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Influence of water addition methods on water mobility characterization and rheological properties of wheat flour dough
Journal of Cereal Science 89 (2019) 102791
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Influence of water addition methods on water mobility characterization and rheological properties of wheat flour dough
T
Yuling Yanga, Erqi Guana,b, Tingjing Zhanga, Mengmeng Lia, Ke Biana,b,* a b
School of Food Science and Technology, Henan University of Technology, Zhengzhou, 450001, China Henan Food Crop Collaborative Innovation Center, Zhengzhou, 450001, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Dough Water adding methods Rheology Biaxial tensile property Stress relaxation
Dough development is the most critical step in the conversion of flour into products. Low field nuclear magnetic resonance (LF-NMR), Texture Analyzer and Rheometer were used to analyze water distribution, uniaxial and biaxial tension, dynamic oscillation characteristics, as well as stress relaxation and creep-recovery characteristics of a series of wheat flour and water prepared in different water adding methods. A certain quantity of water was added to wheat flour for several times, water content and water-holding capacity of dough were improved compared with the dough adding all water to flour once. Meanwhile, tensile resistance and tensile area of dough enhanced. When rheological properties of dough were measured, it was found that tanδ were significantly changed and the degree of polymerization increased. The dough obtained by adding water three times had the largest consistency coefficient, relaxation modulus and smallest flow behavior index, creep compliance, exhibiting well elasticity and poor viscosity. In addition, there was no significant change in doughs with two times water adding in stress relaxation and creep recovery experiments.
1. Introduction Dough preparation is one of the major factors that affect the quality of flour products(Dobraszczyk and Morgenstern, 2003). The properties of dough during mixing are affected by interaction of flour, water and air. Other factors such as salt, yeast, oxidant and emulsifier are widely known(Luchian and Csatlos, 2011; Zheng et al., 2000). In the process of making flour products, rheological properties of wheat flour dough are largely governed by the contribution of starch, protein and water (Marchetti et al., 2012). The interaction of flour and water makes it the second most important ingredient in dough after wheat flour. Once contacted with water, protein and starch form a continuous network with dispersed particles, giving dough elasticity and ductility (Bhattacharya, 2010). Even a change in moisture content of just 1% can significantly alter the rheological properties of cookie dough(Manohar and Rao, 2015). Therefore, understanding the rheological properties of wheat flour-water system is very important for better control of food making process and production of high quality final products (Dobraszczyk and Morgenstern, 2003). The preparation methods of dough can be divided into hand-making dough and machine-making dough. There are many types of mixers at present, all of which are make flour, water and other ingredients mixed quickly and evenly, thus realizing the hydration of flour and forming *
the dough with certain strength(Ktenioudaki et al., 2010). Although mixers are widely used in actual production and processing, it is undeniable that the mixing blade may cause strong shearing and tearing effect on the dough, even increase the temperature of dough, causing the partial denaturation of the protein, and destroy of gluten network to a certain extent. In production of Chinese wheat flour products, handmade foods can meet the needs of consumers better. This may be largely responsibility for people's preference for handmade noodles or steamed bread. Instead of adding water to flour at once using mixing equipments, water is added by several times when the dough is made by hand. The mixture of flour and water comes in the form of "floc", then "small soft dough", and finally "real dough", with a unique three-dimensional network structure. It called "three-step water adding approach", which can make the whole process clean and efficient, and finally achieved the result that the dough is smooth and uniform, as well as the mixing bowl and hands are clean. In this process, the interaction of wheat flour and water is extremely important, and the change of contact mode between water and flour makes the study of water fluidity particularly complicated. However, there is little research on the formation of dough for traditional Chinese noodles. Therefore, the purpose of this study is to examine the dynamic behaviour of a basic wheat flour─water dough and the influence of different water adding methods. By simulating the
Corresponding author. College of Food Science and technology, Henan University of Technology, Zhengzhou, Henan, 450001, China. E-mail address: [email protected] (K. Bian).
https://doi.org/10.1016/j.jcs.2019.102791 Received 18 October 2018; Received in revised form 28 April 2019; Accepted 20 June 2019 Available online 05 July 2019 0733-5210/ © 2019 Elsevier Ltd. All rights reserved.
Journal of Cereal Science 89 (2019) 102791
Y. Yang, et al.
and 0.08 mm/s. Nine samples (three for every speed) were prepared in total for each replicate from the same batch of dough and the results were averaged. Force (F) was recorded continuously as a function of Displacement (δ). According to the original data of F- δ, strain εB (-), strain rate έB (s−1) and stress σB (Pa) were calculated, and biaxial tensile viscosity ηB (Pa·s) was finally obtained.
hand-mixing method, we compared the dough difference between doughs made by adding water to flour at a time (control) and many times to flour, analyzing the influence of different water adding methods on rheological properties of doughs, in order to provide technical support for the processing of wheat flour products. 2. Experimental
1 H − δ⎞ εB = − ln ⎛ 0 2 ⎝ H0 ⎠
2.1. Experimental materials
⎜
The dough was obtained by mixing flour without any additives provided by Tianfeng Flour Manufacturing Co., Ltd. (Kaifeng, China), containing 11.22% protein and 12.53% water with a fixed level of water addition: 67% on total wet basis of the water absorption of Farinograph test for all measurements. The water temperature was 30 °C, and mixed with wheat flour for 7min in pin mixer (JHMZ-200, Dongfujiuheng Instrument Technology Co., Ltd, Beijing, China). The specific mixing conditions are as follows. All water is added to wheat flour to make dough, and the dough is named A-1. Dividing water into two parts by a certain ratio of 7:3, 5:5 and 3:7. First, we add the first part of water to the flour and add the second part after mixing of 1min and get A-2, A-3 and A-4, respectively. Similarly, all the water was divided into three parts in the proportion of 4:4:2 and the dough A-5 was obtained finally. Among them, the dough A-1 was used as control group.
⎟
(1)
εB˙ =
d εB v =− dt 2(H0 − δ )
σB =
F F ⎛ δ ⎞ 1− = πR2 πR 0 2 ⎝ H0 ⎠
ηB = −
⎜
(2)
⎟
σB ε˙B
(3) (4)
where ν is displacement speed; H0 is the initial height of dough; R is the radius of the dough and the R0 is the initial radius of the dough. 2.5. Dynamic rheological measurement Dynamic oscillation characteristic of dough was determined according to Yazar et al. (2016) with some modification. Dough was wrapped with plastic film and placed in the environment of 90% humidity, 30 °C temperature for 20min before analysis, and a small dough was placed on the test platform (diameter 35 mm) of advanced rotating Rheometer (MARS 60, HAAKE Co., Ltd). The dough was pressed to the thickness of 2 mm, and rested for 5min. The external surface of dough was covered with silicone oil to prevent moisture loss. Preliminary tests indicated that the deformation was well within the linear viscoelastic region of the sample. During the oscillatory frequency sweep the frequency was varied from 0.1 to 10.0 Hz at constant strain amplitude (0.1% strain). Storage modulus (G'), loss modulus (G″) and tanδ (G''/G') as a function of amplitude or frequency were recorded. Each treatment was analyzed in duplicate.
2.2. Water content and water mobility characterization The moisture content was determined using AACC Method 44-15A (2000).14. Water mobility characterization was conducted according to the method of Ali (Ali et al., 2010) with some modifications. The LF-Nuclear Magnetic Resonance (LF-NMR) was used to determine the transverse relaxation time (T2) of dough using the CPMG (Carr-PurcellMeiboom-Gill) pulse sequence. The measurement parameters are as follows: Echo Count = 3000, EchoTime = 0.1 ms, TD = 10004, SW = 333.33 kHz, TW = 2000.000 ms, NS = 8. Preserving the data and entering the T2 inversion program, we get the T2 relaxation time inversion spectrum of the dough.
2.6. Stress relaxation property 2.3. Uniaxial extension The stress relaxation measurement of large deformation can be applied to the processing of dough(Bhattacharya, 2010). The stress relaxation property were measured by P50 probe of TA-XT Plus texture analyzer. The sample preparation method was consistent with Bi-extensinal measurement. A single compression test was used to determine the deformation degree of 80%. The velocity of pre-test, test and posttest was 1 mm/s, 1 mm/s and 10 mm/s respectively. The strain was maintained for 60s when the dough deformation degree reached 80%. Force F was recorded continuously as a function of time t. The stress relaxation curve of dough was fitted to with MaxwellKelvin three element model(Schramm, 1994). The stress relaxation equation was as follows:
The uniaxial tensile properties of the dough to obtain values for extensibility was executed with the TA-XT Plus Instrument (SMS,UK) using a A/KIE rig according to Dobraszczyk et al.(Dobraszczyk and Salmanowicz, 2008). The mode was measure force in tension, option return to start, pre-test speed 2.0 mms−1, test speed 3.3 mms−1, posttest speed 10.0 mms−1,distance 50.0 mm and trigger force 5 g. The prepared dough was placed directly in the environment of 90% humidity, 30 °C temperature for 20 min before analysis. Output values were Rmax (Maximum resistance), E (Extensibility) and A (Area under the curve). Each At least 7 measurements per dough were performed. 2.4. Biaxial tensile property (Lubricated squeezing flow)
t σ (t ) = ε0 E1 exp⎛− ⎞ + ε0 E2 ⎝ τ⎠
Bi-extensinal tests were determined according to Zhao(Zhao et al., 2013) and Rouille(Rouille et al., 2005) with some modification at T = 30 °C using a texture analyzer (TA-XT Plus) from Stable Micro System (SMS, UK) by P50 rig. A cylindrical piece of dough (diameter 20 mm, high 15 mm) was prepared and placed to rest with a controlled temperature (30 °C) and relative humidity (90%) atmosphere for 1 h before analysis. The surface of dough and platform was covered with olive oil to avoid shearing action during deformation and ensure that deformation was essentially biaxial extension, consequently. The deformation degree of dough was 80%, and the pre-test speed and posttest speed were 2 mm/s. Three displacement speeds were used: 2, 0.2
(5)
where σ (t) is the stress that the dough bears, Pa; ε0 is the deformation degree, %, E1 is the first factor of the elastic modulus of Hooke, namely the instantaneous modulus, Pa; E2 is the high modulus of elasticity, Pa; η is the viscous coefficient of the damping body, Pa·s; τ is the relaxation time, the time needed when the stress σ is reduced to the 1/η, stress of the initial stress. s, τ = η/E1。 Degree of deformation:
R (%) = 2
(σmax − σe ) × 100% σmax
(6)
Journal of Cereal Science 89 (2019) 102791
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where σmax is the maximum strain; σe is the strain of relaxation equilibrium. 2.7. Creep-recovery measurement A constant shear stress τ0 of 250 Pa at 30 °C was applied to the dough for 100s and afterwards removed (τ0 = 0Pa). Dough relaxation was recorded for 300s, providing that the recovery time was long enough for the steady state to be reached(Wang and Sun, 2002). Strain values were collected as a function of time. The time strain curve of dough creep recovery was fitted to Eq. (7) by Maxwell-Kelvin 4 element model(Schramm, 1994). The creep equation is as follows:
ε (t ) =
σ0 σ −t t + 0 ⎡1 − exp⎛ ⎞⎤ + E1 E2 ⎢ η ⎝ τk ⎠⎥ ⎦ ⎣ ⎜
⎟
(7)
In data calculation, the concept of compliance is introduced, and the creep equation can be changed into:
−t t J (t ) = J1 + J2 ⎡1 − exp⎛ ⎞⎤ + ⎢ η ⎝ τk ⎠⎥ ⎦ ⎣ ⎜
⎟
(8) −1
where, J(t) is the compliance of the creep process, Pa ; J1 is the first factor of Hooke body elastic compliance, that is, elastic compliance, instantaneous compliance, Pa−1; J2 is high elasticity compliance, Pa−1; t is time, s; η is the time of hysteresis, Pa·s; τK is the time of delay, that is, the time needed for creep recovery, s. 2.8. Statistical analysis Fig. 1. a, Change of water content of dough made in different ways of water adding. Values with a common letter within each diagram are not significantly different (P < 0.05); b, Distribution of relaxation time (T2) obtained by CPMG sequence for dough made in different ways of water adding.
All the data obtained in the study were expressed as mean ± standard deviation (SD). P < 0.05 was used to define the significance of differences between the samples. The statistical significance of results was assessed using one-way analysis of variance (ANOVA) with the software SPSS 20 (SPSS Inc., Chicago, IL, USA) and Duncan's multiple-range test. Origin 8.5 software was used for plotting analysis.
of other doughs. The dough A-2 was the opposite, as a consequence water holding property were the worst. This indicated that the moisture migration ability of dough produced by adding water to flour several times was reduced, and the water holding capacity of dough inhanced with the increase of bound water and intermediate state water.
3. Results and discussion 3.1. Water content and water mobility characterization
3.2. Uniaxial extension
Fig. 1a showed the variation of moisture content made by different water adding methods. In the control dough, the moisture content was 36.19%. After changing the way of adding water, the moisture content were increased by 1.5%, significantly. And, there was no significant difference between the four doughs (A-2, A-3, A-4, A-5). Low field nuclear magnetic resonance (LF-NMR) is an effective tool for observing the distribution and migration of protons in food. It can be used for the non-destructive examination of food to study the properties and amplitude of combination of water and other components. The technology can quickly, intuitively and accurately determine the distribution of moisture in the dough formed(Cornillon and Salim, 2000; Kuo et al., 2001). Distribution of transverse relaxation time (T2) obtained by a spin-echo sequence (CPMG) for dough made in different ways of water adding water showed three populations observed at T21 (0.08–0.26 ms), T22 (8.11–11.91 ms) and T23 (132.52–187.38 ms) (Fig. 1b). There were three peaks on each curve, representing three forms of water, indicated that there were different fluidity of moisture in dough. The T21 was less than 1 ms, which showed that this part of water had poor fluidity and belonged to bound water. The T22 was the main peak because the percentage of the integral area of the peak occupied the percentage of the total peak area was about 80%, indicating that the main form of water in the dough was the intermediate water (Assifaoui et al., 2006). The relaxation time of bound water in dough A-3 and A-4 were shorter, and the water content of intermediate water were less than that
Uniaxial extension tests are commonly used to investigate the behavior of dough. In this study variation of uniaxial tensile properties of dough prepared by different methods was shown in Fig. 2. A higher resistance to extension indicates that the dough requires a larger force to stretch(Wang et al., 2014). The Rmax (maximum resistance) and A (Area under the curve) of dough increased and the Extensibility (E) did not change significantly after changing the way of adding water. The results showed that the elasticity and strength of gluten network increased when changing the way of adding water. In addition, the dough (A-3/A-5) prepared by adding the same amount of water two times or adding the different amount of water three times to the flour, the tensile properties of the dough were the best. This resistance to uniaxial extension may be attributed to increasing of the strength of the gluten network in the dough due to increasing of water content and decreasing of low molecular moisture fluidity. 3.3. Biaxial tensile property (Lubricated squeezing flow) The rheological properties of dough are divided into large deformation rheological characteristics and small deformation rheological properties according to the degree of deformation of dough(Zhao et al., 2013). In the actual production of Chinese flour products, the deformation of dough is mainly caused by biaxial tensile deformation 3
Journal of Cereal Science 89 (2019) 102791
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Fig. 2. Variation of uniaxial tensile properties of dough made by different mixing methods.
evaluated by lubrication and extrusion flow measurement. Fig. 3a showed a typical σ-δ curve of dough A-1 at three probe speeds. For all doughs, the σ-δ curve were similar. The velocity of the probe had a great influence on the biaxial tensile properties of dough. Faster the pressure of the probe, greater the force needed to produce the same displacement. Fig. 3b showed a typical variation in apparent biaxial extensional viscosity (ABEV) with biaxial strain rate for the three displacement speeds as strain rate increasing. Apparent biaxial extensional viscosity increased at three cross head speeds with increase of strain rate (Stojceska et al., 2008). When the dough deformation is small, the viscosity increases rapidly with the increase of the
Fig. 4. a, Example curves of elastic modulus (G'), viscous modulus (G″), complex viscosity (|η*|) and tanδ obtained by dynamic oscillatory frequency sweep of dough A-1. b, Tanδ at 1 Hz for each dough.
Fig. 3. a, Typical variation in Stress (σ) as a function of displacement (δ) of dough for three cross-head speeds; b, a typical variation in apparent biaxial extensional viscosity (η) with the biaxial strain rate for the three displacement speeds as strain rate increasing. c, K value of doughs prepared by different mixing methods. d, n value of different doughs. 4
Journal of Cereal Science 89 (2019) 102791
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deformation rate. In general, when the deformation reaches 12.5%, the viscosity reaches the maximum and then decreases, then further increases the deformation rate, and the viscosity increases slowly. The steep increase of viscosity is believed to be due to the elastic properties of the dough and is not true viscosity. In addition, the velocity of displacement has great influence on viscosity, and velocity of displacement is faster, viscosity is smaller, vice versa. ηB decreases linearly with increasing of strain rate, appearing as strain rate thinning behavior. The thinning phenomenon can be fitted by the power law model. Taking this formula as a regression model, the rheological data of different strains are analyzed, and the results were shown in Fig. 4a and b.
σB = K ε˙nB
(9)
where K is consistency coefficient and n is the flow behavior index. Eq. (9) is used to analyze biaxial extensional viscosity as a function of strain rate and the resultant values of K and n are plotted against strain rate in Fig. 3c and d, respectively. It showed that all doughs exhibited strain rate thinning behavior. The K increases fast when strain rate was 0.125 while it increases slowly at high strains. The n increases at small strains, passed through a maximum at εB = 0.125 and then decreased. With the increase of the strain rate, the K value always keeps rising. The n value of all doughs were less than 1. When the strain rate was about 0.125s−1, K increased at the highest speed, and the n was the greatest. The K and n conformed to the general law of dough consistency and viscosity with strain rate. The change of water adding methods leaded to the difference of K and N, of which the K/n of dough A-3 were the largest, indicating that the viscosity was the largest and the flow resistance greatest. The K and n of other doughs were all smaller than those of the control group. The results showed that the K and n of dough prepared by adding the same amount of water two times was largest. On the contrary, doughs prepared by adding the different amount of water two times were smaller than the control group. It might be due to the difference of flour hydration degree or the position of the mixture in the dough, the lubrication of the water soluble components, resulting in a decrease in the viscosity of dough (Huang and Lai, 2010; Masi et al., 1998).
Fig. 5. a, Stress relaxation curve of different doughs; b, Creep recovery curve of the doughs prepared by different methods.
Compared with the control group, tanδ of all doughs obtained by adding water to flour several times decreased, in which the tanδ of dough A-2 was the smallest, and there was no significant difference from dough A-3 and A-4 (Fig. 5b). It showed that when the water was added to flour two times, the elasticity of dough was larger and the degree of polymerization was greater, but the viscoelasticity has no significant difference between doughs when the water was added for three times and the control group. The dynamic rheological properties are likely to be greatly affected only by the water phase viscosity (Upadhyay et al., 2012). In addition, a more uniform distribution of gliadin may also have an effect on dough viscosity with the increasing of mixing (Bozkurt et al., 2014).
3.4. Dynamic rheological measurement Small oscillating deformations have been used to track changes in wheat flour and water because it can determine the properties of basic mechanical dough materials. In particular, small amplitude oscillation dynamic testing is a powerful tool to provide opportunity to study the structural characteristics of materials in a relatively wide range of conditions (Kuktaite et al., 2007). It also measures the viscosity and elastic properties of dough, assessing its amplitude dependence and frequency dependent behavior. A typical example of dynamic frequency scanning of dough was shown in Fig. 4a. Qualitatively similar viscoelastic profiles were obtained for flour doughs. Elastic behavior (G') plays a dominant role compared with viscous modulus (G") throughout the measured frequency range (0.1–10 Hz), which exhibiting a predominant solid-like behavior(Ahmed et al., 2015). It also showed a relatively high dependence of the viscoelastic modulus upon oscillatory frequency, meaning that the overall chain mobility within the network is relatively high (Lopesdasilva et al., 2007). Furthermore, the complex viscosity (|η*|) of dough decreased with increasing frequency, indicating that the dependence of dough on shear behavior and shear thinning phenomenon, which is consistent with the results of the biaxial tensile test. The tanδ of dough decreases rapidly with the frequency in the lower frequency range, and increases sharply in a higher frequency, indicating that the dough system is less stable (Fig. 5a). Therefore, the tanδ at f = 1 Hz was chosen as the representative to compare the viscoelasticity of dough prepared by different water adding methods (Fig. 4b).
3.5. Stress relaxation property Fundamental rheological methods can provide more information about final product. The measurement of stress relaxation by large deformation is applicable to the actual processing of dough. The stress trend of experimental samples over time accords with the typical characteristics of stress relaxation measurement (Rouille et al., 2005). The stress of all doughs reached the maximum at about t = 12s, and then entered the relaxation stage, and then slowed down to approach a fixed value gradually (Fig. 5a). The σ-t curve of experiment was processed by Maxwell-3 element model, and the stress relaxation parameters of doughs with different water addition methods were shown in Table 1a. Maximum stress (σmax) and equilibrium stress (σe) were 4.65 × 104–5.83 × 104Pa and 7.39 × 103–9.57 × 103Pa. E1 was distributed between 6.70 × 104Pa and 9.31 × 104Pa, and E2 was distributed between 9.23 × 103Pa and 11.96 × 103Pa. It showed that the hardness of dough A-5 was the largest, followed by dough A-2, and dough A-1 was the softest. In the later stage of dough compression, the stress of dough produced by adding water to flour several times varied significantly, and there was a significant difference when the dough reached equilibrium stress, which 5
Journal of Cereal Science 89 (2019) 102791
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Table 1 a, Stress relaxation parameters of dough prepared by different water addition methods; b, Creep-recovery parameters of dough prepared by different mixing methods. Different small letters following the value in same column represent the difference significant at 0.05 level. a Water adding method
A-1 A-2 A-3 A-4 A-5
σmax × 104
σe × 103
E1 × 104
E2 × 103
η × 105
τ
R
/Pa
/Pa
/Pa
/Pa
/Pa˙s
/s
/%
± ± ± ± ±
6.70 ± 0.08d 8.25 ± 0.40 ab 7.88 ± 0.13b 8.28 ± 0.23 ab 8.63 ± 0.35a
9.23 ± 0.01d 10.57 ± 0.11b 10.06 ± 0.03c 10.56 ± 0.01b 11.96 ± 0.01a
7.14 ± 0.06d 8.73 ± 0.52 ab 8.37 ± 0.09b 8.81 ± 0.21 ab 9.31 ± 0.36a
4.65 5.52 5.30 5.46 5.83
± ± ± ± ±
0.05c 0.19b 0.01b 0.01b 0.11a
7.39 8.46 8.05 8.45 9.57
0.01d 0.09b 0.03c 0.01b 0.01a
10.66 10.59 10.62 10.64 10.64
± ± ± ± ±
0.03a 0.12a 0.07a 0.04a 0.00a
84.13 ± 0.19 bc 84.67 ± 0.37 ab 84.81 ± 0.02a 84.52 ± 0.04 ab 83.60 ± 0.31c
b Water adding method
A-1 A-2 A-3 A-4 A-5
Jmax × 10−5
εmax
J1 × 10−5
J2 × 10−5
η × 105
τK
/Pa−1
× 10−5
/Pa−1
/Pa−1
/Pa˙s
/s
19.85 ± 3.78a 10.01 ± 2.22b 9.12 ± 0.82b 10.68 ± 1.40b 8.09 ± 0.80b
7.63 ± 0.11a 3.22 ± 0.67bc 3.37 ± 0.53bc 4.59 ± 0.59b 2.67 ± 0.53d
2.25 ± 0.35b 4.17 ± 1.18 ab 4.17 ± 1.18 ab 4.17 ± 1.18 ab 5.00 ± 0.00a
9.64 ± 0.81c 22.84 ± 3.50 ab 24.29 ± 1.91 ab 19.69 ± 0.33b 28.09 ± 2.11a
9.13 4.01 3.65 4.27 3.23
± ± ± ± ±
0.17a 0.89b 0.33b 0.56b 0.32b
3.50 1.50 1.50 2.00 1.00
± ± ± ± ±
0.71a 0.71b 0.71b 0.00b 0.00b
2015; Rouille et al., 2005). The time-compliance relationship curve of dough's creep recovery measurement was well fitted with the Maxwell-Kelvin 4 element model, and the fitting degree was 0.98–0.99. The creep recovery parameters of doughs made by different methods were shown in Table 1b. The maximum compliance (Jmax) was obtained when t = 100s. The η of doughs were 2.25 × 10−5–5.00 × 10−5 Pa s. In the creep recovery stage, the dough made by different methods showed similar results. Jmax of the dough A-1 reached the maximum, the creep curves of dough A-2 and A3 were almost coincided, the deformation of dough A-5 was the smallest. Water acts as a plasticizer in dough A-1 and produces viscous dough that exhibits more extensibility under a specified load(Ahmed et al., 2015). However, the retardation time was not consistent with the trend of compliance values, or even the opposite, which may be related to the water distribution in the dough, and a part of water acts as a lubricant to prolong the recovery of dough. The lubricating effect of water-soluble components may also be reflected(Huang and Lai, 2010).
was greater than that in the control group. In the initial stage of relaxation, the decrease of dough stress may be due to the fracture of the secondary bond inside the dough, which is related to the response of the dough to the compression, kneading and mixing. It may also be because when the water was added to the flour several times, starch granules absorb water fully, promoting the formation of the gluten network and the dough can produce greater resistance during the compression. The equilibrium stress is related to the covalent bond. In addition, the viscosity coefficient (η) was distributed between 7.14 × 105 Pa s and 9.31 × 105 Pa s, which was consistent with the trend of modulus value, reflecting the viscosity of dough. Compared with biaxial tensile viscosity, the viscosity coefficient was smaller, which may be that the water-soluble component had more obvious lubrication effect during the stress relaxation determination(Rouille et al., 2005). When the stress relaxation was measured, the ideal elastomer can recover the original structure instantaneously with the recovery degree of 100% and relaxation degree of 0%, while the relaxation degree is 100% for ideal viscous (or liquid). The equilibrium stress in polymer of liquid food is almost 0% without any permanent cross-link. However, there is a partial cross linking in solid food, which does not reach zero value. The deformation degree (R) is large, which indicates that the dough has a high viscosity. Therefore, the viscosity of dough made by two water adding was larger, and the viscosity of dough made by adding water to flour three times was smaller. For viscoelastic materials, it takes a long time to achieve stress balance. Relaxation time (τ) is the result of combined action of elastic behavior and viscous behavior. Longer the relaxation time is, more obvious the elastic deformation is, otherwise, the viscous deformation is more apparent. The relaxation time of doughs were distributed between 10.62s and 10.66s, and the stress attenuation speed of dough decreases, but there was no significant change, showing that the internal friction force and structure of doughs were similar.
4. Conclusion The interaction between flour and water is very important for the development of the dough. This paper reviewed the effects of water addition sequence on the viscoelasticity of dough. Compared with the control group, the rheological properties of dough made by adding water to flour several times were significantly changed, and there was no significant difference between dough made by water adding two times. The rheological properties of dough made with three time water adding method to flour was better than others. The contact between flour and water is carried out step by step by step by adding water, so that flour and water can be fully contacted, rather than partially bonded to form a cluster, part of which is still dry flour. This results in moisture migration to the inside of the dough, the full formation of gluten network, tensile properties increased, dough under external force was easier to restore. The water holding capacity of dough was enhanced and the water content of dough increased. When the uniaxial tensile properties were tested, the tensile properties of the dough are the strongest and the dough polymerization degree is the highest. At the same time, due to the contact between flour and water, more water soluble components are incorporated into the water, and their lubrication was strengthened. This made the viscosity of the dough increased and the fluidity was weakened, and the viscosity coefficient of dough was larger when the dough stress relaxation and the creep
3.6. Creep-recovery measurement The creep test can reflect the rheological properties of the dough intuitively, which is helpful to the development and design of the products, and can be used to evaluate the viscoelasticity of dough and the quality of noodles(Rouille et al., 2005). Fig. 5b was the result of the creep recovery experiment of different doughs. For all doughs, the curve were similar, which is consistent with the creep recovery characteristics of dough creep recovery in related literatures (Ahmed et al., 6
Journal of Cereal Science 89 (2019) 102791
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recovery characteristics were measured. The role of water as plasticizer and the lubrication of water-soluble components played in the preparation of dough are important, which will also be the focus of future research. In addition, two fundamental rheological techniques, stress relaxation and creep-recovery may be more effective in differentiating small differences between samples.
characteristics and suitability of model. J. Food Eng. 97, 539–546. Bozkurt, F., Ansari, S., Yau, P., Yazar, G., Ryan, V., Kokini, J., 2014. Distribution and location of ethanol soluble proteins (Osborne gliadin) as a function of mixing time in strong wheat flour dough using quantum dots as a labeling tool with confocal laser scanning microscopy. Food Res. Int. 66, 279–288. Cornillon, P., Salim, L.C., 2000. Characterization of water mobility and distribution in low- and intermediate-moisture food systems. Magn. Reson. Imag. 18, 335–341. Dobraszczyk, B.J., Morgenstern, M.P., 2003. Rheology and the breadmaking process. J. Cereal Sci. 38, 229–245. Dobraszczyk, B.J., Salmanowicz, B.P., 2008. Comparison of predictions of baking volume using large deformation rheological properties. J. Cereal Sci. 47, 292–301. Huang, Y.C., Lai, H.M., 2010. Noodle quality affected by different cereal starches. J. Food Eng. 97, 135–143. Ktenioudaki, A., Butler, F., Gallagher, E., 2010. The effect of different mixing processes on dough extensional rheology and baked attributes. J. Sci. Food Agric. 90, 2098–2104. Kuktaite, R., Larsson, H., Johansson, E., 2007. The Influence of Dough Mixing Time on Wheat Protein Composition and Gluten Quality for Four Commercial Flour Mixtures. Springer Netherlands. Kuo, M.I., Gunasekaran, S., Johnson, M., Chen, C., 2001. Nuclear magnetic resonance study of water mobility in pasta filata and non-pasta filata mozzarella. J. Dairy Sci. 84, 1950–1958. Lopesdasilva, J.A., Santos, D.M., Freitas, A., Brites, C., Gil, A.M., 2007. Rheological and nuclear magnetic resonance (NMR) study of the hydration and heating of undeveloped wheat doughs. J. Agric. Food Chem. 55, 5636–5644. Luchian, M.I., Csatlos, C., 2011. Research on change in protein composition during dough processing. Bull. Transilvania Univ. Brasov 53, 109–114. Manohar, R.S., Rao, P.H., 2015. Effects of water on the rheological characteristics of biscuit dough and quality of biscuits. J. Sci. Food Agric. 75, 383–390. Marchetti, L., Cardós, M., Campaña, L., Ferrero, C., 2012. Effect of glutens of different quality on dough characteristics and breadmaking performance. LWT - Food Sci. Technol. (Lebensmittel-Wissenschaft -Technol.) 46, 224–231. Masi, P., Cavella, S., Sepe, M., 1998. Characterization of dynamic viscoelastic behavior of wheat flour doughs at different moisture contents. Cereal Chem. 75, 428–432. Rouille, J., Della, V.G., Lefebvre, J., Sliwinski, E., Tvan, V., 2005. Shear and extensional properties of bread doughs affected by their minor components. J. Cereal Sci. 42, 45–57. Schramm, G., 1994. A Practical Approach to Rheology and Rheometry. Stojceska, V., Butler, F., Gallagher, E., Keehan, D., 2008. A comparison of the ability of several small and large deformation rheological measurements of wheat dough to predict baking behaviour. J. Food Eng. 83, 475–482. Upadhyay, R., Ghosal, D., Mehra, A., 2012. Characterization of bread dough: rheological properties and microstructure. J. Food Eng. 109, 104–113. Wang, F.C., Sun, X.S., 2002. Creep㏑ecovery of wheat flour doughs and relationship to other physical dough tests and breadmaking performance. Cereal Chem. 79, 567–571. Wang, X., Lu, F., Zhang, C., Lu, Y., Bie, X., Xie, Y., Lu, Z., 2014. Effects of recombinated Anabaena sp. lipoxygenase on the protein component and dough property of wheat flour. J. Agric. Food Chem. 62, 9885. Yazar, G., Duvarci, O., Tavman, S., Kokini, J.L., 2016. Effect of mixing on Laos properties of hard wheat flour dough. J. Food Eng. 190, 195–204. Zhao, X.W., Jiang, C.P., Li, R.F., An, G.J., 2013. Equibiaxial extensional viscosity and network formation of wheat gluten - Xanthan gum dough. Adv. Mater. Res. 787, 306–310. Zheng, H., Morgenstern, M.P., Campanella, O.H., Larsen, N.G., 2000. Rheological properties of dough during mechanical dough development. J. Cereal Sci. 32, 293–306.
Author contributions The authors are grateful to Ke Bian, Erqi Guan for critically reviewing this manuscript. The authors are pleased to acknowledge Tingjing Zhang, Mengmeng Li for improving the communication of manuscript. Compliance with ethical standards Conflict of interest None. Compliance with ethics requirements This article does not contain any studies with human or animal subjects. Acknowledgments This research was supported by the National Natural Science Foundation of China (U1604235) and National Key Research and Development Program of China (2018YFD0401001). We gratefully acknowledge the entire technical staff of the National Engineering Laboratory for Wheat & Corn Further Processing for the supply of instruments. References Ahmed, J., Thomas, L., Al‐Attar, H., 2015. Oscillatory rheology and creep behavior of Barley β‐d‐glucan concentrate dough: effect of particle size, temperature, and water content. J. Food Sci. 80, E73–E83. Ali, A., Dominique, C., Eleni, C., Aliette, V., 2010. Rheological behaviour of biscuit dough in relation to water mobility. Int. J. Food Sci. Technol. 41, 124–128. Assifaoui, A., Champion, D., Chiotelli, E., Verel, A., 2006. Characterization of water mobility in biscuit dough using a low-field H NMR technique. Carbohydr. Polym. 64, 197–204. Bhattacharya, S., 2010. Stress relaxation behaviour of moth bean flour dough: product
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Influence of water addition methods on water mobility characterization and rheological properties of wheat flour dough
T
Yuling Yanga, Erqi Guana,b, Tingjing Zhanga, Mengmeng Lia, Ke Biana,b,* a b
School of Food Science and Technology, Henan University of Technology, Zhengzhou, 450001, China Henan Food Crop Collaborative Innovation Center, Zhengzhou, 450001, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Dough Water adding methods Rheology Biaxial tensile property Stress relaxation
Dough development is the most critical step in the conversion of flour into products. Low field nuclear magnetic resonance (LF-NMR), Texture Analyzer and Rheometer were used to analyze water distribution, uniaxial and biaxial tension, dynamic oscillation characteristics, as well as stress relaxation and creep-recovery characteristics of a series of wheat flour and water prepared in different water adding methods. A certain quantity of water was added to wheat flour for several times, water content and water-holding capacity of dough were improved compared with the dough adding all water to flour once. Meanwhile, tensile resistance and tensile area of dough enhanced. When rheological properties of dough were measured, it was found that tanδ were significantly changed and the degree of polymerization increased. The dough obtained by adding water three times had the largest consistency coefficient, relaxation modulus and smallest flow behavior index, creep compliance, exhibiting well elasticity and poor viscosity. In addition, there was no significant change in doughs with two times water adding in stress relaxation and creep recovery experiments.
1. Introduction Dough preparation is one of the major factors that affect the quality of flour products(Dobraszczyk and Morgenstern, 2003). The properties of dough during mixing are affected by interaction of flour, water and air. Other factors such as salt, yeast, oxidant and emulsifier are widely known(Luchian and Csatlos, 2011; Zheng et al., 2000). In the process of making flour products, rheological properties of wheat flour dough are largely governed by the contribution of starch, protein and water (Marchetti et al., 2012). The interaction of flour and water makes it the second most important ingredient in dough after wheat flour. Once contacted with water, protein and starch form a continuous network with dispersed particles, giving dough elasticity and ductility (Bhattacharya, 2010). Even a change in moisture content of just 1% can significantly alter the rheological properties of cookie dough(Manohar and Rao, 2015). Therefore, understanding the rheological properties of wheat flour-water system is very important for better control of food making process and production of high quality final products (Dobraszczyk and Morgenstern, 2003). The preparation methods of dough can be divided into hand-making dough and machine-making dough. There are many types of mixers at present, all of which are make flour, water and other ingredients mixed quickly and evenly, thus realizing the hydration of flour and forming *
the dough with certain strength(Ktenioudaki et al., 2010). Although mixers are widely used in actual production and processing, it is undeniable that the mixing blade may cause strong shearing and tearing effect on the dough, even increase the temperature of dough, causing the partial denaturation of the protein, and destroy of gluten network to a certain extent. In production of Chinese wheat flour products, handmade foods can meet the needs of consumers better. This may be largely responsibility for people's preference for handmade noodles or steamed bread. Instead of adding water to flour at once using mixing equipments, water is added by several times when the dough is made by hand. The mixture of flour and water comes in the form of "floc", then "small soft dough", and finally "real dough", with a unique three-dimensional network structure. It called "three-step water adding approach", which can make the whole process clean and efficient, and finally achieved the result that the dough is smooth and uniform, as well as the mixing bowl and hands are clean. In this process, the interaction of wheat flour and water is extremely important, and the change of contact mode between water and flour makes the study of water fluidity particularly complicated. However, there is little research on the formation of dough for traditional Chinese noodles. Therefore, the purpose of this study is to examine the dynamic behaviour of a basic wheat flour─water dough and the influence of different water adding methods. By simulating the
Corresponding author. College of Food Science and technology, Henan University of Technology, Zhengzhou, Henan, 450001, China. E-mail address: [email protected] (K. Bian).
https://doi.org/10.1016/j.jcs.2019.102791 Received 18 October 2018; Received in revised form 28 April 2019; Accepted 20 June 2019 Available online 05 July 2019 0733-5210/ © 2019 Elsevier Ltd. All rights reserved.
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and 0.08 mm/s. Nine samples (three for every speed) were prepared in total for each replicate from the same batch of dough and the results were averaged. Force (F) was recorded continuously as a function of Displacement (δ). According to the original data of F- δ, strain εB (-), strain rate έB (s−1) and stress σB (Pa) were calculated, and biaxial tensile viscosity ηB (Pa·s) was finally obtained.
hand-mixing method, we compared the dough difference between doughs made by adding water to flour at a time (control) and many times to flour, analyzing the influence of different water adding methods on rheological properties of doughs, in order to provide technical support for the processing of wheat flour products. 2. Experimental
1 H − δ⎞ εB = − ln ⎛ 0 2 ⎝ H0 ⎠
2.1. Experimental materials
⎜
The dough was obtained by mixing flour without any additives provided by Tianfeng Flour Manufacturing Co., Ltd. (Kaifeng, China), containing 11.22% protein and 12.53% water with a fixed level of water addition: 67% on total wet basis of the water absorption of Farinograph test for all measurements. The water temperature was 30 °C, and mixed with wheat flour for 7min in pin mixer (JHMZ-200, Dongfujiuheng Instrument Technology Co., Ltd, Beijing, China). The specific mixing conditions are as follows. All water is added to wheat flour to make dough, and the dough is named A-1. Dividing water into two parts by a certain ratio of 7:3, 5:5 and 3:7. First, we add the first part of water to the flour and add the second part after mixing of 1min and get A-2, A-3 and A-4, respectively. Similarly, all the water was divided into three parts in the proportion of 4:4:2 and the dough A-5 was obtained finally. Among them, the dough A-1 was used as control group.
⎟
(1)
εB˙ =
d εB v =− dt 2(H0 − δ )
σB =
F F ⎛ δ ⎞ 1− = πR2 πR 0 2 ⎝ H0 ⎠
ηB = −
⎜
(2)
⎟
σB ε˙B
(3) (4)
where ν is displacement speed; H0 is the initial height of dough; R is the radius of the dough and the R0 is the initial radius of the dough. 2.5. Dynamic rheological measurement Dynamic oscillation characteristic of dough was determined according to Yazar et al. (2016) with some modification. Dough was wrapped with plastic film and placed in the environment of 90% humidity, 30 °C temperature for 20min before analysis, and a small dough was placed on the test platform (diameter 35 mm) of advanced rotating Rheometer (MARS 60, HAAKE Co., Ltd). The dough was pressed to the thickness of 2 mm, and rested for 5min. The external surface of dough was covered with silicone oil to prevent moisture loss. Preliminary tests indicated that the deformation was well within the linear viscoelastic region of the sample. During the oscillatory frequency sweep the frequency was varied from 0.1 to 10.0 Hz at constant strain amplitude (0.1% strain). Storage modulus (G'), loss modulus (G″) and tanδ (G''/G') as a function of amplitude or frequency were recorded. Each treatment was analyzed in duplicate.
2.2. Water content and water mobility characterization The moisture content was determined using AACC Method 44-15A (2000).14. Water mobility characterization was conducted according to the method of Ali (Ali et al., 2010) with some modifications. The LF-Nuclear Magnetic Resonance (LF-NMR) was used to determine the transverse relaxation time (T2) of dough using the CPMG (Carr-PurcellMeiboom-Gill) pulse sequence. The measurement parameters are as follows: Echo Count = 3000, EchoTime = 0.1 ms, TD = 10004, SW = 333.33 kHz, TW = 2000.000 ms, NS = 8. Preserving the data and entering the T2 inversion program, we get the T2 relaxation time inversion spectrum of the dough.
2.6. Stress relaxation property 2.3. Uniaxial extension The stress relaxation measurement of large deformation can be applied to the processing of dough(Bhattacharya, 2010). The stress relaxation property were measured by P50 probe of TA-XT Plus texture analyzer. The sample preparation method was consistent with Bi-extensinal measurement. A single compression test was used to determine the deformation degree of 80%. The velocity of pre-test, test and posttest was 1 mm/s, 1 mm/s and 10 mm/s respectively. The strain was maintained for 60s when the dough deformation degree reached 80%. Force F was recorded continuously as a function of time t. The stress relaxation curve of dough was fitted to with MaxwellKelvin three element model(Schramm, 1994). The stress relaxation equation was as follows:
The uniaxial tensile properties of the dough to obtain values for extensibility was executed with the TA-XT Plus Instrument (SMS,UK) using a A/KIE rig according to Dobraszczyk et al.(Dobraszczyk and Salmanowicz, 2008). The mode was measure force in tension, option return to start, pre-test speed 2.0 mms−1, test speed 3.3 mms−1, posttest speed 10.0 mms−1,distance 50.0 mm and trigger force 5 g. The prepared dough was placed directly in the environment of 90% humidity, 30 °C temperature for 20 min before analysis. Output values were Rmax (Maximum resistance), E (Extensibility) and A (Area under the curve). Each At least 7 measurements per dough were performed. 2.4. Biaxial tensile property (Lubricated squeezing flow)
t σ (t ) = ε0 E1 exp⎛− ⎞ + ε0 E2 ⎝ τ⎠
Bi-extensinal tests were determined according to Zhao(Zhao et al., 2013) and Rouille(Rouille et al., 2005) with some modification at T = 30 °C using a texture analyzer (TA-XT Plus) from Stable Micro System (SMS, UK) by P50 rig. A cylindrical piece of dough (diameter 20 mm, high 15 mm) was prepared and placed to rest with a controlled temperature (30 °C) and relative humidity (90%) atmosphere for 1 h before analysis. The surface of dough and platform was covered with olive oil to avoid shearing action during deformation and ensure that deformation was essentially biaxial extension, consequently. The deformation degree of dough was 80%, and the pre-test speed and posttest speed were 2 mm/s. Three displacement speeds were used: 2, 0.2
(5)
where σ (t) is the stress that the dough bears, Pa; ε0 is the deformation degree, %, E1 is the first factor of the elastic modulus of Hooke, namely the instantaneous modulus, Pa; E2 is the high modulus of elasticity, Pa; η is the viscous coefficient of the damping body, Pa·s; τ is the relaxation time, the time needed when the stress σ is reduced to the 1/η, stress of the initial stress. s, τ = η/E1。 Degree of deformation:
R (%) = 2
(σmax − σe ) × 100% σmax
(6)
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where σmax is the maximum strain; σe is the strain of relaxation equilibrium. 2.7. Creep-recovery measurement A constant shear stress τ0 of 250 Pa at 30 °C was applied to the dough for 100s and afterwards removed (τ0 = 0Pa). Dough relaxation was recorded for 300s, providing that the recovery time was long enough for the steady state to be reached(Wang and Sun, 2002). Strain values were collected as a function of time. The time strain curve of dough creep recovery was fitted to Eq. (7) by Maxwell-Kelvin 4 element model(Schramm, 1994). The creep equation is as follows:
ε (t ) =
σ0 σ −t t + 0 ⎡1 − exp⎛ ⎞⎤ + E1 E2 ⎢ η ⎝ τk ⎠⎥ ⎦ ⎣ ⎜
⎟
(7)
In data calculation, the concept of compliance is introduced, and the creep equation can be changed into:
−t t J (t ) = J1 + J2 ⎡1 − exp⎛ ⎞⎤ + ⎢ η ⎝ τk ⎠⎥ ⎦ ⎣ ⎜
⎟
(8) −1
where, J(t) is the compliance of the creep process, Pa ; J1 is the first factor of Hooke body elastic compliance, that is, elastic compliance, instantaneous compliance, Pa−1; J2 is high elasticity compliance, Pa−1; t is time, s; η is the time of hysteresis, Pa·s; τK is the time of delay, that is, the time needed for creep recovery, s. 2.8. Statistical analysis Fig. 1. a, Change of water content of dough made in different ways of water adding. Values with a common letter within each diagram are not significantly different (P < 0.05); b, Distribution of relaxation time (T2) obtained by CPMG sequence for dough made in different ways of water adding.
All the data obtained in the study were expressed as mean ± standard deviation (SD). P < 0.05 was used to define the significance of differences between the samples. The statistical significance of results was assessed using one-way analysis of variance (ANOVA) with the software SPSS 20 (SPSS Inc., Chicago, IL, USA) and Duncan's multiple-range test. Origin 8.5 software was used for plotting analysis.
of other doughs. The dough A-2 was the opposite, as a consequence water holding property were the worst. This indicated that the moisture migration ability of dough produced by adding water to flour several times was reduced, and the water holding capacity of dough inhanced with the increase of bound water and intermediate state water.
3. Results and discussion 3.1. Water content and water mobility characterization
3.2. Uniaxial extension
Fig. 1a showed the variation of moisture content made by different water adding methods. In the control dough, the moisture content was 36.19%. After changing the way of adding water, the moisture content were increased by 1.5%, significantly. And, there was no significant difference between the four doughs (A-2, A-3, A-4, A-5). Low field nuclear magnetic resonance (LF-NMR) is an effective tool for observing the distribution and migration of protons in food. It can be used for the non-destructive examination of food to study the properties and amplitude of combination of water and other components. The technology can quickly, intuitively and accurately determine the distribution of moisture in the dough formed(Cornillon and Salim, 2000; Kuo et al., 2001). Distribution of transverse relaxation time (T2) obtained by a spin-echo sequence (CPMG) for dough made in different ways of water adding water showed three populations observed at T21 (0.08–0.26 ms), T22 (8.11–11.91 ms) and T23 (132.52–187.38 ms) (Fig. 1b). There were three peaks on each curve, representing three forms of water, indicated that there were different fluidity of moisture in dough. The T21 was less than 1 ms, which showed that this part of water had poor fluidity and belonged to bound water. The T22 was the main peak because the percentage of the integral area of the peak occupied the percentage of the total peak area was about 80%, indicating that the main form of water in the dough was the intermediate water (Assifaoui et al., 2006). The relaxation time of bound water in dough A-3 and A-4 were shorter, and the water content of intermediate water were less than that
Uniaxial extension tests are commonly used to investigate the behavior of dough. In this study variation of uniaxial tensile properties of dough prepared by different methods was shown in Fig. 2. A higher resistance to extension indicates that the dough requires a larger force to stretch(Wang et al., 2014). The Rmax (maximum resistance) and A (Area under the curve) of dough increased and the Extensibility (E) did not change significantly after changing the way of adding water. The results showed that the elasticity and strength of gluten network increased when changing the way of adding water. In addition, the dough (A-3/A-5) prepared by adding the same amount of water two times or adding the different amount of water three times to the flour, the tensile properties of the dough were the best. This resistance to uniaxial extension may be attributed to increasing of the strength of the gluten network in the dough due to increasing of water content and decreasing of low molecular moisture fluidity. 3.3. Biaxial tensile property (Lubricated squeezing flow) The rheological properties of dough are divided into large deformation rheological characteristics and small deformation rheological properties according to the degree of deformation of dough(Zhao et al., 2013). In the actual production of Chinese flour products, the deformation of dough is mainly caused by biaxial tensile deformation 3
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Fig. 2. Variation of uniaxial tensile properties of dough made by different mixing methods.
evaluated by lubrication and extrusion flow measurement. Fig. 3a showed a typical σ-δ curve of dough A-1 at three probe speeds. For all doughs, the σ-δ curve were similar. The velocity of the probe had a great influence on the biaxial tensile properties of dough. Faster the pressure of the probe, greater the force needed to produce the same displacement. Fig. 3b showed a typical variation in apparent biaxial extensional viscosity (ABEV) with biaxial strain rate for the three displacement speeds as strain rate increasing. Apparent biaxial extensional viscosity increased at three cross head speeds with increase of strain rate (Stojceska et al., 2008). When the dough deformation is small, the viscosity increases rapidly with the increase of the
Fig. 4. a, Example curves of elastic modulus (G'), viscous modulus (G″), complex viscosity (|η*|) and tanδ obtained by dynamic oscillatory frequency sweep of dough A-1. b, Tanδ at 1 Hz for each dough.
Fig. 3. a, Typical variation in Stress (σ) as a function of displacement (δ) of dough for three cross-head speeds; b, a typical variation in apparent biaxial extensional viscosity (η) with the biaxial strain rate for the three displacement speeds as strain rate increasing. c, K value of doughs prepared by different mixing methods. d, n value of different doughs. 4
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deformation rate. In general, when the deformation reaches 12.5%, the viscosity reaches the maximum and then decreases, then further increases the deformation rate, and the viscosity increases slowly. The steep increase of viscosity is believed to be due to the elastic properties of the dough and is not true viscosity. In addition, the velocity of displacement has great influence on viscosity, and velocity of displacement is faster, viscosity is smaller, vice versa. ηB decreases linearly with increasing of strain rate, appearing as strain rate thinning behavior. The thinning phenomenon can be fitted by the power law model. Taking this formula as a regression model, the rheological data of different strains are analyzed, and the results were shown in Fig. 4a and b.
σB = K ε˙nB
(9)
where K is consistency coefficient and n is the flow behavior index. Eq. (9) is used to analyze biaxial extensional viscosity as a function of strain rate and the resultant values of K and n are plotted against strain rate in Fig. 3c and d, respectively. It showed that all doughs exhibited strain rate thinning behavior. The K increases fast when strain rate was 0.125 while it increases slowly at high strains. The n increases at small strains, passed through a maximum at εB = 0.125 and then decreased. With the increase of the strain rate, the K value always keeps rising. The n value of all doughs were less than 1. When the strain rate was about 0.125s−1, K increased at the highest speed, and the n was the greatest. The K and n conformed to the general law of dough consistency and viscosity with strain rate. The change of water adding methods leaded to the difference of K and N, of which the K/n of dough A-3 were the largest, indicating that the viscosity was the largest and the flow resistance greatest. The K and n of other doughs were all smaller than those of the control group. The results showed that the K and n of dough prepared by adding the same amount of water two times was largest. On the contrary, doughs prepared by adding the different amount of water two times were smaller than the control group. It might be due to the difference of flour hydration degree or the position of the mixture in the dough, the lubrication of the water soluble components, resulting in a decrease in the viscosity of dough (Huang and Lai, 2010; Masi et al., 1998).
Fig. 5. a, Stress relaxation curve of different doughs; b, Creep recovery curve of the doughs prepared by different methods.
Compared with the control group, tanδ of all doughs obtained by adding water to flour several times decreased, in which the tanδ of dough A-2 was the smallest, and there was no significant difference from dough A-3 and A-4 (Fig. 5b). It showed that when the water was added to flour two times, the elasticity of dough was larger and the degree of polymerization was greater, but the viscoelasticity has no significant difference between doughs when the water was added for three times and the control group. The dynamic rheological properties are likely to be greatly affected only by the water phase viscosity (Upadhyay et al., 2012). In addition, a more uniform distribution of gliadin may also have an effect on dough viscosity with the increasing of mixing (Bozkurt et al., 2014).
3.4. Dynamic rheological measurement Small oscillating deformations have been used to track changes in wheat flour and water because it can determine the properties of basic mechanical dough materials. In particular, small amplitude oscillation dynamic testing is a powerful tool to provide opportunity to study the structural characteristics of materials in a relatively wide range of conditions (Kuktaite et al., 2007). It also measures the viscosity and elastic properties of dough, assessing its amplitude dependence and frequency dependent behavior. A typical example of dynamic frequency scanning of dough was shown in Fig. 4a. Qualitatively similar viscoelastic profiles were obtained for flour doughs. Elastic behavior (G') plays a dominant role compared with viscous modulus (G") throughout the measured frequency range (0.1–10 Hz), which exhibiting a predominant solid-like behavior(Ahmed et al., 2015). It also showed a relatively high dependence of the viscoelastic modulus upon oscillatory frequency, meaning that the overall chain mobility within the network is relatively high (Lopesdasilva et al., 2007). Furthermore, the complex viscosity (|η*|) of dough decreased with increasing frequency, indicating that the dependence of dough on shear behavior and shear thinning phenomenon, which is consistent with the results of the biaxial tensile test. The tanδ of dough decreases rapidly with the frequency in the lower frequency range, and increases sharply in a higher frequency, indicating that the dough system is less stable (Fig. 5a). Therefore, the tanδ at f = 1 Hz was chosen as the representative to compare the viscoelasticity of dough prepared by different water adding methods (Fig. 4b).
3.5. Stress relaxation property Fundamental rheological methods can provide more information about final product. The measurement of stress relaxation by large deformation is applicable to the actual processing of dough. The stress trend of experimental samples over time accords with the typical characteristics of stress relaxation measurement (Rouille et al., 2005). The stress of all doughs reached the maximum at about t = 12s, and then entered the relaxation stage, and then slowed down to approach a fixed value gradually (Fig. 5a). The σ-t curve of experiment was processed by Maxwell-3 element model, and the stress relaxation parameters of doughs with different water addition methods were shown in Table 1a. Maximum stress (σmax) and equilibrium stress (σe) were 4.65 × 104–5.83 × 104Pa and 7.39 × 103–9.57 × 103Pa. E1 was distributed between 6.70 × 104Pa and 9.31 × 104Pa, and E2 was distributed between 9.23 × 103Pa and 11.96 × 103Pa. It showed that the hardness of dough A-5 was the largest, followed by dough A-2, and dough A-1 was the softest. In the later stage of dough compression, the stress of dough produced by adding water to flour several times varied significantly, and there was a significant difference when the dough reached equilibrium stress, which 5
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Table 1 a, Stress relaxation parameters of dough prepared by different water addition methods; b, Creep-recovery parameters of dough prepared by different mixing methods. Different small letters following the value in same column represent the difference significant at 0.05 level. a Water adding method
A-1 A-2 A-3 A-4 A-5
σmax × 104
σe × 103
E1 × 104
E2 × 103
η × 105
τ
R
/Pa
/Pa
/Pa
/Pa
/Pa˙s
/s
/%
± ± ± ± ±
6.70 ± 0.08d 8.25 ± 0.40 ab 7.88 ± 0.13b 8.28 ± 0.23 ab 8.63 ± 0.35a
9.23 ± 0.01d 10.57 ± 0.11b 10.06 ± 0.03c 10.56 ± 0.01b 11.96 ± 0.01a
7.14 ± 0.06d 8.73 ± 0.52 ab 8.37 ± 0.09b 8.81 ± 0.21 ab 9.31 ± 0.36a
4.65 5.52 5.30 5.46 5.83
± ± ± ± ±
0.05c 0.19b 0.01b 0.01b 0.11a
7.39 8.46 8.05 8.45 9.57
0.01d 0.09b 0.03c 0.01b 0.01a
10.66 10.59 10.62 10.64 10.64
± ± ± ± ±
0.03a 0.12a 0.07a 0.04a 0.00a
84.13 ± 0.19 bc 84.67 ± 0.37 ab 84.81 ± 0.02a 84.52 ± 0.04 ab 83.60 ± 0.31c
b Water adding method
A-1 A-2 A-3 A-4 A-5
Jmax × 10−5
εmax
J1 × 10−5
J2 × 10−5
η × 105
τK
/Pa−1
× 10−5
/Pa−1
/Pa−1
/Pa˙s
/s
19.85 ± 3.78a 10.01 ± 2.22b 9.12 ± 0.82b 10.68 ± 1.40b 8.09 ± 0.80b
7.63 ± 0.11a 3.22 ± 0.67bc 3.37 ± 0.53bc 4.59 ± 0.59b 2.67 ± 0.53d
2.25 ± 0.35b 4.17 ± 1.18 ab 4.17 ± 1.18 ab 4.17 ± 1.18 ab 5.00 ± 0.00a
9.64 ± 0.81c 22.84 ± 3.50 ab 24.29 ± 1.91 ab 19.69 ± 0.33b 28.09 ± 2.11a
9.13 4.01 3.65 4.27 3.23
± ± ± ± ±
0.17a 0.89b 0.33b 0.56b 0.32b
3.50 1.50 1.50 2.00 1.00
± ± ± ± ±
0.71a 0.71b 0.71b 0.00b 0.00b
2015; Rouille et al., 2005). The time-compliance relationship curve of dough's creep recovery measurement was well fitted with the Maxwell-Kelvin 4 element model, and the fitting degree was 0.98–0.99. The creep recovery parameters of doughs made by different methods were shown in Table 1b. The maximum compliance (Jmax) was obtained when t = 100s. The η of doughs were 2.25 × 10−5–5.00 × 10−5 Pa s. In the creep recovery stage, the dough made by different methods showed similar results. Jmax of the dough A-1 reached the maximum, the creep curves of dough A-2 and A3 were almost coincided, the deformation of dough A-5 was the smallest. Water acts as a plasticizer in dough A-1 and produces viscous dough that exhibits more extensibility under a specified load(Ahmed et al., 2015). However, the retardation time was not consistent with the trend of compliance values, or even the opposite, which may be related to the water distribution in the dough, and a part of water acts as a lubricant to prolong the recovery of dough. The lubricating effect of water-soluble components may also be reflected(Huang and Lai, 2010).
was greater than that in the control group. In the initial stage of relaxation, the decrease of dough stress may be due to the fracture of the secondary bond inside the dough, which is related to the response of the dough to the compression, kneading and mixing. It may also be because when the water was added to the flour several times, starch granules absorb water fully, promoting the formation of the gluten network and the dough can produce greater resistance during the compression. The equilibrium stress is related to the covalent bond. In addition, the viscosity coefficient (η) was distributed between 7.14 × 105 Pa s and 9.31 × 105 Pa s, which was consistent with the trend of modulus value, reflecting the viscosity of dough. Compared with biaxial tensile viscosity, the viscosity coefficient was smaller, which may be that the water-soluble component had more obvious lubrication effect during the stress relaxation determination(Rouille et al., 2005). When the stress relaxation was measured, the ideal elastomer can recover the original structure instantaneously with the recovery degree of 100% and relaxation degree of 0%, while the relaxation degree is 100% for ideal viscous (or liquid). The equilibrium stress in polymer of liquid food is almost 0% without any permanent cross-link. However, there is a partial cross linking in solid food, which does not reach zero value. The deformation degree (R) is large, which indicates that the dough has a high viscosity. Therefore, the viscosity of dough made by two water adding was larger, and the viscosity of dough made by adding water to flour three times was smaller. For viscoelastic materials, it takes a long time to achieve stress balance. Relaxation time (τ) is the result of combined action of elastic behavior and viscous behavior. Longer the relaxation time is, more obvious the elastic deformation is, otherwise, the viscous deformation is more apparent. The relaxation time of doughs were distributed between 10.62s and 10.66s, and the stress attenuation speed of dough decreases, but there was no significant change, showing that the internal friction force and structure of doughs were similar.
4. Conclusion The interaction between flour and water is very important for the development of the dough. This paper reviewed the effects of water addition sequence on the viscoelasticity of dough. Compared with the control group, the rheological properties of dough made by adding water to flour several times were significantly changed, and there was no significant difference between dough made by water adding two times. The rheological properties of dough made with three time water adding method to flour was better than others. The contact between flour and water is carried out step by step by step by adding water, so that flour and water can be fully contacted, rather than partially bonded to form a cluster, part of which is still dry flour. This results in moisture migration to the inside of the dough, the full formation of gluten network, tensile properties increased, dough under external force was easier to restore. The water holding capacity of dough was enhanced and the water content of dough increased. When the uniaxial tensile properties were tested, the tensile properties of the dough are the strongest and the dough polymerization degree is the highest. At the same time, due to the contact between flour and water, more water soluble components are incorporated into the water, and their lubrication was strengthened. This made the viscosity of the dough increased and the fluidity was weakened, and the viscosity coefficient of dough was larger when the dough stress relaxation and the creep
3.6. Creep-recovery measurement The creep test can reflect the rheological properties of the dough intuitively, which is helpful to the development and design of the products, and can be used to evaluate the viscoelasticity of dough and the quality of noodles(Rouille et al., 2005). Fig. 5b was the result of the creep recovery experiment of different doughs. For all doughs, the curve were similar, which is consistent with the creep recovery characteristics of dough creep recovery in related literatures (Ahmed et al., 6
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recovery characteristics were measured. The role of water as plasticizer and the lubrication of water-soluble components played in the preparation of dough are important, which will also be the focus of future research. In addition, two fundamental rheological techniques, stress relaxation and creep-recovery may be more effective in differentiating small differences between samples.
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Author contributions The authors are grateful to Ke Bian, Erqi Guan for critically reviewing this manuscript. The authors are pleased to acknowledge Tingjing Zhang, Mengmeng Li for improving the communication of manuscript. Compliance with ethical standards Conflict of interest None. Compliance with ethics requirements This article does not contain any studies with human or animal subjects. Acknowledgments This research was supported by the National Natural Science Foundation of China (U1604235) and National Key Research and Development Program of China (2018YFD0401001). We gratefully acknowledge the entire technical staff of the National Engineering Laboratory for Wheat & Corn Further Processing for the supply of instruments. References Ahmed, J., Thomas, L., Al‐Attar, H., 2015. Oscillatory rheology and creep behavior of Barley β‐d‐glucan concentrate dough: effect of particle size, temperature, and water content. J. Food Sci. 80, E73–E83. Ali, A., Dominique, C., Eleni, C., Aliette, V., 2010. Rheological behaviour of biscuit dough in relation to water mobility. Int. J. Food Sci. Technol. 41, 124–128. Assifaoui, A., Champion, D., Chiotelli, E., Verel, A., 2006. Characterization of water mobility in biscuit dough using a low-field H NMR technique. Carbohydr. Polym. 64, 197–204. Bhattacharya, S., 2010. Stress relaxation behaviour of moth bean flour dough: product
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