of the second gelatinization enthalpy (H2 ) to the first (H1 ) reflects the degree of retrogradation [30]. Each sample was run in triplicate to determine the mean value.
2.8. Intrinsic viscosity Intrinsic viscosity was determined based on the method described by Chan et al. [31] with minor modifications. Starch suspensions (0.5%) were prepared by dissolving starch in dimethylsulfoxide (DMSO 90%). Samples were homogenized using an orbital incubator shaker SI-600R (JEIOTech, Seoul, Korea) at 150 rpm for 16 h at room temperature. An Ubbelohde-type capillary viscometer (Poulten Selfe & Lee Ltd., Essex, United Kingdom; PSL ASTM IP IC, constant = 0.03009 [mm2 /s]/s) with a diameter of 0.75 mm was used to measure the intrinsic viscosity. The temperature was fixed using a temperature controlled water bath at 25.0 ± 0.1 ◦ C. Exactly 10 mL of starch solution was transferred to the viscometer and held for 5 min to equilibrate temperature. The samples were further diluted with 90% DMSO to yield four different concentrations within the range of 0.27–0.5% (w/w). By extrapolating the specific viscosity values measured for the successive dilutions, the intrinsic viscosity of the starch solution at an infinite dilution was obtained. Triplicate determinations were performed for each starch.
2.9. Statistical analysis ANOVA was performed using ANOVA of the IBM SPSS 21.0 statistical software for Windows (SPSS, Inc., Chicago, IL, USA). Duncan’s least significant test was used to compare the means at the 5% significance level.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
216 217 218 219 220
221
222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238
239
240 241 242 243
G Model
ARTICLE IN PRESS
BIOMAC 4337 1–7
E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
4
Table 1 Molar substitution of hydrolyzed sago starches at different ratio of propylene oxide. Propylene oxide ratio 10% 20% 30%
Native
AH6
AH12
AH18
AH24
0.007 ± 0.001bC 0.100 ± 0.005aB 0.150 ± 0.008aA
0.021 ± 0.001aC 0.080 ± 0.002aB 0.142 ± 0.004aA
0.019 ± 0.001aC 0.088 ± 0.002aB 0.148 ± 0.005aA
0.018 ± 0.001a 0.087 ± 0.004a 0.154 ± 0.010a
0.020 ± 0.001aC 0.088 ± 0.005aB 0.146 ± 0.007aA
The values are mean ± SE (n = 3). Different small letters show significant difference at 5% level of probability between values in same rows, and capital letters for same columns. The numbers after ‘AH’ represent the time (in hours) of acid hydrolysis.
244
3. Results and discussions
3.3. Pasting properties of dually modified sago starch
245
3.1. Structural characterization of dually modified sago starch
Pasting properties are mostly related to the properties of starch granules. The modification of starch affects the granules and consequently changes the pasting properties. Both hydrolysis and hydroxypropylation decrease the pasting properties, especially peak viscosity [32]. Fig. 2 compares one sample of acidhydrolyzed (AH12) sago starch with another sample of combined acid-hydrolysis (AH12) + hydroxypropylation (20% PO) sago starch; the peak viscosity of sago starch decreased more in the combined sample than that in hydrolysis only. The pasting temperature also shifted to a lower temperature by dual modification compared with that by acid-hydrolysis alone. The effects of hydroxypropylation on pasting properties for hydrolyzed starch are the same as those observed in native starch discussed in previous studies [18]. Upon gelatinization, dually modified sago starch differed from gels of native starches and gels of starches modified by hydrolysis alone. Although the concentration tests for hydrolyzed starch (14%) were lower than those for dually modified (16%) sago starch (as recommended in the use of RVA equipment for modified starch), the final viscosity (at 50 ◦ C) for hydrolyzed starch was very high (1460 cP). Conversely, the final viscosity of dually modified sago starch did not show changes, except for a small peak during gelatinization. These results show that dually modified sago starch is cold-water soluble, but hydrolyzed starch is not. Moreover, dual modification causes substantial loss of viscosity and gel forming capacity. Fig. 3 represents the pasting properties of hydrolyzed and hydroxypropylated sago starch. Starches were hydrolyzed at various times and substituted by propylene oxide at approximately 0.1 DS. Dual modification significantly altered the pasting properties of sago starch unlike in those of hydrolyzed starch [18]. The higher
246 247 248 249 250 251 252 253 254
255
256 257 258 259 260 261 262 263 264 265 266 267 268 269
Acid hydrolysis of starches reduces the molecular weight of starch components, especially amylopectin [15,18]. Fig. 1 compares the GPC chromatograms of acid-thinned sago starch at the 12 h reaction time (AH12) and dually modified sago starches hydrolyzed at 12 h and modified with 20% and 30% propylene oxide (AH12HP20, AH12HP30). The introduction of propylene oxide into the structure of the hydrolyzed starch did not significantly change the low molecular weight fraction, but it slightly increased the molecular weight of the high molecular weight fraction.
3.2. Effects of hydrolysis on the DS of sago starch Table 1 shows the DS of native and hydrolyzed sago starch with different hydrolysis reaction duration times. The results indicate a significant difference between native and hydrolyzed sago starch for DS at 10% propylene oxide. However, no significant difference was observed in the higher propylene oxide ratio. Karim et al. [15] reported that hydrolysis could improve hydroxypropylation at 10% of propylene oxide (per dried starch) because of the effects of hydrolysis on the surface of granules of sago starch that improves the penetration of propylene oxide. Our results are consistent with those of Karim et al. at 10% propylene oxide ratio. In higher ratios (20% and 30%) of propylene oxide, the effects of hydrolysis were negligible because the concentration of the reactant was high and the time was enough for the penetration of propylene oxide to occur.
Fig. 2. RVA pasting profiles of hydrolyzed sago starch before and after hydroxypropylation (20% propylene oxide).
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
270
271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300
G Model
ARTICLE IN PRESS
BIOMAC 4337 1–7
E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
5
Fig. 3. RVA pasting profiles of dual modified sago starch. The numbers after ‘AH’ represent the time (in hours) of acid hydrolysis. All samples hydroxypropylated by 20% propylene oxide.
301 302 303
304
305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321
degree of hydrolysis at the same degree of substitution effectively decreased the peak viscosity, but gelatinization viscosity did not change with decreasing temperature.
3.4. Solubility and swelling power Introducing a hydrophilic group to the starch structure increases the solubility of the starch. The increase in the DS level also improves the solubility of the starch in water. A 1.25% (w/w) solution of starch was used to evaluate its solubility and swelling power. The solubility of dually modified sago starches at this concentration (1.25%, w/w) was almost 100%, but no swelling was observed (Table 2). High concentrations of dually modified sago starches were prepared after gelatinization at 90 ◦ C, and the solubility of dually modified sago starches was determined. Starches hydrolyzed for more than 12 h and hydroxypropylated at a DS level of 0.08 and above were completely soluble in cold water up to 25% soluble solid concentration. These results are consistent with the data gathered from the evaluation of pasting properties. The high concentration and low viscosity of dually modified sago starch solutions makes them an ideal alternative for gelatin in certain applications such as dip-molding process.
3.5. Gelatinization and tendency for retrogradation
322
Fig. 4 shows the gelatinization of dually modified sago starches compared with that of hydrolyzed and native starches. As discussed in previous studies [18], hydrolysis increases the gelatinization temperature, but hydroxypropylation, as stated in another research [21], decreases the gelatinization temperature. The combination of these two modifications decreases the gelatinization temperature (Fig. 4). Results show (not shown) that in dual modification of sago starch, hydroxypropylation plays a basic role in thermal properties, and increasing the degree of hydrolysis has not significant effects on the gelatinization properties [18,21]. Retrogradation was investigated by immediately scanning the samples after preparation and then rescanning after 7 days of storage at 4 ◦ C. Although retrogradation was increased by hydrolysis, dual modification with hydroxypropylation overcame this disadvantage. Fig. 5 shows a peak for the hydrolyzed sago starch upon rescan, but no peak was observed for dually modified starch. One of the possible applications of this material is in dip-molding or coating process. Retrogradation significantly affects the functional properties and reduces the shelf-life of the starch films. Therefore, hydroxypropylation can improve the properties of starch so that it can be used as an alternative to gelatin in processes in which low viscous materials are needed as basic constituents.
Table 2 Solubility and Swelling power of dually modified sago starch compared to hydrolyzed, hydroxypropylated and native sago starch after gelatinization at 90 ◦ C. Native
AH6
AH12
AH18
AH24
Solubility (%)
Propylene oxide ratio 0% 10% 20% 30%
44.62 ± 1.83cD 66.62 ± 2.1cC 93.02 ± 1.2bB 97.64 ± 0.88bA
58.90 ± 2.41bD 88.46 ± 0.29bC 99.62 ± 0.18aB 100 ± 0.0aA
99.42 ± 0.42aB 99.84 ± 0.11aAB 100 ± 0.0aA 100 ± 0.0aA
99.45 ± 0.24aB 100 ± 0.00aA 100 ± 0.0aA 100 ± 0.0aA
99.60 ± 0.26aB 100 ± 0.00aA 100 ± 0.0aA 100 ± 0.0aA
Swelling power (g/g dried starch)
0% 10% 20% 30%
18.24 ± 1.54aA 15.66 ± 1.12aB 2.69 ± 0.44aC 1.99 ± 0.28aD
14.63 ± 0.98bA 8.26 ± 1.2bB 0.49 ± 0.15bC 0 ± 0.0bD
0.95 ± 0.24cA 0.37 ± 0.07cB 0 ± 0.0cC 0 ± 0.0bC
0.78 ± 0.26cA 0 ± 0.0 dB 0 ± 0.0cB 0 ± 0.0bB
0.60 ± 0.14cA 0 ± 0.0 dB 0 ± 0.0cB 0 ± 0.0bB
Values are means ±SE (n = 5). Mean within a row with different small letter or within a column with different capital letter are significantly different at 5% level of probability. The numbers after ‘AH’ represents the time (h) of hydrolysis.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345
G Model BIOMAC 4337 1–7
ARTICLE IN PRESS E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
6
Fig. 4. DSC thermograms of native, hydrolyzed (12 h) and dually modified sago starch (12 h hydrolysis and indicated molar substitutions).
346
347 348 349
3.6. Intrinsic viscosity The intrinsic viscosities of native, hydrolyzed, hydroxypropylated, and dually modified sago starches are listed in Table 3. In previous studies [18,21], researchers showed that both hydrolysis
and hydroxypropylation decreased intrinsic viscosity. Dual modification results in synergistic effects and decreased intrinsic viscosity, which are the reasons why dually modified sago starch readily dissolves in water. Statistical analysis showed that when hydrolyzed for more than 12 h and when molar substitution was
Fig. 5. DSC thermograms of hydrolyzed (12 h) and dually modified sago starches with 12 hr hydrolysis time and MS = 0.15 for scan and 7 days rescan.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
350 351 352 353 354
G Model
ARTICLE IN PRESS
BIOMAC 4337 1–7
E. Fouladi, A.M. Nafchi / International Journal of Biological Macromolecules xxx (2014) xxx–xxx
7
Table 3 Intrinsic viscosity of native and modified sago starch. Propylene oxide ratio (molar substitution) 0% 10% (MS = 0.02) 20% (MS = 0.10) 30% (MS = 0.15)
Intrinsic viscosity (mL/g)a Native
AH6
AH12
AH18
AH24
121.2 ± 5.1aA 98.3 ± 4.7aB 82.2 ± 2.1aC 79.6 ± 3.3aD
88.5 ± 4.2bA 73.2 ± 3.4bB 54.1 ± 2.1bC 42.7 ± 1.7bD
36.4 ± 3.4cA 17.4 ± 1.6cB 5.7 ± 0.1cC 4.3 ± 0.1cD
21.5 ± 4.1dA 8.3 ± 0.2 dB 3.8 ± 0.2cC 3.6 ± 0.1cC
14.4 ± 3.8dA 4.4 ± 0.1eB 3.5 ± 0.2cC 3.1 ± 0.2cC
a Values are means (n = 5) ± SE. Mean within a row with different small letter or within a column with different capital letter are significantly different at 5% level of probability. The numbers after ‘AH’ represents the time (h) of hydrolysis
357
equal to or greater than 0.1, the intrinsic viscosity was very low and did not change significantly with the change in hydrolysis time or extent of substitution.
358
4. Conclusion
355 356
369
Starch in native form cannot be used in most industrial applications because of low solubility and tendency to retrogradation. In this study, starch was first hydrolyzed into short chains and then propylene oxide, a hydrophilic group, was introduced to the structure. The hydrolysis and hydroxypropylation of sago starch improved solubility in water up to 25%. This study found that hydroxypropylation and hydrolysis have synergistic effects unlike in individual modifications. Dually modified sago starch was soluble in cold water at high concentration and had a low tendency to retrogradation. This dually modified sago starch is useful in food or pharmaceutical processes like dip-molding.
370
References
359 360 361 362 363 364 365 366 367 368
371 372 373 374 375 376 377 378 379 380 381
[1] K. Krogars, O. Antikainen, J. Heinämäki, N. Laitinen, J. Yliruusi, European Journal of Pharmaceutical Sciences 17 (2002) 23–30. [2] L. Nouri, A. Mohammadi Nafchi, International Journal of Biological Macromolecules 66 (2014) 254–259. [3] A.M. Nafchi, R. Nassiri, S. Sheibani, F. Ariffin, A.A. Karim, Carbohydrate Polymers 96 (2013) 233–239. [4] O. Wurzburg, Food Polysaccharides and Their Applications, CRC Press, 2006. [5] J. Huber, K. BeMiller, in: A.C. Bertolini (Ed.), Starches, CRC Press, 2010. [6] A.C. Bertolini, in: A.C. Bertolini (Ed.), Starches, CRC Press, 2009. [7] X. Xia, Z. Hu, M. Marquez, Journal of Controlled Release 103 (2005) 21–30. [8] A. Mohammadi Nafchi, R.H. Tabatabaei, B. Pashania, H.Z. Rajabi, A.A. Karim, International Journal of Biological Macromolecules 62 (2013) 397–404.
[9] J. Singh, L. Kaur, O.J. McCarthy, Food Hydrocolloids 21 (2007) 1–22. [10] A. Gunaratne, H. Corke, Cereal Chemistry 84 (2007) 30–37. [11] W. Liu, Z. Xie, B. Zhang, Q. Wang, W. Yao, X. Gao, L. Yu, Journal of Agricultural and Food Chemistry 58 (2010) 1615–1621. [12] I. Arvanitoyannis, A. Nakayama, S.-i. Aiba, Carbohydrate Polymers 36 (1998) 105–119. [13] N.M. Sereno, S.E. Hill, A.J. Taylor, J.R. Mitchell, S.J. Davies, Journal of Agricultural and Food Chemistry 57 (2009) 985–990. [14] W. Vorwerg, J. Dijksterhuis, J. Borghuis, S. Radosta, A. Kröger, Starch - Stärke 56 (2004) 297–306. [15] A.A. Karim, E.H. Sufha, I.S.M. Zaidul, Journal of Agricultural and Food Chemistry 56 (2008) 10901–10907. [16] R.L. Whistler, M.A. Madson, J. Zhao, J.R. Daniel, Cereal Chemistry 75 (1998) 72–74. [17] Y.-C. Shi, P.A. Seib, Carbohydrate Research 227 (1992) 131–145. [18] M.N. Abdorreza, M. Robal, L.H. Cheng, A.Y. Tajul, A.A. Karim, LWT - Food Science and Technology 46 (2012) 135–141. [19] D. Thirathumthavorn, S. Charoenrein, Starch - Stärke 57 (2005) 217–222. [20] R. Hoover, D. Hannouz, F.W. Sosulski, Starch - Stärke 40 (1988) 383–387. Q3 [21] M. Aminian, A.M. Nafchi, M. Bolandi, A.K. Alias, Starch - Stärke (2013). [22] L. Wang, Y.J. Wang, Starch - Stärke 53 (2001) 570–576. [23] E.T. Hjermstad, US Patent 3577407, 1971. [24] D.P. Johnson, Analytical Chemistry 41 (1969) 859–860. [25] O.S. Lawal, Food Hydrocolloids 23 (2009) 415–425. [26] H. Liu, L. Ramsden, H. Corke, Starch - Stärke 51 (1999) 249–252. [27] A.M.L. Huijbrechts, M. Desse, T. Budtova, M.C.R. Franssen, G.M. Visser, C.G. Boeriu, E.J.R. Sudhölter, Carbohydrate Polymers 74 (2008) 170–184. [28] A.A. Karim, M.Z. Nadiha, F.K. Chen, Y.P. Phuah, Y.M. Chui, A. Fazilah, Food Hydrocolloids 22 (2008) 1044–1053. [29] Z.A.N. Fadzlina, A.A. Karim, T.T. Teng, Journal of Food Science 70 (2005) C560–C567. [30] K. Morikawa, K. Nishinari, Food Hydrocolloids 14 (2000) 395–401. [31] H.T. Chan, R. Bhat, A.A. Karim, Journal of Agricultural and Food Chemistry 57 (2009) 5965–5970. [32] Q. Liu, S. Xie, Food Carbohydrates, CRC Press, 2005.
Please cite this article in press as: E. Fouladi, A.M. Nafchi, Int. J. Biol. Macromol. (2014), http://dx.doi.org/10.1016/j.ijbiomac.2014.05.013
382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417
