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High-speed shear effect on properties and octenylsuccinic anhydride modification of corn starch
Food Hydrocolloids 44 (2015) 32e39
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Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd
High-speed shear effect on properties and octenylsuccinic anhydride modification of corn starch Chan Wang, Xiaowei He, Xiong Fu, Faxing Luo, Qiang Huang* College of Food Sciences, South China University of Technology, 381 Wushan Road, Guangzhou 510640, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 July 2014 Accepted 3 September 2014 Available online 16 September 2014
The reaction between starch granules and octenylsuccinic anhydride (OSA) is normally retarded due to poor penetration of big oily OSA droplets into starch granules in an aqueous reaction system. High-speed shear was used to improve the degree of substitution (DS) and reaction efficiency (RE) of octenylsuccinate (OS) starch. Effects of high-speed shear on the physicochemical properties of corn starch and OS-starch synthesis were investigated. Results showed that no significant difference was observed in melting temperature and crystalline structure of treated starch when shear rate was less than 1.5 104 rpm. Treatment could degrade the starch molecule and release soluble saccharides. High-speed shear treated starch (H-starch) exhibited lower enthalpy change, and higher stability of hot and cold paste. OSstarch prepared using high-speed shear (H-OS-starch) showed more homogenous substitute group distribution in starch granule than that of control, as shown by confocal laser scanning microscopy. HOS-starch also showed higher DS and RE, slightly lower pasting temperature, higher stability of hot and cold paste, and higher clarity and freeze-thaw stability, compared with the control. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Octenylsuccinate starch High speed shearing Starch pasting properties Reaction efficiency
1. Introduction Octenylsuccinate (OS) starch shows excellent emulsification properties because of its amphiphilic character (Jeon, Viswanathan, & Gross, 1999). The application of OS-starch is involved in a variety of oil-in-water emulsions for food, pharmaceutical and industrial products such as beverages, salad dressings, flavor-encapsulating agents, clouding agents, processing aids, body powders and lotions (Jeon et al., 1999; Park, Chung, & Yoo, 2004). The reaction of OSA and starch carried out in aqueous phase was resulted in poor reaction efficiency and uneven distribution of OS groups (Shogren, Viswanathan, Felker, & Gross, 2000). The distribution of OS groups in starch granules has been studied extensively (Chen, He, & Huang, 2014; Chen, Huang, Fu, & Luo, 2014; Huang et al., 2010; Shogren et al., 2000). It has been noted that the concentration of OS groups on the surface of the OS-starch granules was about 2e4 times than that of the bulk. High-speed shear, which is widely used in food industry, provides a high shear, cavitation and collision force, making the material be blended, disintegrated, dispersed, homogenized and emulsified. Effects of high-speed shear on starch physicochemical
* Corresponding author. Tel.: þ86 20 8711 3845; fax: þ86 20 8711 3848. E-mail address: [email protected] (Q. Huang). http://dx.doi.org/10.1016/j.foodhyd.2014.09.007 0268-005X/© 2014 Elsevier Ltd. All rights reserved.
properties were studied, results showed that the onset (To), peak (Tp), and conclusion (Tc) temperatures and crystallinity decreased with an increase in the shear speed, due to the disintegration and fragmentations of granules (Kaur, Kaur, Singh, & Sodhi, 2013). Corn starch granules have many narrow channels (0.07e0.1 mm) leading from the surface pinholes (0.1e0.3 mm) to the central cavity, only allowing < 100 nm droplets accessible (Huber & BeMiller, 1997; Zhang, Dhital, & Gidley, 2013). In our previous studies, we found that the solubility of OSA in water is low (Wang, He, Huang, Fu, et al., 2013). The droplets of OSA could react with the granular surface or, depending on their size, travel into the channels and the interior cavity (Shogren et al., 2000). Higher reaction efficiency can be achieved by phase transition catalyst (Wang, He, Huang, Luo, & Fu, 2013), ultrasound (Chen, Huang, et al., 2014), or hydrothermal treatment (Chen, He, et al., 2014). Results indicated that OSA groups could go deep into the interior of starch granules and distributed throughout the OS-starch granules by ultrasound or hydrothermal treatment (Chen, He, et al., 2014; Chen, Huang, et al., 2014). High-speed shear has advantages of being a simple process, presenting minimal environmental problems and subject to convenient operation. Our previous study showed that the size of OSA droplets could be decreased under a high-speed shear (Wang, He, Huang, Fu, et al., 2013). Our hypothesis is that high-speed shear would improve the reaction efficiency and physicochemical properties of OS-starch, which has potential application in food industry.
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
2. Materials and methods 2.1. Materials Normal corn starch (13.5% moisture content) was obtained from the Dacheng Company (Changchun, China). OSA was obtained from Nanjing Golden Chemical Co., Ltd (Nanjing, China). Other chemicals used in the study were all analytical grade. 2.2. High-speed shear treatment and preparation of OS-starch High-speed shear treated corn starch. Starch suspension (35%, w/ w) was treated using a high-speed homogenizer (FJ200-SH, Shanghai specimen and model factory, China) at different agitation speeds for 1.5 h (5 103, 8 103, 1.0 104 and 1.5 104 rpm, the shear rates of these agitation speeds were: 5588, 8942, 11,775, and 16,766 s1, respectively).
Speed rate ¼
p 18 v 60 0:8
p: 3.14; 18 mm: the diameter of rotor; n: agitation speed; 0.8 mm: the distance between rotor and stator. 60:60 s. The samples were signed as K2eK4 and the native starch was signed as K0. The control sample (K1) was treated at 0.5 103 rpm by a mechanical stirrer (RW 20 digital, IKA, Germany) for same time. Samples were centrifuged at 4000 g for 20 min and the supernatant was determined by a high performance liquid chromatography (HPLC). The solids were oven-dried at 40 C for 24 h, manually grinded and passed through a 100 mesh nylon sieve. OS-starch synthesis assisted by high-speed shear. Corn starch was suspended in distilled water (35%, w/w) at different agitation speed (5 103, 8 103, 1.0 104 and 1.5 104 rpm) with the high-speed homogenizer, and a control sample was treated at 0.5 103 rpm by a mechanical stirrer. The pH of the suspension was adjusted to 8.0e9.0 by adding NaOH solution (3%, w/w) with a pH meter, and the temperature was controlled at 35 C. Different amount of OSA (3e7%, dsb) was added slowly within 1 h. After the reaction, the pH was adjusted to 6.5 with HCl solution (3%, w/w). The mixture was washed two times with distilled water and two times with ethanol. The starch samples were oven-dried at 40 C for 24 h, and then passed through a 100 mesh nylon sieve. 2.3. Determination of the degree of substitution Degree of substitution was determined as previously described (Wang, He, Huang, Fu, et al., 2013). The OS-starch sample (5 g, dry weight) was accurately weighed and suspended by stirring for 30 min in 25 mL of HCl-isopropyl alcohol solution (2.5 M). Aqueous isopropyl alcohol solution [100 mL 90% (v/v)] was added and the slurry stirred for an additional 10 min. The suspension was filtered through a glass filter and the residue was washed with 90% isopropyl alcohol solution until no Cl could be detected (using 0.1 M AgNO3 solution). The starch was re-dispersed in 300 mL distilled water and heated in a boiling water-bath for 20 min with stirring. The starch solution was titrated with 0.1 M standard NaOH solution, using phenolphthalein as an indicator. A blank was simultaneously titrated with native starch as a control. The DS was calculated by the following equation:
DS ¼
0:162 ðA MÞ=W 1 ½0:209 ðA MÞ=W
where A is the titration volume of NaOH solution (mL); M is the molarity of NaOH solution; and W is the dry weight (g) of the OS-
33
starch. 162 is the molecular weight of anhydroglucose unit; 209 is (molecular weight of octenyl succinic anhydride e 1). The reaction efficiency (RE) was calculated as follows:
RE ¼
Actual DS 100% Theoretical DS
The theoretical DS was calculated by assuming that all of the added anhydride reacted with starch to form the ester derivative. 2.4. Determination of molecular weight distribution of soluble components HPLC was done on a high performance liquid chromatography instrument (Agilent Co., USA) equipped with a Shodex OHpak SB803 M HQ column (Tosoh Co., Japan), and a Shodex OHpak SB-G guard column, an automatic injector with a 20 uL loop, an Agilent 1260 ISO pump (Agilent Co., USA) and an Agilent 1260 Refractive Index Detector (RID) (Agilent Co., USA). The eluting solvent was distilled water, and the flow rate was 0.8 mL/min. The column oven temperature was controlled at 70 C. The molecular weight of the supernatant was calculated by comparison to a calibration curve (Fig. 2) made with pullulan standards. A regression equation for the pullulan standards was: y ¼ 0.9573x þ 11.363 (R2 ¼ 0.9991). 2.5. X-ray diffraction The crystalline structure and relative crystallinity of H-starches were identified and quantified by an X-ray diffractometer (D/Max200, Rigaku Denki Co. Ltd., Tokyo, Japan) (Chen, Huang, et al., 2014). 2.6. Scanning electron microscopy (SEM) Images of starches were taken by scanning electron microscope (EVO18, Carl Zeiss, Germany). Starch samples were mounted on an aluminum stub using double-sided stick tape, coated with a thin film of gold (10 nm), and then examined at an accelerating voltage of 10 kV. 2.7. Confocal laser scanning microscopy CLSM was measured using a method of Wang, He, Huang, Fu, et al. (2013). A TCS SP5 CLSM fitted with an Argon ion laser (Leica, Wetzlar, Germany) was used for the detection of the fluorescence signal from the dye-stained starch granules. The details of the Leica objective lens used were 40 /1.25 oil. The excitation wavelength was 514 nm with 56 capacity. During the image acquisition, each line was scanned two times and the average was calculated to reduce the noise. 2.8. Differential scanning calorimetry A differential scanning calorimeter (DSC 8000, PerkineElmer, Norwalk, CT, USA) with an intra cooler was used to analyze the gelatinization properties of starch, following the method of (Li, Ward, & Gao, 2011). The enthalpy change (DH), onset (To), peak (Tp), and conclusion (Tc) temperature of starch gelatinization were calculated by using a Pyris software (PerkineElmer, Norwalk, CT, USA). The samples were scanned from 30 C to 150 C at 10 C/min. An empty pan was used as a reference. 2.9. Pasting properties Pasting properties were analyzed on a Brabender Micro ViscoAmylo-Craph (Melchers Co., Germany). Pasting temperature (TP),
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peak viscosity (PV), hot paste viscosity (HPV), break down (BD) and setback (SB) values were recorded (Chen, Huang, et al., 2014). 2.10. Paste clarity Pasting clarity was measured using a method of Craig, Maningat, Seib, and Hoseney (1989). The percent transmittance (% T) was determined at 650 nm against water as blank in a 721G spectrophotometer (Anal. Instr. Factory, Shanghai, China). 2.11. Freeze-thaw stability Starch paste (6%, w/v) was kept in 100 mL sealed bottles, stored at 18 C for 18 h, and thawed at 25 C for 6 h (one freeze and thaw cycle defined as ‘1 time’). After each cycle, the sample was centrifuged at 4000 rpm for 20 min and the percentage of the separated water measured of the ratio of the weight of the water separated to the weight of the paste. The process was repeated till water expelled or the paste turned into sponginess (Huang et al., 2010). 2.12. Statistical analysis Each sample was measured in triplicates and means and standard deviations were reported. The mean values and differences were analyzed using Duncan's multiple-range test. Means were tested for least significant differences (LSD) with SPSS 18.0 statistical software for Windows. 3. Results and discussion 3.1. Effect of high-speed shear condition on starch structure Electron micrographs of starch granules subjected to different shear conditions are shown in Fig. 1. There was little evidence differences in morphology composition between the native starch granules and mechanical stirrer treated sample (Fig. 1). After highspeed shear treatment, a few large corn starch granules were
damaged. Results proved that mechanical force damaged the native starch granule in a limited extent. The chromatogram of soluble components of H-starch is shown in Fig. 2a. One major peak was detected in the profile at retention time of 6.5 min for all samples. Based on the equation of the calibration curve made by pullulan standards and the retention time, the molecular weight of the soluble components were mainly distributed in range of 5.02 kDa, i.e., the average degree of polymerization (DP) of soluble saccharides was 31. The concentration of soluble components increased with the shear speed increasing, which indicated the degradation accelerated under higher shear speed. The possible mechanisms for the appearance of soluble saccharides during mechanical action, such as snapping of amylopectin clusters breakage of glycosidic bonds in the vicinity of a-1, 6branching points in the interior of amylopectin molecules, and splitting of granules along radii (i.e. parallel to double helix axes likely to cause molecular breakage) have been described previous (Dhital, Shrestha, Flanagan, Hasjim, & Gidley, 2011; Morrison, Tester, & Gidley, 1994; Yamada, Tamaki, & Hisamatsu, 1997). X-ray diffraction spectra of the residue starch samples are shown in Fig. 2b. All samples exhibited the A-type diffraction pattern with major peaks at 15 , 17 , 18 and 23 2q. High-speed shear did not change the crystalline type but relative crystallinity. Compared with the native corn starch, the relative crystallinity of H-starch decreased from 36.90% to 34.68% when the shear speed increased from 500 rpm to 1.5 104 rpm shear speed. Results indicated that native starch display resistance to mechanical force. This resistance was attributed to intermolecular and intramolecular hydrogen bonding and to the entanglement of starch as well, such as the double helix formation between branch chains of amylopectin molecules and the intertwining between amylose and amylopectin (Jane, Shen, Wang, & Maningat, 1992). Thermal properties of native corn starch and H-starch are summarized in Table 1. There was no significant difference in To, Tp and Tc among K0eK4. The onset temperature of the starches decreased with increases of the shear speed. Native corn starch required more energy to gelatinize (K0, 11.46 J/g) than that of K4
Fig. 1. Scanning electron micrographs of native corn starch and high-speed shear treated starch. K0: native starch; K1: corn starch was treated at 0.5 103 rpm by a mechanical stirrer for 1.5 h; K2eK5: corn starch was treated at different agitation speed (5 103 rpm, 8 103 rpm, 1.0 104 rpm, 1.5 104 rpm) by a high-speed homogenizer for 1.5 h.
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
35
between grinding matrix and starch causes atomic and hydrogen bonds to break, this could weaken the crystalline region and the structure of starch granules (Huang, Lu, Li, & Tong, 2007). The pasting parameters of starches with different agitation speed are shown in Table 1. The pasting temperature and viscosity of H-starch did not change significantly when agitated at different speeds in most cases. However, compared with native starch, it exhibited lower peak viscosity (PV); hot paste viscosity (HPV); break down value (BD), and higher setback value when the speed increased to 1.5 104 rpm. The decrease in PV, HPV and BD was presumably due to attrition-induced damage of granules. The amylopectin in H-starch have been more damaged and a lower molecular weight than native starch. The cleavage of short chains of amylopectin might give a smaller contribution to paste viscosity compared to the cleavage of long chains of amylopectin due to smaller gyration radius of the molecules in pastes (Han, Campanella, Mix, & Hamaker, 2002). The shear forces are caused by cavitation that are capable to break the chains of polymers and damaging granules. Meanwhile, the water can partially decompose into OH radicals and H atoms in the collapsing cavitation bubbles, which can react with solute molecules causing polymer degradation (Czechowska-Biskup, Rokita, Lotfy, Ulanski, & Rosiak, 2005). The degradation could be due to the breakage of covalent bonds, i.e., intramolecular, or it could be due to the disruption of aggregates, i.e., the breakage of intermolecular bonds (Nilsson, Leeman, Wahlund, & Bergenståhl, 2006). The amylopectin has larger molecule size and branching fraction compared with amylose (Thitipraphunkul, Uttapap, Piyachomkwan, & Takeda, 2003), is more sensitive to the mechanical force. In this study, high-speed shear treatment weakened the crystalline region of starch granules, but not enough change the crystalline type (Fig. 2b).
3.2. Effects of high-speed shear treatment on OSA modification
Fig. 2. The chromatogram of dissolved components of native corn starch and highspeed shear treated starch (a), and X-ray diffraction pattern of starch granules (b). B0eB5: dissolved components of K0eK5, respectively. K0: native starch; K1: corn starch was treated at 0.5 103 rpm by a mechanical stirrer for 1.5 h; K2eK5: corn starch was treated at different agitation speed (5 103 rpm, 8 103 rpm, 1.0 104 rpm, 1.5 104 rpm) for 1.5 h by a high-speed homogenizer .
(8.71 J/g) and K5 (7.96 J/g), indicating that high-speed shear treatment reduced the amount of energy required to gelatinize corn starch, which was consistent with a previous study (Kaur et al., 2013). The broad endotherm from 65 C to 85 C was attributed to the gelatinization of starch (Jane et al., 1999). In the mechanical activation process, the impact, shear and friction operating
Effects of high-speed shear treatment on the OSA modification are shown in Fig. 3A. Compared with the control, the DS and RE of OS-starch treated by high-speed shear (H-OS-starch) increased from 0.0182 to 0.0202 and from 78.45% to 86.86%, respectively. While the DS decreased with the agitation speed increased from 1.0 104 rpm to 1.5 104 rpm. OS-starch prepared by varying OSA concentration (3e7%) at 1 104 rpm was investigated (Fig. 3B). Compared with the control, H-OS-starch showed higher RE. More OSA added, higher RE could be achieved. High-speed shear treatment promoted the formation OS-starch. The reaction between OSA and starch was retarded due to insufficient mixing in an aqueous suspension. The cavitation effect of high-speed shear increased the surface area by destroying the granular surface. The high-speed shear could reduce the drop size of OSA (Wang, He,
Table 1 Gelatinization and pasting characteristics of starches with different agitation speed treatment.a Samples
Gelatinization characteristics To( C)
K0 K1 K2 K3 K4 K5
71.21 71.14 71.51 70.51 69.56 67.60
Pasting characteristics
Tp( C) ± ± ± ± ± ±
b
0.39 0.77bc 0.91bc 1.18bc 0.88bc 0.04c
76.85 75.61 75.45 75.99 75.93 75.51
DH (J/g)
Tc( C) ± ± ± ± ± ±
b
0.28 0.14c 0.31d 0.52d 0.12bc 0.28c
83.49 83.48 83.42 83.09 81.82 81.12
± ± ± ± ± ±
b
0.79 0.87bc 0.25bc 0.04bc 1.69bc 0.60c
11.46 10.61 8.80 8.98 8.71 7.96
± ± ± ± ± ±
TP( C) b
0.32 0.62b 0.47c 0.14c 1.70c 0.47c
78.6 78.3 79.0 78.9 79.1 79.0
± ± ± ± ± ±
PV(BU) b
0.3 0.9b 0.8b 0.4b 0.5b 0.6b
211 201 196 188 194 192
± ± ± ± ± ±
HPV(BU) b
2.8 8.5b 3.5b 1.4c 3.5c 4.2c
159 157 150 146 152 148
± ± ± ± ± ±
FV(BU) b
3.5 2.8bc 2.8bc 1.4c 4.0bc 2.1bc
294 304 307 298 302 303
± ± ± ± ± ±
BD(BU) b
4.9 2.3bc 2.1c 5.7bc 4.2bc 3.5bc
52 44 46 42 42 44
± ± ± ± ± ±
SB(BU) b
2.8 2.1c 3.5c 1.4c 0.7c 0.7c
135 147 157 152 150 155
± ± ± ± ± ±
6.3b 1.4c 4.2c 2.1c 3.5c 4.9c
a Means within a column with different letters are significantly different (p < 0.05) by LSD least significant test. K0: native starch; K1: corn starch was suspended in distilled water (35%, w/w) at 0.5 103 rpm by a mechanical stirrer for 1.5 h; K2eK5: corn starch was suspended in distilled water (35%, w/w) at different agitation speed (5 103 rpm; 8 103 rpm; 1.0 104 rpm; 1.5 104 rpm) for the same time (1.5 h) by a high-speed homogenizer. TP, pasting temperature; PV, peak viscosity; HPV, hot paste viscosity; FV, final viscosity; SB, set back value (SB]FV-HPV); BD, beak down value (BD¼PV-HPV); BU, Brabender unit.
36
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
Fig. 3. Effect of high-speed shear on the DS and RE of OS-starch (A, B); photos of OS-starch slurry at different time of standing (C); CLSM of OS starches (D). A: OSA concentration: 3%. C: a, the OS-starch was prepared by a mechanical stirrer (agitation speed: 0.5 103 rpm); b-d, H-OS-starch was prepared by a high-speed homogenizer at different agitation speed (5 103 rpm, 1.0 104 rpm, 1.5 104 rpm).D: e OS-starch prepared by a high-speed homogenizer at 1.0 104 rpm.
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
Huang, Fu, et al., 2013), which increased the reaction area between OSA and starch granules. Further increasing shear speed could not increase the DS of HOS-starch, probably due to the emulsion formed during higherspeed shear. An emulsion is a system of dispersed droplets of one immiscible liquid in another stabilized by an emulsifier. A particlestabilized emulsion usually referred to as Pickering emulsions €o €, & Timgren, 2012). It was reported (Marku, Wahlgren, Rayner, Sjo that the OS-starch with hydrophobic groups achieved higher oil binding ability and affinity to the oil water interface, using as the particle fraction in the emulsion (Marku et al., 2012). During the modification, when two-thirds of total OSA was added, part of modified starch slurry (10 mL) was removed, stored quiescently and photos were taken at different time of standing (Fig. 3C). The freshly made modified starch slurry displayed homogonously emulsions (Fig. 3C, 0 h). After 2 h, the H-OS-starch (d) prepared with 1.5 104 rpm agitation speed formed a stable emulsion, while other samples started to cream. After 4 h, the creaming of H-OSstarches (Fig. 3C, a, b) was more obvious, while H-OS-starch (d) did not show any cream. These results indicated that the Pickering emulsion between OS-starch granules and OSA was formed when the agitation speed was 1.5 104 rpm. The emulsion might form a barrier between native starch granules and OSA, leading to a decreased of DS value. The CLSM optical sections of OS starch granules are shown in Fig. 3D. The native starch granules did not show any fluorescence (data not shown), while OS starch showed stronger fluorescence intensity as the DS increased. Compared with control, the interior of H-OS-starch granules showed stronger fluorescence intensity. This implied that OS groups were slightly more evenly distributed in the granules of H-OS-starch. In other words, more OS groups were induced to the inner region of the H-OS-starches when the reaction was assisted by high speed shear. This is due to high-speed shear procedure can promote the reduction and uniformity of droplet size, leading to more OS groups travel to interior of starch granules. The viscosity, clarity and freeze-thaw stability of starch paste were investigated. Pasting properties of modified starch are showed in Fig. 4. All OS-starch showed lower pasting temperature, higher peak viscosity, breakdown and setback values when compared with native corn starch, which was consistent with a previous study (Bao, Xing, Phillips, & Corke, 2003). The incorporation of a bulky OS group destroys the ordered structure and changes the pasting properties of native starch. With the increase of DS, the structure of OS-starch becomes more inflexible and the negative charged OS group repels with each other, leading to be gelatinized at a lower temperature (Song, Zhu, Li, & Zhu, 2010). In addition, the network formation of amylose-OSA inclusion complexes could enhance the pasting viscosity (Thirathumthavorn & Charoenrein, 2006). Compared with the control OS-starch (DS: 0.0267), H-OS-starch (DS: 0.0267) was observed slightly lower TP, BD, PV values and higher SB value. The high-speed shear force damages some granules producing fissures on surfaces or creating fractured particles that prone to be destroyed by heat, leading to a slightly lower pasting temperature. H-OS-starch also showed lower peak viscosity than the control OS-starch, due to the degradation of starch molecules and the distribution of OS groups in starch granule. Molecular degradation will result in a strong decrease in swelling power because of disruption of the internal network structure of the granule. Moreover, strong shear force generated by high-speed shear could reduce the drop size of OSA, resulting in much more homogeneous OS group distribution in H-OS-starch granules and lower viscosity profile. The break down viscosity, which is the difference between the peak viscosity and the viscosity after holding for certain minutes at 95 C (Chen, Huang, et al., 2014), was
37
Fig. 4. Pasting characteristics of OS-starches. NCS: normal corn starch; A, B, E: OS starch prepared by a mechanical stirrer at 500 rpm, DS ¼ 0.018, 0.0267, 0.0391, respectively; C, D: OS starch prepared by a high-speed homogenizer at 10000 rpm, DS ¼ 0.0267, 0.0385, respectively.
lower than that of the control OS-starch, indicating that H-OSstarch was resistant to shear force. OSA-modified starch showed a considerably higher clarity than that of native starch (Table 2). As DS increasing, the paste clarity was improved. In addition, H-OS-starch showed a higher clarity than the OS-starch with similar DS. The increase in the clarity of OSstarch might be attributed to the introduction of carboxyl groups, which retained water molecules to form hydrogen bonds in the starch granules. Moreover, chemical substitution of the hydroxyl group by succinyl moiety caused the inhibition of ordered structure of starch paste, thus retarding retrogradation and resulting in a more fluid paste with improved clarity (Craig et al., 1989). The highspeed shear could decrease the particle size of OSA, leading to the distribution of OS groups more uniform, especially into the inner part of starch granules. During storage, the amylopectin of H-OSstarch recrystallized was less than that of control OS-starch. Moreover, the distortion of the crystalline regions had more carboxyl group which could form more hydrogen bonds with water, resulting in retaining the water molecules in the starch granules. As a result, H-OS-starch showed higher paste clarity. When starch paste is employed as a thickening agent in frozen foods, the accelerated retrogradation at a low temperature may produce undesirable physical changes including gel formation and syneresis. Freeze-thaw cycle indicates the storage stability at low temperatures and one such cycle is equivalent to 2e3 weeks of frozen storage (Liu, Ramsden, & Corke, 1997). The paste stability of
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C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
Table 2 Paste clarity and freeze-thaw stability of OS-starch.a DS
Paste clarity/T%
% Syneresis after freeze-thaw cycles 1
0 0.0182 0.0267 0.0267e 0.0385e 0.0391
8.89 23.79 25.72 27.53 28.69 26.88
± ± ± ± ± ±
b
0.012 0.006c 0.056d 0.019de 0.047e 0.016d
2 b
45.35 ± 0.43 33.39 ± 1.78c 16.52 ± 0.96d 12.21 ± 0.63e NIL 4.04 ± 0.025f
57.61 43.35 25.18 15.03 9.65 11.75
3 ± ± ± ± ± ±
b
2.11 1.82c 1.72d 1.10e 0.58f 0.51ef
63.67 54.34 40.93 35.12 21.03 24.53
4 ± ± ± ± ± ±
b
1.29 3.13c 1.32d 1.15e 0.77f 0.39f
81.64 58.72 43.83 41.03 28.32 31.42
± ± ± ± ± ±
1.11b 1.02c 1.81d 1.65d 0.37e 1.27e
a Means within a column with different letters are significantly different (p < 0.05) by LSD least significant test. e: H-OS-starch prepared by a high-speed homogenizer at 1.0 104 rpm. NIL: no syneresis.
OS-starches is presented in Table 2. The poor freeze-thaw stability exhibited by native starch indicated that extensive retrogradation during freeze storage. The OSA modified starches at all DS levels had a lower degree of syneresis compared with native starch. Moreover, the freeze-thaw stability increased along with an increase in DS. However, the OS-starch showed to be more susceptible to syneresis compared to H-OS-starch paste with the same DS. Reduction in the extent of retrogradation of OSA-modified starches could be attributed to the steric effect imposed by the bulky OSA group, which prevents the alignment of chain of starch (Islam & Azemi, 1997). 4. Conclusions High-speed shear condition can destroy the surface of starch granules and improve the stability of starch paste. Compared with the control, the DS of OS-starch prepared under high-speed shear was significantly increased. High-speed shear treatment showed a pronounced effect on the viscosity profile of the OS-starch. The granular interior of H-OS-starch showed stronger fluorescence intensity than that of control. And it also showed slightly lower TP, BD, PV values, higher ED and paste clarity and freeze-thaw stability than the control OS-starch. The results indicated that the highspeed shear condition can be used to improve the reaction efficiency, and improve clarity and freeze-thaw stability, which has potential application in food industry. Acknowledgments The authors would like to thank the financial support received from National Natural Science Foundation of China (31101378), the Fundamental Research Funds for the Central Universities (2013ZZ0065), Science and Technology Planning Project of Guangdong Province, China (2012NL016), Department of Science and Information Technology of Guangzhou, China (2013J4500036) are acknowledged. Abbreviations BD break down value CLSM confocal laser scanning microscopy DS degree of substitution FV final viscosity H-OS-starch OS-starch prepared under high-speed shear condition H-starch starches treat by high-speed shear condition HPV hot paste viscosity NCS normal corn starch OS octenylsuccinic OSA octenylsuccinic anhydride PV peak viscosity
RE SB SEM TP
reaction efficiency setback value scanning electron microscope pasting temperature
References Bao, J. S., Xing, J., Phillips, D. L., & Corke, H. (2003). Physical properties of octenylsuccinic anhydride modified rice, wheat, and potato starches. Journal of Agricultural and Food Chemistry, 51, 2283e2287. Chen, H. M., Huang, Q., Fu, X., & Luo, F. X. (2014). Ultrasonic effect on the octenyl succinate starch synthesis and substitution patterns in starch granules. Food Hydrocolloids, 35, 636e643. Chen, X., He, X. W., & Huang, Q. (2014). Effects of hydrothermal pretreatment on subsequent octenylsuccinicanhydride (OSA) modification of corn starch. Carbohydrate Polymers, 101, 493e498. Craig, S. A. S., Maningat, C. C., Seib, P. A., & Hoseney, R. C. (1989). Starch paste clarity. Cereal Chemistry, 66, 173e182. Czechowska-Biskup, R., Rokita, B., Lotfy, S., Ulanski, P., & Rosiak, J. M. (2005). Degradation of chitosan and starch by 360-kHz ultrasound. Carbohydrate Polymers, 60, 175e184. Dhital, S., Shrestha, A. K., Flanagan, B. M., Hasjim, J., & Gidley, M. J. (2011). Cryomilling of starch granules leads to differential effects on molecular size and conformation. Carbohydrate Polymers, 84, 1133e1140. Han, X.-Z., Campanella, O. H., Mix, N. C., & Hamaker, B. R. (2002). Consequence of starch damage on rheological properties of maize starch pastes. Cereal Chemistry, 79, 897e901. Huang, Q., Fu, X., He, X. W., Luo, F. X., Yu, S. J., & Li, L. (2010). The effect of enzymatic pretreatments on subsequent octenyl succinic anhydride modifications of corn starch. Food Hydrocolloids, 24(1), 60e65. Huang, Z.-Q., Lu, J.-P., Li, X.-H., & Tong, Z.-F. (2007). Effect of mechanical activation on physicochemical properties and structure of cassava starch. Carbohydrate Polymers, 68, 128e135. Huber, K., & BeMiller, J. N. (1997). Visualization of channels and cavities of corn and sorghum starch granules. Cereal chemistry, 74, 537e541. Islam, N. M., & Azemi, B. M. N. M. (1997). Rheological properties of calcium treated €rke, 49, 136e141. hydroxypropyl rice starches. Starch/Sta Jeon, Y. S., Viswanathan, A., & Gross, R. A. (1999). Studies of starch esterification re€rke, 51, 90e93. actions with alkenylsuccinates in aqueous slurry systems. Starch/Sta Jane, J. L., Chen, Y. Y., Lee, L. F., McPherson, A. E., Wong, K. S., Radosavljevic, M., et al. (1999). Effects of amylopectin branch chain length and amylose contenton the gelatinization and pasting properties of starch. Cereal Chemistry, 76, 629e637. Jane, J., Shen, L., Wang, L., & Maningat, C. C. (1992). Preparation and properties of small-particle corn starch. Cereal Chemistry, 69, 280e283. Kaur, S., Kaur, A., Singh, N., & Sodhi, N. S. (2013). Effect of shearing on functional €rke, 65, properties of starches isolated from Indian kidney beans. Starch/Sta 808e813. Li, S. L., Ward, R., & Gao, Q. Y. (2011). Effect of heat-moisture treatment on the formation and physicochemical properties of resistant starch from mung bean (Phaseolus radiatus) starch. Food Hydrocolloids, 25, 1702e1709. Liu, H., Ramsden, L., & Corke, H. (1997). Physical properties and enzymatic digestibility of hydroxypropylated ae, wx and normal corn starch. Carbohydrate Polymers, 40, 175e182. €o €, M., & Timgren, A. (2012). Characterization Marku, D., Wahlgren, M., Rayner, M., Sjo of starch pickering emulsions for potential applications in topical formulations. International Journal of Pharmaceutics, 428, 1e7. Morrison, W. R., Tester, R. F., & Gidley, M. J. (1994). Properties of damaged starch granules. 2. Crystallinity, molecular order and gelatinization of ball-milled starches. Journal of Cereal Science, 19, 209e217. Nilsson, L., Leeman, M., Wahlund, K. G., & Bergenståhl, B. (2006). Mechanical degradation and changes in conformation of hydrophobically modified starch. Biomacromolecules, 7, 2671e2679. Park, S., Chung, M. G., & Yoo, B. (2004). Effect of octenylsuccinylation on rheological €rke, 2004(56), 399e406. properties of corn starch pastes. Starch/Sta
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39 Shogren, R. L., Viswanathan, A., Felker, F., & Gross, R. A. (2000). Distribution of octenyl succinate groups in octenyl succinic anhydride modified waxy corn €rke, 52, 196e204. starch. Starch/Sta Song, X. Y., Zhu, W., Li, Z., & Zhu, J. J. (2010). Characteristics and application of €rke, octenyl succinic anhydride modified waxy corn starch in sausage. Starch/Sta 62, 629e636. Thirathumthavorn, D., & Charoenrein, S. (2006). Thermal and pasting properties of native and acid-treated starches derivatized by 1-octeyl succinic anhydride. Carbohydrate Polymers, 66, 258e265. Thitipraphunkul, K., Uttapap, D., Piyachomkwan, K., & Takeda, Y. (2003). A comparative study of edible canna (Canna edulis) starch from different cultivars. Part II. Molecular structure of amylose and amylopectin. Carbohydrate Polymers, 54, 489e498.
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Wang, C., He, X. W., Huang, Q., Fu, X., Luo, F. X., & Li, L. (2013). Distribution of octenylsuccinic substituents in modified A- and B- polymorph starch granules. Journal of Agricultural and Food Chemistry, 61, 12492e12498. Wang, C., He, X. W., Huang, Q., Luo, F. X., & Fu, X. (2013). The mechanism of starch granule reacted with OSA by phase transition catalyst in aqueous medium. Food chemistry, 141, 3381e3385. Yamada, M., Tamaki, S., & Hisamatsu, M. (1997). Molecular change of starch granules with physical treatment. Potato starch by ball-mill treatment. In P. J. Frazier, A. M. Donald, & P. Richmond (Eds.), Starch structure and functionality (pp. 59e67). Cambridge: The Royal Society of Chemistry. Zhang, B., Dhital, S., & Gidley, M. J. (2013). Synergistic and antagonistic effects of aamylase and amyloglucosidase on starch digestion. Biomacromolecules, 14, 1945e1954.
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High-speed shear effect on properties and octenylsuccinic anhydride modification of corn starch Chan Wang, Xiaowei He, Xiong Fu, Faxing Luo, Qiang Huang* College of Food Sciences, South China University of Technology, 381 Wushan Road, Guangzhou 510640, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 7 July 2014 Accepted 3 September 2014 Available online 16 September 2014
The reaction between starch granules and octenylsuccinic anhydride (OSA) is normally retarded due to poor penetration of big oily OSA droplets into starch granules in an aqueous reaction system. High-speed shear was used to improve the degree of substitution (DS) and reaction efficiency (RE) of octenylsuccinate (OS) starch. Effects of high-speed shear on the physicochemical properties of corn starch and OS-starch synthesis were investigated. Results showed that no significant difference was observed in melting temperature and crystalline structure of treated starch when shear rate was less than 1.5 104 rpm. Treatment could degrade the starch molecule and release soluble saccharides. High-speed shear treated starch (H-starch) exhibited lower enthalpy change, and higher stability of hot and cold paste. OSstarch prepared using high-speed shear (H-OS-starch) showed more homogenous substitute group distribution in starch granule than that of control, as shown by confocal laser scanning microscopy. HOS-starch also showed higher DS and RE, slightly lower pasting temperature, higher stability of hot and cold paste, and higher clarity and freeze-thaw stability, compared with the control. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Octenylsuccinate starch High speed shearing Starch pasting properties Reaction efficiency
1. Introduction Octenylsuccinate (OS) starch shows excellent emulsification properties because of its amphiphilic character (Jeon, Viswanathan, & Gross, 1999). The application of OS-starch is involved in a variety of oil-in-water emulsions for food, pharmaceutical and industrial products such as beverages, salad dressings, flavor-encapsulating agents, clouding agents, processing aids, body powders and lotions (Jeon et al., 1999; Park, Chung, & Yoo, 2004). The reaction of OSA and starch carried out in aqueous phase was resulted in poor reaction efficiency and uneven distribution of OS groups (Shogren, Viswanathan, Felker, & Gross, 2000). The distribution of OS groups in starch granules has been studied extensively (Chen, He, & Huang, 2014; Chen, Huang, Fu, & Luo, 2014; Huang et al., 2010; Shogren et al., 2000). It has been noted that the concentration of OS groups on the surface of the OS-starch granules was about 2e4 times than that of the bulk. High-speed shear, which is widely used in food industry, provides a high shear, cavitation and collision force, making the material be blended, disintegrated, dispersed, homogenized and emulsified. Effects of high-speed shear on starch physicochemical
* Corresponding author. Tel.: þ86 20 8711 3845; fax: þ86 20 8711 3848. E-mail address: [email protected] (Q. Huang). http://dx.doi.org/10.1016/j.foodhyd.2014.09.007 0268-005X/© 2014 Elsevier Ltd. All rights reserved.
properties were studied, results showed that the onset (To), peak (Tp), and conclusion (Tc) temperatures and crystallinity decreased with an increase in the shear speed, due to the disintegration and fragmentations of granules (Kaur, Kaur, Singh, & Sodhi, 2013). Corn starch granules have many narrow channels (0.07e0.1 mm) leading from the surface pinholes (0.1e0.3 mm) to the central cavity, only allowing < 100 nm droplets accessible (Huber & BeMiller, 1997; Zhang, Dhital, & Gidley, 2013). In our previous studies, we found that the solubility of OSA in water is low (Wang, He, Huang, Fu, et al., 2013). The droplets of OSA could react with the granular surface or, depending on their size, travel into the channels and the interior cavity (Shogren et al., 2000). Higher reaction efficiency can be achieved by phase transition catalyst (Wang, He, Huang, Luo, & Fu, 2013), ultrasound (Chen, Huang, et al., 2014), or hydrothermal treatment (Chen, He, et al., 2014). Results indicated that OSA groups could go deep into the interior of starch granules and distributed throughout the OS-starch granules by ultrasound or hydrothermal treatment (Chen, He, et al., 2014; Chen, Huang, et al., 2014). High-speed shear has advantages of being a simple process, presenting minimal environmental problems and subject to convenient operation. Our previous study showed that the size of OSA droplets could be decreased under a high-speed shear (Wang, He, Huang, Fu, et al., 2013). Our hypothesis is that high-speed shear would improve the reaction efficiency and physicochemical properties of OS-starch, which has potential application in food industry.
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
2. Materials and methods 2.1. Materials Normal corn starch (13.5% moisture content) was obtained from the Dacheng Company (Changchun, China). OSA was obtained from Nanjing Golden Chemical Co., Ltd (Nanjing, China). Other chemicals used in the study were all analytical grade. 2.2. High-speed shear treatment and preparation of OS-starch High-speed shear treated corn starch. Starch suspension (35%, w/ w) was treated using a high-speed homogenizer (FJ200-SH, Shanghai specimen and model factory, China) at different agitation speeds for 1.5 h (5 103, 8 103, 1.0 104 and 1.5 104 rpm, the shear rates of these agitation speeds were: 5588, 8942, 11,775, and 16,766 s1, respectively).
Speed rate ¼
p 18 v 60 0:8
p: 3.14; 18 mm: the diameter of rotor; n: agitation speed; 0.8 mm: the distance between rotor and stator. 60:60 s. The samples were signed as K2eK4 and the native starch was signed as K0. The control sample (K1) was treated at 0.5 103 rpm by a mechanical stirrer (RW 20 digital, IKA, Germany) for same time. Samples were centrifuged at 4000 g for 20 min and the supernatant was determined by a high performance liquid chromatography (HPLC). The solids were oven-dried at 40 C for 24 h, manually grinded and passed through a 100 mesh nylon sieve. OS-starch synthesis assisted by high-speed shear. Corn starch was suspended in distilled water (35%, w/w) at different agitation speed (5 103, 8 103, 1.0 104 and 1.5 104 rpm) with the high-speed homogenizer, and a control sample was treated at 0.5 103 rpm by a mechanical stirrer. The pH of the suspension was adjusted to 8.0e9.0 by adding NaOH solution (3%, w/w) with a pH meter, and the temperature was controlled at 35 C. Different amount of OSA (3e7%, dsb) was added slowly within 1 h. After the reaction, the pH was adjusted to 6.5 with HCl solution (3%, w/w). The mixture was washed two times with distilled water and two times with ethanol. The starch samples were oven-dried at 40 C for 24 h, and then passed through a 100 mesh nylon sieve. 2.3. Determination of the degree of substitution Degree of substitution was determined as previously described (Wang, He, Huang, Fu, et al., 2013). The OS-starch sample (5 g, dry weight) was accurately weighed and suspended by stirring for 30 min in 25 mL of HCl-isopropyl alcohol solution (2.5 M). Aqueous isopropyl alcohol solution [100 mL 90% (v/v)] was added and the slurry stirred for an additional 10 min. The suspension was filtered through a glass filter and the residue was washed with 90% isopropyl alcohol solution until no Cl could be detected (using 0.1 M AgNO3 solution). The starch was re-dispersed in 300 mL distilled water and heated in a boiling water-bath for 20 min with stirring. The starch solution was titrated with 0.1 M standard NaOH solution, using phenolphthalein as an indicator. A blank was simultaneously titrated with native starch as a control. The DS was calculated by the following equation:
DS ¼
0:162 ðA MÞ=W 1 ½0:209 ðA MÞ=W
where A is the titration volume of NaOH solution (mL); M is the molarity of NaOH solution; and W is the dry weight (g) of the OS-
33
starch. 162 is the molecular weight of anhydroglucose unit; 209 is (molecular weight of octenyl succinic anhydride e 1). The reaction efficiency (RE) was calculated as follows:
RE ¼
Actual DS 100% Theoretical DS
The theoretical DS was calculated by assuming that all of the added anhydride reacted with starch to form the ester derivative. 2.4. Determination of molecular weight distribution of soluble components HPLC was done on a high performance liquid chromatography instrument (Agilent Co., USA) equipped with a Shodex OHpak SB803 M HQ column (Tosoh Co., Japan), and a Shodex OHpak SB-G guard column, an automatic injector with a 20 uL loop, an Agilent 1260 ISO pump (Agilent Co., USA) and an Agilent 1260 Refractive Index Detector (RID) (Agilent Co., USA). The eluting solvent was distilled water, and the flow rate was 0.8 mL/min. The column oven temperature was controlled at 70 C. The molecular weight of the supernatant was calculated by comparison to a calibration curve (Fig. 2) made with pullulan standards. A regression equation for the pullulan standards was: y ¼ 0.9573x þ 11.363 (R2 ¼ 0.9991). 2.5. X-ray diffraction The crystalline structure and relative crystallinity of H-starches were identified and quantified by an X-ray diffractometer (D/Max200, Rigaku Denki Co. Ltd., Tokyo, Japan) (Chen, Huang, et al., 2014). 2.6. Scanning electron microscopy (SEM) Images of starches were taken by scanning electron microscope (EVO18, Carl Zeiss, Germany). Starch samples were mounted on an aluminum stub using double-sided stick tape, coated with a thin film of gold (10 nm), and then examined at an accelerating voltage of 10 kV. 2.7. Confocal laser scanning microscopy CLSM was measured using a method of Wang, He, Huang, Fu, et al. (2013). A TCS SP5 CLSM fitted with an Argon ion laser (Leica, Wetzlar, Germany) was used for the detection of the fluorescence signal from the dye-stained starch granules. The details of the Leica objective lens used were 40 /1.25 oil. The excitation wavelength was 514 nm with 56 capacity. During the image acquisition, each line was scanned two times and the average was calculated to reduce the noise. 2.8. Differential scanning calorimetry A differential scanning calorimeter (DSC 8000, PerkineElmer, Norwalk, CT, USA) with an intra cooler was used to analyze the gelatinization properties of starch, following the method of (Li, Ward, & Gao, 2011). The enthalpy change (DH), onset (To), peak (Tp), and conclusion (Tc) temperature of starch gelatinization were calculated by using a Pyris software (PerkineElmer, Norwalk, CT, USA). The samples were scanned from 30 C to 150 C at 10 C/min. An empty pan was used as a reference. 2.9. Pasting properties Pasting properties were analyzed on a Brabender Micro ViscoAmylo-Craph (Melchers Co., Germany). Pasting temperature (TP),
34
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
peak viscosity (PV), hot paste viscosity (HPV), break down (BD) and setback (SB) values were recorded (Chen, Huang, et al., 2014). 2.10. Paste clarity Pasting clarity was measured using a method of Craig, Maningat, Seib, and Hoseney (1989). The percent transmittance (% T) was determined at 650 nm against water as blank in a 721G spectrophotometer (Anal. Instr. Factory, Shanghai, China). 2.11. Freeze-thaw stability Starch paste (6%, w/v) was kept in 100 mL sealed bottles, stored at 18 C for 18 h, and thawed at 25 C for 6 h (one freeze and thaw cycle defined as ‘1 time’). After each cycle, the sample was centrifuged at 4000 rpm for 20 min and the percentage of the separated water measured of the ratio of the weight of the water separated to the weight of the paste. The process was repeated till water expelled or the paste turned into sponginess (Huang et al., 2010). 2.12. Statistical analysis Each sample was measured in triplicates and means and standard deviations were reported. The mean values and differences were analyzed using Duncan's multiple-range test. Means were tested for least significant differences (LSD) with SPSS 18.0 statistical software for Windows. 3. Results and discussion 3.1. Effect of high-speed shear condition on starch structure Electron micrographs of starch granules subjected to different shear conditions are shown in Fig. 1. There was little evidence differences in morphology composition between the native starch granules and mechanical stirrer treated sample (Fig. 1). After highspeed shear treatment, a few large corn starch granules were
damaged. Results proved that mechanical force damaged the native starch granule in a limited extent. The chromatogram of soluble components of H-starch is shown in Fig. 2a. One major peak was detected in the profile at retention time of 6.5 min for all samples. Based on the equation of the calibration curve made by pullulan standards and the retention time, the molecular weight of the soluble components were mainly distributed in range of 5.02 kDa, i.e., the average degree of polymerization (DP) of soluble saccharides was 31. The concentration of soluble components increased with the shear speed increasing, which indicated the degradation accelerated under higher shear speed. The possible mechanisms for the appearance of soluble saccharides during mechanical action, such as snapping of amylopectin clusters breakage of glycosidic bonds in the vicinity of a-1, 6branching points in the interior of amylopectin molecules, and splitting of granules along radii (i.e. parallel to double helix axes likely to cause molecular breakage) have been described previous (Dhital, Shrestha, Flanagan, Hasjim, & Gidley, 2011; Morrison, Tester, & Gidley, 1994; Yamada, Tamaki, & Hisamatsu, 1997). X-ray diffraction spectra of the residue starch samples are shown in Fig. 2b. All samples exhibited the A-type diffraction pattern with major peaks at 15 , 17 , 18 and 23 2q. High-speed shear did not change the crystalline type but relative crystallinity. Compared with the native corn starch, the relative crystallinity of H-starch decreased from 36.90% to 34.68% when the shear speed increased from 500 rpm to 1.5 104 rpm shear speed. Results indicated that native starch display resistance to mechanical force. This resistance was attributed to intermolecular and intramolecular hydrogen bonding and to the entanglement of starch as well, such as the double helix formation between branch chains of amylopectin molecules and the intertwining between amylose and amylopectin (Jane, Shen, Wang, & Maningat, 1992). Thermal properties of native corn starch and H-starch are summarized in Table 1. There was no significant difference in To, Tp and Tc among K0eK4. The onset temperature of the starches decreased with increases of the shear speed. Native corn starch required more energy to gelatinize (K0, 11.46 J/g) than that of K4
Fig. 1. Scanning electron micrographs of native corn starch and high-speed shear treated starch. K0: native starch; K1: corn starch was treated at 0.5 103 rpm by a mechanical stirrer for 1.5 h; K2eK5: corn starch was treated at different agitation speed (5 103 rpm, 8 103 rpm, 1.0 104 rpm, 1.5 104 rpm) by a high-speed homogenizer for 1.5 h.
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
35
between grinding matrix and starch causes atomic and hydrogen bonds to break, this could weaken the crystalline region and the structure of starch granules (Huang, Lu, Li, & Tong, 2007). The pasting parameters of starches with different agitation speed are shown in Table 1. The pasting temperature and viscosity of H-starch did not change significantly when agitated at different speeds in most cases. However, compared with native starch, it exhibited lower peak viscosity (PV); hot paste viscosity (HPV); break down value (BD), and higher setback value when the speed increased to 1.5 104 rpm. The decrease in PV, HPV and BD was presumably due to attrition-induced damage of granules. The amylopectin in H-starch have been more damaged and a lower molecular weight than native starch. The cleavage of short chains of amylopectin might give a smaller contribution to paste viscosity compared to the cleavage of long chains of amylopectin due to smaller gyration radius of the molecules in pastes (Han, Campanella, Mix, & Hamaker, 2002). The shear forces are caused by cavitation that are capable to break the chains of polymers and damaging granules. Meanwhile, the water can partially decompose into OH radicals and H atoms in the collapsing cavitation bubbles, which can react with solute molecules causing polymer degradation (Czechowska-Biskup, Rokita, Lotfy, Ulanski, & Rosiak, 2005). The degradation could be due to the breakage of covalent bonds, i.e., intramolecular, or it could be due to the disruption of aggregates, i.e., the breakage of intermolecular bonds (Nilsson, Leeman, Wahlund, & Bergenståhl, 2006). The amylopectin has larger molecule size and branching fraction compared with amylose (Thitipraphunkul, Uttapap, Piyachomkwan, & Takeda, 2003), is more sensitive to the mechanical force. In this study, high-speed shear treatment weakened the crystalline region of starch granules, but not enough change the crystalline type (Fig. 2b).
3.2. Effects of high-speed shear treatment on OSA modification
Fig. 2. The chromatogram of dissolved components of native corn starch and highspeed shear treated starch (a), and X-ray diffraction pattern of starch granules (b). B0eB5: dissolved components of K0eK5, respectively. K0: native starch; K1: corn starch was treated at 0.5 103 rpm by a mechanical stirrer for 1.5 h; K2eK5: corn starch was treated at different agitation speed (5 103 rpm, 8 103 rpm, 1.0 104 rpm, 1.5 104 rpm) for 1.5 h by a high-speed homogenizer .
(8.71 J/g) and K5 (7.96 J/g), indicating that high-speed shear treatment reduced the amount of energy required to gelatinize corn starch, which was consistent with a previous study (Kaur et al., 2013). The broad endotherm from 65 C to 85 C was attributed to the gelatinization of starch (Jane et al., 1999). In the mechanical activation process, the impact, shear and friction operating
Effects of high-speed shear treatment on the OSA modification are shown in Fig. 3A. Compared with the control, the DS and RE of OS-starch treated by high-speed shear (H-OS-starch) increased from 0.0182 to 0.0202 and from 78.45% to 86.86%, respectively. While the DS decreased with the agitation speed increased from 1.0 104 rpm to 1.5 104 rpm. OS-starch prepared by varying OSA concentration (3e7%) at 1 104 rpm was investigated (Fig. 3B). Compared with the control, H-OS-starch showed higher RE. More OSA added, higher RE could be achieved. High-speed shear treatment promoted the formation OS-starch. The reaction between OSA and starch was retarded due to insufficient mixing in an aqueous suspension. The cavitation effect of high-speed shear increased the surface area by destroying the granular surface. The high-speed shear could reduce the drop size of OSA (Wang, He,
Table 1 Gelatinization and pasting characteristics of starches with different agitation speed treatment.a Samples
Gelatinization characteristics To( C)
K0 K1 K2 K3 K4 K5
71.21 71.14 71.51 70.51 69.56 67.60
Pasting characteristics
Tp( C) ± ± ± ± ± ±
b
0.39 0.77bc 0.91bc 1.18bc 0.88bc 0.04c
76.85 75.61 75.45 75.99 75.93 75.51
DH (J/g)
Tc( C) ± ± ± ± ± ±
b
0.28 0.14c 0.31d 0.52d 0.12bc 0.28c
83.49 83.48 83.42 83.09 81.82 81.12
± ± ± ± ± ±
b
0.79 0.87bc 0.25bc 0.04bc 1.69bc 0.60c
11.46 10.61 8.80 8.98 8.71 7.96
± ± ± ± ± ±
TP( C) b
0.32 0.62b 0.47c 0.14c 1.70c 0.47c
78.6 78.3 79.0 78.9 79.1 79.0
± ± ± ± ± ±
PV(BU) b
0.3 0.9b 0.8b 0.4b 0.5b 0.6b
211 201 196 188 194 192
± ± ± ± ± ±
HPV(BU) b
2.8 8.5b 3.5b 1.4c 3.5c 4.2c
159 157 150 146 152 148
± ± ± ± ± ±
FV(BU) b
3.5 2.8bc 2.8bc 1.4c 4.0bc 2.1bc
294 304 307 298 302 303
± ± ± ± ± ±
BD(BU) b
4.9 2.3bc 2.1c 5.7bc 4.2bc 3.5bc
52 44 46 42 42 44
± ± ± ± ± ±
SB(BU) b
2.8 2.1c 3.5c 1.4c 0.7c 0.7c
135 147 157 152 150 155
± ± ± ± ± ±
6.3b 1.4c 4.2c 2.1c 3.5c 4.9c
a Means within a column with different letters are significantly different (p < 0.05) by LSD least significant test. K0: native starch; K1: corn starch was suspended in distilled water (35%, w/w) at 0.5 103 rpm by a mechanical stirrer for 1.5 h; K2eK5: corn starch was suspended in distilled water (35%, w/w) at different agitation speed (5 103 rpm; 8 103 rpm; 1.0 104 rpm; 1.5 104 rpm) for the same time (1.5 h) by a high-speed homogenizer. TP, pasting temperature; PV, peak viscosity; HPV, hot paste viscosity; FV, final viscosity; SB, set back value (SB]FV-HPV); BD, beak down value (BD¼PV-HPV); BU, Brabender unit.
36
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
Fig. 3. Effect of high-speed shear on the DS and RE of OS-starch (A, B); photos of OS-starch slurry at different time of standing (C); CLSM of OS starches (D). A: OSA concentration: 3%. C: a, the OS-starch was prepared by a mechanical stirrer (agitation speed: 0.5 103 rpm); b-d, H-OS-starch was prepared by a high-speed homogenizer at different agitation speed (5 103 rpm, 1.0 104 rpm, 1.5 104 rpm).D: e OS-starch prepared by a high-speed homogenizer at 1.0 104 rpm.
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
Huang, Fu, et al., 2013), which increased the reaction area between OSA and starch granules. Further increasing shear speed could not increase the DS of HOS-starch, probably due to the emulsion formed during higherspeed shear. An emulsion is a system of dispersed droplets of one immiscible liquid in another stabilized by an emulsifier. A particlestabilized emulsion usually referred to as Pickering emulsions €o €, & Timgren, 2012). It was reported (Marku, Wahlgren, Rayner, Sjo that the OS-starch with hydrophobic groups achieved higher oil binding ability and affinity to the oil water interface, using as the particle fraction in the emulsion (Marku et al., 2012). During the modification, when two-thirds of total OSA was added, part of modified starch slurry (10 mL) was removed, stored quiescently and photos were taken at different time of standing (Fig. 3C). The freshly made modified starch slurry displayed homogonously emulsions (Fig. 3C, 0 h). After 2 h, the H-OS-starch (d) prepared with 1.5 104 rpm agitation speed formed a stable emulsion, while other samples started to cream. After 4 h, the creaming of H-OSstarches (Fig. 3C, a, b) was more obvious, while H-OS-starch (d) did not show any cream. These results indicated that the Pickering emulsion between OS-starch granules and OSA was formed when the agitation speed was 1.5 104 rpm. The emulsion might form a barrier between native starch granules and OSA, leading to a decreased of DS value. The CLSM optical sections of OS starch granules are shown in Fig. 3D. The native starch granules did not show any fluorescence (data not shown), while OS starch showed stronger fluorescence intensity as the DS increased. Compared with control, the interior of H-OS-starch granules showed stronger fluorescence intensity. This implied that OS groups were slightly more evenly distributed in the granules of H-OS-starch. In other words, more OS groups were induced to the inner region of the H-OS-starches when the reaction was assisted by high speed shear. This is due to high-speed shear procedure can promote the reduction and uniformity of droplet size, leading to more OS groups travel to interior of starch granules. The viscosity, clarity and freeze-thaw stability of starch paste were investigated. Pasting properties of modified starch are showed in Fig. 4. All OS-starch showed lower pasting temperature, higher peak viscosity, breakdown and setback values when compared with native corn starch, which was consistent with a previous study (Bao, Xing, Phillips, & Corke, 2003). The incorporation of a bulky OS group destroys the ordered structure and changes the pasting properties of native starch. With the increase of DS, the structure of OS-starch becomes more inflexible and the negative charged OS group repels with each other, leading to be gelatinized at a lower temperature (Song, Zhu, Li, & Zhu, 2010). In addition, the network formation of amylose-OSA inclusion complexes could enhance the pasting viscosity (Thirathumthavorn & Charoenrein, 2006). Compared with the control OS-starch (DS: 0.0267), H-OS-starch (DS: 0.0267) was observed slightly lower TP, BD, PV values and higher SB value. The high-speed shear force damages some granules producing fissures on surfaces or creating fractured particles that prone to be destroyed by heat, leading to a slightly lower pasting temperature. H-OS-starch also showed lower peak viscosity than the control OS-starch, due to the degradation of starch molecules and the distribution of OS groups in starch granule. Molecular degradation will result in a strong decrease in swelling power because of disruption of the internal network structure of the granule. Moreover, strong shear force generated by high-speed shear could reduce the drop size of OSA, resulting in much more homogeneous OS group distribution in H-OS-starch granules and lower viscosity profile. The break down viscosity, which is the difference between the peak viscosity and the viscosity after holding for certain minutes at 95 C (Chen, Huang, et al., 2014), was
37
Fig. 4. Pasting characteristics of OS-starches. NCS: normal corn starch; A, B, E: OS starch prepared by a mechanical stirrer at 500 rpm, DS ¼ 0.018, 0.0267, 0.0391, respectively; C, D: OS starch prepared by a high-speed homogenizer at 10000 rpm, DS ¼ 0.0267, 0.0385, respectively.
lower than that of the control OS-starch, indicating that H-OSstarch was resistant to shear force. OSA-modified starch showed a considerably higher clarity than that of native starch (Table 2). As DS increasing, the paste clarity was improved. In addition, H-OS-starch showed a higher clarity than the OS-starch with similar DS. The increase in the clarity of OSstarch might be attributed to the introduction of carboxyl groups, which retained water molecules to form hydrogen bonds in the starch granules. Moreover, chemical substitution of the hydroxyl group by succinyl moiety caused the inhibition of ordered structure of starch paste, thus retarding retrogradation and resulting in a more fluid paste with improved clarity (Craig et al., 1989). The highspeed shear could decrease the particle size of OSA, leading to the distribution of OS groups more uniform, especially into the inner part of starch granules. During storage, the amylopectin of H-OSstarch recrystallized was less than that of control OS-starch. Moreover, the distortion of the crystalline regions had more carboxyl group which could form more hydrogen bonds with water, resulting in retaining the water molecules in the starch granules. As a result, H-OS-starch showed higher paste clarity. When starch paste is employed as a thickening agent in frozen foods, the accelerated retrogradation at a low temperature may produce undesirable physical changes including gel formation and syneresis. Freeze-thaw cycle indicates the storage stability at low temperatures and one such cycle is equivalent to 2e3 weeks of frozen storage (Liu, Ramsden, & Corke, 1997). The paste stability of
38
C. Wang et al. / Food Hydrocolloids 44 (2015) 32e39
Table 2 Paste clarity and freeze-thaw stability of OS-starch.a DS
Paste clarity/T%
% Syneresis after freeze-thaw cycles 1
0 0.0182 0.0267 0.0267e 0.0385e 0.0391
8.89 23.79 25.72 27.53 28.69 26.88
± ± ± ± ± ±
b
0.012 0.006c 0.056d 0.019de 0.047e 0.016d
2 b
45.35 ± 0.43 33.39 ± 1.78c 16.52 ± 0.96d 12.21 ± 0.63e NIL 4.04 ± 0.025f
57.61 43.35 25.18 15.03 9.65 11.75
3 ± ± ± ± ± ±
b
2.11 1.82c 1.72d 1.10e 0.58f 0.51ef
63.67 54.34 40.93 35.12 21.03 24.53
4 ± ± ± ± ± ±
b
1.29 3.13c 1.32d 1.15e 0.77f 0.39f
81.64 58.72 43.83 41.03 28.32 31.42
± ± ± ± ± ±
1.11b 1.02c 1.81d 1.65d 0.37e 1.27e
a Means within a column with different letters are significantly different (p < 0.05) by LSD least significant test. e: H-OS-starch prepared by a high-speed homogenizer at 1.0 104 rpm. NIL: no syneresis.
OS-starches is presented in Table 2. The poor freeze-thaw stability exhibited by native starch indicated that extensive retrogradation during freeze storage. The OSA modified starches at all DS levels had a lower degree of syneresis compared with native starch. Moreover, the freeze-thaw stability increased along with an increase in DS. However, the OS-starch showed to be more susceptible to syneresis compared to H-OS-starch paste with the same DS. Reduction in the extent of retrogradation of OSA-modified starches could be attributed to the steric effect imposed by the bulky OSA group, which prevents the alignment of chain of starch (Islam & Azemi, 1997). 4. Conclusions High-speed shear condition can destroy the surface of starch granules and improve the stability of starch paste. Compared with the control, the DS of OS-starch prepared under high-speed shear was significantly increased. High-speed shear treatment showed a pronounced effect on the viscosity profile of the OS-starch. The granular interior of H-OS-starch showed stronger fluorescence intensity than that of control. And it also showed slightly lower TP, BD, PV values, higher ED and paste clarity and freeze-thaw stability than the control OS-starch. The results indicated that the highspeed shear condition can be used to improve the reaction efficiency, and improve clarity and freeze-thaw stability, which has potential application in food industry. Acknowledgments The authors would like to thank the financial support received from National Natural Science Foundation of China (31101378), the Fundamental Research Funds for the Central Universities (2013ZZ0065), Science and Technology Planning Project of Guangdong Province, China (2012NL016), Department of Science and Information Technology of Guangzhou, China (2013J4500036) are acknowledged. Abbreviations BD break down value CLSM confocal laser scanning microscopy DS degree of substitution FV final viscosity H-OS-starch OS-starch prepared under high-speed shear condition H-starch starches treat by high-speed shear condition HPV hot paste viscosity NCS normal corn starch OS octenylsuccinic OSA octenylsuccinic anhydride PV peak viscosity
RE SB SEM TP
reaction efficiency setback value scanning electron microscope pasting temperature
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