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Effects of potato starch addition and cooling rate on rheological characteristics of flaxseed protein concentrate
Journal of Food Engineering 91 (2009) 392–401
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Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng
Effects of potato starch addition and cooling rate on rheological characteristics of flaxseed protein concentrate Bo Wang a, Li-Jun Wang b, Dong Li a,*, Bhesh Bhandari c, Wen-Fu Wu d,*, John Shi e, Xiao Dong Chen a,f, Zhi-Huai Mao a a
College of Engineering, China Agricultural University, P.O. Box 50, 17 Qinghua Donglu, Beijing 100083, China College of Food Science and Nutritional Engineering, China Agricultural University, Beijing, China c School of Land, Crop and Food Sciences, The University of Queensland, Brisbane QLD, Australia d School of Biological and Agricultural Engineering, Jilin University, 142 Renmin Street, Changchun 130025, China e Guelph Food Research Center, Agriculture and Agri-Food Canada, Ontario, Canada f Department of Chemical Engineering, Monash University, Victoria, Australia b
a r t i c l e
i n f o
Article history: Received 18 February 2008 Received in revised form 18 September 2008 Accepted 24 September 2008 Available online 7 October 2008 Keywords: Rheological characteristics Flaxseed protein concentrate Potato starch
a b s t r a c t Rheological characteristics of potato starch/flaxseed protein concentrate composites were investigated using a rheometer. Effects of starch/protein mass ratio (0.2–1.0) and different cooling rate (2 °C/min, 4 °C/min and 6 °C/min) on rheological behavior of composites were studied. The study showed that G’ and G’’ increased with increase of starch mass ratio in the temperature range of 40–95 °C, in both heating and cooling process. The composites exhibited similar T G0initial and T G0MAX , higher than those of potato starch alone at 60.3 °C. The result of frequency sweep of the composites at the end of the cooling at 25 °C exhibited an elastic behavior at all test frequency ranges (0.06283–62.83 rad/s). Study of cooling rate on rheological characteristic of composites exhibited an increase in the G’ and G’’ values with decrease of cooling rate, probably because of gel network having a stronger structure with more time for dynamic equilibration. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Flaxseed, also called linseed, is a small flat oval seed of flax (Linum suitatissimum). Flaxseed is abundant in many nutrients, such as polyunsaturated fatty acid, protein, and lignans (Wang et al., 2007). Flaxseed has been shown to reduce total cholesterol and low-density lipoprotein cholesterol in some studies in humans and animals (Bhathena et al., 2002). Many researchers have investigated the nutritional elements of the flaxseed (Zhang et al., 2007; Wang et al., 2008; Wu et al., 2008). The current market for edible flaxseed is limited to the whole intact flaxseed and its oil because x-3 polyunsaturated fatty acids and phytoestrogens are proposed to promote health (Khan et al., 2007), while the defatted meal, is primarily used as livestock feed. However, with the increasing demand for vegetable sources of proteins, there is a potential for utilizing flaxseed proteins present in defatted meal as a food source. The amino acid composition of flaxseed is viewed as one of the most nutritious of plant proteins. The studies about flaxseed protein concentrate have shown that there are two proteins in the flaxseed: a salt-soluble fraction with high molecular weight (11– 12 S) and a water-soluble with low molecular weight (1.6–2 S) (Madhusudhan and Singh, 1983, 1985a; Marcone et al., 1998a; * Corresponding authors. Tel./fax: +86 10 62737351 (D. Li). E-mail addresses: [email protected] (D. Li), [email protected] (W.-F. Wu). 0260-8774/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2008.09.032
Youle and Huang, 1981). The major protein isolated from flaxseed was shown to have high contents of the amino acids arginine, glutamate/glutamine, and aspartate/asparagines (Chung et al., 2005). Flaxseed proteins are proposed to have an effect on various diseases, including coronary heart disease, kidney disease and cancer (Oomah and Mazza, 2000). Starches are known gelling agents with their water-holding and thickening properties and thereby contribute to the structural and textural properties. Dickinson (2003) and Singh et al. (2003) have described the interfaces properties of the hydrocolloids. Various starches are being added in protein to form gels for reducing cost and improving texture. Associated interactions typically occur by electrostatic attraction between negatively charged polysaccharides and positively charged proteins, often result in formation of insoluble complexes (Fitzsimons et al., 2008). So, starch has been recognized as filler to increase the firmness of products (Li and Yeh, 2003). Rheology, which was originally defined by Bingham in 1930, is now well established as the science of the deformation and flow of matter: it is the study of the manner in which materials respond to applied stress or strain (Steffe, 1992). In food engineering, rheology helps to understand how food structure responds to applied force and deformation. Hence, from a practical point of view, the rheological characteristics of foods are very important, particularly in relation to structure, sensory evaluation, quality control,
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Nomenclature G0 G00 d T G0initial G0MAX
storage modulus (Pa) loss modulus (Pa) phase angle (°) the temperature when G’ started swelling (°C) the storage modulus when G’ became maximums (Pa)
T G0MAX dG0MAX K0
x n0
processing design and new product development (Yang et al., 2004). Knowledge of specific interactions and synergistic effects is highly desirable for creating new textures and enable ingredient substitutions and numerous studies have been conducted on the rheological characteristics of edible composites, for example, soy
Table 1 Components of the composite dispersions at different starch mass ratio. Starch/protein mass ratio
Starch percentage in dispersion (%)
Protein percentage in dispersion (%)
Water percentage in dispersion (%)
FPC 0.2 0.3 0.4 0.6 0.8 1.0 PS
0.00 3.34 4.62 5.72 7.50 8.88 10.00 20.00
20.00 16.66 15.38 14.28 12.50 11.12 10.00 0.00
80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00
protein-based pudding (Lim and Narsimhan, 2006), blend of rice flour and soy protein (Hagenimana et al., 2007) and composites of wheat dough and protein (Song and Zheng, 2007). But to the best of our knowledge, there are very few literatures having been investigated on rheological properties of flaxseed protein and starch composites. To help to the development of new protein products with starch, the objective of this study was to investigate the rheological characteristics of potato starch/flaxseed protein concentrate composite and the effects of cooling rate on its rheological behaviors. 2. Materials and methods 2.1. Materials
FPC stands for flaxseed protein concentrate only, PS stands for potato starch only.
a
the temperature when G’ became maximums (°C) the phase angle when G’ became maximums (°) constant (Pa (s/rad)n) angular frequency (rad/s) frequency exponent (dimensionless)
Potato starch obtained from a commercial source (Aoboxing Biotechnology Ltd., Beijing, China) was used as a starch source. Flaxseed protein concentrate was kindly provided by Hengkang Biotechnology Ltd. (Inner Mongolia Autonomous Region, China).
10 1
G'(kPa)
0.1 0.01 0.001 flaxseed protein concentrate
0.0001
potato starch
0.00001 0.000001 40
b
50
60
70 Temperature (°C)
80
90
100
1 0.1
G'' (kPa)
0.01 0.001 flaxseed protein concentrate potato starch
0.0001 0.00001 40
50
60
70
80
90
100
Temperature (°C) Fig. 1. Temperature sweep for flaxseed concentrate and potato starch. (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
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a
10
G' (kPa)
1 0.2 0.3 0.4 0.6
0.1
0.8 1.0 0.01 30
40
50
60
70
80
90
100
Temperature (°C) 1
b
G'' (kPa)
0.1
0.2 0.3 0.4
0.01
0.6 0.8 1.0 0.001 30
40
50
60
70
80
90
100
Temperature (°C) Fig. 2. Rheological characteristics of potato starch/flaxseed protein concentrate composites at different ratios (labeled on the right side of curves) during heating with a heating rate of 2 °C/min. (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
Table 2 Experimental and Calculated G’ (Pa) of flaxseed protein concentrate, potato starch and starch/protein composites at 40 °C. G’ (Pa) at 40 °C
Experimental data Calculated data
Starch/protein mass ratio FPC
0.2
0.3
0.4
0.6
0.8
1.0
PS
863.5 ± 97.1a 863.5 ± 97.1a
149.2 ± 23.0a 719.6 ± 80.9b
111.6 ± 22.0a 664.2 ± 74.7b
75.4 ± 13.2a 616.8 ± 69.3b
35.0 ± 4.2a 593.7 ± 60.7b
26.4 ± 2.3a 479.7 ± 54.0b
12.0 ± 2.8a 431.2 ± 48.6b
(3.84 ± 0.04) 103a (3.84 ± 0.04) 103a
FPC stands for flaxseed protein concentrate only; PS stands for potato starch only. The parameters with different letters in a column are significantly different (P < 0.05) as determined by ANOVA.
The flaxseed protein concentrate has following characteristics: protein content 71.98% (Kjeldhal methods), moisture content 6.22% (105 °C for 24 h), ash 4.36% (550 °C for 12 h), 5.74% fat (Soxhlet extraction) and 11.7% carbohydrate. Flaxseed protein concentrate and potato starch were stored in the sealed polyethylene bags at room temperature until used. The moisture content of these raw materials was kept below 10%. 2.2. Preparation of potato starch/flaxseed protein concentrate composites Potato starch and flaxseed protein concentrate were mixed at ratios of 0, 0.2, 0.3, 0.4, 0.6, 0.8 and 1.0 (solid basis). Distilled water was added into the uniform mass to yield a water content of 80%. The components of different dispersions were shown as Table 1. The composites were stirred at a speed of 150 rpm with a mixer
Table 3 Rheological characteristics of flaxseed protein concentrate, potato starch and starch/ protein composites in heating process. Starch/ protein mass ratio
T G0initial (°C)
T G0MAX (°C)
G0MAX (kPa)
dG0MAX (°)
G’ (kPa) at 95 °C
FPC 0.2 0.3 0.4 0.6 0.8 1.0 PS
– 62.0 ± 0.5a 61.0 ± 0.4b 61.2 ± 0.4b 60.3 ± 0.4c 61.7 ± 0.8a 60.0 ± 0.3c 60.3 ± 0.2c
– 77.3 ± 0.3a 78.0 ± 0.4b 78.0 ± 0.6b 78.0 ± 0.3b 77.0 ± 0.5a 76.6 ± 0.5c 70.9 ± 0.4d
– 0.65 ± 0.09a 0.94 ± 0.04b 1.17 ± 0.07c 1.76 ± 0.06d 2.50 ± 0.07e 2.94 ± 0.06f 2.99 ± 0.07f
(13.35 ± 0.21) 16.53 ± 0.32a 16.02 ± 0.16b 15.11 ± 0.36c 12.82 ± 0.33c 13.26 ± 0.46d 11.68 ± 0.42e 15.14 ± 0.44f
– 0.50 ± 0.07a 0.50 ± 0.07a 0.66 ± 0.06b 0.96 ± 0.09c 1.21 ± 0.07d 1.60 ± 0.08e 1.38 ± 0.08e
FPC stands for flaxseed protein concentrate only; PS stands for potato starch only. The parameters with different letters in a column are significantly different (P < 0.05) as determined by ANOVA. The numbers in parentheses were determined at 40 °C.
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(JJ-6, Medical Instrument Ltd., Jintan, China) for 1 h at room temperature.
(A) A ‘‘heating” temperature sweep test was carried out by heating the composites from 25 °C to 95 °C at 2 °C /min and a frequency of 1 Hz. (B) The composites were put into stainless steel cylinder molds with a diameter of 50 mm and a height of 50 mm. The molds were then heated up to 95 °C in a thermally controlled water bath and kept at this temperature for 20 min to make the gel form. Then the gel was immediately transferred to the rheometer for a ‘‘cooling down” temperature sweep tests. The gel was cooled down from 95 °C to 25 °C at 2 °C/min and a frequency of 1 Hz. A frequency sweep was carried out at 25 °C to determine the viscoelastic characteristics of the gel at last.
2.3. Rheological experiments The rheological characteristics of potato starch/flaxseed protein concentrate composites were measured in five replications using a controlled strain rheometer (AR2000ex, TA Instrument, Crawley, UK), operated with a parallel-plate geometry of 40 mm diameter and a gap of 1 mm. The linear viscoelastic region was found below a strain of 4% in all samples. Thus a strain of 0.5% was used to assure the tests being in the linear viscoelastic region. The different rheological measurements were defined as follows:
a
10000 0.2
1000
G' (kPa)
0.3 0.4
100
0.6 PS
10
1
0.1 20
30
40
50
60
70
80
90
100
Temperature (°C)
b
1000 0.2 0.3
G'' (kPa)
100
0.4 0.6
10
PS
1 0.1 0.01 20
30
40
50
60
70
80
90
100
Temperature (°C)
c
16
δ
12
0.2 0.3 0.4 0.6 PS
8
4 20
40
60
80
100
Temperature (°C) Fig. 3. Rheological characteristics of potato starch/flaxseed protein concentrate composites at different ratios (labeled on the right side of the curves) during cooling with cooling rate of 2 °C/min. (a) Storage modulus (G’), (b) loss modulus (G’’) and (c) phase angle (d).
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a
10000 0.2 0.3
G' (kPa)
1000
0.4 0.6 PS
100
10
1 0.01
0.1
1
10
100
10
100
log ω (rad/s)
b
1000.0
0.2 0.3
G'' (kPa)
100.0
0.4 0.6 PS
10.0
1.0
0.1 0.01
0.1
1
log ω (rad/s) Fig. 4. Frequency sweep of the potato starch/flaxseed protein concentrate composites at 25 °C (the starch/protein ratios are labeled on the right side of the curves). (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
Parameters including storage modulus (G’), loss modulus (G’’) and phase angle (d) were obtained using the TA Rheological Advantage Data Analysis software V 5.4.7 (TA Instrument Ltd., Crawley, UK). Silicone oil was coated on the outer edge of sample to minimize the water loss during the measurements.
protein concentrate was decreased to 0.64 kPa when the composite was heated to 95 oC, possibly due to the increased kinetic energy of molecules. The reduction in G0 was similar to the pre-treated soy protein isolate (Vliet et al., 2002), gluten protein (Rosell and
a
3000000
2000000
K'
(C) The heated composites at starch/protein mass ratio of 0.2 and 0.6 were cooled down from 95 °C to 25 °C at 2 °C/min, 4 °C/min and 6 °C/min with a frequency of 1 Hz, and a frequency sweep was carried out at 25 °C at last to investigate the effect of cooling rate on viscoelastic characteristics of mix gel.
1000000
2.4. Data analysis 0
The averages of five replications for the rheological parameters of the samples were used and the relative standard deviation of the average parameter was shown in tables and figures. The analysis of variance (ANOVA) was carried out based on the experimental data by using the SAS statistical package (SAS Institute, Cary, NC).
0.2
0.3
0.4
0.6
starch/protein mass ratio 0.12
b
0.1
n'
0.08
3. Results and discussion 3.1. Results of ‘‘heating” temperature sweep
0.06 0.04 0.02
Since there was no significant change at temperatures of lower than 40 °C, the data were recorded from 40 °C to 95 °C. Flaxseed protein concentrate exhibited high G’ (0.86 kPa) at 40 °C during ‘‘heating” temperature sweep (Fig. 1a). G0 of flaxseed
0.2
0.3
0.4
0.6
starch/protein mass ratio Fig. 5. Constants (K’) and frequency exponents (n’) of composites with different starch:protein mass ratios. (a) constants (K0 ) and frequency exponents (n0 ).
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Foegeding, 2007), and soy protein concentrate (Li et al., 2007). It is shown that there was no denaturation or gelation of flaxseed protein concentrate. It is agreed with the earlier thermal study by LiChan and Ma (2002), which has shown that flaxseed protein would not denature below 100 °C. As shown in Fig. 1a, non-gelatinized potato starch suspension exhibited very low G0 (3.84 103 Pa) at temperatures lower than 60 °C. When temperature reached 60.3 °C, which was defined as T G0initial , G0 of potato starch increased significantly because of starch granules swelled. After swelling, starch granule absorbs heat for gelatinization, which resulted in the deformation, disruption, and melting of starch granules. There existed a maximum G0 (G0MAX ) of 2.99 kPa at 70.9 °C due to the deformation of starch granules (Li and Yeh, 2001). The trend of change of G’’ was similar to that of G0 for both flaxseed protein concentrate and potato starch (Fig. 1b). The value of G’’ was much lower than G0 which indicated that the samples exhibited obvious elastic behavior. Fig. 2 depicts the rheological characteristics of composite when heated, which is quite similar to that of potato starch. At 40 oC, both G0 and G’’ of all the composites were between those of flaxseed protein concentrate and potato starch. Increasing the starch reduced the G0 and G’’ of the composite. According the work before (Van Ness and Abbott, 1982), if the system as an ideal mixture, G0 of the composite was calculated as
G0 of composites ¼ ðmass percentage G0 ÞFPC þ ðmass percentage G0 ÞPS
a
where FPC stands for flaxseed protein concentrate, PS stands for potato starch. As listed in Table 2, the calculated G0 was much greater than the experimental data. It seemed that the addition of potato starch into flaxseed protein concentrate weakened the structure of the composite. However, the rheological characteristics of the composites were similar to that of potato starch when heated. It demonstrated that the increase of G0 of composites were attributed to the gelatinization of potato starch. At 95 °C, the composites had G0 values in the range of 0.50–1.60 kPa (Fig. 2a), which was also significantly affected by the starch mass ratio (Table 3). All potato starch/flaxseed protein concentrate exhibited the similar T G0initial , which were little higher than that of potato starch alone (60.3 °C), except for the composites with starch/protein ratio of 1.0, which had the lower T G0initial (60.0 °C). G0MAX increased with the increase of starch mass ratio. The presence of protein increased T G0initial and T G0MAX , which was similar to the presence of skim milk powder in the rice starch as reported by Noisuwan et al. (2008). The results also demonstrated that G0MAX of composites was primarily contributed by the gelatinization of the starch. And when the starch/protein mass ratio increased from 0.2 to 1.0, the dG0MAX of the composites decreased from 16.53o to 11.68o (Table 3). This reduction in dG0MAX indicated that the composites tended to be more solid-like in viscoelastic characteristics probably due to the addition of potato starch. The addition of starch significantly increased the G0 of flaxseed protein concentrate (data not shown), which is similar to the addition of potato starch to acid milk (Oh et al.,
10000
G' (kPa)
1000
100
10 2 °C/min 4 °C/min
1
6 °C/min
0.1 20
30
40
50
60
70
80
90
100
80
90
100
Temperature (°C)
b
1000
G'' (kPa)
100
10
1 2 °C/min 4 °C/min
0.1
6 °C/min
0.01 20
30
40
50
60
70
Temperature (°C) Fig. 6. Rheological characteristics of composites (0.2 starch/protein mass ratio) during three different cooling rates (2, 4 and 6 °C/min). (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
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2007) and addition of corn starch to soy protein concentrate (Li et al., 2007). It may be because during heating, the added starch absorbs water, which could increase the concentration of protein; the protein could form a continuous phase. Then the leached amylose during starch gelatinization will increase the viscosity of composites, which strengthen the network of protein. Finally the starch granules embedded in the dominant protein network, and contribute to the gel strength of composite (Oh et al., 2007). This study also showed that when there is a less amount of protein, there would be higher storage modulus (G0 ) and lower phase degree (d). It is because when the composites were heated, protein interacted with the starch granules; as a consequence protein acted as a barrier to the leaching of amylose molecules from the granules, hence the increase of starch in the mixture resulted in a weaker gel. Bejosano and Corke (1999), Li et al. (2007) and Oh et al. (2007) had the same conclusion, when different starch levels were used in their study. 3.2. Results of ‘‘cooling down” temperature sweep The rheological behaviors of potato starch and composite gels with starch/protein mass ratio of 0.2, 0.3, 0.4, and 0.6, were measured during cooling down from 95 °C to 25 °C. Fig. 3 shows the changes in storage modulus (G0 ), loss modulus (G’’) and phase angle (d) of these gels as a function of temperature. The G0 and G’’ significantly increased with the decrease of temperature for all the gels. The increase in G0 and G’’ upon cooling was also noted for egusi
a
seeds (Uruakpa and Aluko, 2004), composites of whey protein isolate and crosslinked waxy maize starch (Fitzsimons et al., 2008), and rice-based fat (Yang and Xu, 2007). This behavior can be attributed to the cross-linkage formations by disulfide bonds and hydrophobic interactions. The increase in rigidity during cooling is also due to contributions from physical interactions, especially hydrogen bonding (Dickinson, 1997; Chen et al., 2000). The G0 and G’’ curve of pure starch was similar to study of Singh et al. (2008), except for the modulus values, which may be caused by the different potato species (Fig. 3). Comparing with the pure starch, composites gel has greater G0 . It may be because in the cooling process, starch granules still absorb water, making the gel more viscous and a more compact protein network. As the phase angle decreased (Fig. 3c), less energy is lost as heat and the gels become more elastic. The decrease of angle indicates a high elastic component of the composites gels; probably this is associated with interactions between flaxseed protein and potato starch. The low phase angle values were also noted for whey protein concentrate/potato starch gels (El-Garawany and Abd El Salam, 2005). Frequency sweep of the composites at the end of the run at 25 °C are shown in Fig. 4. Double logarithmic plots of G0 and G’’ vs angular frequency resulted in straight lines with positive slopes of small magnitude. The spectra of all the samples showed storage modulus (G0 ) higher than loss modulus (G’’) at all the angular frequency range tested, and were both frequency dependent. G0 and G’’ increased with the increase of starch mass ratio, but still higher
10000
G' (kPa)
1000
100
10 2 °C/min 4 °C/min
1
6 °C/min
0.1
20
30
40
50
60
70
80
90
100
Temperature (°C)
b
1000
G'' (kPa)
100
10
1 2 °C/min 4 °C/min
0.1
6 °C/min
0.01 20
30
40
50
60
70
80
90
100
Temperature (°C) Fig. 7. Rheological characteristics of composites (0.6 starch/protein mass ratio) during different cooling rate (2, 4 and 6 °C/min). (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
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a
10 2°C/ min 4°C/ min
G' (kPa)
6°C/ min
1 20
30
40
50
60
70
80
90
100
Temperature (°C) 1
G'' (kPa)
b
2°C/ min 4°C/ min 6°C/ min
0.1 20
30
40
50
60
70
80
90
100
Temperature (°C) Fig. 8. Rheological characteristics of gelled potato starch during three different cooling rates (2, 4 and 6 °C/min). (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
comparing with pure starch alone. This indicated that the increase of starch mass ratio in the composites caused the increase of the gel strength, which is in agreement with the study of starch/dairy ingredient composites (Yang et al., 2004; Oh et al., 2007; Mounsey and O’Riordan, 2008). The frequency dependence of G0 can be described by the power law equation 0
G0 ¼ K 0 xn
ð1Þ
where K0 is a constant and n0 may be referred to as the frequency exponent, x is the angular frequency. The value of n0 can provide useful information regarding the viscoelastic characteristics of food materials. For an ideal elastic material, the value of n0 is zero and becomes higher with increasing relative contribution from the viscous component (Özkan et al., 2002). The calculated parameters K0 and n0 are shown in Fig. 5. Composites of protein and starch exhibited an elastic behavior, characterized by n0 less than 1 at all test conditions. An increase in mass ratio of starch was accompanied with a decrease in the n0 values. As it is seen in Fig. 5, K0 increased from 0.42 106 to 2 106 and n0 decreased from 0.0931 to 0.0803 when starch/protein mass ratio increased in the range of 0.2–0.6. It is because that gelatinization of starch granules was more dominant factor on the rheological characteristics of composite compared with protein during heating (Li et al., 2007). The firmness of the gel depends on the extent of junction zone formation. In this study, the frequency sweep of the G0 and G’’, for all samples, indicated the lower possibility of rupture at junction zone with the increase of starch amount within the angular frequency range used (0.06283–62.83 rad/s).
3.3. Effect of cooling rate on rheological characteristics During the cooling process (Figs. 6–8), storage modulus (G0 ) and loss modulus (G’’) of different composites exhibited similar trend from 95 °C to 25 °C with different cooling rate. Both composites G0 and G’’ increased faster as the cooling rate decreased, unlike to the pure starch (Fig. 8). The sudden increase of G0 often revealed a gel structure. When the system was maintained at a temperature for a long time, which is to say, at lower cooling rates, there was more time for dynamic equilibration of the gel network to take place. Some gel structure maturation, led to a more structured network. The trend in this experiment is similar to the reported study of pea protein/r-carrageenan/starch gels (Nunes et al., 2006), and insoluble starch (Ahmed et al., 2008), when they were cooled (heated) with different cooling (heating) rates. The frequency sweep results of composites with 0.2 and 0.6 starch mass ratios in different cooling rate at the end of cooling process at 25 °C are shown in Fig. 9. It is shown that constant (K0 ) decreased, while frequency exponents (n0 ) increased, with the increase of cooling rate. This is because that the gel would have weaker structure with the increase of cooling rate, which is in agreement with the results shown in Figs. 6 and 7.
3.4. Statistical analysis Considering all results, it was evident that the mass ratio of potato starch and cooling rate had a significant effect on the rheological characteristic of potato starch/flaxseed protein concentrate composites.
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a
2500000
2000000
0.2 0.6
K'
1500000
1000000
500000
0 2
4
6
Cooling rate (˚C/min)
b
0.2 0.18
0.2 0.6
0.16
n'
0.14 0.12 0.1 0.08 0.06 2
4
6
Cooling rate (˚C/min) Fig. 9. Constants (K’) and frequency exponents (n’) of composites (0.2 and 0.6 starch/protein mass ratio) with three different cooling rate (2, 4 and 6 °C/min). (a) Constants (K0 ) and frequency exponents (n0 ).
4. Conclusions
References
The rheological characteristics of potato starch/flaxseed protein concentrate composites were studied. It was found that G0 and G’’ would increase with the increase of starch mass ratio in the temperature range of 40–95 °C, due to the gelatinization and gelation of potato starch, both during heating or cooling, respectively. The composites exhibited the similar T G0initial and T G0MAX . The result of frequency sweep of the composites at the end of the cooling at 25 °C could be fitted with the power-low model. The study showed that composites exhibited an elastic behavior (G0 G’’, little frequency dependence) at all test frequency range (0.06283–62.83 rad/s). Effect of cooling rate on rheological characteristic was studied in two composites with different starch mass ratio. G0 and G’’ increased with the decrease of cooling rate due to the longer time available for dynamic equilibration of the gel network.
Ahmed, J., Ramaswamy, H.S., Ayad, A., Alli, I., 2008. Thermal and dynamic rheology of insoluble starch from basmati rice. Food Hydrocolloids 22, 278–287. Bejosano, F.P., Corke, H., 1999. Effect of Amaranthus and buckwheat proteins on the rheological properties of maize starch. Food Chemistry 65, 493–501. Bhathena, S.J., Ali, A.A., Mohamed, A.I., Hansen, C.T., Velasquez, M.T., 2002. Differential effects of dietary flaxseed protein and soy protein on plasma triglyceride and uric acid levels in animal models. Journal of Nutritional Biochemistry 13, 684–689. Chen, J.S., Dickinson, E., Langton, M., Hermansson, A.M., 2000. Mechanical properties and microstructure of heat-set whey protein emulsion gels: effect of emulsifiers. Lebensmittel-Wissenschaft und-Technologie 33, 299–307. Chung, M.W.Y., Lei, B., Li-Chan, E.C.Y., 2005. Isolation and structural characterization of the major protein fraction from Norman flaxseed (Linum usitatissimum L.). Food Chemistry 90, 271–279. Dickinson, E., 1997. Enzymic crosslinking as a tool for food colloid rheology control and interfacial stabilization. Trends in Food Science and Technology 8, 334–339. Dickinson, E., 2003. Hydrocolloids at interfaces and the influence on the properties of dispersed systems. Food Hydrocolloids 17, 25–39. El-Garawany, G.A., Abd El Salam, M.H., 2005. Preparation and rheological properties of a dairy dessert based on whey protein/potato starch. Food Chemistry 91, 261–267. Fitzsimons, S.M., Mulvihill, D.M., Morris, E.R., 2008. Co-gels of whey protein isolate with crosslinked waxy maize starch: analysis of solvent partition and phase structure by polymer blending laws. Food Hydrocolloids 22, 468–484. Hagenimana, A., Ding, X.L., Gu, W.Y., 2007. Steady state flow behaviours of extruded blend of rice flour and soy protein concentrate. Food Chemistry 101, 241–247. Khan, G., Penttinen, P., Cabanes, A., Foxworth, A., Chezek, A., Mastropole, K., Yu, B., Smeds, A., Halttunen, T., Good, C., Mäkelä, S., Hilakivi-Clarke, L., 2007. Maternal flaxseed diet during pregnancy or lactation increases female rat offspring’s susceptibility to carcinogen-induced mammary tumorigenesis. Reproductive Toxicology 23, 397–406. Li-Chan, E.C.Y., Ma, C.Y., 2002. Thermal analysis of flaxseed (Linum usitatissimum) proteins by differential scanning calorimetry. Food Chemistry 77, 495–502. Li, J.Y., Yeh, A.I., 2001. Relationships between thermal, rheological characteristics and swelling power for various starches. Journal of Food Engineering 50, 141–148.
Acknowledgments Research support was provided by the Research and Development Fund for University’s Doctoral Discipline of the Chinese Ministry of Education (No. 20050019029), the Science and Technology Support Project of China (No. 2006BAD05A0401), the Science and Technology Research Key Project of Chinese Ministry of Education (No. 105014), and the High Technology Research and Development Project of Chinese Ministry of Science and Technology (No. 2006AA10256-02).
B. Wang et al. / Journal of Food Engineering 91 (2009) 392–401 Li, J.Y., Yeh, A.I., 2003. Effects of starch properties on rheological characteristics of starch/meat complexes. Journal of Food Engineering 57, 287–294. Li, J.Y., Yeh, A.I., Fan, K.L., 2007. Gelation characteristics and morphology of corn starch/soy protein concentrate composites during heating. Journal of Food Engineering 78, 1240–1247. Lim, H.S., Narsimhan, G., 2006. Pasting and rheological behavior of soy proteinbased pudding. Lebensmittel-Wissenschaft und-Technologie 39, 343–349. Madhusudhan, K.T., Singh, N., 1983. Studies on linseed proteins. Journal of Agricultural and Food Chemistry 31, 959–963. Madhusudhan, K.T., Singh, N., 1985. Isolation and characterization of the major fraction (12S) of linseed proteins. Journal of Agricultural and Food Chemistry 33, 673–677. Marcone, M.F., Kakuda, Y., Yada, R.Y., 1998. Salt-soluble seed globulins of various dicotyledonous and monocotyledonous plants I. Isolation/purification and characterization. Food Chemistry 62, 27–47. Mounsey, J.S., O’Riordan, E.D., 2008. Influence of pre-gelatinised maize starch on the rheology, microstructure and processing of imitation cheese. Journal of Food Engineering 84, 57–64. Noisuwan, A., Bronlund, J., Wilkinson, B., Hemar, Y., 2008. Effect of milk protein products on the rheological and thermal (DSC) properties of normal rice starch and waxy rice starch. Food Hydrocolloids 22, 174–183. Nunes, M.C., Raymundo, A., Sousa, I., 2006. Rheological behaviour and microstructure of pea protein/r-carrageenan/starch gels with different setting conditions. Food Hydrocolloids 20, 106–113. Oh, H.E., Anema, S., Wong, G.M., Pinder, D.N., Hemar, Y., 2007. Effect of potato starch addition on the acid gelation of milk. International Dairy Journal 17, 808–815. Oomah, B.D., Mazza, G., 2000. Bioactive components of flaxseed: occurrence and health benefits. In: Shahidi, F., Ho, C.T. (Eds.), Phytochemicals and phytopharmaceuticals. AOCS press, Champaign, pp. 105–120. Özkan, N., Xin, H., Chen, X.D., 2002. Applications of a depth sensing indentation hardness test to evaluate the mechanical properties of food materials. Journal of Food Science 65, 1814–1820. Rosell, C.M., Foegeding, A., 2007. Interaction of hydroxypropylmethylcellulose with gluten proteins: small deformation properties during thermal treatment. Food Hydrocolloids 21, 1092–1100. Singh, N., Isono, N., Srichuwong, S., Noda, T., Nishnari, K., 2008. Structural, thermal and viscoelastic properties of potato starches. Food Hydrocolloids 22, 979–988.
401
Singh, H., Tamehana, M., Hemar, Y., Munro, P.A., 2003. Interfacial compositions, microstructures and properties of oil-in-water emulsions formed with mixtures of milk proteins and r-carrageenan: 1 Sodium caseinate. Food Hydrocolloids 17, 539–548. Song, Y.H., Zheng, Q., 2007. Dynamic rheological properties of wheat flour dough and proteins. Trends in Food Science and Technology 18, 132–138. Steffe, J.F., 1992. Chapter 1: Introduction to Rheology. In: Steffe, James F. (Ed.), Rheological Methods in Food Process Engineering. Freeman Press, Champaign, pp. 1–2. Uruakpa, F.O., Aluko, R.E., 2004. Heat-induced gelation of whole egusi (Colocynthis citrullus L.) seeds. Food Chemistry 87, 349–354. Van Ness, H.C., Abbott, M.M., 1982. Classical Thermodynamics of Nonelectrolyte Solutions with Applications to Phase Equilibria. McGraw-Hill, New York. pp. 184–261. Vliet, T.V., Martin, A.H., Bos, M.A., 2002. Gelation and interfacial behaviour of vegetable proteins. Current Option in Colloid and Interface Science 7, 462– 468. Wang, B., Li, D., Wang, L.J., Huang, Z.G., Zhang, L., Chen, X.D., Mao, Z.H., 2007. Effect of moisture content on the physical properties of fibered flaxseed. International Journal of Food Engineering 3, 1. Wang, Y., Li, D., Wang, L.J., Chiu, Y.L., Chen, X.D., Mao, Z.H., Song, C.F., 2008. Optimization of extrusion of flaxseeds for in vitro protein digestibility analysis using response surface methodology. Journal of Food Engineering 85, 59–64. Wu, M., Li, D., Wang, L.J., Zhou, Y.G., Brooks, M.S., Chen, X.D., Mao, Z.H., 2008. Extrusion detoxification technique on flaxseed by uniform design optimization. Separation and Purification Technology 61, 51–59. Yang, H., Irudayaraj, J., Otgonchimeg, S., Walsh, M., 2004. Rheological study of starch and dairy ingredient-based food systems. Food Chemistry 86, 571–578. Yang, Y.L., Xu, S.Y., 2007. Roles of components of rice-based fat substitute in gelation. Food Research International 40, 1155–1160. Youle, R.J., Huang, H.C., 1981. Occurrence of low molecular weight and high cysteine containing albumin storage proteins in oilseeds of diverse species. American Journal of Botany 68, 44–48. Zhang, Z.S., Li, D., Wang, L.J., Özkan, N., Chen, X.D., Mao, Z.H., Yang, H.Z., 2007. Optimization of ethanol–water extraction of lignans from flaxseed. Separation and Purification Technology 57, 17–24.
Contents lists available at ScienceDirect
Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng
Effects of potato starch addition and cooling rate on rheological characteristics of flaxseed protein concentrate Bo Wang a, Li-Jun Wang b, Dong Li a,*, Bhesh Bhandari c, Wen-Fu Wu d,*, John Shi e, Xiao Dong Chen a,f, Zhi-Huai Mao a a
College of Engineering, China Agricultural University, P.O. Box 50, 17 Qinghua Donglu, Beijing 100083, China College of Food Science and Nutritional Engineering, China Agricultural University, Beijing, China c School of Land, Crop and Food Sciences, The University of Queensland, Brisbane QLD, Australia d School of Biological and Agricultural Engineering, Jilin University, 142 Renmin Street, Changchun 130025, China e Guelph Food Research Center, Agriculture and Agri-Food Canada, Ontario, Canada f Department of Chemical Engineering, Monash University, Victoria, Australia b
a r t i c l e
i n f o
Article history: Received 18 February 2008 Received in revised form 18 September 2008 Accepted 24 September 2008 Available online 7 October 2008 Keywords: Rheological characteristics Flaxseed protein concentrate Potato starch
a b s t r a c t Rheological characteristics of potato starch/flaxseed protein concentrate composites were investigated using a rheometer. Effects of starch/protein mass ratio (0.2–1.0) and different cooling rate (2 °C/min, 4 °C/min and 6 °C/min) on rheological behavior of composites were studied. The study showed that G’ and G’’ increased with increase of starch mass ratio in the temperature range of 40–95 °C, in both heating and cooling process. The composites exhibited similar T G0initial and T G0MAX , higher than those of potato starch alone at 60.3 °C. The result of frequency sweep of the composites at the end of the cooling at 25 °C exhibited an elastic behavior at all test frequency ranges (0.06283–62.83 rad/s). Study of cooling rate on rheological characteristic of composites exhibited an increase in the G’ and G’’ values with decrease of cooling rate, probably because of gel network having a stronger structure with more time for dynamic equilibration. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Flaxseed, also called linseed, is a small flat oval seed of flax (Linum suitatissimum). Flaxseed is abundant in many nutrients, such as polyunsaturated fatty acid, protein, and lignans (Wang et al., 2007). Flaxseed has been shown to reduce total cholesterol and low-density lipoprotein cholesterol in some studies in humans and animals (Bhathena et al., 2002). Many researchers have investigated the nutritional elements of the flaxseed (Zhang et al., 2007; Wang et al., 2008; Wu et al., 2008). The current market for edible flaxseed is limited to the whole intact flaxseed and its oil because x-3 polyunsaturated fatty acids and phytoestrogens are proposed to promote health (Khan et al., 2007), while the defatted meal, is primarily used as livestock feed. However, with the increasing demand for vegetable sources of proteins, there is a potential for utilizing flaxseed proteins present in defatted meal as a food source. The amino acid composition of flaxseed is viewed as one of the most nutritious of plant proteins. The studies about flaxseed protein concentrate have shown that there are two proteins in the flaxseed: a salt-soluble fraction with high molecular weight (11– 12 S) and a water-soluble with low molecular weight (1.6–2 S) (Madhusudhan and Singh, 1983, 1985a; Marcone et al., 1998a; * Corresponding authors. Tel./fax: +86 10 62737351 (D. Li). E-mail addresses: [email protected] (D. Li), [email protected] (W.-F. Wu). 0260-8774/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2008.09.032
Youle and Huang, 1981). The major protein isolated from flaxseed was shown to have high contents of the amino acids arginine, glutamate/glutamine, and aspartate/asparagines (Chung et al., 2005). Flaxseed proteins are proposed to have an effect on various diseases, including coronary heart disease, kidney disease and cancer (Oomah and Mazza, 2000). Starches are known gelling agents with their water-holding and thickening properties and thereby contribute to the structural and textural properties. Dickinson (2003) and Singh et al. (2003) have described the interfaces properties of the hydrocolloids. Various starches are being added in protein to form gels for reducing cost and improving texture. Associated interactions typically occur by electrostatic attraction between negatively charged polysaccharides and positively charged proteins, often result in formation of insoluble complexes (Fitzsimons et al., 2008). So, starch has been recognized as filler to increase the firmness of products (Li and Yeh, 2003). Rheology, which was originally defined by Bingham in 1930, is now well established as the science of the deformation and flow of matter: it is the study of the manner in which materials respond to applied stress or strain (Steffe, 1992). In food engineering, rheology helps to understand how food structure responds to applied force and deformation. Hence, from a practical point of view, the rheological characteristics of foods are very important, particularly in relation to structure, sensory evaluation, quality control,
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Nomenclature G0 G00 d T G0initial G0MAX
storage modulus (Pa) loss modulus (Pa) phase angle (°) the temperature when G’ started swelling (°C) the storage modulus when G’ became maximums (Pa)
T G0MAX dG0MAX K0
x n0
processing design and new product development (Yang et al., 2004). Knowledge of specific interactions and synergistic effects is highly desirable for creating new textures and enable ingredient substitutions and numerous studies have been conducted on the rheological characteristics of edible composites, for example, soy
Table 1 Components of the composite dispersions at different starch mass ratio. Starch/protein mass ratio
Starch percentage in dispersion (%)
Protein percentage in dispersion (%)
Water percentage in dispersion (%)
FPC 0.2 0.3 0.4 0.6 0.8 1.0 PS
0.00 3.34 4.62 5.72 7.50 8.88 10.00 20.00
20.00 16.66 15.38 14.28 12.50 11.12 10.00 0.00
80.00 80.00 80.00 80.00 80.00 80.00 80.00 80.00
protein-based pudding (Lim and Narsimhan, 2006), blend of rice flour and soy protein (Hagenimana et al., 2007) and composites of wheat dough and protein (Song and Zheng, 2007). But to the best of our knowledge, there are very few literatures having been investigated on rheological properties of flaxseed protein and starch composites. To help to the development of new protein products with starch, the objective of this study was to investigate the rheological characteristics of potato starch/flaxseed protein concentrate composite and the effects of cooling rate on its rheological behaviors. 2. Materials and methods 2.1. Materials
FPC stands for flaxseed protein concentrate only, PS stands for potato starch only.
a
the temperature when G’ became maximums (°C) the phase angle when G’ became maximums (°) constant (Pa (s/rad)n) angular frequency (rad/s) frequency exponent (dimensionless)
Potato starch obtained from a commercial source (Aoboxing Biotechnology Ltd., Beijing, China) was used as a starch source. Flaxseed protein concentrate was kindly provided by Hengkang Biotechnology Ltd. (Inner Mongolia Autonomous Region, China).
10 1
G'(kPa)
0.1 0.01 0.001 flaxseed protein concentrate
0.0001
potato starch
0.00001 0.000001 40
b
50
60
70 Temperature (°C)
80
90
100
1 0.1
G'' (kPa)
0.01 0.001 flaxseed protein concentrate potato starch
0.0001 0.00001 40
50
60
70
80
90
100
Temperature (°C) Fig. 1. Temperature sweep for flaxseed concentrate and potato starch. (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
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a
10
G' (kPa)
1 0.2 0.3 0.4 0.6
0.1
0.8 1.0 0.01 30
40
50
60
70
80
90
100
Temperature (°C) 1
b
G'' (kPa)
0.1
0.2 0.3 0.4
0.01
0.6 0.8 1.0 0.001 30
40
50
60
70
80
90
100
Temperature (°C) Fig. 2. Rheological characteristics of potato starch/flaxseed protein concentrate composites at different ratios (labeled on the right side of curves) during heating with a heating rate of 2 °C/min. (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
Table 2 Experimental and Calculated G’ (Pa) of flaxseed protein concentrate, potato starch and starch/protein composites at 40 °C. G’ (Pa) at 40 °C
Experimental data Calculated data
Starch/protein mass ratio FPC
0.2
0.3
0.4
0.6
0.8
1.0
PS
863.5 ± 97.1a 863.5 ± 97.1a
149.2 ± 23.0a 719.6 ± 80.9b
111.6 ± 22.0a 664.2 ± 74.7b
75.4 ± 13.2a 616.8 ± 69.3b
35.0 ± 4.2a 593.7 ± 60.7b
26.4 ± 2.3a 479.7 ± 54.0b
12.0 ± 2.8a 431.2 ± 48.6b
(3.84 ± 0.04) 103a (3.84 ± 0.04) 103a
FPC stands for flaxseed protein concentrate only; PS stands for potato starch only. The parameters with different letters in a column are significantly different (P < 0.05) as determined by ANOVA.
The flaxseed protein concentrate has following characteristics: protein content 71.98% (Kjeldhal methods), moisture content 6.22% (105 °C for 24 h), ash 4.36% (550 °C for 12 h), 5.74% fat (Soxhlet extraction) and 11.7% carbohydrate. Flaxseed protein concentrate and potato starch were stored in the sealed polyethylene bags at room temperature until used. The moisture content of these raw materials was kept below 10%. 2.2. Preparation of potato starch/flaxseed protein concentrate composites Potato starch and flaxseed protein concentrate were mixed at ratios of 0, 0.2, 0.3, 0.4, 0.6, 0.8 and 1.0 (solid basis). Distilled water was added into the uniform mass to yield a water content of 80%. The components of different dispersions were shown as Table 1. The composites were stirred at a speed of 150 rpm with a mixer
Table 3 Rheological characteristics of flaxseed protein concentrate, potato starch and starch/ protein composites in heating process. Starch/ protein mass ratio
T G0initial (°C)
T G0MAX (°C)
G0MAX (kPa)
dG0MAX (°)
G’ (kPa) at 95 °C
FPC 0.2 0.3 0.4 0.6 0.8 1.0 PS
– 62.0 ± 0.5a 61.0 ± 0.4b 61.2 ± 0.4b 60.3 ± 0.4c 61.7 ± 0.8a 60.0 ± 0.3c 60.3 ± 0.2c
– 77.3 ± 0.3a 78.0 ± 0.4b 78.0 ± 0.6b 78.0 ± 0.3b 77.0 ± 0.5a 76.6 ± 0.5c 70.9 ± 0.4d
– 0.65 ± 0.09a 0.94 ± 0.04b 1.17 ± 0.07c 1.76 ± 0.06d 2.50 ± 0.07e 2.94 ± 0.06f 2.99 ± 0.07f
(13.35 ± 0.21) 16.53 ± 0.32a 16.02 ± 0.16b 15.11 ± 0.36c 12.82 ± 0.33c 13.26 ± 0.46d 11.68 ± 0.42e 15.14 ± 0.44f
– 0.50 ± 0.07a 0.50 ± 0.07a 0.66 ± 0.06b 0.96 ± 0.09c 1.21 ± 0.07d 1.60 ± 0.08e 1.38 ± 0.08e
FPC stands for flaxseed protein concentrate only; PS stands for potato starch only. The parameters with different letters in a column are significantly different (P < 0.05) as determined by ANOVA. The numbers in parentheses were determined at 40 °C.
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(JJ-6, Medical Instrument Ltd., Jintan, China) for 1 h at room temperature.
(A) A ‘‘heating” temperature sweep test was carried out by heating the composites from 25 °C to 95 °C at 2 °C /min and a frequency of 1 Hz. (B) The composites were put into stainless steel cylinder molds with a diameter of 50 mm and a height of 50 mm. The molds were then heated up to 95 °C in a thermally controlled water bath and kept at this temperature for 20 min to make the gel form. Then the gel was immediately transferred to the rheometer for a ‘‘cooling down” temperature sweep tests. The gel was cooled down from 95 °C to 25 °C at 2 °C/min and a frequency of 1 Hz. A frequency sweep was carried out at 25 °C to determine the viscoelastic characteristics of the gel at last.
2.3. Rheological experiments The rheological characteristics of potato starch/flaxseed protein concentrate composites were measured in five replications using a controlled strain rheometer (AR2000ex, TA Instrument, Crawley, UK), operated with a parallel-plate geometry of 40 mm diameter and a gap of 1 mm. The linear viscoelastic region was found below a strain of 4% in all samples. Thus a strain of 0.5% was used to assure the tests being in the linear viscoelastic region. The different rheological measurements were defined as follows:
a
10000 0.2
1000
G' (kPa)
0.3 0.4
100
0.6 PS
10
1
0.1 20
30
40
50
60
70
80
90
100
Temperature (°C)
b
1000 0.2 0.3
G'' (kPa)
100
0.4 0.6
10
PS
1 0.1 0.01 20
30
40
50
60
70
80
90
100
Temperature (°C)
c
16
δ
12
0.2 0.3 0.4 0.6 PS
8
4 20
40
60
80
100
Temperature (°C) Fig. 3. Rheological characteristics of potato starch/flaxseed protein concentrate composites at different ratios (labeled on the right side of the curves) during cooling with cooling rate of 2 °C/min. (a) Storage modulus (G’), (b) loss modulus (G’’) and (c) phase angle (d).
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a
10000 0.2 0.3
G' (kPa)
1000
0.4 0.6 PS
100
10
1 0.01
0.1
1
10
100
10
100
log ω (rad/s)
b
1000.0
0.2 0.3
G'' (kPa)
100.0
0.4 0.6 PS
10.0
1.0
0.1 0.01
0.1
1
log ω (rad/s) Fig. 4. Frequency sweep of the potato starch/flaxseed protein concentrate composites at 25 °C (the starch/protein ratios are labeled on the right side of the curves). (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
Parameters including storage modulus (G’), loss modulus (G’’) and phase angle (d) were obtained using the TA Rheological Advantage Data Analysis software V 5.4.7 (TA Instrument Ltd., Crawley, UK). Silicone oil was coated on the outer edge of sample to minimize the water loss during the measurements.
protein concentrate was decreased to 0.64 kPa when the composite was heated to 95 oC, possibly due to the increased kinetic energy of molecules. The reduction in G0 was similar to the pre-treated soy protein isolate (Vliet et al., 2002), gluten protein (Rosell and
a
3000000
2000000
K'
(C) The heated composites at starch/protein mass ratio of 0.2 and 0.6 were cooled down from 95 °C to 25 °C at 2 °C/min, 4 °C/min and 6 °C/min with a frequency of 1 Hz, and a frequency sweep was carried out at 25 °C at last to investigate the effect of cooling rate on viscoelastic characteristics of mix gel.
1000000
2.4. Data analysis 0
The averages of five replications for the rheological parameters of the samples were used and the relative standard deviation of the average parameter was shown in tables and figures. The analysis of variance (ANOVA) was carried out based on the experimental data by using the SAS statistical package (SAS Institute, Cary, NC).
0.2
0.3
0.4
0.6
starch/protein mass ratio 0.12
b
0.1
n'
0.08
3. Results and discussion 3.1. Results of ‘‘heating” temperature sweep
0.06 0.04 0.02
Since there was no significant change at temperatures of lower than 40 °C, the data were recorded from 40 °C to 95 °C. Flaxseed protein concentrate exhibited high G’ (0.86 kPa) at 40 °C during ‘‘heating” temperature sweep (Fig. 1a). G0 of flaxseed
0.2
0.3
0.4
0.6
starch/protein mass ratio Fig. 5. Constants (K’) and frequency exponents (n’) of composites with different starch:protein mass ratios. (a) constants (K0 ) and frequency exponents (n0 ).
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Foegeding, 2007), and soy protein concentrate (Li et al., 2007). It is shown that there was no denaturation or gelation of flaxseed protein concentrate. It is agreed with the earlier thermal study by LiChan and Ma (2002), which has shown that flaxseed protein would not denature below 100 °C. As shown in Fig. 1a, non-gelatinized potato starch suspension exhibited very low G0 (3.84 103 Pa) at temperatures lower than 60 °C. When temperature reached 60.3 °C, which was defined as T G0initial , G0 of potato starch increased significantly because of starch granules swelled. After swelling, starch granule absorbs heat for gelatinization, which resulted in the deformation, disruption, and melting of starch granules. There existed a maximum G0 (G0MAX ) of 2.99 kPa at 70.9 °C due to the deformation of starch granules (Li and Yeh, 2001). The trend of change of G’’ was similar to that of G0 for both flaxseed protein concentrate and potato starch (Fig. 1b). The value of G’’ was much lower than G0 which indicated that the samples exhibited obvious elastic behavior. Fig. 2 depicts the rheological characteristics of composite when heated, which is quite similar to that of potato starch. At 40 oC, both G0 and G’’ of all the composites were between those of flaxseed protein concentrate and potato starch. Increasing the starch reduced the G0 and G’’ of the composite. According the work before (Van Ness and Abbott, 1982), if the system as an ideal mixture, G0 of the composite was calculated as
G0 of composites ¼ ðmass percentage G0 ÞFPC þ ðmass percentage G0 ÞPS
a
where FPC stands for flaxseed protein concentrate, PS stands for potato starch. As listed in Table 2, the calculated G0 was much greater than the experimental data. It seemed that the addition of potato starch into flaxseed protein concentrate weakened the structure of the composite. However, the rheological characteristics of the composites were similar to that of potato starch when heated. It demonstrated that the increase of G0 of composites were attributed to the gelatinization of potato starch. At 95 °C, the composites had G0 values in the range of 0.50–1.60 kPa (Fig. 2a), which was also significantly affected by the starch mass ratio (Table 3). All potato starch/flaxseed protein concentrate exhibited the similar T G0initial , which were little higher than that of potato starch alone (60.3 °C), except for the composites with starch/protein ratio of 1.0, which had the lower T G0initial (60.0 °C). G0MAX increased with the increase of starch mass ratio. The presence of protein increased T G0initial and T G0MAX , which was similar to the presence of skim milk powder in the rice starch as reported by Noisuwan et al. (2008). The results also demonstrated that G0MAX of composites was primarily contributed by the gelatinization of the starch. And when the starch/protein mass ratio increased from 0.2 to 1.0, the dG0MAX of the composites decreased from 16.53o to 11.68o (Table 3). This reduction in dG0MAX indicated that the composites tended to be more solid-like in viscoelastic characteristics probably due to the addition of potato starch. The addition of starch significantly increased the G0 of flaxseed protein concentrate (data not shown), which is similar to the addition of potato starch to acid milk (Oh et al.,
10000
G' (kPa)
1000
100
10 2 °C/min 4 °C/min
1
6 °C/min
0.1 20
30
40
50
60
70
80
90
100
80
90
100
Temperature (°C)
b
1000
G'' (kPa)
100
10
1 2 °C/min 4 °C/min
0.1
6 °C/min
0.01 20
30
40
50
60
70
Temperature (°C) Fig. 6. Rheological characteristics of composites (0.2 starch/protein mass ratio) during three different cooling rates (2, 4 and 6 °C/min). (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
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2007) and addition of corn starch to soy protein concentrate (Li et al., 2007). It may be because during heating, the added starch absorbs water, which could increase the concentration of protein; the protein could form a continuous phase. Then the leached amylose during starch gelatinization will increase the viscosity of composites, which strengthen the network of protein. Finally the starch granules embedded in the dominant protein network, and contribute to the gel strength of composite (Oh et al., 2007). This study also showed that when there is a less amount of protein, there would be higher storage modulus (G0 ) and lower phase degree (d). It is because when the composites were heated, protein interacted with the starch granules; as a consequence protein acted as a barrier to the leaching of amylose molecules from the granules, hence the increase of starch in the mixture resulted in a weaker gel. Bejosano and Corke (1999), Li et al. (2007) and Oh et al. (2007) had the same conclusion, when different starch levels were used in their study. 3.2. Results of ‘‘cooling down” temperature sweep The rheological behaviors of potato starch and composite gels with starch/protein mass ratio of 0.2, 0.3, 0.4, and 0.6, were measured during cooling down from 95 °C to 25 °C. Fig. 3 shows the changes in storage modulus (G0 ), loss modulus (G’’) and phase angle (d) of these gels as a function of temperature. The G0 and G’’ significantly increased with the decrease of temperature for all the gels. The increase in G0 and G’’ upon cooling was also noted for egusi
a
seeds (Uruakpa and Aluko, 2004), composites of whey protein isolate and crosslinked waxy maize starch (Fitzsimons et al., 2008), and rice-based fat (Yang and Xu, 2007). This behavior can be attributed to the cross-linkage formations by disulfide bonds and hydrophobic interactions. The increase in rigidity during cooling is also due to contributions from physical interactions, especially hydrogen bonding (Dickinson, 1997; Chen et al., 2000). The G0 and G’’ curve of pure starch was similar to study of Singh et al. (2008), except for the modulus values, which may be caused by the different potato species (Fig. 3). Comparing with the pure starch, composites gel has greater G0 . It may be because in the cooling process, starch granules still absorb water, making the gel more viscous and a more compact protein network. As the phase angle decreased (Fig. 3c), less energy is lost as heat and the gels become more elastic. The decrease of angle indicates a high elastic component of the composites gels; probably this is associated with interactions between flaxseed protein and potato starch. The low phase angle values were also noted for whey protein concentrate/potato starch gels (El-Garawany and Abd El Salam, 2005). Frequency sweep of the composites at the end of the run at 25 °C are shown in Fig. 4. Double logarithmic plots of G0 and G’’ vs angular frequency resulted in straight lines with positive slopes of small magnitude. The spectra of all the samples showed storage modulus (G0 ) higher than loss modulus (G’’) at all the angular frequency range tested, and were both frequency dependent. G0 and G’’ increased with the increase of starch mass ratio, but still higher
10000
G' (kPa)
1000
100
10 2 °C/min 4 °C/min
1
6 °C/min
0.1
20
30
40
50
60
70
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90
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Temperature (°C)
b
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10
1 2 °C/min 4 °C/min
0.1
6 °C/min
0.01 20
30
40
50
60
70
80
90
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Temperature (°C) Fig. 7. Rheological characteristics of composites (0.6 starch/protein mass ratio) during different cooling rate (2, 4 and 6 °C/min). (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
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a
10 2°C/ min 4°C/ min
G' (kPa)
6°C/ min
1 20
30
40
50
60
70
80
90
100
Temperature (°C) 1
G'' (kPa)
b
2°C/ min 4°C/ min 6°C/ min
0.1 20
30
40
50
60
70
80
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Temperature (°C) Fig. 8. Rheological characteristics of gelled potato starch during three different cooling rates (2, 4 and 6 °C/min). (a) Storage modulus (G0 ) and (b) loss modulus (G’’).
comparing with pure starch alone. This indicated that the increase of starch mass ratio in the composites caused the increase of the gel strength, which is in agreement with the study of starch/dairy ingredient composites (Yang et al., 2004; Oh et al., 2007; Mounsey and O’Riordan, 2008). The frequency dependence of G0 can be described by the power law equation 0
G0 ¼ K 0 xn
ð1Þ
where K0 is a constant and n0 may be referred to as the frequency exponent, x is the angular frequency. The value of n0 can provide useful information regarding the viscoelastic characteristics of food materials. For an ideal elastic material, the value of n0 is zero and becomes higher with increasing relative contribution from the viscous component (Özkan et al., 2002). The calculated parameters K0 and n0 are shown in Fig. 5. Composites of protein and starch exhibited an elastic behavior, characterized by n0 less than 1 at all test conditions. An increase in mass ratio of starch was accompanied with a decrease in the n0 values. As it is seen in Fig. 5, K0 increased from 0.42 106 to 2 106 and n0 decreased from 0.0931 to 0.0803 when starch/protein mass ratio increased in the range of 0.2–0.6. It is because that gelatinization of starch granules was more dominant factor on the rheological characteristics of composite compared with protein during heating (Li et al., 2007). The firmness of the gel depends on the extent of junction zone formation. In this study, the frequency sweep of the G0 and G’’, for all samples, indicated the lower possibility of rupture at junction zone with the increase of starch amount within the angular frequency range used (0.06283–62.83 rad/s).
3.3. Effect of cooling rate on rheological characteristics During the cooling process (Figs. 6–8), storage modulus (G0 ) and loss modulus (G’’) of different composites exhibited similar trend from 95 °C to 25 °C with different cooling rate. Both composites G0 and G’’ increased faster as the cooling rate decreased, unlike to the pure starch (Fig. 8). The sudden increase of G0 often revealed a gel structure. When the system was maintained at a temperature for a long time, which is to say, at lower cooling rates, there was more time for dynamic equilibration of the gel network to take place. Some gel structure maturation, led to a more structured network. The trend in this experiment is similar to the reported study of pea protein/r-carrageenan/starch gels (Nunes et al., 2006), and insoluble starch (Ahmed et al., 2008), when they were cooled (heated) with different cooling (heating) rates. The frequency sweep results of composites with 0.2 and 0.6 starch mass ratios in different cooling rate at the end of cooling process at 25 °C are shown in Fig. 9. It is shown that constant (K0 ) decreased, while frequency exponents (n0 ) increased, with the increase of cooling rate. This is because that the gel would have weaker structure with the increase of cooling rate, which is in agreement with the results shown in Figs. 6 and 7.
3.4. Statistical analysis Considering all results, it was evident that the mass ratio of potato starch and cooling rate had a significant effect on the rheological characteristic of potato starch/flaxseed protein concentrate composites.
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a
2500000
2000000
0.2 0.6
K'
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0 2
4
6
Cooling rate (˚C/min)
b
0.2 0.18
0.2 0.6
0.16
n'
0.14 0.12 0.1 0.08 0.06 2
4
6
Cooling rate (˚C/min) Fig. 9. Constants (K’) and frequency exponents (n’) of composites (0.2 and 0.6 starch/protein mass ratio) with three different cooling rate (2, 4 and 6 °C/min). (a) Constants (K0 ) and frequency exponents (n0 ).
4. Conclusions
References
The rheological characteristics of potato starch/flaxseed protein concentrate composites were studied. It was found that G0 and G’’ would increase with the increase of starch mass ratio in the temperature range of 40–95 °C, due to the gelatinization and gelation of potato starch, both during heating or cooling, respectively. The composites exhibited the similar T G0initial and T G0MAX . The result of frequency sweep of the composites at the end of the cooling at 25 °C could be fitted with the power-low model. The study showed that composites exhibited an elastic behavior (G0 G’’, little frequency dependence) at all test frequency range (0.06283–62.83 rad/s). Effect of cooling rate on rheological characteristic was studied in two composites with different starch mass ratio. G0 and G’’ increased with the decrease of cooling rate due to the longer time available for dynamic equilibration of the gel network.
Ahmed, J., Ramaswamy, H.S., Ayad, A., Alli, I., 2008. Thermal and dynamic rheology of insoluble starch from basmati rice. Food Hydrocolloids 22, 278–287. Bejosano, F.P., Corke, H., 1999. Effect of Amaranthus and buckwheat proteins on the rheological properties of maize starch. Food Chemistry 65, 493–501. Bhathena, S.J., Ali, A.A., Mohamed, A.I., Hansen, C.T., Velasquez, M.T., 2002. Differential effects of dietary flaxseed protein and soy protein on plasma triglyceride and uric acid levels in animal models. Journal of Nutritional Biochemistry 13, 684–689. Chen, J.S., Dickinson, E., Langton, M., Hermansson, A.M., 2000. Mechanical properties and microstructure of heat-set whey protein emulsion gels: effect of emulsifiers. Lebensmittel-Wissenschaft und-Technologie 33, 299–307. Chung, M.W.Y., Lei, B., Li-Chan, E.C.Y., 2005. Isolation and structural characterization of the major protein fraction from Norman flaxseed (Linum usitatissimum L.). Food Chemistry 90, 271–279. Dickinson, E., 1997. Enzymic crosslinking as a tool for food colloid rheology control and interfacial stabilization. Trends in Food Science and Technology 8, 334–339. Dickinson, E., 2003. Hydrocolloids at interfaces and the influence on the properties of dispersed systems. Food Hydrocolloids 17, 25–39. El-Garawany, G.A., Abd El Salam, M.H., 2005. Preparation and rheological properties of a dairy dessert based on whey protein/potato starch. Food Chemistry 91, 261–267. Fitzsimons, S.M., Mulvihill, D.M., Morris, E.R., 2008. Co-gels of whey protein isolate with crosslinked waxy maize starch: analysis of solvent partition and phase structure by polymer blending laws. Food Hydrocolloids 22, 468–484. Hagenimana, A., Ding, X.L., Gu, W.Y., 2007. Steady state flow behaviours of extruded blend of rice flour and soy protein concentrate. Food Chemistry 101, 241–247. Khan, G., Penttinen, P., Cabanes, A., Foxworth, A., Chezek, A., Mastropole, K., Yu, B., Smeds, A., Halttunen, T., Good, C., Mäkelä, S., Hilakivi-Clarke, L., 2007. Maternal flaxseed diet during pregnancy or lactation increases female rat offspring’s susceptibility to carcinogen-induced mammary tumorigenesis. Reproductive Toxicology 23, 397–406. Li-Chan, E.C.Y., Ma, C.Y., 2002. Thermal analysis of flaxseed (Linum usitatissimum) proteins by differential scanning calorimetry. Food Chemistry 77, 495–502. Li, J.Y., Yeh, A.I., 2001. Relationships between thermal, rheological characteristics and swelling power for various starches. Journal of Food Engineering 50, 141–148.
Acknowledgments Research support was provided by the Research and Development Fund for University’s Doctoral Discipline of the Chinese Ministry of Education (No. 20050019029), the Science and Technology Support Project of China (No. 2006BAD05A0401), the Science and Technology Research Key Project of Chinese Ministry of Education (No. 105014), and the High Technology Research and Development Project of Chinese Ministry of Science and Technology (No. 2006AA10256-02).
B. Wang et al. / Journal of Food Engineering 91 (2009) 392–401 Li, J.Y., Yeh, A.I., 2003. Effects of starch properties on rheological characteristics of starch/meat complexes. Journal of Food Engineering 57, 287–294. Li, J.Y., Yeh, A.I., Fan, K.L., 2007. Gelation characteristics and morphology of corn starch/soy protein concentrate composites during heating. Journal of Food Engineering 78, 1240–1247. Lim, H.S., Narsimhan, G., 2006. Pasting and rheological behavior of soy proteinbased pudding. Lebensmittel-Wissenschaft und-Technologie 39, 343–349. Madhusudhan, K.T., Singh, N., 1983. Studies on linseed proteins. Journal of Agricultural and Food Chemistry 31, 959–963. Madhusudhan, K.T., Singh, N., 1985. Isolation and characterization of the major fraction (12S) of linseed proteins. Journal of Agricultural and Food Chemistry 33, 673–677. Marcone, M.F., Kakuda, Y., Yada, R.Y., 1998. Salt-soluble seed globulins of various dicotyledonous and monocotyledonous plants I. Isolation/purification and characterization. Food Chemistry 62, 27–47. Mounsey, J.S., O’Riordan, E.D., 2008. Influence of pre-gelatinised maize starch on the rheology, microstructure and processing of imitation cheese. Journal of Food Engineering 84, 57–64. Noisuwan, A., Bronlund, J., Wilkinson, B., Hemar, Y., 2008. Effect of milk protein products on the rheological and thermal (DSC) properties of normal rice starch and waxy rice starch. Food Hydrocolloids 22, 174–183. Nunes, M.C., Raymundo, A., Sousa, I., 2006. Rheological behaviour and microstructure of pea protein/r-carrageenan/starch gels with different setting conditions. Food Hydrocolloids 20, 106–113. Oh, H.E., Anema, S., Wong, G.M., Pinder, D.N., Hemar, Y., 2007. Effect of potato starch addition on the acid gelation of milk. International Dairy Journal 17, 808–815. Oomah, B.D., Mazza, G., 2000. Bioactive components of flaxseed: occurrence and health benefits. In: Shahidi, F., Ho, C.T. (Eds.), Phytochemicals and phytopharmaceuticals. AOCS press, Champaign, pp. 105–120. Özkan, N., Xin, H., Chen, X.D., 2002. Applications of a depth sensing indentation hardness test to evaluate the mechanical properties of food materials. Journal of Food Science 65, 1814–1820. Rosell, C.M., Foegeding, A., 2007. Interaction of hydroxypropylmethylcellulose with gluten proteins: small deformation properties during thermal treatment. Food Hydrocolloids 21, 1092–1100. Singh, N., Isono, N., Srichuwong, S., Noda, T., Nishnari, K., 2008. Structural, thermal and viscoelastic properties of potato starches. Food Hydrocolloids 22, 979–988.
401
Singh, H., Tamehana, M., Hemar, Y., Munro, P.A., 2003. Interfacial compositions, microstructures and properties of oil-in-water emulsions formed with mixtures of milk proteins and r-carrageenan: 1 Sodium caseinate. Food Hydrocolloids 17, 539–548. Song, Y.H., Zheng, Q., 2007. Dynamic rheological properties of wheat flour dough and proteins. Trends in Food Science and Technology 18, 132–138. Steffe, J.F., 1992. Chapter 1: Introduction to Rheology. In: Steffe, James F. (Ed.), Rheological Methods in Food Process Engineering. Freeman Press, Champaign, pp. 1–2. Uruakpa, F.O., Aluko, R.E., 2004. Heat-induced gelation of whole egusi (Colocynthis citrullus L.) seeds. Food Chemistry 87, 349–354. Van Ness, H.C., Abbott, M.M., 1982. Classical Thermodynamics of Nonelectrolyte Solutions with Applications to Phase Equilibria. McGraw-Hill, New York. pp. 184–261. Vliet, T.V., Martin, A.H., Bos, M.A., 2002. Gelation and interfacial behaviour of vegetable proteins. Current Option in Colloid and Interface Science 7, 462– 468. Wang, B., Li, D., Wang, L.J., Huang, Z.G., Zhang, L., Chen, X.D., Mao, Z.H., 2007. Effect of moisture content on the physical properties of fibered flaxseed. International Journal of Food Engineering 3, 1. Wang, Y., Li, D., Wang, L.J., Chiu, Y.L., Chen, X.D., Mao, Z.H., Song, C.F., 2008. Optimization of extrusion of flaxseeds for in vitro protein digestibility analysis using response surface methodology. Journal of Food Engineering 85, 59–64. Wu, M., Li, D., Wang, L.J., Zhou, Y.G., Brooks, M.S., Chen, X.D., Mao, Z.H., 2008. Extrusion detoxification technique on flaxseed by uniform design optimization. Separation and Purification Technology 61, 51–59. Yang, H., Irudayaraj, J., Otgonchimeg, S., Walsh, M., 2004. Rheological study of starch and dairy ingredient-based food systems. Food Chemistry 86, 571–578. Yang, Y.L., Xu, S.Y., 2007. Roles of components of rice-based fat substitute in gelation. Food Research International 40, 1155–1160. Youle, R.J., Huang, H.C., 1981. Occurrence of low molecular weight and high cysteine containing albumin storage proteins in oilseeds of diverse species. American Journal of Botany 68, 44–48. Zhang, Z.S., Li, D., Wang, L.J., Özkan, N., Chen, X.D., Mao, Z.H., Yang, H.Z., 2007. Optimization of ethanol–water extraction of lignans from flaxseed. Separation and Purification Technology 57, 17–24.