- Email: [email protected]
Effect of tapioca starch addition on rheological, thermal, and gelling properties of rice starch
LWT - Food Science and Technology 64 (2015) 205e211
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Effect of tapioca starch addition on rheological, thermal, and gelling properties of rice starch D. Sun, B. Yoo* Department of Food Science and Biotechnology, Dongguk University-Seoul, Seoul 100-715, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 January 2015 Received in revised form 27 May 2015 Accepted 29 May 2015 Available online 9 June 2015
The rheological, thermal, and gelling properties of blends of rice starch (RS) with tapioca starch (TS) at different RS/TS ratios (10/0, 9/1, 8/2, 7/3, 6/4, and 5/5) were examined. Steady and dynamic shear rheological tests indicated that the consistency index (K) and yield stress (soc) of the RSeTS blends increased with an increase in the mixing ratio of TS while the dynamic moduli (G0 and G00 ) values decreased. Tan d (ratio of G00 /G0 ) values of all the blends were higher than that of RS, indicating that there is a more pronounced synergistic effect on the viscous properties of RS in the presence of TS. DSC studies found that the transition temperatures and enthalpies of gelatinization of the blends appeared to be greatly influenced by the addition of TS. The blend gels showed higher gel strength and also better freeze ethaw stability with a significant decrease in syneresis (%) in higher ratios of TS. In general, these results suggest that in the RSeTS blend systems, the addition of TS modified the rheological, thermal, and gelling properties of RS, and that these modifications were dependent on the mixing ratio of TS as well as the physical properties of the two component starches. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Rice starch Tapioca starch Starch blend Rheological property Thermal property
1. Introduction Starch has been widely used and is a very important ingredient in the food industry because of its thickening and gelling properties. It is also known that native starches are limited in their food applications due to their heat, shear, and acid instability associated with the processing conditions, even though they can provide thickening, bulk, and body as well as improved texture with the advantages of lower cost and easier handling and processing (BeMiller & Whistler, 2007). Therefore, native starches are often chemically modified to expand the range of their applications in the food industry because the chemical modifications can increase the resistance to shear, acid, and high temperature, reduce retrogradation, and improve freezeethaw stability (Waterschoot, Gomand, Willebrords, Fierens, & Delcour, 2014). However, recently, interest in finding new ways to improve the rheological and physical properties of native starches without using chemical modifications has grown due to the increased consumer demand for natural food ingredients and products (Zhang, Gu, Hong, Li, & Cheng, 2011).
* Corresponding author. Department of Food Science and Biotechnology, Dongguk University-Seoul, 3 Pil-dong, Chung-gu, Seoul 100-715, Republic of Korea. Tel.: þ82 2 2260 3368; fax: þ82 2 2264 3368. E-mail address: [email protected] (B. Yoo). http://dx.doi.org/10.1016/j.lwt.2015.05.062 0023-6438/© 2015 Elsevier Ltd. All rights reserved.
As an alternative approach to chemical modifications, native starch blends are frequently employed in starch-based food products to provide desirable physical and rheological properties because these blends may influence the viscosity and retrogradation of starch pastes, as well as the syneresis of starch gels (PunchaArnon, Pathipanawat, Puttanlek, Rungsardthong, & Uttapap, 2008). It may also offer an economic advantage when a more expensive starch can be partially replaced by a cheaper alternative without affecting product quality (Waterschoot et al., 2014). Several researchers have studied the gelatinization behaviors (Gunaratne & Corke, 2007; Ortega-Ojeda & Eliasson, 2001; Puncha-Arnon et al., 2008; Zhu & Corke, 2011), pasting properties (Gunaratne & Corke, 2007; Lin, Kao, Tsai, & Chang, 2013; Obanni & Bemiller, 1997; Park, Kim, Kim, & Lim, 2009; Waterschoot et al., 2014; Zhang et al., 2011), and rheological properties (Ortega-Ojeda & Eliasson, 2001; Sasaki, Yasui, Matsuki, & Satake, 2002; Zhang et al., 2011) of various starch blends. They found that the use of starch blends instead of starch alone provided great benefit in terms of pasting, gelatinizing, and rheological properties, and that these effects were dependent on the type of starch and the concentration of starch added. However, to the best of our knowledge, no comprehensive research has been reported to date on the rheological and physical properties of blended pastes of rice starch (RS) and tapioca starch (TS) in order to expand the industry application of RS by improving
206
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211
its functional properties or reducing its undesirable properties. In Asian countries, RS is mainly used as a primary ingredient in processed rice products, such as rice cakes, soup, snack food, noodles, baby food, and breakfast cereals. TS was chosen for the present study because it has been used in numerous industrial and food applications, including as a thickening and gelling agent and an adhesive for paper, and its price in the world market is low compared to other starches (Chaisawang & Suphantharika, 2006). In the starch blend systems, TS is normally added into the preparation of starch-based products with expanded, porous and low density characteristics because it gives high expansion (Tongdang, Meenun, & Chainui, 2008). The main objective of this study was to investigate the rheological, thermal, and gelling properties of blends of RS and TS at different RS/TS ratios. In addition, information about the modification of the gelatinization, rheological, gelling properties of blends of RS and TS at different RS/TS ratios will be helpful in understanding their structural and functional properties, and also in improving the rheological and physical properties of RS-based products for further application in product development. 2. Materials and methods 2.1. Materials and starch isolation Rice was purchased from a rice farm in Cheongpyung, Gangwon, Korea, and was milled and ground into flour at a local mill. Rice starch (RS) was isolated from the rice flour according to the alkaline method reported by Yamamoto, Sawada, and Onogaki (1973), with minor modifications. Rice flour was suspended in 0.2 g/100 g NaOH solution with mild stirring for 1 h at 25 C. The suspension was then centrifuged at 1800 g for 20 min and the supernatants were discarded. The alkaline treatment was repeated seven times, after which the recovered starch suspension was neutralized to pH 7.0 with 0.1 N HCl. The isolated starch was washed three times with distilled water and then dried in an oven drier at 40 C. The dried starch was ground and then passed through a 100-mesh standard sieve (Chung Gye Inc., Seoul, Korea) with 150 mm openings using an analytical sieve shaker (Model AS200, Retsch GmbH & Co., Haan, Germany). Its proximate composition was: 10.9 g/100 g moisture, 5.6 g/100 g protein (N 6.25), 0.9 g/100 g fat, 0.24 g/100 g ash and 81.26 g/100 g carbohydrate (by difference), and amylose content was 15.0 g/100 g. Tapioca starch (20.8 g/100 g amylose content) was provided from AVEBE, Inc. (Veendam, The Netherlands). 2.2. Preparation of starch pastes Blends of RS with TS were prepared at ratios of 9/1, 8/2, 7/3, 6/4, and 5/5 (RS/TS) based on dry weight by mixing each in a mixer. The starch blend dispersions (5 g/100 g) were prepared by mixing the blended samples with distilled water. RS and TS dispersions were also prepared for comparison with the RFeTS blends. Each blend was moderately stirred in an Erlenmeyer flask with a screw cap for 1 h at room temperature and then heated at 95 C in a water bath for 30 min with mild agitation provided by a magnetic stirrer. These hot pastes (95 C) were then used to examine the steady and dynamic shear rheological properties of RFeTS blends. 2.3. Swelling power and solubility The swelling power and solubility of RS, TS, and blend samples were determined as described by Leach, McCowen, and Schoch (1959). A sample dispersion at 0.5 g/100 g was prepared by mixing the sample with distilled water. The dispersion was then moderately stirred for 1 h at room temperature, followed by being
heated at 95 C in a water bath for 30 min. The hot paste was cooled to room temperature in an ice water bath and centrifuged at 2100 g for 20 min. The supernatant was decanted and the swelling power was defined as the ratio of the weight of the sediment to the weight of dry sample. An aliquot of the supernatant was then evaporated for 4 h in a vacuum oven at 120 C. The solubility was determined to be the ratio of the weight of the dried supernatant to the weight of dry sample. All measurements were made in triplicate.
2.4. Steady and dynamic shear rheological properties The steady shear rheological properties of the RSePS blends were observed under both steady and dynamic shear conditions, as described in a previous study (Chun & Yoo, 2004). A rotational concentric cylinder viscometer (VT550 Haake, Haake Inc., Karlsruhe, Germany) was used to measure the steady shear rheological properties. The measuring system (MV2) consists of a rotating cylinder with an 18.4 mm radius, a length of 60 mm, and a gap width of 2.6 mm. Temperature control was carried out with a constant temperature circulator (Model DS50-K10, Haake GmbH, Karlsruhe, Germany) which provide a working temperature range of 0e90 C (±0.1 C). The hot pastes (as described earlier) were immediately transferred to a viscometer cup for the measurements of steady shear rheological properties at 25 C. The sample was sheared continuously from 0.4 to 300 s1. Each measurement was taken after 20 min after loading which also allowed for temperature equilibrium. As a means to describe the variation in the rheological properties of RSeTS blend paste under steady shear, the data were fitted to the well-known power law model (Eq. (1)) and Casson (Eq. (2)) models in order to illustrate the steady shear rheological properties of the samples, which are as follows:
s ¼ Kg_ n
(1)
s0:5 ¼ Koc þ Kc g_ 0:5
(2)
where s is the shear stress (Pa), g_ is the shear rate (s1), K is the consistency index (Pa sn), n is the flow behavior index (dimensionless), and (Kc)2 is the Casson plastic viscosity (hc). Casson yield stress (soc) was defined as the square of the intercept (Koc), which was obtained from a linear regression of the square roots of shear rateeshear stress data. Dynamic shear rheological properties were carried out using an AR 1000 rheometer (TA Instruments, New Castle, DE, USA) with the plateeplate geometry (diameter 4 mm; gap 500 mm). Temperature was controlled by a water bath connected to the Peltier system in the bottom plate. Dynamic shear data were obtained from the frequency sweeps over the range of 0.63e62.8 rad s1 at the 2% strain, which was in the linear viscoelastic region. Frequency sweep tests were also conducted at 25 C. The TA rheometer Data Analysis software (ver. VI. 1.76) was used to obtain the experimental data as well as to calculate the storage modulus (G0 ), loss modulus (G00 ), and loss tangent (tan d ¼ G00 /G0 ). All samples were allowed to rest for 5 min at their initial temperatures prior to the steady and dynamic shear rheological measurements. Additionally, all rheological measurements were performed in triplicate. For G0 measurements in the aging process at 4 C, each sample was loaded onto the 4 C platen of the rheometer and the exposed sample edge was covered with a thin layer of light paraffin oil to prevent evaporation during measurements. G0 values were monitored for 10 h at 6.28 rad s1 and 2% strain. The rheological measurements during aging were conducted in duplicate.
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211
2.5. Gelatinization thermal properties Thermal analyses of the RSeTS blend samples were conducted using a differential scanning calorimeter (DSC; Q200, TA Instruments, New Castle, DE, USA) equipped with a refrigerated cooling system in order to investigate the gelatinization process. The starch blend sample was directly weighed onto the aluminum DSC pan, and distilled water was added with a micropipette in order to create suspensions with a 20 g/100 g starch blend concentration. The sample pan was hermetically sealed and allowed to stand for 1 h at room temperature prior to heating in the DSC. Next, the samples were heated at 5 C min1 from 30 to 130 C. The instrument was calibrated using an indium and an empty pan as reference. From the curve obtained, the onset temperature (To), peak temperature (Tp), conclusion temperature (Tc), and enthalpy (DH) of the starch gelatinization were calculated using the Universal Analysis software provided by the manufacturer. The results reported were the average of the three measurements. 2.6. Freezeethaw stability Freezeethaw stability of the RSeTS blend samples were determined as described by Lee and Yoo (2011). An aqueous suspension of starch (5 g/100 g) was heated at 95 C under constant mild agitation for 30 min and then cooled to room temperature in an ice water bath. The paste was weighed (15 g) in centrifuge tubes and subjected to successive freezeethaw cycles by freezing at 18 C for 24 h and thawing at 30 C for 1.5 h, followed by centrifugation at 2300 g for 30 min. The supernatant eliminated from the gel was weighed, and the extent of syneresis was expressed as the percentage of liquid separated per total weight of sample in the centrifuge tube. In this study, 3 freezeethaw cycles were performed. 2.7. Gel strength Gel strength was measured using a Brookfield Texture Analyzer (TA-CT3, Brookfield Engineering Laboratories, Inc., Middleboro, MA, USA) as described by Lee and Yoo (2011). Starch pastes (10 g/100 g) were prepared, as described previously. The hot starch pastes were poured into cylindrical plastic tubes (35 mm diameter and 40 mm height) that were covered, cooled at room temperature for at least 1 h, and kept at 4 C for 24 h. The starch gels were placed at room temperature at least 1 h before measuring their gel strength. A plastic cylindrical probe with a diameter of 10 mm was used and penetrated into the gel at a speed of 1 mm s1 for a distance of 10 mm. The maximum force at 10 mm of penetration was recorded as the gel strength (N), and the measurement was repeated five times.
207
Table 1 Swelling power and solubility of rice starch (RS)etapioca starch (TS) blends at different ratios of RS/TS.a Sampleb
Swelling power (g/g)
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
40.6 44.4 51.9 64.7 71.0 75.4 93.6
± ± ± ± ± ± ±
0.83G 1.13F 0.67E 1.61D 0.28C 0.86B 1.41A
Solubility (%) 64.3 64.6 66.1 67.5 69.1 70.5 76.1
± ± ± ± ± ± ±
0.54E 1.79E 1.46DE 1.00CD 1.00BC 0.23B 1.41A
a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
swelling power (93.6 g g1) of TS when compared to that of RS (40.6 g g1). The greater swelling power of TS could be due to the larger granule size, capable of holding more water than RS (Tongdang et al., 2008). In addition, lower swelling power values of blends other than that of TS were in accord with the previous findings that the swelling of larger starch granules can be inhibited by the large numbers of surrounding smaller granules, as described by Puncha-Arnon et al. (2008). In general, it is known that RS has very small granules (1e3 mm), while TS typically consists of medium-size granules of around 4e35 mm and has weaker associative force compared to cereal starches (Thomas & Atwell, 1999). Solubility (76.1 g/100 g) of TS was found to be greater than that (64.3 g/100 g) of RS. In contrast to the low swelling power of RS, its high solubility could be attributed to its small granule size. Small granule size of starch results in granule suspension and loss in supernatant during centrifugation (Lin et al., 2013). The solubility values of all blend samples were slightly higher than that of RS alone. Furthermore, no significant differences in solubility values were observed between blend samples at lower mixing ratios (9/1 and 8/2) of TS and RS alone even though the solubility levels of the blends increased with an increase in mixing ratio of TS, which has a higher solubility compared to other cereal starches (Anggraini, Sudarmonowati, Hartati, Suurs, & Visser, 2009). It is known that the higher solubility can be attributed partly to the high swelling TS undergoes during gelatinization (Moorthy, 2002). Tsai, Li, and Lii (1997) also found that weaker granular rigidity resulted in higher swelling power and solubility of starch. Based on these observations, it was found that the swelling power and solubility values of all blend samples were in between those of individual starches (RS and TS) due to the much higher swelling power and solubility of TS when compared to RS. In addition, in the RSeTS blend system, the presence of TS greatly promoted changes in the swelling power and solubility of RS. 3.2. Flow behavior
2.8. Statistical analysis All results are expressed as mean ± standard deviation. Analysis of variance (ANOVA) was performed using Statistical Analysis System software (version 9.2, SAS Institute, Cary, USA). Differences in means were determined using Duncan's multiple-range test. 3. Results and discussion 3.1. Swelling power and solubility The swelling power and solubility values of the RSeTS blends at different RS/TS ratios were in the range of 44.4e75.4 g g1 and 64.6e70.5 g/100 g, respectively (Table 1). The swelling power of the blends increased with a rise in mixing ratio of TS due to the higher
_ data for RSeTS blends The shear stress (s) versus shear rate (g) with different RS/TS ratios at 25 C are shown in Fig. 1. The experimental results of s and g_ data were well fitted to the simple power law model (Eq. (1)) and the Casson model (Eq. (2)) with high determination coefficients (R2 ¼ 0.99) (Table 2). All blend samples had shear-thinning behavior with flow behavior index values (n ¼ 0.31e0.37). This shear-thinning behavior can be explained by the progressive orientation of soluble starch molecules in the direction of the flow as well as the breaking of hydrogen bonds formed between amylose molecules during shearing (McGrane, Mainwaring, Cornell, & Rix, 2004). The n values (0.31e0.37) of all blends decreased with an increase in mixing ratio of TS and were also much lower than that (n ¼ 0.55) of TS alone, suggesting that the addition of TS, especially higher mixing ratios of TS, resulted in
208
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211
250
3.3. Dynamic shear properties Plots of frequency (u) versus storage modulus (G0 ) and loss modulus (G00 ) for the RSeTS blends at 25 C (Fig. 2) revealed that the magnitudes of G0 and G00 increased with an increase in u and that G0 was much higher than G00 at all values of u with frequency dependency. All samples exhibited a weak gel-like behavior because the slopes are positive and the magnitudes of G0 are much
Shear Stress (Pa)
200
150
100
50
0 0
50
100
150
200
250
300
Shear rate (sec-1) Fig. 1. Shear stresseshear rate plots for RSeTS blends at different RS/TS ratios, 25 C: (B) RS, ( ) RS9/TS1, ( ) RS8/TS2, (◊) RS7/TS3, (þ) RS6/TS4, () RS5/TS5, (C) TS.
▫
▵
Table 2 Magnitudes of consistency index (K), flow behavior index (n), and Casson yield stress (soc) of rice starch (RS)-tapioca starch (TS) blends at different ratios of RS/TS.a Sampleb
K (Pa sn)
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
24.7 24.4 27.8 31.0 35.5 38.2 9.84
± ± ± ± ± ± ±
0.62E 0.43E 0.38D 0.58C 0.14B 0.02A 0.10F
soc (Pa)
n (e) 0.35 0.37 0.35 0.34 0.32 0.31 0.55
± ± ± ± ± ± ±
0.00C 0.00B 0.00C 0.00D 0.00E 0.00F 0.02A
19.2 27.8 30.1 33.9 35.4 42.1 10.7
± ± ± ± ± ± ±
0.32F 0.21E 0.71D 0.02C 0.70B 0.00A 0.32G
R2 0.99 0.99 0.99 0.99 0.99 0.99 0.99
a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
more pseudoplastic, even though TS had low shear-thinning behavior with an n value as high as 0.55. The observed higher shear-thinning behavior may be interpreted as a result of the higher degree of breakage of the intra- and intermolecular bonding system in the starch blend network. From these results, it was found that the n values of RSeTS blends were strongly influenced by the addition of TS. In general, the consistency index (K, 24.4e38.2 Pa sn) and yield stress (soc, 27.8e42.1 Pa) values of the RSeTS blends, which were obtained from the power law and Casson models, were higher than those (24.7 Pa sn and 9.84 Pa sn) of RS and TS alone; moreover, they also increased with an increase in mixing ratio of TS (Table 2), suggesting that the addition of TS resulted in more resistance to flow. Therefore, the synergistic effect of TS on the RSeTS blend systems in regard to increasing flow rheological parameters (K and sco) is more effective, probably due to the interactions between the two components in the blend systems due to increased interactions between leached molecules and swollen granule remnants (Park et al., 2009; Puncha-Arnon et al., 2008; Zhang et al., 2011). From these observations, it can be concluded that the steady shear properties of RSeTS blends were apparently influenced by the mixing ratio of TS, and the desirable flow properties of RS for industrial use can also be controlled and improved by the addition of TS.
Fig. 2. Plot of G0 , G00 , tan d versus u for RSeTS blends at different RS/TS ratios, 25 C: (B) RS, ( ) RS9/TS1, ( ) RS8/TS2, (◊) RS7/TS3, (þ) RS6/TS4, () RS5/TS5, (C) TS.
▫
▵
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211
higher than those of G00 . In general, the dynamic moduli (G0 and G00 ) results revealed that changes in the G0 of RS after adding TS were greater than changes in G00 , indicating that the addition of TS greatly influenced the elastic property of RS. RS showed higher dynamic moduli values compared to TS due to its smaller granule size, as noted by Li and Yeh (2001) who found that low swelling starches, such as RS, had greater dynamic moduli values. Therefore, the dynamic moduli values of RSeTS blends decreased with an increase in the mixing ratio of TS. Such lower dynamic moduli may also be attributed to the much lower dynamic moduli of TS itself due to the strong swelling power of TS granules compared to those of RS, as described previously. Therefore, they fell between the dynamic moduli values obtained for RS and TS. This observed result suggests that RSeTS blend samples could have been diluted by TS with its lower dynamic moduli in comparison to RS, as described by Oh, Kim, and Yoo (2010). The tan d (ratio of G00 /G0 ) values of all blend samples were less than “1” (Fig. 2), indicating that all the samples were more elastic than viscous. As stated previously, if the tan d is in a range greater than 0.1, a sample is deemed to be a weak gel, as described previously. In general, all blend samples produced higher tan d values than RS, showing that their tan d values were in between the tan d values obtained for RS and TS. Therefore, the viscous properties of the blends were more pronounced than the elastic properties after the addition of TS to RS. This implies that the TS did not provide an effective contribution to the elastic properties of the RSeTS blends due to the TS having the higher tan d. Such higher tan d of TS can be attributed to the presence of more liquid phase, possibly due to the capability of absorbing more water, as described by Li and Yeh (2001). They also reported that tan d was positively associated with swelling power. Similar results were reported by Lin et al. (2013), who found that TS exhibited rheological and pasting properties similar to waxy starches. Thus, the observed tan d values in RSeTS blend systems indicate that the viscous properties of RS paste appear to be strongly influenced by the addition of TS as well as the granular characteristics of two component starches. This may be a helpful recommendation when substituting RS in RS-based food products to increase their viscous properties. 3.4. Effect of TS addition on G0 of RSeTS blends during aging The gelation phenomenon of starch pastes containing amylose can be detected using measurements of the dynamic mechanical storage modulus (G0 ) that reflect the elastic property of the sample and have a characteristic pattern as a function of time (Eidam, Kulicke, Kuhn, & Stute, 1995). Fig. 3 shows changes in G0 for RSeTS blends with different mixing ratios of TS as a function of aging time (10 h at 4 C). This change of G0 values during a long aging period corresponds to the retrogradation of amylose. The rapid increase and plateau of G0 can be due to the rapid aggregation of amylose chains at the early stage. RS alone, like other cereal starches, showed a plateau value of G0 after a long aging period. A similar trend was reported for other starches, such as corn (Chang, Lim, & Yoo, 2004), rice (Yoo & Yoo, 2005) and sweet potato starch (Lee & Yoo, 2009). In contrast, TS alone showed almost the same G0 values during aging, showing that TS dispersion at 5 g/100 g concentration produced gels too weak to give a stable G0 detectable by the instrument. Such weak gel network structure may be attributed to the increased water uptake caused by the swollen granules due to very weak associative forces between starch granules, easy penetration of water molecules, and large swelling (Anggraini et al., 2009). All blend samples displayed lower G0 values than RS alone. The plateau values of G0 after a long aging time were observed for the RS alone as well as the blends at lower mixing ratios (9/1 and 8/ 2). In contrast, the blends at higher mixing ratios (7/3, 6/4, and 5/5)
209
Fig. 3. Changes in G0 during aging at 5 C for 10 h for RSeTS blends at different RS/TS ratios: (B) RS, ( ) RS9/TS1, ( ) RS8/TS2, (◊) RS7/TS3, (þ) RS6/TS4, () RS5/TS5, (C) TS.
▫
▵
showed a slow and continuous increase of G0 without a clear plateau region, indicating that the aggregation speed appears to be slowed down by the addition of TS. The values of G0 after a long aging interval were also reduced by the addition of TS, and decreased with the increase in mixing ratio of TS. These findings support the observation that the addition of TS leads to a decrease of the structure development rate. 3.5. Gelatinization thermal properties Details of transition temperatures (To, Tp, and Tc) and enthalpies (DH) associated with gelatinization of RSeTS blends at different mixing ratios are summarized in Table 3 and their thermograms are shown in Fig. 4. All blend samples at different mixing ratios displayed single endotherms. The transition temperatures of TS alone were much higher than those of RS alone. The To (60.4e60.9 C) values of blend samples were similar at all mixing ratios of TS, as were the Tp (66.8e67.0 C) values, the only exception being for mixing ratio (5/5) with a high proportion of TS. In contrast, the magnitudes of Tc of the blend samples were found to be significantly increased by the addition of TS; moreover, they also increased with an increase in the mixing ratio of TS. The gelatinization temperature (Tceo) of RS and TS were 14.5 and 16.0 C, respectively. This difference of Tceo is due to the difference of the degrees of heterogeneity of crystallites within granules of the studied starches (Hagenimana, Pu, & Ding, 2005). The Tceo values of blends increased with an increase in the mixing ratio of TS. In addition, all blend samples displayed single endotherms (Fig. 4), supporting the possibility of each component gelatinizing independently. Liu and Lelievre (1992) found that DSC thermograms were the sum of each individual component in the starch blends at low starch concentrations, though this phenomenon did not occur when the blends were at high concentrations (>30 g/ 100 g), due to competition for water. Therefore, it was found that the gelatinization of RS seems to be influenced by the addition of TS, and the sum of each individual component can exist in starch blends. The enthalpy value (15.4 J g1) of gelatinization (DH) of TS was much higher than that (11.0 J g1) of RS, and the DH values of the blends also increased with an increase in mixing ratio of TS from 9/
210
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211 Table 3 Thermal properties of rice starch (RS)-tapioca starch (TS) blends at different RS/TS ratios.a Sampleb
To ( C)
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
61.2 60.9 60.9 60.6 60.6 60.4 64.8
± ± ± ± ± ± ±
Tp ( C) 0.06B 0.04C 0.06C 0.09D 0.06D 0.10D 0.23A
67.3 67.0 66.9 66.9 66.8 72.4 72.0
± ± ± ± ± ± ±
Tc ( C) 0.06C 0.08CD 0.02CD 0.16CD 0.01D 0.15A 0.42B
75.7 76.3 80.7 81.3 82.0 83.3 80.8
± ± ± ± ± ± ±
DH (J/g)
Tceo ( C) 0.07F 0.09E 0.01D 0.11C 0.03B 0.06A 0.45CD
14.5 15.4 19.8 20.7 21.4 22.9 16.0
± ± ± ± ± ± ±
0.01G 0.13F 0.07D 0.20C 0.03B 0.16A 0.22E
11.0 9.30 12.6 13.2 13.9 14.3 15.4
± ± ± ± ± ± ±
0.28E 0.12F 0.11D 0.25C 0.15B 0.13B 0.35A
Tceo, range of gelatinization temperature (TceTo). a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
Table 4 Effect of blends on syneresis (%) of rice starch (RS)-tapioca starch (TS) blends at different ratios of RS/TS.a Sampleb
Syneresis (%) 1 cycle
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
37.7 44.1 43.9 41.0 40.1 34.6 35.7
± ± ± ± ± ± ±
2 cycle 0.34C 0.73A 0.61A 0.98B 0.57B 0.91D 0.93D
42.9 47.2 45.0 42.4 40.9 35.2 36.4
± ± ± ± ± ± ±
3 cycle 2.18BC 0.50A 1.64AB 1.79BC 1.16C 0.42D 1.36D
52.3 50.6 45.4 42.7 41.4 35.6 36.5
± ± ± ± ± ± ±
1.06A 0.34B 0.84C 0.97D 1.20D 0.85E 0.53E
a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
Fig. 4. Gelatinization thermograms of RSeTS blends at different RS/TS ratios.
1 to 5/5 due to the higher DH of TS compared to RS. However, the DH value (9.30 J g1) at a lower mixing ratio (9/1) was much lower than that (11.0 J g1) of RS. This implies that RS might have influenced the gelatinization behavior of blends at lower ratios of TS. Due to the much smaller size of RS, a large number of RS granules surrounding the TS granules could impede the accessibility of water to the TS granules, Hence, the TS granules would not be fully gelatinized, resulting in lower DH values for blends at lower ratios of TS, as reported by Ortega-Ojeda and Eliasson (2001) and PunchaArnon et al. (2008). In general, it is also known that the DH value of a single starch decreases with a decrease in water content (Blanshard, 1987). Similar observations have been reported by Ortega-Ojeda and Eliasson (2001) for potato starch-other starch blends. From these observations, it was found that in the RSeTS blend systems, the gelatinization thermal properties of RS were apparently influenced by the addition of TS and the mixing ratio of TS.
3.6. Freezeethaw stability of starch blend gel Table 4 shows the percentage syneresis of the RSeTS blend samples during 3 freezeethaw cycles. The syneresis (%) values of the RSeTS blends decreased with an increase in the mixing ratio of
TS from 9/1 to 5/5. The syneresis (%) values (35.7e36.5%) of the TS gel were much lower than those (37.7e52.3%) of the RS, and those of the blends decreased with an increase in the mixing ratio of TS from 9/1 to 5/5. In particular, the syneresis values (35.6e50.6%) at the third freezeethaw cycle were significantly lower than that (52.3%) of RS alone, and also significantly decreased with an increase in the mixing ratio of TS. These results indicate that the freezeethaw stability of RSeTS gels can be improved by the addition of TS during a long storage, resulting in decreased retrogradation. Among the blend samples, a blend gel at 5/5 mixing ratio showed significant lower syneresis values (34.6e35.6%), which were similar to those of TS alone during all 3 freezeethaw cycles. Such superior freezeethaw stability means that the RSeTS blend samples would have suitable textural properties for developing RSbased products. 3.7. Gel strength The gel strength values (0.30e0.64 N) of the blend samples were much higher compared to the RS and TS alone, and increased with an increase in the mixing ratio of TS (Table 5), indicating that the blend gels were harder, especially at higher mixing ratios of TS. This also shows that RSeTS blends were significantly harder than what might be expected based on the weight percentage of each starch in the blend. Such a trend is in contradiction to previous reports on other starch blends (Gunaratne & Corke, 2007; Karam, Grossmann, Silva, Ferrero, & Zaritzky, 2005; Puncha-Arnon et al., 2008; Yao, Zhang, & Ding, 2003) which showed firmness values lower than those of the individual starches. These opposite results may also be explained by the non-additive effect due to an interaction between the starches, as described by Yao et al. (2003) and Puncha-Arnon et al. (2008). This also is in solid agreement with the large increase of flow rheological parameters (K and sco) in the RSeTS blend systems, as described previously (Table 2). Therefore, the synergistic effect of TS on the RSeTS blend systems in increasing gel
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211 Table 5 Gel strength of rice starch (RS)etapioca starch (TS) blends at different ratios of RS/TS.a Sampleb
Gel strength (N)
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
0.17 0.30 0.41 0.47 0.56 0.64 0.16
± ± ± ± ± ± ±
0.01F 0.01E 0.01D 0.01C 0.02B 0.02A 0.01F
a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
strength is probably due to the interactions between the two starch components in the blend systems. 4. Conclusions In the RSeTS blend systems, the synergistic effect of TS on RS paste increasing K and soc is more effective than when compared to the RS alone. A decrease in the dynamic moduli (G0 and G00 ) and the higher tan d values of the RSeTS blends compared to RS alone appeared to be attributed to the higher swelling power of TS granules versus that of RS. All dynamic rheological parameter values were in between the values obtained for RS and TS. The values of G0 of RSeTS blends during aging for 10 h at 4 C decreased with an increase in the mixing ratio of TS due to the inhibition of starch retrogradation. Freezeethaw stability of the RSeTS blends was also improved by the addition of TS. The synergistic effect of TS on the RSeTS blend systems in increasing gel strength can be attributed to a non-additive effect due to an interaction between the two starch components. These results support that the blend samples at higher ratios of TS would have the desirable and improved rheological properties for developing RS-based products. In addition, these results will be useful for formulating desirable rheological and physical properties for a wide range of industrial food applications, and also in designing and developing new starch blends. References Anggraini, V., Sudarmonowati, E., Hartati, N. S., Suurs, L., & Visser, R. G. F. (2009). Characterization of cassava starch attributes of different genotypes. StarchStarke, 61(8), 472e481. BeMiller, J. N., & Whistler, R. L. (2007). Carbohydrate chemistry for food scientists (2nd ed.). St. Paul, Minn.: AACC International. Blanshard, J. M. V. (1987). Starch granule structure and function: a physicochemical approach. In T. Galliard (Ed.), Starch: Properties and potentials, critical reports on applied chemistry (pp. 16e54). New York, NY: Wiley. Chaisawang, M., & Suphantharika, M. (2006). Pasting and rheological properties of native and anionic tapioca starches as modified by guar gum and xanthan gum. Food Hydrocolloids, 20(5), 641e649. Chang, Y. H., Lim, S. T., & Yoo, B. (2004). Dynamic rheology of corn starch-sugar composites. Journal of Food Engineering, 64(4), 521e527.
211
Chun, S. Y., & Yoo, B. (2004). Rheological behavior of cooked rice flour dispersions in steady and dynamic shear. Journal of Food Engineering, 65(3), 363e370. Eidam, D., Kulicke, W. M., Kuhn, K., & Stute, R. (1995). Formation of maize starch gels selectively regulated by the addition of hydrocolloids. Starch-Starke, 47(10), 378e384. Gunaratne, A., & Corke, H. (2007). Gelatinizing, pasting, and gelling properties of potato and amaranth starch mixtures. Cereal Chemistry, 84(1), 22e29. Hagenimana, A., Pu, P. P., & Ding, X. L. (2005). Study on thermal and rheological properties of native rice starches and their corresponding mixtures. Food Research International, 38(3), 257e266. Karam, L. B., Grossmann, M. V. E., Silva, R. S. S. F., Ferrero, C., & Zaritzky, N. E. (2005). Gel textural characteristics of corn, cassava and yam starch blends: a mixture surface response methodology approach. Starch-Starke, 57(2), 62e70. Leach, H. W., McCowen, L. D., & Schoch, T. J. (1959). Structure of the starch granule. II. Swelling power and solubility patterns of various starches. Cereal Chemistry, 36, 534e544. Lee, H. L., & Yoo, B. (2009). Dynamic rheological and thermal properties of acetylated sweet potato starch. Starch-Starke, 61(7), 407e413. Lee, H. L., & Yoo, B. (2011). Effect of hydroxypropylation on physical and rheological properties of sweet potato starch. LWT e Food Science and Technology, 44(3), 765e770. Li, J. Y., & Yeh, A. I. (2001). Relationships between thermal, rheological characteristics and swelling power for various starches. Journal of Food Engineering, 50(3), 141e148. Lin, J. H., Kao, W. T., Tsai, Y. C., & Chang, Y. H. (2013). Effect of granular characteristics on pasting properties of starch blends. Carbohydrate Polymers, 98(2), 1553e1560. Liu, H., & Lelievre, L. A. (1992). Differential scanning calorimetry study of melting transitions in aqueous suspensions containing blends of wheat and rice starch. Carbohydrate Polymers, 17, 145e149. McGrane, S. J., Mainwaring, D. E., Cornell, H. J., & Rix, C. J. (2004). The role of hydrogen bonding in amylose gelation. Starch-Starke, 56(3e4), 122e131. Moorthy, S. N. (2002). Physicochemical and functional properties of tropical tuber starches: a review. Starch-Starke, 54(12), 559e592. Obanni, M., & Bemiller, J. N. (1997). Properties of some starch blends. Cereal Chemistry, 74(4), 431e436. Oh, J. H., Kim, M. J., & Yoo, B. (2010). Dynamic rheological properties of rice flourestarch blends. Starch-Starke, 62(6), 321e325. Ortega-Ojeda, F. E., & Eliasson, A. C. (2001). Gelatinisation and retrogradation behaviour of some starch mixtures. Starch-Starke, 53(10), 520e529. Park, E. Y., Kim, H. N., Kim, J. Y., & Lim, S. T. (2009). Pasting properties of potato starch and waxy maize starch mixtures. Starch-Starke, 61(6), 352e357. Puncha-Arnon, S., Pathipanawat, W., Puttanlek, C., Rungsardthong, V., & Uttapap, D. (2008). Effects of relative granule size and gelatinization temperature on paste and gel properties of starch blends. Food Research International, 41(5), 552e561. Sasaki, T., Yasui, T., Matsuki, J., & Satake, T. (2002). Rheological properties of mixed gels using waxy and non-waxy wheat starch. Starch-Starke, 54(9), 410e414. Thomas, D. J., & Atwell, W. A. (1999). Starches (pp. 31e48). ST. Paul, MN: Eagan Press. Tongdang, T., Meenun, M., & Chainui, J. (2008). Effect of sago starch addition and steaming time on making cassava cracker (Keropok). Starch-Starke, 60(10), 568e576. Tsai, M. L., Li, C. F., & Lii, C. Y. (1997). Effects of granular structures on the pasting behaviors of starches. Cereal Chemistry, 74(6), 750e757. Waterschoot, J., Gomand, S. V., Willebrords, J. K., Fierens, E., & Delcour, J. A. (2014). Pasting properties of blends of potato, rice and maize starches. Food Hydrocolloids, 41, 298e308. Yamamoto, K., Sawada, S., & Onogaki, T. (1973). Properties of rice starch prepared by alkali method with various conditions. Denpun Kagaku, 20, 99e104. Yao, Y., Zhang, J., & Ding, X. (2003). Retrogradation of starch mixtures containing rice starch. Journal of Food Science, 68(1), 260e265. Yoo, D., & Yoo, B. (2005). Rheology of rice starchesucrose composites. Starch-Starke, 57(6), 254e261. Zhang, Y. Y., Gu, Z. B., Hong, Y., Li, Z. F., & Cheng, L. (2011). Pasting and rheologic properties of potato starch and maize starch mixtures. Starch-Starke, 63(1), 11e16. Zhu, F., & Corke, H. (2011). Gelatinization, pasting, and gelling properties of sweet potato and wheat starch blends. Cereal Chemistry, 88(3), 302e309.
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Effect of tapioca starch addition on rheological, thermal, and gelling properties of rice starch D. Sun, B. Yoo* Department of Food Science and Biotechnology, Dongguk University-Seoul, Seoul 100-715, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 January 2015 Received in revised form 27 May 2015 Accepted 29 May 2015 Available online 9 June 2015
The rheological, thermal, and gelling properties of blends of rice starch (RS) with tapioca starch (TS) at different RS/TS ratios (10/0, 9/1, 8/2, 7/3, 6/4, and 5/5) were examined. Steady and dynamic shear rheological tests indicated that the consistency index (K) and yield stress (soc) of the RSeTS blends increased with an increase in the mixing ratio of TS while the dynamic moduli (G0 and G00 ) values decreased. Tan d (ratio of G00 /G0 ) values of all the blends were higher than that of RS, indicating that there is a more pronounced synergistic effect on the viscous properties of RS in the presence of TS. DSC studies found that the transition temperatures and enthalpies of gelatinization of the blends appeared to be greatly influenced by the addition of TS. The blend gels showed higher gel strength and also better freeze ethaw stability with a significant decrease in syneresis (%) in higher ratios of TS. In general, these results suggest that in the RSeTS blend systems, the addition of TS modified the rheological, thermal, and gelling properties of RS, and that these modifications were dependent on the mixing ratio of TS as well as the physical properties of the two component starches. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Rice starch Tapioca starch Starch blend Rheological property Thermal property
1. Introduction Starch has been widely used and is a very important ingredient in the food industry because of its thickening and gelling properties. It is also known that native starches are limited in their food applications due to their heat, shear, and acid instability associated with the processing conditions, even though they can provide thickening, bulk, and body as well as improved texture with the advantages of lower cost and easier handling and processing (BeMiller & Whistler, 2007). Therefore, native starches are often chemically modified to expand the range of their applications in the food industry because the chemical modifications can increase the resistance to shear, acid, and high temperature, reduce retrogradation, and improve freezeethaw stability (Waterschoot, Gomand, Willebrords, Fierens, & Delcour, 2014). However, recently, interest in finding new ways to improve the rheological and physical properties of native starches without using chemical modifications has grown due to the increased consumer demand for natural food ingredients and products (Zhang, Gu, Hong, Li, & Cheng, 2011).
* Corresponding author. Department of Food Science and Biotechnology, Dongguk University-Seoul, 3 Pil-dong, Chung-gu, Seoul 100-715, Republic of Korea. Tel.: þ82 2 2260 3368; fax: þ82 2 2264 3368. E-mail address: [email protected] (B. Yoo). http://dx.doi.org/10.1016/j.lwt.2015.05.062 0023-6438/© 2015 Elsevier Ltd. All rights reserved.
As an alternative approach to chemical modifications, native starch blends are frequently employed in starch-based food products to provide desirable physical and rheological properties because these blends may influence the viscosity and retrogradation of starch pastes, as well as the syneresis of starch gels (PunchaArnon, Pathipanawat, Puttanlek, Rungsardthong, & Uttapap, 2008). It may also offer an economic advantage when a more expensive starch can be partially replaced by a cheaper alternative without affecting product quality (Waterschoot et al., 2014). Several researchers have studied the gelatinization behaviors (Gunaratne & Corke, 2007; Ortega-Ojeda & Eliasson, 2001; Puncha-Arnon et al., 2008; Zhu & Corke, 2011), pasting properties (Gunaratne & Corke, 2007; Lin, Kao, Tsai, & Chang, 2013; Obanni & Bemiller, 1997; Park, Kim, Kim, & Lim, 2009; Waterschoot et al., 2014; Zhang et al., 2011), and rheological properties (Ortega-Ojeda & Eliasson, 2001; Sasaki, Yasui, Matsuki, & Satake, 2002; Zhang et al., 2011) of various starch blends. They found that the use of starch blends instead of starch alone provided great benefit in terms of pasting, gelatinizing, and rheological properties, and that these effects were dependent on the type of starch and the concentration of starch added. However, to the best of our knowledge, no comprehensive research has been reported to date on the rheological and physical properties of blended pastes of rice starch (RS) and tapioca starch (TS) in order to expand the industry application of RS by improving
206
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211
its functional properties or reducing its undesirable properties. In Asian countries, RS is mainly used as a primary ingredient in processed rice products, such as rice cakes, soup, snack food, noodles, baby food, and breakfast cereals. TS was chosen for the present study because it has been used in numerous industrial and food applications, including as a thickening and gelling agent and an adhesive for paper, and its price in the world market is low compared to other starches (Chaisawang & Suphantharika, 2006). In the starch blend systems, TS is normally added into the preparation of starch-based products with expanded, porous and low density characteristics because it gives high expansion (Tongdang, Meenun, & Chainui, 2008). The main objective of this study was to investigate the rheological, thermal, and gelling properties of blends of RS and TS at different RS/TS ratios. In addition, information about the modification of the gelatinization, rheological, gelling properties of blends of RS and TS at different RS/TS ratios will be helpful in understanding their structural and functional properties, and also in improving the rheological and physical properties of RS-based products for further application in product development. 2. Materials and methods 2.1. Materials and starch isolation Rice was purchased from a rice farm in Cheongpyung, Gangwon, Korea, and was milled and ground into flour at a local mill. Rice starch (RS) was isolated from the rice flour according to the alkaline method reported by Yamamoto, Sawada, and Onogaki (1973), with minor modifications. Rice flour was suspended in 0.2 g/100 g NaOH solution with mild stirring for 1 h at 25 C. The suspension was then centrifuged at 1800 g for 20 min and the supernatants were discarded. The alkaline treatment was repeated seven times, after which the recovered starch suspension was neutralized to pH 7.0 with 0.1 N HCl. The isolated starch was washed three times with distilled water and then dried in an oven drier at 40 C. The dried starch was ground and then passed through a 100-mesh standard sieve (Chung Gye Inc., Seoul, Korea) with 150 mm openings using an analytical sieve shaker (Model AS200, Retsch GmbH & Co., Haan, Germany). Its proximate composition was: 10.9 g/100 g moisture, 5.6 g/100 g protein (N 6.25), 0.9 g/100 g fat, 0.24 g/100 g ash and 81.26 g/100 g carbohydrate (by difference), and amylose content was 15.0 g/100 g. Tapioca starch (20.8 g/100 g amylose content) was provided from AVEBE, Inc. (Veendam, The Netherlands). 2.2. Preparation of starch pastes Blends of RS with TS were prepared at ratios of 9/1, 8/2, 7/3, 6/4, and 5/5 (RS/TS) based on dry weight by mixing each in a mixer. The starch blend dispersions (5 g/100 g) were prepared by mixing the blended samples with distilled water. RS and TS dispersions were also prepared for comparison with the RFeTS blends. Each blend was moderately stirred in an Erlenmeyer flask with a screw cap for 1 h at room temperature and then heated at 95 C in a water bath for 30 min with mild agitation provided by a magnetic stirrer. These hot pastes (95 C) were then used to examine the steady and dynamic shear rheological properties of RFeTS blends. 2.3. Swelling power and solubility The swelling power and solubility of RS, TS, and blend samples were determined as described by Leach, McCowen, and Schoch (1959). A sample dispersion at 0.5 g/100 g was prepared by mixing the sample with distilled water. The dispersion was then moderately stirred for 1 h at room temperature, followed by being
heated at 95 C in a water bath for 30 min. The hot paste was cooled to room temperature in an ice water bath and centrifuged at 2100 g for 20 min. The supernatant was decanted and the swelling power was defined as the ratio of the weight of the sediment to the weight of dry sample. An aliquot of the supernatant was then evaporated for 4 h in a vacuum oven at 120 C. The solubility was determined to be the ratio of the weight of the dried supernatant to the weight of dry sample. All measurements were made in triplicate.
2.4. Steady and dynamic shear rheological properties The steady shear rheological properties of the RSePS blends were observed under both steady and dynamic shear conditions, as described in a previous study (Chun & Yoo, 2004). A rotational concentric cylinder viscometer (VT550 Haake, Haake Inc., Karlsruhe, Germany) was used to measure the steady shear rheological properties. The measuring system (MV2) consists of a rotating cylinder with an 18.4 mm radius, a length of 60 mm, and a gap width of 2.6 mm. Temperature control was carried out with a constant temperature circulator (Model DS50-K10, Haake GmbH, Karlsruhe, Germany) which provide a working temperature range of 0e90 C (±0.1 C). The hot pastes (as described earlier) were immediately transferred to a viscometer cup for the measurements of steady shear rheological properties at 25 C. The sample was sheared continuously from 0.4 to 300 s1. Each measurement was taken after 20 min after loading which also allowed for temperature equilibrium. As a means to describe the variation in the rheological properties of RSeTS blend paste under steady shear, the data were fitted to the well-known power law model (Eq. (1)) and Casson (Eq. (2)) models in order to illustrate the steady shear rheological properties of the samples, which are as follows:
s ¼ Kg_ n
(1)
s0:5 ¼ Koc þ Kc g_ 0:5
(2)
where s is the shear stress (Pa), g_ is the shear rate (s1), K is the consistency index (Pa sn), n is the flow behavior index (dimensionless), and (Kc)2 is the Casson plastic viscosity (hc). Casson yield stress (soc) was defined as the square of the intercept (Koc), which was obtained from a linear regression of the square roots of shear rateeshear stress data. Dynamic shear rheological properties were carried out using an AR 1000 rheometer (TA Instruments, New Castle, DE, USA) with the plateeplate geometry (diameter 4 mm; gap 500 mm). Temperature was controlled by a water bath connected to the Peltier system in the bottom plate. Dynamic shear data were obtained from the frequency sweeps over the range of 0.63e62.8 rad s1 at the 2% strain, which was in the linear viscoelastic region. Frequency sweep tests were also conducted at 25 C. The TA rheometer Data Analysis software (ver. VI. 1.76) was used to obtain the experimental data as well as to calculate the storage modulus (G0 ), loss modulus (G00 ), and loss tangent (tan d ¼ G00 /G0 ). All samples were allowed to rest for 5 min at their initial temperatures prior to the steady and dynamic shear rheological measurements. Additionally, all rheological measurements were performed in triplicate. For G0 measurements in the aging process at 4 C, each sample was loaded onto the 4 C platen of the rheometer and the exposed sample edge was covered with a thin layer of light paraffin oil to prevent evaporation during measurements. G0 values were monitored for 10 h at 6.28 rad s1 and 2% strain. The rheological measurements during aging were conducted in duplicate.
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211
2.5. Gelatinization thermal properties Thermal analyses of the RSeTS blend samples were conducted using a differential scanning calorimeter (DSC; Q200, TA Instruments, New Castle, DE, USA) equipped with a refrigerated cooling system in order to investigate the gelatinization process. The starch blend sample was directly weighed onto the aluminum DSC pan, and distilled water was added with a micropipette in order to create suspensions with a 20 g/100 g starch blend concentration. The sample pan was hermetically sealed and allowed to stand for 1 h at room temperature prior to heating in the DSC. Next, the samples were heated at 5 C min1 from 30 to 130 C. The instrument was calibrated using an indium and an empty pan as reference. From the curve obtained, the onset temperature (To), peak temperature (Tp), conclusion temperature (Tc), and enthalpy (DH) of the starch gelatinization were calculated using the Universal Analysis software provided by the manufacturer. The results reported were the average of the three measurements. 2.6. Freezeethaw stability Freezeethaw stability of the RSeTS blend samples were determined as described by Lee and Yoo (2011). An aqueous suspension of starch (5 g/100 g) was heated at 95 C under constant mild agitation for 30 min and then cooled to room temperature in an ice water bath. The paste was weighed (15 g) in centrifuge tubes and subjected to successive freezeethaw cycles by freezing at 18 C for 24 h and thawing at 30 C for 1.5 h, followed by centrifugation at 2300 g for 30 min. The supernatant eliminated from the gel was weighed, and the extent of syneresis was expressed as the percentage of liquid separated per total weight of sample in the centrifuge tube. In this study, 3 freezeethaw cycles were performed. 2.7. Gel strength Gel strength was measured using a Brookfield Texture Analyzer (TA-CT3, Brookfield Engineering Laboratories, Inc., Middleboro, MA, USA) as described by Lee and Yoo (2011). Starch pastes (10 g/100 g) were prepared, as described previously. The hot starch pastes were poured into cylindrical plastic tubes (35 mm diameter and 40 mm height) that were covered, cooled at room temperature for at least 1 h, and kept at 4 C for 24 h. The starch gels were placed at room temperature at least 1 h before measuring their gel strength. A plastic cylindrical probe with a diameter of 10 mm was used and penetrated into the gel at a speed of 1 mm s1 for a distance of 10 mm. The maximum force at 10 mm of penetration was recorded as the gel strength (N), and the measurement was repeated five times.
207
Table 1 Swelling power and solubility of rice starch (RS)etapioca starch (TS) blends at different ratios of RS/TS.a Sampleb
Swelling power (g/g)
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
40.6 44.4 51.9 64.7 71.0 75.4 93.6
± ± ± ± ± ± ±
0.83G 1.13F 0.67E 1.61D 0.28C 0.86B 1.41A
Solubility (%) 64.3 64.6 66.1 67.5 69.1 70.5 76.1
± ± ± ± ± ± ±
0.54E 1.79E 1.46DE 1.00CD 1.00BC 0.23B 1.41A
a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
swelling power (93.6 g g1) of TS when compared to that of RS (40.6 g g1). The greater swelling power of TS could be due to the larger granule size, capable of holding more water than RS (Tongdang et al., 2008). In addition, lower swelling power values of blends other than that of TS were in accord with the previous findings that the swelling of larger starch granules can be inhibited by the large numbers of surrounding smaller granules, as described by Puncha-Arnon et al. (2008). In general, it is known that RS has very small granules (1e3 mm), while TS typically consists of medium-size granules of around 4e35 mm and has weaker associative force compared to cereal starches (Thomas & Atwell, 1999). Solubility (76.1 g/100 g) of TS was found to be greater than that (64.3 g/100 g) of RS. In contrast to the low swelling power of RS, its high solubility could be attributed to its small granule size. Small granule size of starch results in granule suspension and loss in supernatant during centrifugation (Lin et al., 2013). The solubility values of all blend samples were slightly higher than that of RS alone. Furthermore, no significant differences in solubility values were observed between blend samples at lower mixing ratios (9/1 and 8/2) of TS and RS alone even though the solubility levels of the blends increased with an increase in mixing ratio of TS, which has a higher solubility compared to other cereal starches (Anggraini, Sudarmonowati, Hartati, Suurs, & Visser, 2009). It is known that the higher solubility can be attributed partly to the high swelling TS undergoes during gelatinization (Moorthy, 2002). Tsai, Li, and Lii (1997) also found that weaker granular rigidity resulted in higher swelling power and solubility of starch. Based on these observations, it was found that the swelling power and solubility values of all blend samples were in between those of individual starches (RS and TS) due to the much higher swelling power and solubility of TS when compared to RS. In addition, in the RSeTS blend system, the presence of TS greatly promoted changes in the swelling power and solubility of RS. 3.2. Flow behavior
2.8. Statistical analysis All results are expressed as mean ± standard deviation. Analysis of variance (ANOVA) was performed using Statistical Analysis System software (version 9.2, SAS Institute, Cary, USA). Differences in means were determined using Duncan's multiple-range test. 3. Results and discussion 3.1. Swelling power and solubility The swelling power and solubility values of the RSeTS blends at different RS/TS ratios were in the range of 44.4e75.4 g g1 and 64.6e70.5 g/100 g, respectively (Table 1). The swelling power of the blends increased with a rise in mixing ratio of TS due to the higher
_ data for RSeTS blends The shear stress (s) versus shear rate (g) with different RS/TS ratios at 25 C are shown in Fig. 1. The experimental results of s and g_ data were well fitted to the simple power law model (Eq. (1)) and the Casson model (Eq. (2)) with high determination coefficients (R2 ¼ 0.99) (Table 2). All blend samples had shear-thinning behavior with flow behavior index values (n ¼ 0.31e0.37). This shear-thinning behavior can be explained by the progressive orientation of soluble starch molecules in the direction of the flow as well as the breaking of hydrogen bonds formed between amylose molecules during shearing (McGrane, Mainwaring, Cornell, & Rix, 2004). The n values (0.31e0.37) of all blends decreased with an increase in mixing ratio of TS and were also much lower than that (n ¼ 0.55) of TS alone, suggesting that the addition of TS, especially higher mixing ratios of TS, resulted in
208
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211
250
3.3. Dynamic shear properties Plots of frequency (u) versus storage modulus (G0 ) and loss modulus (G00 ) for the RSeTS blends at 25 C (Fig. 2) revealed that the magnitudes of G0 and G00 increased with an increase in u and that G0 was much higher than G00 at all values of u with frequency dependency. All samples exhibited a weak gel-like behavior because the slopes are positive and the magnitudes of G0 are much
Shear Stress (Pa)
200
150
100
50
0 0
50
100
150
200
250
300
Shear rate (sec-1) Fig. 1. Shear stresseshear rate plots for RSeTS blends at different RS/TS ratios, 25 C: (B) RS, ( ) RS9/TS1, ( ) RS8/TS2, (◊) RS7/TS3, (þ) RS6/TS4, () RS5/TS5, (C) TS.
▫
▵
Table 2 Magnitudes of consistency index (K), flow behavior index (n), and Casson yield stress (soc) of rice starch (RS)-tapioca starch (TS) blends at different ratios of RS/TS.a Sampleb
K (Pa sn)
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
24.7 24.4 27.8 31.0 35.5 38.2 9.84
± ± ± ± ± ± ±
0.62E 0.43E 0.38D 0.58C 0.14B 0.02A 0.10F
soc (Pa)
n (e) 0.35 0.37 0.35 0.34 0.32 0.31 0.55
± ± ± ± ± ± ±
0.00C 0.00B 0.00C 0.00D 0.00E 0.00F 0.02A
19.2 27.8 30.1 33.9 35.4 42.1 10.7
± ± ± ± ± ± ±
0.32F 0.21E 0.71D 0.02C 0.70B 0.00A 0.32G
R2 0.99 0.99 0.99 0.99 0.99 0.99 0.99
a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
more pseudoplastic, even though TS had low shear-thinning behavior with an n value as high as 0.55. The observed higher shear-thinning behavior may be interpreted as a result of the higher degree of breakage of the intra- and intermolecular bonding system in the starch blend network. From these results, it was found that the n values of RSeTS blends were strongly influenced by the addition of TS. In general, the consistency index (K, 24.4e38.2 Pa sn) and yield stress (soc, 27.8e42.1 Pa) values of the RSeTS blends, which were obtained from the power law and Casson models, were higher than those (24.7 Pa sn and 9.84 Pa sn) of RS and TS alone; moreover, they also increased with an increase in mixing ratio of TS (Table 2), suggesting that the addition of TS resulted in more resistance to flow. Therefore, the synergistic effect of TS on the RSeTS blend systems in regard to increasing flow rheological parameters (K and sco) is more effective, probably due to the interactions between the two components in the blend systems due to increased interactions between leached molecules and swollen granule remnants (Park et al., 2009; Puncha-Arnon et al., 2008; Zhang et al., 2011). From these observations, it can be concluded that the steady shear properties of RSeTS blends were apparently influenced by the mixing ratio of TS, and the desirable flow properties of RS for industrial use can also be controlled and improved by the addition of TS.
Fig. 2. Plot of G0 , G00 , tan d versus u for RSeTS blends at different RS/TS ratios, 25 C: (B) RS, ( ) RS9/TS1, ( ) RS8/TS2, (◊) RS7/TS3, (þ) RS6/TS4, () RS5/TS5, (C) TS.
▫
▵
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211
higher than those of G00 . In general, the dynamic moduli (G0 and G00 ) results revealed that changes in the G0 of RS after adding TS were greater than changes in G00 , indicating that the addition of TS greatly influenced the elastic property of RS. RS showed higher dynamic moduli values compared to TS due to its smaller granule size, as noted by Li and Yeh (2001) who found that low swelling starches, such as RS, had greater dynamic moduli values. Therefore, the dynamic moduli values of RSeTS blends decreased with an increase in the mixing ratio of TS. Such lower dynamic moduli may also be attributed to the much lower dynamic moduli of TS itself due to the strong swelling power of TS granules compared to those of RS, as described previously. Therefore, they fell between the dynamic moduli values obtained for RS and TS. This observed result suggests that RSeTS blend samples could have been diluted by TS with its lower dynamic moduli in comparison to RS, as described by Oh, Kim, and Yoo (2010). The tan d (ratio of G00 /G0 ) values of all blend samples were less than “1” (Fig. 2), indicating that all the samples were more elastic than viscous. As stated previously, if the tan d is in a range greater than 0.1, a sample is deemed to be a weak gel, as described previously. In general, all blend samples produced higher tan d values than RS, showing that their tan d values were in between the tan d values obtained for RS and TS. Therefore, the viscous properties of the blends were more pronounced than the elastic properties after the addition of TS to RS. This implies that the TS did not provide an effective contribution to the elastic properties of the RSeTS blends due to the TS having the higher tan d. Such higher tan d of TS can be attributed to the presence of more liquid phase, possibly due to the capability of absorbing more water, as described by Li and Yeh (2001). They also reported that tan d was positively associated with swelling power. Similar results were reported by Lin et al. (2013), who found that TS exhibited rheological and pasting properties similar to waxy starches. Thus, the observed tan d values in RSeTS blend systems indicate that the viscous properties of RS paste appear to be strongly influenced by the addition of TS as well as the granular characteristics of two component starches. This may be a helpful recommendation when substituting RS in RS-based food products to increase their viscous properties. 3.4. Effect of TS addition on G0 of RSeTS blends during aging The gelation phenomenon of starch pastes containing amylose can be detected using measurements of the dynamic mechanical storage modulus (G0 ) that reflect the elastic property of the sample and have a characteristic pattern as a function of time (Eidam, Kulicke, Kuhn, & Stute, 1995). Fig. 3 shows changes in G0 for RSeTS blends with different mixing ratios of TS as a function of aging time (10 h at 4 C). This change of G0 values during a long aging period corresponds to the retrogradation of amylose. The rapid increase and plateau of G0 can be due to the rapid aggregation of amylose chains at the early stage. RS alone, like other cereal starches, showed a plateau value of G0 after a long aging period. A similar trend was reported for other starches, such as corn (Chang, Lim, & Yoo, 2004), rice (Yoo & Yoo, 2005) and sweet potato starch (Lee & Yoo, 2009). In contrast, TS alone showed almost the same G0 values during aging, showing that TS dispersion at 5 g/100 g concentration produced gels too weak to give a stable G0 detectable by the instrument. Such weak gel network structure may be attributed to the increased water uptake caused by the swollen granules due to very weak associative forces between starch granules, easy penetration of water molecules, and large swelling (Anggraini et al., 2009). All blend samples displayed lower G0 values than RS alone. The plateau values of G0 after a long aging time were observed for the RS alone as well as the blends at lower mixing ratios (9/1 and 8/ 2). In contrast, the blends at higher mixing ratios (7/3, 6/4, and 5/5)
209
Fig. 3. Changes in G0 during aging at 5 C for 10 h for RSeTS blends at different RS/TS ratios: (B) RS, ( ) RS9/TS1, ( ) RS8/TS2, (◊) RS7/TS3, (þ) RS6/TS4, () RS5/TS5, (C) TS.
▫
▵
showed a slow and continuous increase of G0 without a clear plateau region, indicating that the aggregation speed appears to be slowed down by the addition of TS. The values of G0 after a long aging interval were also reduced by the addition of TS, and decreased with the increase in mixing ratio of TS. These findings support the observation that the addition of TS leads to a decrease of the structure development rate. 3.5. Gelatinization thermal properties Details of transition temperatures (To, Tp, and Tc) and enthalpies (DH) associated with gelatinization of RSeTS blends at different mixing ratios are summarized in Table 3 and their thermograms are shown in Fig. 4. All blend samples at different mixing ratios displayed single endotherms. The transition temperatures of TS alone were much higher than those of RS alone. The To (60.4e60.9 C) values of blend samples were similar at all mixing ratios of TS, as were the Tp (66.8e67.0 C) values, the only exception being for mixing ratio (5/5) with a high proportion of TS. In contrast, the magnitudes of Tc of the blend samples were found to be significantly increased by the addition of TS; moreover, they also increased with an increase in the mixing ratio of TS. The gelatinization temperature (Tceo) of RS and TS were 14.5 and 16.0 C, respectively. This difference of Tceo is due to the difference of the degrees of heterogeneity of crystallites within granules of the studied starches (Hagenimana, Pu, & Ding, 2005). The Tceo values of blends increased with an increase in the mixing ratio of TS. In addition, all blend samples displayed single endotherms (Fig. 4), supporting the possibility of each component gelatinizing independently. Liu and Lelievre (1992) found that DSC thermograms were the sum of each individual component in the starch blends at low starch concentrations, though this phenomenon did not occur when the blends were at high concentrations (>30 g/ 100 g), due to competition for water. Therefore, it was found that the gelatinization of RS seems to be influenced by the addition of TS, and the sum of each individual component can exist in starch blends. The enthalpy value (15.4 J g1) of gelatinization (DH) of TS was much higher than that (11.0 J g1) of RS, and the DH values of the blends also increased with an increase in mixing ratio of TS from 9/
210
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211 Table 3 Thermal properties of rice starch (RS)-tapioca starch (TS) blends at different RS/TS ratios.a Sampleb
To ( C)
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
61.2 60.9 60.9 60.6 60.6 60.4 64.8
± ± ± ± ± ± ±
Tp ( C) 0.06B 0.04C 0.06C 0.09D 0.06D 0.10D 0.23A
67.3 67.0 66.9 66.9 66.8 72.4 72.0
± ± ± ± ± ± ±
Tc ( C) 0.06C 0.08CD 0.02CD 0.16CD 0.01D 0.15A 0.42B
75.7 76.3 80.7 81.3 82.0 83.3 80.8
± ± ± ± ± ± ±
DH (J/g)
Tceo ( C) 0.07F 0.09E 0.01D 0.11C 0.03B 0.06A 0.45CD
14.5 15.4 19.8 20.7 21.4 22.9 16.0
± ± ± ± ± ± ±
0.01G 0.13F 0.07D 0.20C 0.03B 0.16A 0.22E
11.0 9.30 12.6 13.2 13.9 14.3 15.4
± ± ± ± ± ± ±
0.28E 0.12F 0.11D 0.25C 0.15B 0.13B 0.35A
Tceo, range of gelatinization temperature (TceTo). a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
Table 4 Effect of blends on syneresis (%) of rice starch (RS)-tapioca starch (TS) blends at different ratios of RS/TS.a Sampleb
Syneresis (%) 1 cycle
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
37.7 44.1 43.9 41.0 40.1 34.6 35.7
± ± ± ± ± ± ±
2 cycle 0.34C 0.73A 0.61A 0.98B 0.57B 0.91D 0.93D
42.9 47.2 45.0 42.4 40.9 35.2 36.4
± ± ± ± ± ± ±
3 cycle 2.18BC 0.50A 1.64AB 1.79BC 1.16C 0.42D 1.36D
52.3 50.6 45.4 42.7 41.4 35.6 36.5
± ± ± ± ± ± ±
1.06A 0.34B 0.84C 0.97D 1.20D 0.85E 0.53E
a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
Fig. 4. Gelatinization thermograms of RSeTS blends at different RS/TS ratios.
1 to 5/5 due to the higher DH of TS compared to RS. However, the DH value (9.30 J g1) at a lower mixing ratio (9/1) was much lower than that (11.0 J g1) of RS. This implies that RS might have influenced the gelatinization behavior of blends at lower ratios of TS. Due to the much smaller size of RS, a large number of RS granules surrounding the TS granules could impede the accessibility of water to the TS granules, Hence, the TS granules would not be fully gelatinized, resulting in lower DH values for blends at lower ratios of TS, as reported by Ortega-Ojeda and Eliasson (2001) and PunchaArnon et al. (2008). In general, it is also known that the DH value of a single starch decreases with a decrease in water content (Blanshard, 1987). Similar observations have been reported by Ortega-Ojeda and Eliasson (2001) for potato starch-other starch blends. From these observations, it was found that in the RSeTS blend systems, the gelatinization thermal properties of RS were apparently influenced by the addition of TS and the mixing ratio of TS.
3.6. Freezeethaw stability of starch blend gel Table 4 shows the percentage syneresis of the RSeTS blend samples during 3 freezeethaw cycles. The syneresis (%) values of the RSeTS blends decreased with an increase in the mixing ratio of
TS from 9/1 to 5/5. The syneresis (%) values (35.7e36.5%) of the TS gel were much lower than those (37.7e52.3%) of the RS, and those of the blends decreased with an increase in the mixing ratio of TS from 9/1 to 5/5. In particular, the syneresis values (35.6e50.6%) at the third freezeethaw cycle were significantly lower than that (52.3%) of RS alone, and also significantly decreased with an increase in the mixing ratio of TS. These results indicate that the freezeethaw stability of RSeTS gels can be improved by the addition of TS during a long storage, resulting in decreased retrogradation. Among the blend samples, a blend gel at 5/5 mixing ratio showed significant lower syneresis values (34.6e35.6%), which were similar to those of TS alone during all 3 freezeethaw cycles. Such superior freezeethaw stability means that the RSeTS blend samples would have suitable textural properties for developing RSbased products. 3.7. Gel strength The gel strength values (0.30e0.64 N) of the blend samples were much higher compared to the RS and TS alone, and increased with an increase in the mixing ratio of TS (Table 5), indicating that the blend gels were harder, especially at higher mixing ratios of TS. This also shows that RSeTS blends were significantly harder than what might be expected based on the weight percentage of each starch in the blend. Such a trend is in contradiction to previous reports on other starch blends (Gunaratne & Corke, 2007; Karam, Grossmann, Silva, Ferrero, & Zaritzky, 2005; Puncha-Arnon et al., 2008; Yao, Zhang, & Ding, 2003) which showed firmness values lower than those of the individual starches. These opposite results may also be explained by the non-additive effect due to an interaction between the starches, as described by Yao et al. (2003) and Puncha-Arnon et al. (2008). This also is in solid agreement with the large increase of flow rheological parameters (K and sco) in the RSeTS blend systems, as described previously (Table 2). Therefore, the synergistic effect of TS on the RSeTS blend systems in increasing gel
D. Sun, B. Yoo / LWT - Food Science and Technology 64 (2015) 205e211 Table 5 Gel strength of rice starch (RS)etapioca starch (TS) blends at different ratios of RS/TS.a Sampleb
Gel strength (N)
RS RS9/TS1 RS8/TS2 RS7/TS3 RS6/TS4 RS5/TS5 TS
0.17 0.30 0.41 0.47 0.56 0.64 0.16
± ± ± ± ± ± ±
0.01F 0.01E 0.01D 0.01C 0.02B 0.02A 0.01F
a Mean values in the same column with different letters are significantly different (p < 0.05). b Numbers for RS and TS indicate the weight ratio of RS and TS.
strength is probably due to the interactions between the two starch components in the blend systems. 4. Conclusions In the RSeTS blend systems, the synergistic effect of TS on RS paste increasing K and soc is more effective than when compared to the RS alone. A decrease in the dynamic moduli (G0 and G00 ) and the higher tan d values of the RSeTS blends compared to RS alone appeared to be attributed to the higher swelling power of TS granules versus that of RS. All dynamic rheological parameter values were in between the values obtained for RS and TS. The values of G0 of RSeTS blends during aging for 10 h at 4 C decreased with an increase in the mixing ratio of TS due to the inhibition of starch retrogradation. Freezeethaw stability of the RSeTS blends was also improved by the addition of TS. The synergistic effect of TS on the RSeTS blend systems in increasing gel strength can be attributed to a non-additive effect due to an interaction between the two starch components. These results support that the blend samples at higher ratios of TS would have the desirable and improved rheological properties for developing RS-based products. In addition, these results will be useful for formulating desirable rheological and physical properties for a wide range of industrial food applications, and also in designing and developing new starch blends. References Anggraini, V., Sudarmonowati, E., Hartati, N. S., Suurs, L., & Visser, R. G. F. (2009). Characterization of cassava starch attributes of different genotypes. StarchStarke, 61(8), 472e481. BeMiller, J. N., & Whistler, R. L. (2007). Carbohydrate chemistry for food scientists (2nd ed.). St. Paul, Minn.: AACC International. Blanshard, J. M. V. (1987). Starch granule structure and function: a physicochemical approach. In T. Galliard (Ed.), Starch: Properties and potentials, critical reports on applied chemistry (pp. 16e54). New York, NY: Wiley. Chaisawang, M., & Suphantharika, M. (2006). Pasting and rheological properties of native and anionic tapioca starches as modified by guar gum and xanthan gum. Food Hydrocolloids, 20(5), 641e649. Chang, Y. H., Lim, S. T., & Yoo, B. (2004). Dynamic rheology of corn starch-sugar composites. Journal of Food Engineering, 64(4), 521e527.
211
Chun, S. Y., & Yoo, B. (2004). Rheological behavior of cooked rice flour dispersions in steady and dynamic shear. Journal of Food Engineering, 65(3), 363e370. Eidam, D., Kulicke, W. M., Kuhn, K., & Stute, R. (1995). Formation of maize starch gels selectively regulated by the addition of hydrocolloids. Starch-Starke, 47(10), 378e384. Gunaratne, A., & Corke, H. (2007). Gelatinizing, pasting, and gelling properties of potato and amaranth starch mixtures. Cereal Chemistry, 84(1), 22e29. Hagenimana, A., Pu, P. P., & Ding, X. L. (2005). Study on thermal and rheological properties of native rice starches and their corresponding mixtures. Food Research International, 38(3), 257e266. Karam, L. B., Grossmann, M. V. E., Silva, R. S. S. F., Ferrero, C., & Zaritzky, N. E. (2005). Gel textural characteristics of corn, cassava and yam starch blends: a mixture surface response methodology approach. Starch-Starke, 57(2), 62e70. Leach, H. W., McCowen, L. D., & Schoch, T. J. (1959). Structure of the starch granule. II. Swelling power and solubility patterns of various starches. Cereal Chemistry, 36, 534e544. Lee, H. L., & Yoo, B. (2009). Dynamic rheological and thermal properties of acetylated sweet potato starch. Starch-Starke, 61(7), 407e413. Lee, H. L., & Yoo, B. (2011). Effect of hydroxypropylation on physical and rheological properties of sweet potato starch. LWT e Food Science and Technology, 44(3), 765e770. Li, J. Y., & Yeh, A. I. (2001). Relationships between thermal, rheological characteristics and swelling power for various starches. Journal of Food Engineering, 50(3), 141e148. Lin, J. H., Kao, W. T., Tsai, Y. C., & Chang, Y. H. (2013). Effect of granular characteristics on pasting properties of starch blends. Carbohydrate Polymers, 98(2), 1553e1560. Liu, H., & Lelievre, L. A. (1992). Differential scanning calorimetry study of melting transitions in aqueous suspensions containing blends of wheat and rice starch. Carbohydrate Polymers, 17, 145e149. McGrane, S. J., Mainwaring, D. E., Cornell, H. J., & Rix, C. J. (2004). The role of hydrogen bonding in amylose gelation. Starch-Starke, 56(3e4), 122e131. Moorthy, S. N. (2002). Physicochemical and functional properties of tropical tuber starches: a review. Starch-Starke, 54(12), 559e592. Obanni, M., & Bemiller, J. N. (1997). Properties of some starch blends. Cereal Chemistry, 74(4), 431e436. Oh, J. H., Kim, M. J., & Yoo, B. (2010). Dynamic rheological properties of rice flourestarch blends. Starch-Starke, 62(6), 321e325. Ortega-Ojeda, F. E., & Eliasson, A. C. (2001). Gelatinisation and retrogradation behaviour of some starch mixtures. Starch-Starke, 53(10), 520e529. Park, E. Y., Kim, H. N., Kim, J. Y., & Lim, S. T. (2009). Pasting properties of potato starch and waxy maize starch mixtures. Starch-Starke, 61(6), 352e357. Puncha-Arnon, S., Pathipanawat, W., Puttanlek, C., Rungsardthong, V., & Uttapap, D. (2008). Effects of relative granule size and gelatinization temperature on paste and gel properties of starch blends. Food Research International, 41(5), 552e561. Sasaki, T., Yasui, T., Matsuki, J., & Satake, T. (2002). Rheological properties of mixed gels using waxy and non-waxy wheat starch. Starch-Starke, 54(9), 410e414. Thomas, D. J., & Atwell, W. A. (1999). Starches (pp. 31e48). ST. Paul, MN: Eagan Press. Tongdang, T., Meenun, M., & Chainui, J. (2008). Effect of sago starch addition and steaming time on making cassava cracker (Keropok). Starch-Starke, 60(10), 568e576. Tsai, M. L., Li, C. F., & Lii, C. Y. (1997). Effects of granular structures on the pasting behaviors of starches. Cereal Chemistry, 74(6), 750e757. Waterschoot, J., Gomand, S. V., Willebrords, J. K., Fierens, E., & Delcour, J. A. (2014). Pasting properties of blends of potato, rice and maize starches. Food Hydrocolloids, 41, 298e308. Yamamoto, K., Sawada, S., & Onogaki, T. (1973). Properties of rice starch prepared by alkali method with various conditions. Denpun Kagaku, 20, 99e104. Yao, Y., Zhang, J., & Ding, X. (2003). Retrogradation of starch mixtures containing rice starch. Journal of Food Science, 68(1), 260e265. Yoo, D., & Yoo, B. (2005). Rheology of rice starchesucrose composites. Starch-Starke, 57(6), 254e261. Zhang, Y. Y., Gu, Z. B., Hong, Y., Li, Z. F., & Cheng, L. (2011). Pasting and rheologic properties of potato starch and maize starch mixtures. Starch-Starke, 63(1), 11e16. Zhu, F., & Corke, H. (2011). Gelatinization, pasting, and gelling properties of sweet potato and wheat starch blends. Cereal Chemistry, 88(3), 302e309.