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Study on creep properties of indica rice gel
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Journal of Food Engineering 86 (2008) 10–16 www.elsevier.com/locate/jfoodeng
Study on creep properties of indica rice gel Yong-Liang Xu, Shan-Bai Xiong, Yun-Bo Li, Si-Ming Zhao * College of Food Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, China Received 9 May 2007; received in revised form 22 July 2007; accepted 3 September 2007 Available online 8 September 2007
Abstract Rice gels from 16 various types of indica rice were prepared. Their rheological parameters based on creep behavior were determined and the effect of the chemical compositions on the rheological parameters of rice gel was assessed. The creep process of rice gel consisted mainly of retarded elastic deformation, e2, and viscosity flow deformation, e3. The retarded elastic modulus, E2, relaxation time, s, and the viscosity coefficient, g3, of the rice gel were estimated according to the Burger model. The creep parameters of indica rice gel were related to rice variety. The complex of protein or lipid with amylose and embedment in gel network made an important contribution to the state of the network structure formed by starch molecular chain, and that affected the creep properties of rice gel. Correlation analysis indicated that the creep properties showed a dependence on the chemical compositions. The retarded elastic modulus, E2, had positive correlations with amylose (P = 0.004) and fat content (P = 0.066). The relaxation time, s, had negative correlations with amylose (P = 0.006) and fat content (P = 0.012). The viscosity coefficient, g3, was positively correlated to both amylose (P = 0.079) and protein content (P = 0.089). Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Creep property; Gel; Rice
1. Introduction Heating in the presence of limited moisture causes starch granules to swell, the crystal structure to collapse (Atkin, Cheng, Abeysekera, & Robards, 1999) and the amylose to diffuse out of the granular entities (Jenkins et al., 1994), which results in a viscoelastic gel whose structure consists mainly of a network of amylose and a block of amylopectin (Lai & Kokini, 1991). Gel food is the major type of solid food derived from rice grain. Creep tests can provide information about the texture of the gel, its mouth sensation and so on (Gilsenan & Ross-Murphy, 2001). Several researches have shown that gel foods such as dough (Lazaridou, Duta, Papageorgiou, Belc, & Biliaderis, 2007; Peressini et al., 2002), paste (Njintang et al., 2007) and some vegetable products (Alvarez & Canet, 2000; Alvarez, Canet, Cuesta, & Lamua, 1998) exhibit viscoelas-
*
Corresponding author. Tel./fax: +86 027 87288375. E-mail address: [email protected] (S.-M. Zhao).
0260-8774/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2007.09.002
tic behavior. Analysis of creep behavior using a stress relaxation test can be facilitated by Burgers model (Chuang & Yeh, 2006). In creep relaxation tests, samples of polymer materials are subjected to compression up to a constant stress; once the maximum force is attained, relaxation is then measured as a function of time and the results are plotted graphically as shown in Fig. 1. The creep curve can be subdivided into three main regions: OA and BC which are straight lines and AB which is a curve. Point O is the origin of the creep curve. Point A demarcates the end of the vertical line OA and the beginning of curve AB, and point B demarcates the end of the curve AB and the beginning of the straight line BC. If the straight line CB is extrapolated, it intersects the y-coordinate at point D. Point E is the projection of point C onto the y-coordinate. O–A is the region where instantaneous elastic deformation, e1, occurs during which the linkages between the structural units are stretched elastically. If the stress is removed at, or before, the time coincident with the point A, then the sample will recover its original structure
Y.-L. Xu et al. / Journal of Food Engineering 86 (2008) 10–16
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Nomenclature relaxation deformation (%) time (s) initially sample height (m) change value of the sample height during relaxation (m) applied compressive stress (Pa) instantaneous elastic deformation (%)
e t L0 DL r e1
C
Deformation, ε (%) ε2 ε3
E
B
D
ε1
A
O
Time, t (s) Fig. 1. Creep curve of polymer material.
completely. This recovery is instantaneous and is made possible by the potential energy of the material. Over longer periods of compression, the A–B region becomes apparent; this represents the time-dependent retarded elasticity which is described as retarded elastic deformation, e2. Gel samples consist of a complex network of interlinked filaments and linkages in the network begin to rupture in this region as the rate of deformation gradually increases. The proportion of linkages which are broken increases with time until point B is reached. During this period, the retarded elastic deformation, e2, which corresponds to the conformational movement of macromolecules rises as an exponential function of time (Alvarez et al., 1998). The region B–C is a linear region associated with viscosity flow and described as viscosity deformation, e3, in which some of the linkages are permanently ruptured. The viscosity flow of the gel is mainly resulted from the relative displacement of linear molecules (Alvarez et al., 1998). If the stress is removed after point C, the sample recovers to a certain extent which is determined by the degree of permanent structural breakdown (Alvarez et al., 1998). Creep properties of gel are expected to depend on the constituents of the gel (Bhattacharya, 1998). Creep properties of rice starch gel are strongly corrected with amylose content (Noosuk, Hill, Farhat, Mitchell, & Pradipasena, 2005; Noosuk, Hill, Pradipasena, & Mitchell, 2003). Rice
e2 e3 E1 E2 g3 s
retarded elastic deformation (%) viscosity flow deformation (%) instantaneous elastic modulus (Pa) retarded elastic modulus (Pa) viscosity coefficient (Pa s) relaxation time (s)
gel foods are composed of multi-components. Besides starch, protein and lipid in rice may also affect the properties of rice gels. It is well known that indica rice containing high concentrations of amylose and protein which gives the gel greater strength and elasticity is a suitable starting material for rice noodle production in China (Sun, 2004). It is also possible that the presence of other compositions such as fat and water may affect, to some degree, the rheological properties of rice gel (Chuang & Yeh, 2002). The selection of a suitable rice variety according to their chemical composition contents to obtain moderate stickiness and elasticity gel is essential for the production of rice gel foods. The objectives of this work are to test the creep behavior of various indica rice gels, taking into account the constituents of the rice, and to analyze the relationship between creep parameters and chemical compositions and thereby, to establish guidelines for the choice of raw material for the production of rice gel foods. 2. Materials and methods 2.1. Materials Fresh rice samples (16 varieties) harvested in the same year were used. Ten early indica rice varieties (Liangyou103, Liangyou106, Liangyou105, M103s/20257, Jinyou402, M104s/20257, Liangyou407, Liangyou301, M103s/ Zhongzu1 and M102s/Zhongzu1) were obtained from the College of Plant Science and Technology (Huazhong Agricultural University, Wuhan, Hubei, China). Five late indica rice varieties (Jinyou207, 89-3, Yuhong, Simiao, Yuchi) and one early indica rice variety (Zhefu802) were obtained from Hunan Gaea gem Ltd. (Changde, Hunan, China). The material was stored at room temperature until required for experimentation. The grain was dehulled with a roller sheller (JLGJ4.5, Grain & Instrument Industry Co., Ltd., Zhejiang, China) and polished in a polishing machine (JNMJ3, Grain & Instrument Industry Co., Ltd., Zhejiang, China). The polishing time was 60 s. 2.2. Method 2.2.1. Gel sample preparation The processing conditions used in rice noodle technology in China were also employed to produce indica rice
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gels. Rice samples were cleaned with copious tap water to remove any dust and other foreign matter manually. The rice sample was then soaked in distilled water at a ratio (rice to water) of 1:1 for 16 h at 40 °C. After soaking, the rice was removed from the water and milled in a refiner (YU8022, Electronic and Machinery Co., Ltd., Hebei, China). The rice slurry was adjusted to 1.115 g/cm3 (1.115 g rice flour per 1 cubic centimeter of rice slurry). Then the slurry was heated at 90 °C for 10 min, and maintained at 40 °C for 35 min. The formed gel was reheated for 5 min at 90 °C and cooled to room temperature. The gel was then immersed in boiling water for 3 min and soaked in lactic acid solution (1.5%, w/w) for 10 min. 2.2.2. Testing the creep properties of rice gel The creep behavior of indica rice gel prepared as described in Section 2.2.1, was measured using an XTPlus Texture Analyzer (TA-XT2, Stable Micro Systems Ltd., Haselmere, Surrey, UK). Each of the mechanical tests was replicated three times. In the creep relaxation test, rectangular specimens (dimensions: 20 mm long, 20 mm wide, 7 mm height) were compressed with a cylindrical probe 36 mm in diameter (P/36). In order to eliminate the effect of shear stress, the cross-sectional area of the samples was smaller than that of the cylindrical probe. When samples underwent compression, the contact area between samples and probe would increase. But the change was slightly (less than 0.07%), so we neglected it in our study. Deformation–time curves were obtained at a pre-test speed of 5 mm/s, test speed of 10 mm/s and post-test speed of 10 mm/s at 25 °C. The force was then held constant at 1 kg and the specimens were allowed to relax for 120 s. The relaxation deformation e (%) was calculated as follows: e¼
DL 100% L0
compressive stress 1 9:81 ¼ ¼ 2:45 104 Pa length width 0:02 0:02
2.2.4. Protein content measurement The protein content of the rice flour was determined by the Kjeldahl method with a nitrogen conversion factor of 5.95 (Nakasathien, Israel, Wilson, & Kwanyuen, 2000). The protein content of the rice was expressed on a dry weight basis. 2.2.5. Fat content measurement The fat content of the rice flour samples was analyzed using the Soxhlet extraction procedure (Palmquist & Jenkins, 2003). The fat content of the rice was expressed on a dry weight basis. 2.3. Statistical analysis All measurements were repeated three times, and the average values were used as data. Simple linear correlation analysis was carried out using the Statistical Analysis System R8.0 software for Windows (SAS Institute, 1989) (Moore & McCabe, 1989). 3. Results and discussion 3.1. Creep curves of indica rice gel
ð1Þ
where L0 is the initially sample height and DL is the change value of the sample height during relaxation. Under the above conditions, the initially applied compressive stress r (Pa) was: r¼
of 0.01 M I2-KI aqueous solutions was then added to the mixture which was diluted to 100 mL with distilled water. The blank was composed of 0.5 mL 0.1 M HCl and 0.5 mL 0.01 M I2-KI solution and was diluted to 50 mL with distilled water. The test mixture and blank were incubated at 25 °C for 15 min before recording their absorbances at 620 nm with a spectrophotometer (722 s, Precision & Scientific Instrument Co., Ltd., Shanghai, China). The quantification of amylose in rice was determined by the blue value.
ð2Þ
2.2.3. Quantification of amylose Higher blue values (BV) suggest higher amylose content in the rice. The method of Takahiro et al. (2005) was modified to determine the blue value of the rice. Rice was ground with a disintegrator and sifted through a 0.2mm sieve (80-mesh screen). The ground material (0.125 g, dry basis) was dispersed in ethanol, and dissolved in 6 mL of 0.5 M KOH solution. The mixture was heated at 100 °C for 15 min, and was then made up to 25 mL with distilled water. A volume of 2.5 mL of the mixture was adjusted to pH 3 with 0.1 M HCl. A 0.5-mL aliquot
Fig. 2 shows the graphical representation of deformation, e, vs. time, t, for gel samples of various types of indica rice at room temperature (25 °C). Following the application of stress, deformation occurred. Because the initial deformation of retarded elastic deformation was greater in a short time, the initial part of creep curve in Fig. 2a and b was close to being a vertical line. But local enlarged graph (Fig. 2c and d) showed that it was actually not to be a vertical line and the vertical line of creep curve (corresponding to OA in Fig. 1) in the rice gels was hardly present and majority of the creep curve including the initial part of creep curve (before 0.24 seconds) was belonged to the retarded elastic deformation curve (corresponding to AB in Fig. 1). The instantaneous elastic deformation, e1, was taken as the first reading can be inconspicuous. The retarded elastic deformation, e2, following the instantaneous elastic deformation, e1 was clearly measured. When there was sufficient measure time, viscosity flow deformation, e3, was observed.
70
30
60
25
50
Deformation, ε (%)
Deformation, ε (%)
Y.-L. Xu et al. / Journal of Food Engineering 86 (2008) 10–16
40 30
Liangyou103 Liangyou105 Liangyou301 M103s/20257 M103s/zhongzu1
20 10 0
0
30
Liangyou106 Liangyou407 Jinyou207 M104s/20257
60
90
20
15
Jinyou402 89-3 M102s/zhongzu1 Yuhong Simiao Zhefu802 Yuchi
10
5
0
120
0
30
60
90
120
Time, t (s)
Time, t (s) 30
40
30
Liangyou106 Liangyou407 Jinyou207 M104s/20257
Jinyou402 89-3 M102s/zhongzu1 Yuhong Simiao Zhefu802 Yuchi
25
Deformation, ε (%)
Liangyou103 Liangyou105 Liangyou301 M103s/20257 M103s/zhongzu1
35
Deformation, ε (%)
13
25 20 15
20
15
10
10 5
5 0 0
0.1
0.2
0.3
Time, t (s)
0 0
0.1
0.2
0.3
Time, t (s)
Fig. 2. Creep curve of different indica rice gels: (a) Creep curve of indica rice gel showing a high degree of deformation (e120 P 30%). (b) Creep curve of indica rice gel showing a small degree of deformation (e120 < 30%). (c) Local graph of Fig. 1a (0–0.3 s). (d) Local graph of Fig. 1b (0–0.3 s).
3.2. Creep parameters of indica rice gel Eq. (3) (Burger model) describes the creep curve as the sum of the instantaneous elastic deformation, retarded elastic deformation and viscosity flow deformation. r r r e ¼ e1 þ e2 þ e3 ¼ þ ð1 et=s Þ þ t ð3Þ E1 E 2 g3 where e (%) is the total deformation at time t (s) which consists of instantaneous elastic deformation, e1 (%), retarded elastic deformation, e2 (%), and viscosity flow deformation, e3 (%). E1 (Pa) is the instantaneous elastic modulus; E2(Pa) is the retarded elastic modulus; g3 (Pa s) is the coefficient of viscosity associated with viscosity flow; s (s) is the relaxation time; and r (Pa) is the constantly applied compressive stress. r e1 ¼ ð3aÞ E1 r e2 ¼ ð1 et=s Þ ð3bÞ E2 r ð3cÞ e3 ¼ t g3
Eq. (3a) fits the O–A region of the creep curve (Fig. 1) and represents the Hooke model for an ideal spring. The Voigt model (Eq. (3b)) fits the A–B (Fig. 1) region and represents retarded elastic deformation, while the linear model (Eq. (3c)) fits the B–C (Fig. 1) region and represents the viscosity flow deformation. In the Burger model (Eq. (3)), the creep parameters were obtained from the deformation–time curves through nonlinear regression analysis. All the nonlinear regression equations were statistically significant at the P < 0.01 level (F test). The creep parameters are shown in Table 1. When E1 andE2 are large, the heights of curves O–A and A–B (Fig. 1) will decrease, reflecting greater hardness and greater elasticity, respectively. Longer relaxation times, s, correspond to an decreasing slope in curve A–B, indicating that the viscoelastic behavior is sustained over long periods, while higher g3 values correspond to a reduced slope in curve B–C, which reflects the increasing viscosity of the gel. The nonlinear regression analysis shows that the instantaneous elastic deformation, e1 of rice gel was smaller than
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3.3. Relationship between creep parameters and chemical compositions of indica rice gel
Table 1 Creep parameters of different indica rice gels Sample
E2 (104 Pa)
s (s)
g3 (107 Pa s)
e2 (%)
e3 (%)
e (%)
Liangyou103 Liangyou106 Liangyou105 Liangyou407 Liangyou301 Jinyou402 Jinyou207 89-3 M103s/20257 M104s/20257 M103s/Zhongzu1 M102s/Zhongzu1 Yuhong Simiao Zhefu802 Yuchi
9.22 6.67 7.16 8.73 6.08 16.78 8.93 12.65 6.87 7.26 8.24 12.26 10.50 10.69 12.56 13.05
0.138 0.181 0.161 0.150 0.219 0.081 0.161 0.119 0.202 0.189 0.163 0.109 0.120 0.124 0.111 0.101
7.82 3.27 5.97 10.56 1.34 25.20 4.03 14.61 5.32 7.34 4.93 8.52 10.30 8.05 17.79 5.91
26.58 36.62 34.18 28.05 39.90 14.62 27.42 19.38 35.46 33.61 29.70 20.00 23.36 22.93 19.53 18.80
3.76 9.00 4.93 2.79 21.88 1.17 7.31 2.01 5.53 4.01 5.97 3.45 2.86 3.66 1.65 4.98
30.34 45.62 39.11 30.84 61.79 15.79 34.73 21.39 40.99 37.62 35.67 23.45 26.22 26.59 21.18 23.78
All experiments were carried out in triplicate. The creep parameters were obtained through nonlinear regression analysis based on the creep curve which was the averaged curve from three measurements.
7 104%, while the instantaneous elastic modulus, E1, was greater than 3 109 Pa. Table 1 shows that the retarded elastic deformation, e2 (14.62–39.90%), and the viscosity flow deformation, e3 (1.17–21.88%), were much greater than the instantaneous elastic deformation, e1. So the retarded elastic deformation, e2, played the most important role in the total creep deformation, followed by the viscosity flow deformation, e3, and the role of instantaneous elastic deformation, e1, could be neglected. Thus creep process of rice gel consisted mainly of retarded elastic deformation, e2, and viscosity flow deformation, e3, which was in accord with Fig. 2. It can be seen from Table 1 that the retarded elastic modulus, E2, and viscosity coefficient, g3, of rice gels were about 6.08–16.78 104 Pa and 1.34–25.20 107 Pa s, which were similar to those of rice starch gels (Noosuk et al., 2005). The relaxation time, s, was about 0.081– 0.219 s, which was similar to taro gels (Njintang et al., 2007), but shorter than that of rice starch gels whose relaxation time are longer than 12 s (Noosuk et al., 2005). Since the water content of rice gels employed (62%, w/w) in our experiment was lower than that of starch gels (about 90%, w/w) used by Noosuk et al. (2005), it can be deduced that relaxation time was sensitive to water content of gels. Furthermore, other chemical compositions such as amylose, protein and fat in rice gels showed negative correlations with relaxation time (Table 3), which would make the relaxation time shorter than that of starch gels. Table 1 also shows that the gel produced from the Jinyou402 variety of rice has the maximum elasticity and viscosity but the shortest relaxation time, while the gel produced from the Liangyou301 variety has the minimum elasticity and viscosity but the longest relaxation time.
Table 2 shows the chemical compositions of the 16 indica rice varieties. Simple linear correlation analysis was used to determine a relationship between creep parameters and chemical compositions, including protein content, blue value and fat content of different indica rice varieties (Table 3). It can be seem from Table 3 that the retarded elastic modulus, E2, had positive correlations with BV (r = 0.684, P = 0.004) and fat content (r = 0.470, P = 0.066). Higher BV values suggest higher amylose content in the rice. When the amylose concentration is high, crystal growth is favored, which leads to a higher molecular order in form and stronger intermolecular hydrogen bonds in the starch, resulting in greater rigidity of gel (Varavinit, Shobsngob, Varanyanond, Chinachoti, & Naivikul, 2003). Thus rice gel with a higher BV had greater values of E2. This is in accord with the finding of Noosuk et al. (2005). In the presence of fat, amylose–lipid complex forms and embeds in gel network which can enhance the springiness of gel (Gunaratne & Corke, 2007). So rice gel with a higher fat content exhibited greater E2 values. For example, in our Table 2 Chemical constituents of different indica rice varieties Sample
Protein content, Pro (%)
Blue value, BV
Fat content, Fat (%)
Liangyou103 Liangyou106 Liangyou105 Liangyou407 Liangyou301 Jinyou402 Jinyou207 89-3 M103s/20257 M104s/20257 M103s/Zhongzu1 M102s/Zhongzu1 Yuhong Simiao Zhefu802 Yuchi
13.26 ± 0.09 11.16 ± 0.21 12.18 ± 0.07 11.88 ± 0.12 11.50 ± 0.11 12.45 ± 0.05 10.80 ± 0.03 11.26 ± 0.13 9.96 ± 0.18 12.28± 0.12 11.06 ± 0.22 11.71 ± 0.06 10.59 ± 0.13 10.89 ± 0.07 12.82 ± 0.03 10.42 ± 0.02
0.406 ± 0.012 0.313 ± 0.011 0.312 ± 0.004 0.372 ± 0.009 0.315 ± 0.005 0.445 ± 0.003 0.418 ± 0.005 0.429 ± 0.001 0.349 ± 0.015 0.418 ± 0.003 0.387 ± 0.004 0.476 ± 0.007 0.390 ± 0.001 0.446 ± 0.009 0.374 ± 0.002 0.401 ± 0.006
2.26 ± 0.08 2.24 ± 0.03 2.10 ± 0.13 1.57 ± 0.09 1.27 ± 0.03 2.00 ± 0.00 2.43 ± 0.13 2.59 ± 0.28 1.66 ± 0.12 1.81 ± 0.06 2.87 ± 0.11 2.78 ± 0.05 2.30 ± 0.14 2.57 ± 0.06 2.65 ± 0.01 2.66 ± 0.10
All experiments were carried out in triplicate. Means ± SD.
Table 3 Correlation of creep parameters with protein content, BV and fat content (r/P)a (n = 16) Creep parameters
Pro
BV
Fat
E2 s g3
0.173/0.522 0.201/0.455 0.439/0.089*
0.684/0.004*** 0.659/0.006*** 0.451/0.079*
0.470/0.066** 0.613/0.012** 0.142/0.601
*, **, ***
means that there was significant correlation at P 6 0.1, 0.05 and 0.01, respectively. a Correlation coefficient of creep parameters with protein content, BV and fat content was expressed as r.
Y.-L. Xu et al. / Journal of Food Engineering 86 (2008) 10–16
study, Yuhong (0.390) had higher BV value than Liangyou106 (0.313), as a result, gel prepared with Yuhong presented higher E2 (10.50 104 Pa) values than that of Liangyou106 (6.67 104 Pa). 89-3 had similar BV value with M104s/20257, but formed gel of 89-3 has higher E2 (12.65 104 Pa) than that of M104s/20257 (7.26 104 Pa) corresponding to higher fat content in 89-3 (2.59%) than M104s/20257 (1.81%). The relaxation time, s, was influenced by the BV (r = 0.659, P = 0.006) and fat content (r = 0.613, P = 0.012). The relaxation time, s, of the gel decreased when the BV and fat content increased. Upon heating, starch granules with a significant moisture content swell, which results in a viscoelastic gel whose structure consists mainly of a network of amylose and a block of amylopectin (Lai & Kokini, 1991). Since gelated starch is composed of linear rigid macromolecules and branched flexible amylopectin macromolecules (Brouillet-Fourmann, Carrot, & Mignard, 2003; Lelivere, Lewis, & Marsden, 1986; Sandera, Thompson, & Boyer, 1990), high concentrations of amylopectin in rice gel facilitate retarded deformation and reduce the efficiency of the recovery process, while high concentrations of amylose reduce the deformation capability of the gel but facilitate its recovery. Thus gels with a high BV have shorter relaxation times. Due to the lubricating effect of fat, the interaction between these macromolecules can be largely overcome (Mor-Rosenberg, Shoemaker, & Rosenberg, 2004), which facilitates the movement of segments of macromolecular chains. Therefore the structure of rice gel containing higher amounts of fat can be re-established rapidly thus reducing the relaxation time after the gel has undergone compression. For instance, Liangyou103 and Liangyou106 have similar fat contents and the BV of Liangyou103 (0.406) was higher than that of Liangyou106 (0.313). As expected, gel prepared from Liangyou103 (0.138 s) exhibited a shorter period of retarded deformation than that prepared from Liangyou106 (0.181 s). The BV of Liangyou407 and Zhefu802 was found to be similar, but the fat content of Liangyou407 (1.57%) was lower than that of Zhefu802 (2.65%) whose relaxation time (0.150 s) was longer than that of Zhefu802 (0.111 s). Table 3 also shows that the viscosity coefficient, g3, is positively correlated to both BV (r = 0.451, P = 0.079) and protein content (r = 0.439, P = 0.089). The viscosity of the gel is mainly due to the relative displacement of linear molecules (Alvarez et al., 1998). A high BV value suggests that the gel contains large amounts of amylose, which is associated with increased gel viscosity and a high g3 value. Teo, Karim, Cheah, Norziah, and Seow (2000) found that the protein content had a dramatic effect on the rheological properties of rice flour. The presence of protein and starch will lead to starch–protein interactions or to disulfide linkages between proteins, thus the viscosity of the rice paste would be increased due to the effects of thiol groups or disulfide binding (Teo et al., 2000). It is rea-
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sonable to expect that rice gel containing a high concentration of protein will be characterized by increased viscosity and a higher g3. For example, in our study, the protein content of Simiao was similar to that in Jinyou207, but the BV of Simiao (0.446) was larger than that of Jinyou207 (0.418). The g3 of Simiao and Jinyou207 were 8.05 107 Pa s and 4.03 107 Pa s, respectively. The effect of the chemical composition of different varieties of rice on the properties of the resultant rice gels is further exemplified by comparison of Liangyou105 and Liangyou106; both have similar BV values, but the protein content of Liangyou105 (12.18%) is greater than that of Liangyou106 (11.16%). The g3 of Liangyou105 and Liangyou106 are 5.97 107 Pa s and 3.27 107 Pa s, respectively. When BV and fat content are greater, retarded elastic modulus, E2 will be greater and relaxation time, s, will be smaller. So rice gel foods made from the rice with high amylose and fat content would have better toughness and springiness. When amylose and protein content are greater, viscosity coefficient, g3 will be greater. Thus the rice with high content of amylose and protein employed in rice noodle production could enhance the viscoelasticity and toughness of rice gel foods. 4. Conclusions The creep process of rice gel consisted mainly of retarded elastic deformation, e2, and viscosity flow deformation, e3. The rheological parameters based on the creep behaviors of indica rice gel were related to the rice variety. Correlation analysis indicated that the creep properties showed a dependence on the chemical compositions. The retarded elastic modulus, E2, had positive correlations with amylose (P = 0.004) and fat content (P = 0.066). The relaxation time, s, had negative correlations with amylose (P = 0.006) and fat content (P = 0.012). The viscosity coefficient, g3, was positively correlated to both amylose (P = 0.079) and protein content (P = 0.089). References Alvarez, M. D., & Canet, W. (2000). Storage time effect on the rheology of refrigerated potato tissue (cv. Monalisa). European Food Research and Technology, 212(1), 48–56. Alvarez, M. D., Canet, W., Cuesta, F., & Lamua, M. (1998). Viscoelastic characterization of solid foods from creep compliance data: application to potato tissues. Zeitschrift fur Lebensmittel-Untersuchung undForschung, 207, 356–362. Atkin, N. J., Cheng, S. L., Abeysekera, R. M., & Robards, A. W. (1999). Localisation of amylose and amylopectin in starch granules using enzyme-gold labelling. Starch/Sta¨rke, 51, 163–172. Bhattacharya, M. (1998). Stress relaxation of starch/synthetic polymer Blends. Journal of Materials Science, 33, 4131–4139. Brouillet-Fourmann, S., Carrot, C., & Mignard, N. (2003). Gelatinization and gelation of corn starch followed by dynamic mechanical spectroscopy analysis. Rheologica Acta, 42, 110–117. Chuang, G. C. C., & Yeh, A. I. (2002). Effects of product temperature and moisture content on viscoelastic properties of glutinous rice extrudates. Cereal Chemistry, 79(1), 36–40.
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Chuang, G. C. C., & Yeh, A. I. (2006). Rheological characteristics and texture attributes of glutinous rice cakes (mochi). Journal of Food Engineering, 74(3), 314–323. Gilsenan, P. M., & Ross-Murphy, S. B. (2001). Shear creep of gelatin gels from mammalian and piscine collagens. International Journal of Biological Macromolecules, 29, 53–61. Gunaratne, A., & Corke, H. (2007). Influence of unmodified and modified cycloheptaamylose (b-cyclodextrin) on transition parameters of amylose–lipid complex and functional properties of starch. Carbohydrate Polymers, 68, 226–234. Jenkins, P. J., Cameron, R. E., Donald, A. M., Bras, W., Derbyshire, G. E., Mant, G. R., et al. (1994). In situ simultaneous small and wide angle X-ray scattering: a new technique to study starch gelatinisation. Journal of Polymer Science, 32, 1579–1583. Lai, L. S., & Kokini, J. L. (1991). Physicochemical changes and rheological properties of starch during extrusion (a review). Biotechnology Progress, 7, 251–266. Lazaridou, A., Duta, D., Papageorgiou, M., Belc, N., & Biliaderis, C. G. (2007). Effects of hydrocolloids on dough rheology and bread quality parameters in gluten-free formulations. Journal of Food Engineering, 79(3), 1033–1047. Lelivere, J., Lewis, J. A., & Marsden, K. (1986). The size and shape of amylopectin: A study using analytical ultracentrifugation. Carbohydrate Research, 153, 195–203. Moore, D. S., & McCabe, G. P. (1989). Introduction to the practice of statistics (pp. 638–642). New York: W.H. Freeman and Company. Mor-Rosenberg, Y., Shoemaker, C. F., & Rosenberg, M. (2004). Mechanical properties of composite gels consisting of fractionated whey proteins and fractionated milk fat. Food Hydrocolloids, 18(1), 153–166. Nakasathien, S., Israel, D. W., Wilson, R. F., & Kwanyuen, P. (2000). Regulation of seed protein concentration in soybean by supra-optimal nitrogen supply. Crop Science, 40, 1277–1284. Njintang, Y. N., Mbofung, C. M. F., Moates, G. K., Parker, M. L., Craig, F., Smith, A. C., et al. (2007). Functional properties of five varieties of taro flour, and relationship to creep recovery and sensory character-
istics of achu (taro based paste). Journal of Food Engineering, 82, 114–120. Noosuk, P., Hill, S. E., Farhat, I. A., Mitchell, J. R., & Pradipasena, P. (2005). Relationship between viscoelastic properties and starch structure in rice from Thailand. Starch/Sta¨rke, 57, 587–598. Noosuk, P., Hill, S. E., Pradipasena, P., & Mitchell, J. R. (2003). Structure-viscosity relationships for Thai rice starches. Starch/Sta¨rke, 55, 337–344. Palmquist, D. L., & Jenkins, T. C. (2003). Challenges with fats and fatty acid methods. Journal of Animal Science, 81, 3250–3254. Peressini, D., Sensidoni, A., Pollini, C. M., Gabriele, D., Migliori, M., & de Cindio, B. (2002). Filled-snacks production by coextrusion-cooking. Part 3. A rheological-based method to compare filler processing properties. Journal of Food Engineering, 54(3), 227–240. Sandera, E. B., Thompson, D. B., & Boyer, C. D. (1990). Thermal behavior during Gelatinization and amylopactin fine structure for selected maize genotypes as expressed in four inbred lines. Cereal Chemistry, 67(6), 594–602. Sun, Q. J. (2004). The studies on the processing technology of long life rice noodle. In Proceedings of Shanghai international symposium on the safety of cereal, oil & food (ISSCOF), Shanghai, China. (Food Session, pp. 64–65). Takahiro, F., Yohei, K., Toshio, O., Yasunori, G., Iwao, A., & Katsuyoshi, N. (2005). Food hydrocolloids control the gelatinization and retrogradation behavior of starch. 2b. Functions of guar gums with different molecular weights on the retrogradation behavior of corn starch. Food Hydrocolloids, 19, 25–36. Teo, C. H., Karim, A. A., Cheah, P. B., Norziah, M. H., & Seow, C. C. (2000). On the roles of protein and starch in the aging of non-waxy rice four. Food Chemistry, 69, 229–236. Varavinit, S., Shobsngob, S., Varanyanond, W., Chinachoti, P., & Naivikul, O. (2003). Effect of amylose content on gelatinization, retrogradation and pasting properties of flours from different cultivars of thai rice. Starch/Sta¨rke, 55, 410–415.
Journal of Food Engineering 86 (2008) 10–16 www.elsevier.com/locate/jfoodeng
Study on creep properties of indica rice gel Yong-Liang Xu, Shan-Bai Xiong, Yun-Bo Li, Si-Ming Zhao * College of Food Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, China Received 9 May 2007; received in revised form 22 July 2007; accepted 3 September 2007 Available online 8 September 2007
Abstract Rice gels from 16 various types of indica rice were prepared. Their rheological parameters based on creep behavior were determined and the effect of the chemical compositions on the rheological parameters of rice gel was assessed. The creep process of rice gel consisted mainly of retarded elastic deformation, e2, and viscosity flow deformation, e3. The retarded elastic modulus, E2, relaxation time, s, and the viscosity coefficient, g3, of the rice gel were estimated according to the Burger model. The creep parameters of indica rice gel were related to rice variety. The complex of protein or lipid with amylose and embedment in gel network made an important contribution to the state of the network structure formed by starch molecular chain, and that affected the creep properties of rice gel. Correlation analysis indicated that the creep properties showed a dependence on the chemical compositions. The retarded elastic modulus, E2, had positive correlations with amylose (P = 0.004) and fat content (P = 0.066). The relaxation time, s, had negative correlations with amylose (P = 0.006) and fat content (P = 0.012). The viscosity coefficient, g3, was positively correlated to both amylose (P = 0.079) and protein content (P = 0.089). Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Creep property; Gel; Rice
1. Introduction Heating in the presence of limited moisture causes starch granules to swell, the crystal structure to collapse (Atkin, Cheng, Abeysekera, & Robards, 1999) and the amylose to diffuse out of the granular entities (Jenkins et al., 1994), which results in a viscoelastic gel whose structure consists mainly of a network of amylose and a block of amylopectin (Lai & Kokini, 1991). Gel food is the major type of solid food derived from rice grain. Creep tests can provide information about the texture of the gel, its mouth sensation and so on (Gilsenan & Ross-Murphy, 2001). Several researches have shown that gel foods such as dough (Lazaridou, Duta, Papageorgiou, Belc, & Biliaderis, 2007; Peressini et al., 2002), paste (Njintang et al., 2007) and some vegetable products (Alvarez & Canet, 2000; Alvarez, Canet, Cuesta, & Lamua, 1998) exhibit viscoelas-
*
Corresponding author. Tel./fax: +86 027 87288375. E-mail address: [email protected] (S.-M. Zhao).
0260-8774/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2007.09.002
tic behavior. Analysis of creep behavior using a stress relaxation test can be facilitated by Burgers model (Chuang & Yeh, 2006). In creep relaxation tests, samples of polymer materials are subjected to compression up to a constant stress; once the maximum force is attained, relaxation is then measured as a function of time and the results are plotted graphically as shown in Fig. 1. The creep curve can be subdivided into three main regions: OA and BC which are straight lines and AB which is a curve. Point O is the origin of the creep curve. Point A demarcates the end of the vertical line OA and the beginning of curve AB, and point B demarcates the end of the curve AB and the beginning of the straight line BC. If the straight line CB is extrapolated, it intersects the y-coordinate at point D. Point E is the projection of point C onto the y-coordinate. O–A is the region where instantaneous elastic deformation, e1, occurs during which the linkages between the structural units are stretched elastically. If the stress is removed at, or before, the time coincident with the point A, then the sample will recover its original structure
Y.-L. Xu et al. / Journal of Food Engineering 86 (2008) 10–16
11
Nomenclature relaxation deformation (%) time (s) initially sample height (m) change value of the sample height during relaxation (m) applied compressive stress (Pa) instantaneous elastic deformation (%)
e t L0 DL r e1
C
Deformation, ε (%) ε2 ε3
E
B
D
ε1
A
O
Time, t (s) Fig. 1. Creep curve of polymer material.
completely. This recovery is instantaneous and is made possible by the potential energy of the material. Over longer periods of compression, the A–B region becomes apparent; this represents the time-dependent retarded elasticity which is described as retarded elastic deformation, e2. Gel samples consist of a complex network of interlinked filaments and linkages in the network begin to rupture in this region as the rate of deformation gradually increases. The proportion of linkages which are broken increases with time until point B is reached. During this period, the retarded elastic deformation, e2, which corresponds to the conformational movement of macromolecules rises as an exponential function of time (Alvarez et al., 1998). The region B–C is a linear region associated with viscosity flow and described as viscosity deformation, e3, in which some of the linkages are permanently ruptured. The viscosity flow of the gel is mainly resulted from the relative displacement of linear molecules (Alvarez et al., 1998). If the stress is removed after point C, the sample recovers to a certain extent which is determined by the degree of permanent structural breakdown (Alvarez et al., 1998). Creep properties of gel are expected to depend on the constituents of the gel (Bhattacharya, 1998). Creep properties of rice starch gel are strongly corrected with amylose content (Noosuk, Hill, Farhat, Mitchell, & Pradipasena, 2005; Noosuk, Hill, Pradipasena, & Mitchell, 2003). Rice
e2 e3 E1 E2 g3 s
retarded elastic deformation (%) viscosity flow deformation (%) instantaneous elastic modulus (Pa) retarded elastic modulus (Pa) viscosity coefficient (Pa s) relaxation time (s)
gel foods are composed of multi-components. Besides starch, protein and lipid in rice may also affect the properties of rice gels. It is well known that indica rice containing high concentrations of amylose and protein which gives the gel greater strength and elasticity is a suitable starting material for rice noodle production in China (Sun, 2004). It is also possible that the presence of other compositions such as fat and water may affect, to some degree, the rheological properties of rice gel (Chuang & Yeh, 2002). The selection of a suitable rice variety according to their chemical composition contents to obtain moderate stickiness and elasticity gel is essential for the production of rice gel foods. The objectives of this work are to test the creep behavior of various indica rice gels, taking into account the constituents of the rice, and to analyze the relationship between creep parameters and chemical compositions and thereby, to establish guidelines for the choice of raw material for the production of rice gel foods. 2. Materials and methods 2.1. Materials Fresh rice samples (16 varieties) harvested in the same year were used. Ten early indica rice varieties (Liangyou103, Liangyou106, Liangyou105, M103s/20257, Jinyou402, M104s/20257, Liangyou407, Liangyou301, M103s/ Zhongzu1 and M102s/Zhongzu1) were obtained from the College of Plant Science and Technology (Huazhong Agricultural University, Wuhan, Hubei, China). Five late indica rice varieties (Jinyou207, 89-3, Yuhong, Simiao, Yuchi) and one early indica rice variety (Zhefu802) were obtained from Hunan Gaea gem Ltd. (Changde, Hunan, China). The material was stored at room temperature until required for experimentation. The grain was dehulled with a roller sheller (JLGJ4.5, Grain & Instrument Industry Co., Ltd., Zhejiang, China) and polished in a polishing machine (JNMJ3, Grain & Instrument Industry Co., Ltd., Zhejiang, China). The polishing time was 60 s. 2.2. Method 2.2.1. Gel sample preparation The processing conditions used in rice noodle technology in China were also employed to produce indica rice
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gels. Rice samples were cleaned with copious tap water to remove any dust and other foreign matter manually. The rice sample was then soaked in distilled water at a ratio (rice to water) of 1:1 for 16 h at 40 °C. After soaking, the rice was removed from the water and milled in a refiner (YU8022, Electronic and Machinery Co., Ltd., Hebei, China). The rice slurry was adjusted to 1.115 g/cm3 (1.115 g rice flour per 1 cubic centimeter of rice slurry). Then the slurry was heated at 90 °C for 10 min, and maintained at 40 °C for 35 min. The formed gel was reheated for 5 min at 90 °C and cooled to room temperature. The gel was then immersed in boiling water for 3 min and soaked in lactic acid solution (1.5%, w/w) for 10 min. 2.2.2. Testing the creep properties of rice gel The creep behavior of indica rice gel prepared as described in Section 2.2.1, was measured using an XTPlus Texture Analyzer (TA-XT2, Stable Micro Systems Ltd., Haselmere, Surrey, UK). Each of the mechanical tests was replicated three times. In the creep relaxation test, rectangular specimens (dimensions: 20 mm long, 20 mm wide, 7 mm height) were compressed with a cylindrical probe 36 mm in diameter (P/36). In order to eliminate the effect of shear stress, the cross-sectional area of the samples was smaller than that of the cylindrical probe. When samples underwent compression, the contact area between samples and probe would increase. But the change was slightly (less than 0.07%), so we neglected it in our study. Deformation–time curves were obtained at a pre-test speed of 5 mm/s, test speed of 10 mm/s and post-test speed of 10 mm/s at 25 °C. The force was then held constant at 1 kg and the specimens were allowed to relax for 120 s. The relaxation deformation e (%) was calculated as follows: e¼
DL 100% L0
compressive stress 1 9:81 ¼ ¼ 2:45 104 Pa length width 0:02 0:02
2.2.4. Protein content measurement The protein content of the rice flour was determined by the Kjeldahl method with a nitrogen conversion factor of 5.95 (Nakasathien, Israel, Wilson, & Kwanyuen, 2000). The protein content of the rice was expressed on a dry weight basis. 2.2.5. Fat content measurement The fat content of the rice flour samples was analyzed using the Soxhlet extraction procedure (Palmquist & Jenkins, 2003). The fat content of the rice was expressed on a dry weight basis. 2.3. Statistical analysis All measurements were repeated three times, and the average values were used as data. Simple linear correlation analysis was carried out using the Statistical Analysis System R8.0 software for Windows (SAS Institute, 1989) (Moore & McCabe, 1989). 3. Results and discussion 3.1. Creep curves of indica rice gel
ð1Þ
where L0 is the initially sample height and DL is the change value of the sample height during relaxation. Under the above conditions, the initially applied compressive stress r (Pa) was: r¼
of 0.01 M I2-KI aqueous solutions was then added to the mixture which was diluted to 100 mL with distilled water. The blank was composed of 0.5 mL 0.1 M HCl and 0.5 mL 0.01 M I2-KI solution and was diluted to 50 mL with distilled water. The test mixture and blank were incubated at 25 °C for 15 min before recording their absorbances at 620 nm with a spectrophotometer (722 s, Precision & Scientific Instrument Co., Ltd., Shanghai, China). The quantification of amylose in rice was determined by the blue value.
ð2Þ
2.2.3. Quantification of amylose Higher blue values (BV) suggest higher amylose content in the rice. The method of Takahiro et al. (2005) was modified to determine the blue value of the rice. Rice was ground with a disintegrator and sifted through a 0.2mm sieve (80-mesh screen). The ground material (0.125 g, dry basis) was dispersed in ethanol, and dissolved in 6 mL of 0.5 M KOH solution. The mixture was heated at 100 °C for 15 min, and was then made up to 25 mL with distilled water. A volume of 2.5 mL of the mixture was adjusted to pH 3 with 0.1 M HCl. A 0.5-mL aliquot
Fig. 2 shows the graphical representation of deformation, e, vs. time, t, for gel samples of various types of indica rice at room temperature (25 °C). Following the application of stress, deformation occurred. Because the initial deformation of retarded elastic deformation was greater in a short time, the initial part of creep curve in Fig. 2a and b was close to being a vertical line. But local enlarged graph (Fig. 2c and d) showed that it was actually not to be a vertical line and the vertical line of creep curve (corresponding to OA in Fig. 1) in the rice gels was hardly present and majority of the creep curve including the initial part of creep curve (before 0.24 seconds) was belonged to the retarded elastic deformation curve (corresponding to AB in Fig. 1). The instantaneous elastic deformation, e1, was taken as the first reading can be inconspicuous. The retarded elastic deformation, e2, following the instantaneous elastic deformation, e1 was clearly measured. When there was sufficient measure time, viscosity flow deformation, e3, was observed.
70
30
60
25
50
Deformation, ε (%)
Deformation, ε (%)
Y.-L. Xu et al. / Journal of Food Engineering 86 (2008) 10–16
40 30
Liangyou103 Liangyou105 Liangyou301 M103s/20257 M103s/zhongzu1
20 10 0
0
30
Liangyou106 Liangyou407 Jinyou207 M104s/20257
60
90
20
15
Jinyou402 89-3 M102s/zhongzu1 Yuhong Simiao Zhefu802 Yuchi
10
5
0
120
0
30
60
90
120
Time, t (s)
Time, t (s) 30
40
30
Liangyou106 Liangyou407 Jinyou207 M104s/20257
Jinyou402 89-3 M102s/zhongzu1 Yuhong Simiao Zhefu802 Yuchi
25
Deformation, ε (%)
Liangyou103 Liangyou105 Liangyou301 M103s/20257 M103s/zhongzu1
35
Deformation, ε (%)
13
25 20 15
20
15
10
10 5
5 0 0
0.1
0.2
0.3
Time, t (s)
0 0
0.1
0.2
0.3
Time, t (s)
Fig. 2. Creep curve of different indica rice gels: (a) Creep curve of indica rice gel showing a high degree of deformation (e120 P 30%). (b) Creep curve of indica rice gel showing a small degree of deformation (e120 < 30%). (c) Local graph of Fig. 1a (0–0.3 s). (d) Local graph of Fig. 1b (0–0.3 s).
3.2. Creep parameters of indica rice gel Eq. (3) (Burger model) describes the creep curve as the sum of the instantaneous elastic deformation, retarded elastic deformation and viscosity flow deformation. r r r e ¼ e1 þ e2 þ e3 ¼ þ ð1 et=s Þ þ t ð3Þ E1 E 2 g3 where e (%) is the total deformation at time t (s) which consists of instantaneous elastic deformation, e1 (%), retarded elastic deformation, e2 (%), and viscosity flow deformation, e3 (%). E1 (Pa) is the instantaneous elastic modulus; E2(Pa) is the retarded elastic modulus; g3 (Pa s) is the coefficient of viscosity associated with viscosity flow; s (s) is the relaxation time; and r (Pa) is the constantly applied compressive stress. r e1 ¼ ð3aÞ E1 r e2 ¼ ð1 et=s Þ ð3bÞ E2 r ð3cÞ e3 ¼ t g3
Eq. (3a) fits the O–A region of the creep curve (Fig. 1) and represents the Hooke model for an ideal spring. The Voigt model (Eq. (3b)) fits the A–B (Fig. 1) region and represents retarded elastic deformation, while the linear model (Eq. (3c)) fits the B–C (Fig. 1) region and represents the viscosity flow deformation. In the Burger model (Eq. (3)), the creep parameters were obtained from the deformation–time curves through nonlinear regression analysis. All the nonlinear regression equations were statistically significant at the P < 0.01 level (F test). The creep parameters are shown in Table 1. When E1 andE2 are large, the heights of curves O–A and A–B (Fig. 1) will decrease, reflecting greater hardness and greater elasticity, respectively. Longer relaxation times, s, correspond to an decreasing slope in curve A–B, indicating that the viscoelastic behavior is sustained over long periods, while higher g3 values correspond to a reduced slope in curve B–C, which reflects the increasing viscosity of the gel. The nonlinear regression analysis shows that the instantaneous elastic deformation, e1 of rice gel was smaller than
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3.3. Relationship between creep parameters and chemical compositions of indica rice gel
Table 1 Creep parameters of different indica rice gels Sample
E2 (104 Pa)
s (s)
g3 (107 Pa s)
e2 (%)
e3 (%)
e (%)
Liangyou103 Liangyou106 Liangyou105 Liangyou407 Liangyou301 Jinyou402 Jinyou207 89-3 M103s/20257 M104s/20257 M103s/Zhongzu1 M102s/Zhongzu1 Yuhong Simiao Zhefu802 Yuchi
9.22 6.67 7.16 8.73 6.08 16.78 8.93 12.65 6.87 7.26 8.24 12.26 10.50 10.69 12.56 13.05
0.138 0.181 0.161 0.150 0.219 0.081 0.161 0.119 0.202 0.189 0.163 0.109 0.120 0.124 0.111 0.101
7.82 3.27 5.97 10.56 1.34 25.20 4.03 14.61 5.32 7.34 4.93 8.52 10.30 8.05 17.79 5.91
26.58 36.62 34.18 28.05 39.90 14.62 27.42 19.38 35.46 33.61 29.70 20.00 23.36 22.93 19.53 18.80
3.76 9.00 4.93 2.79 21.88 1.17 7.31 2.01 5.53 4.01 5.97 3.45 2.86 3.66 1.65 4.98
30.34 45.62 39.11 30.84 61.79 15.79 34.73 21.39 40.99 37.62 35.67 23.45 26.22 26.59 21.18 23.78
All experiments were carried out in triplicate. The creep parameters were obtained through nonlinear regression analysis based on the creep curve which was the averaged curve from three measurements.
7 104%, while the instantaneous elastic modulus, E1, was greater than 3 109 Pa. Table 1 shows that the retarded elastic deformation, e2 (14.62–39.90%), and the viscosity flow deformation, e3 (1.17–21.88%), were much greater than the instantaneous elastic deformation, e1. So the retarded elastic deformation, e2, played the most important role in the total creep deformation, followed by the viscosity flow deformation, e3, and the role of instantaneous elastic deformation, e1, could be neglected. Thus creep process of rice gel consisted mainly of retarded elastic deformation, e2, and viscosity flow deformation, e3, which was in accord with Fig. 2. It can be seen from Table 1 that the retarded elastic modulus, E2, and viscosity coefficient, g3, of rice gels were about 6.08–16.78 104 Pa and 1.34–25.20 107 Pa s, which were similar to those of rice starch gels (Noosuk et al., 2005). The relaxation time, s, was about 0.081– 0.219 s, which was similar to taro gels (Njintang et al., 2007), but shorter than that of rice starch gels whose relaxation time are longer than 12 s (Noosuk et al., 2005). Since the water content of rice gels employed (62%, w/w) in our experiment was lower than that of starch gels (about 90%, w/w) used by Noosuk et al. (2005), it can be deduced that relaxation time was sensitive to water content of gels. Furthermore, other chemical compositions such as amylose, protein and fat in rice gels showed negative correlations with relaxation time (Table 3), which would make the relaxation time shorter than that of starch gels. Table 1 also shows that the gel produced from the Jinyou402 variety of rice has the maximum elasticity and viscosity but the shortest relaxation time, while the gel produced from the Liangyou301 variety has the minimum elasticity and viscosity but the longest relaxation time.
Table 2 shows the chemical compositions of the 16 indica rice varieties. Simple linear correlation analysis was used to determine a relationship between creep parameters and chemical compositions, including protein content, blue value and fat content of different indica rice varieties (Table 3). It can be seem from Table 3 that the retarded elastic modulus, E2, had positive correlations with BV (r = 0.684, P = 0.004) and fat content (r = 0.470, P = 0.066). Higher BV values suggest higher amylose content in the rice. When the amylose concentration is high, crystal growth is favored, which leads to a higher molecular order in form and stronger intermolecular hydrogen bonds in the starch, resulting in greater rigidity of gel (Varavinit, Shobsngob, Varanyanond, Chinachoti, & Naivikul, 2003). Thus rice gel with a higher BV had greater values of E2. This is in accord with the finding of Noosuk et al. (2005). In the presence of fat, amylose–lipid complex forms and embeds in gel network which can enhance the springiness of gel (Gunaratne & Corke, 2007). So rice gel with a higher fat content exhibited greater E2 values. For example, in our Table 2 Chemical constituents of different indica rice varieties Sample
Protein content, Pro (%)
Blue value, BV
Fat content, Fat (%)
Liangyou103 Liangyou106 Liangyou105 Liangyou407 Liangyou301 Jinyou402 Jinyou207 89-3 M103s/20257 M104s/20257 M103s/Zhongzu1 M102s/Zhongzu1 Yuhong Simiao Zhefu802 Yuchi
13.26 ± 0.09 11.16 ± 0.21 12.18 ± 0.07 11.88 ± 0.12 11.50 ± 0.11 12.45 ± 0.05 10.80 ± 0.03 11.26 ± 0.13 9.96 ± 0.18 12.28± 0.12 11.06 ± 0.22 11.71 ± 0.06 10.59 ± 0.13 10.89 ± 0.07 12.82 ± 0.03 10.42 ± 0.02
0.406 ± 0.012 0.313 ± 0.011 0.312 ± 0.004 0.372 ± 0.009 0.315 ± 0.005 0.445 ± 0.003 0.418 ± 0.005 0.429 ± 0.001 0.349 ± 0.015 0.418 ± 0.003 0.387 ± 0.004 0.476 ± 0.007 0.390 ± 0.001 0.446 ± 0.009 0.374 ± 0.002 0.401 ± 0.006
2.26 ± 0.08 2.24 ± 0.03 2.10 ± 0.13 1.57 ± 0.09 1.27 ± 0.03 2.00 ± 0.00 2.43 ± 0.13 2.59 ± 0.28 1.66 ± 0.12 1.81 ± 0.06 2.87 ± 0.11 2.78 ± 0.05 2.30 ± 0.14 2.57 ± 0.06 2.65 ± 0.01 2.66 ± 0.10
All experiments were carried out in triplicate. Means ± SD.
Table 3 Correlation of creep parameters with protein content, BV and fat content (r/P)a (n = 16) Creep parameters
Pro
BV
Fat
E2 s g3
0.173/0.522 0.201/0.455 0.439/0.089*
0.684/0.004*** 0.659/0.006*** 0.451/0.079*
0.470/0.066** 0.613/0.012** 0.142/0.601
*, **, ***
means that there was significant correlation at P 6 0.1, 0.05 and 0.01, respectively. a Correlation coefficient of creep parameters with protein content, BV and fat content was expressed as r.
Y.-L. Xu et al. / Journal of Food Engineering 86 (2008) 10–16
study, Yuhong (0.390) had higher BV value than Liangyou106 (0.313), as a result, gel prepared with Yuhong presented higher E2 (10.50 104 Pa) values than that of Liangyou106 (6.67 104 Pa). 89-3 had similar BV value with M104s/20257, but formed gel of 89-3 has higher E2 (12.65 104 Pa) than that of M104s/20257 (7.26 104 Pa) corresponding to higher fat content in 89-3 (2.59%) than M104s/20257 (1.81%). The relaxation time, s, was influenced by the BV (r = 0.659, P = 0.006) and fat content (r = 0.613, P = 0.012). The relaxation time, s, of the gel decreased when the BV and fat content increased. Upon heating, starch granules with a significant moisture content swell, which results in a viscoelastic gel whose structure consists mainly of a network of amylose and a block of amylopectin (Lai & Kokini, 1991). Since gelated starch is composed of linear rigid macromolecules and branched flexible amylopectin macromolecules (Brouillet-Fourmann, Carrot, & Mignard, 2003; Lelivere, Lewis, & Marsden, 1986; Sandera, Thompson, & Boyer, 1990), high concentrations of amylopectin in rice gel facilitate retarded deformation and reduce the efficiency of the recovery process, while high concentrations of amylose reduce the deformation capability of the gel but facilitate its recovery. Thus gels with a high BV have shorter relaxation times. Due to the lubricating effect of fat, the interaction between these macromolecules can be largely overcome (Mor-Rosenberg, Shoemaker, & Rosenberg, 2004), which facilitates the movement of segments of macromolecular chains. Therefore the structure of rice gel containing higher amounts of fat can be re-established rapidly thus reducing the relaxation time after the gel has undergone compression. For instance, Liangyou103 and Liangyou106 have similar fat contents and the BV of Liangyou103 (0.406) was higher than that of Liangyou106 (0.313). As expected, gel prepared from Liangyou103 (0.138 s) exhibited a shorter period of retarded deformation than that prepared from Liangyou106 (0.181 s). The BV of Liangyou407 and Zhefu802 was found to be similar, but the fat content of Liangyou407 (1.57%) was lower than that of Zhefu802 (2.65%) whose relaxation time (0.150 s) was longer than that of Zhefu802 (0.111 s). Table 3 also shows that the viscosity coefficient, g3, is positively correlated to both BV (r = 0.451, P = 0.079) and protein content (r = 0.439, P = 0.089). The viscosity of the gel is mainly due to the relative displacement of linear molecules (Alvarez et al., 1998). A high BV value suggests that the gel contains large amounts of amylose, which is associated with increased gel viscosity and a high g3 value. Teo, Karim, Cheah, Norziah, and Seow (2000) found that the protein content had a dramatic effect on the rheological properties of rice flour. The presence of protein and starch will lead to starch–protein interactions or to disulfide linkages between proteins, thus the viscosity of the rice paste would be increased due to the effects of thiol groups or disulfide binding (Teo et al., 2000). It is rea-
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sonable to expect that rice gel containing a high concentration of protein will be characterized by increased viscosity and a higher g3. For example, in our study, the protein content of Simiao was similar to that in Jinyou207, but the BV of Simiao (0.446) was larger than that of Jinyou207 (0.418). The g3 of Simiao and Jinyou207 were 8.05 107 Pa s and 4.03 107 Pa s, respectively. The effect of the chemical composition of different varieties of rice on the properties of the resultant rice gels is further exemplified by comparison of Liangyou105 and Liangyou106; both have similar BV values, but the protein content of Liangyou105 (12.18%) is greater than that of Liangyou106 (11.16%). The g3 of Liangyou105 and Liangyou106 are 5.97 107 Pa s and 3.27 107 Pa s, respectively. When BV and fat content are greater, retarded elastic modulus, E2 will be greater and relaxation time, s, will be smaller. So rice gel foods made from the rice with high amylose and fat content would have better toughness and springiness. When amylose and protein content are greater, viscosity coefficient, g3 will be greater. Thus the rice with high content of amylose and protein employed in rice noodle production could enhance the viscoelasticity and toughness of rice gel foods. 4. Conclusions The creep process of rice gel consisted mainly of retarded elastic deformation, e2, and viscosity flow deformation, e3. The rheological parameters based on the creep behaviors of indica rice gel were related to the rice variety. Correlation analysis indicated that the creep properties showed a dependence on the chemical compositions. The retarded elastic modulus, E2, had positive correlations with amylose (P = 0.004) and fat content (P = 0.066). The relaxation time, s, had negative correlations with amylose (P = 0.006) and fat content (P = 0.012). The viscosity coefficient, g3, was positively correlated to both amylose (P = 0.079) and protein content (P = 0.089). References Alvarez, M. D., & Canet, W. (2000). Storage time effect on the rheology of refrigerated potato tissue (cv. Monalisa). European Food Research and Technology, 212(1), 48–56. Alvarez, M. D., Canet, W., Cuesta, F., & Lamua, M. (1998). Viscoelastic characterization of solid foods from creep compliance data: application to potato tissues. Zeitschrift fur Lebensmittel-Untersuchung undForschung, 207, 356–362. Atkin, N. J., Cheng, S. L., Abeysekera, R. M., & Robards, A. W. (1999). Localisation of amylose and amylopectin in starch granules using enzyme-gold labelling. Starch/Sta¨rke, 51, 163–172. Bhattacharya, M. (1998). Stress relaxation of starch/synthetic polymer Blends. Journal of Materials Science, 33, 4131–4139. Brouillet-Fourmann, S., Carrot, C., & Mignard, N. (2003). Gelatinization and gelation of corn starch followed by dynamic mechanical spectroscopy analysis. Rheologica Acta, 42, 110–117. Chuang, G. C. C., & Yeh, A. I. (2002). Effects of product temperature and moisture content on viscoelastic properties of glutinous rice extrudates. Cereal Chemistry, 79(1), 36–40.
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Y.-L. Xu et al. / Journal of Food Engineering 86 (2008) 10–16
Chuang, G. C. C., & Yeh, A. I. (2006). Rheological characteristics and texture attributes of glutinous rice cakes (mochi). Journal of Food Engineering, 74(3), 314–323. Gilsenan, P. M., & Ross-Murphy, S. B. (2001). Shear creep of gelatin gels from mammalian and piscine collagens. International Journal of Biological Macromolecules, 29, 53–61. Gunaratne, A., & Corke, H. (2007). Influence of unmodified and modified cycloheptaamylose (b-cyclodextrin) on transition parameters of amylose–lipid complex and functional properties of starch. Carbohydrate Polymers, 68, 226–234. Jenkins, P. J., Cameron, R. E., Donald, A. M., Bras, W., Derbyshire, G. E., Mant, G. R., et al. (1994). In situ simultaneous small and wide angle X-ray scattering: a new technique to study starch gelatinisation. Journal of Polymer Science, 32, 1579–1583. Lai, L. S., & Kokini, J. L. (1991). Physicochemical changes and rheological properties of starch during extrusion (a review). Biotechnology Progress, 7, 251–266. Lazaridou, A., Duta, D., Papageorgiou, M., Belc, N., & Biliaderis, C. G. (2007). Effects of hydrocolloids on dough rheology and bread quality parameters in gluten-free formulations. Journal of Food Engineering, 79(3), 1033–1047. Lelivere, J., Lewis, J. A., & Marsden, K. (1986). The size and shape of amylopectin: A study using analytical ultracentrifugation. Carbohydrate Research, 153, 195–203. Moore, D. S., & McCabe, G. P. (1989). Introduction to the practice of statistics (pp. 638–642). New York: W.H. Freeman and Company. Mor-Rosenberg, Y., Shoemaker, C. F., & Rosenberg, M. (2004). Mechanical properties of composite gels consisting of fractionated whey proteins and fractionated milk fat. Food Hydrocolloids, 18(1), 153–166. Nakasathien, S., Israel, D. W., Wilson, R. F., & Kwanyuen, P. (2000). Regulation of seed protein concentration in soybean by supra-optimal nitrogen supply. Crop Science, 40, 1277–1284. Njintang, Y. N., Mbofung, C. M. F., Moates, G. K., Parker, M. L., Craig, F., Smith, A. C., et al. (2007). Functional properties of five varieties of taro flour, and relationship to creep recovery and sensory character-
istics of achu (taro based paste). Journal of Food Engineering, 82, 114–120. Noosuk, P., Hill, S. E., Farhat, I. A., Mitchell, J. R., & Pradipasena, P. (2005). Relationship between viscoelastic properties and starch structure in rice from Thailand. Starch/Sta¨rke, 57, 587–598. Noosuk, P., Hill, S. E., Pradipasena, P., & Mitchell, J. R. (2003). Structure-viscosity relationships for Thai rice starches. Starch/Sta¨rke, 55, 337–344. Palmquist, D. L., & Jenkins, T. C. (2003). Challenges with fats and fatty acid methods. Journal of Animal Science, 81, 3250–3254. Peressini, D., Sensidoni, A., Pollini, C. M., Gabriele, D., Migliori, M., & de Cindio, B. (2002). Filled-snacks production by coextrusion-cooking. Part 3. A rheological-based method to compare filler processing properties. Journal of Food Engineering, 54(3), 227–240. Sandera, E. B., Thompson, D. B., & Boyer, C. D. (1990). Thermal behavior during Gelatinization and amylopactin fine structure for selected maize genotypes as expressed in four inbred lines. Cereal Chemistry, 67(6), 594–602. Sun, Q. J. (2004). The studies on the processing technology of long life rice noodle. In Proceedings of Shanghai international symposium on the safety of cereal, oil & food (ISSCOF), Shanghai, China. (Food Session, pp. 64–65). Takahiro, F., Yohei, K., Toshio, O., Yasunori, G., Iwao, A., & Katsuyoshi, N. (2005). Food hydrocolloids control the gelatinization and retrogradation behavior of starch. 2b. Functions of guar gums with different molecular weights on the retrogradation behavior of corn starch. Food Hydrocolloids, 19, 25–36. Teo, C. H., Karim, A. A., Cheah, P. B., Norziah, M. H., & Seow, C. C. (2000). On the roles of protein and starch in the aging of non-waxy rice four. Food Chemistry, 69, 229–236. Varavinit, S., Shobsngob, S., Varanyanond, W., Chinachoti, P., & Naivikul, O. (2003). Effect of amylose content on gelatinization, retrogradation and pasting properties of flours from different cultivars of thai rice. Starch/Sta¨rke, 55, 410–415.