- Email: [email protected]
Starch–gluten interactions during gelatinization and its functionality in dough like model systems
Food Hydrocolloids 54 (2016) 196e201
Contents lists available at ScienceDirect
Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd
Starchegluten interactions during gelatinization and its functionality in dough like model systems Mario Jekle*, Katharina Mühlberger, Thomas Becker €t München, Institute of Brewing and Beverage Technology, Research Group Cereal Process Engineering, Weihenstephaner Steig 20, Technische Universita 85354 Freising, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 May 2015 Received in revised form 6 October 2015 Accepted 8 October 2015 Available online xxx
Glutenestarch interactions are of specific importance during processing of cereal-based products. They become especially relevant during heating because of heat-induced changes within these biopolymers. A comprehensive characterization of the interactions during heating of the starchegluten model dough based on its mechanical behavior taking into account its raw material ratios and dough adapted water additions has yet to be achieved. Thus, the macrostructural characteristics with varying starchegluten ratios (92:8, 89:11, 86:14, 83:17, 80:20) in combination with different water additions (57.77, 60.78, 63.78, 65.58, 69.11 g water 100 g1 blend) was analyzed in dynamic oscillatory study during heating from 30 to 98 C. The delayed gelatinization onset (þ7 C) with increasing gluten content could be referred to a barrier effect of gluten around the starch granules with a hindered diffusion of water into the granules, since a competitive hydration was not significantly detectable. The decreased gelatinization intensity (67%) due to an increased gluten content showed a negligible effect of the barrier effect and a more competitive hydration between gluten and starch. A further reason can be weakening zones in the leached amylose network and a hindered granuleegranule interaction. Moreover, a simple possibility to identify the gelatinization onset in oscillatory tests by the derivative of the loss factor was defined. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Cereal Bread Gelatinization Rheology Baking Gluten denaturation DMTA
1. Introduction Interactions between biopolymers such as polysaccharides and proteins are of direct relevance to the macroscopic properties of many food matrices. They influence its functionality expressed by the rheological behavior, the stability, the texture, and the structure (Doublier, Garnier, Renard, & Sanchez, 2000; de Kruif & Tuinier, 2001). For this reason the interactions between polysaccharides and proteins have been studied in different fields of science and research for identifying functional properties (Considine et al., 2011; Koksel & Scanlon, 2012; Matignon et al., 2014; Navickis, Anderson, Bagley, & Jasberg, 1982; Petrofsky & Hoseney, 1995; Rosell & Foegeding, 2007; Ryan & Brewer, 2005). Among food matrices in particular, dough is a complex matrix of different, closely associated components. Induced by mechanical or thermal energy input, its polymers can be cross-linked creating the macroscopic structure through inter- and intramolecular forces. The matrix of (wheat) dough mainly consist of starch granules,
* Corresponding author. E-mail address: [email protected] (M. Jekle). http://dx.doi.org/10.1016/j.foodhyd.2015.10.005 0268-005X/© 2015 Elsevier Ltd. All rights reserved.
(gluten) proteins, lipids and arabinoxylans. The properties of these components shows a great variety due to its different growing, harvesting, and processing treatments, resulting in varying functionalities. Interactions between the components, which in consequence become visible in the viscoelastic characteristics, can be evaluated by macroscopic examination in dynamic oscillation measurements (Rosell & Foegeding, 2007). For a systematic analysis of different interactions model dough systems containing starch and gluten can be used. Thus the complexity of the real systems is reduced and relations between specific components can be analyzed. Dynamic rheological measurements of these kinds of model dough systems made with only starch and gluten already show that starch does not only act as an inert filler but interacts with gluten and is active in determining the viscoelastic behavior of systems (Champenois, Rao, & Walker, 1998; Miller & Hoseney, 1999; Petrofsky & Hoseney, 1995). Therefore, it is assumed, that not only the functionality of the single ingredients but rather the interactions between them influence the behavior of the matrix. The functionality of starch becomes specially dominant during the heating process (Jekle & Becker, 2012). Interactions between these polymers could also be rearranged. During heating the gelatinization of starch and the denaturation of gluten occurs due
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
to heat-induced conformational changes. The endothermic changes during the gelatinization of starch in the presence of gluten were already comprehensively investigated by Differential Scanning Calorimetry analyses (Delcour et al., 2000; Eliasson, 1983; Homer, Kelly, & Day, 2014; Mohamed & Rayas-Duarte, 2003). Furthermore, mechanical analyses of starch protein mixtures during heating were already conducted to investigate the interactions of starch and protein or gluten during heating: starch and meat protein during heating (Li & Yeh, 2003), starch and soy protein during heating (Li, Yeh, & Fan, 2007), gluten in already gelatinized starch gels (Lindahl & Eliasson, 1986), starch and gluten without a continuous recording of the changes due to the temperature (Yang, Song, & Zheng, 2011), starch and gluten (with different strength) mixtures (Chen, Deng, Wu, Tian, & Xie, 2010), and starch and gluten mixtures as dispersions in excess of water (Champenois et al., 1998). The last study was especially comprehensive in regard to the interactions. Since the high water content in this study varies from a typical dough system, a direct transfer of knowledge to dough based systems is hindered (Schirmer, Zeller, Krause, Jekle, & Becker, 2014). It is known that in starchegluten systems the hydration properties play a major role (Mohamed & Rayas-Duarte, 2003). However, since the water levels of the mentioned studies were fixed or even in excess water, this could be a limitation for some interpretations of interactions of starchegluten model systems in low water systems. From the mentioned studies above two main interactions between starch and gluten during heating are derived: a) a competitive hydration between the polymers during their structural changes, and b) a diffusion barrier by the gluten proteins located on the starch granule surface and thus a changed diffusion of water into the starch granules. In order to enable an elucidation of the interaction between starch and gluten a comprehensive characterization using a full factorial design of the macrostructural changes during heating of starchegluten model dough was conducted in this study. In the course of this, the raw-material ratios in wheat and dough adapted (and thus low) water additions were taken into account. In order to differentiate between the two main interactions different gluten and water additions were used in a full factorial design and in a dynamic mechanical thermal analysis (DMTA) the rheological properties complex shear modulus and loss factor were continuously examined during the heating and the following gelatinization. Since there is still no simple mathematical definition of the onset of starch gelatinization in rheological measurements, a further aim of this analysis was to define a quantitative determination of the start gelatinization temperature. 2. Materials and methods 2.1. Materials € ner Sta €rke, Wheat starch and gluten was kindly provided by Kro Ibbenbüren, Germany. Starch had a moisture content of 11.24 ± 0.50% (n ¼ 2), protein content of 0.24% (n ¼ 1) in the dry mass, and amylose content of 22.18 ± 0.13% (n ¼ 2). Gluten had a moisture content of 6.44 ± 0.39% (n ¼ 2) and protein content of 82.36% (n ¼ 1) in the dry mass. Moisture content was analyzed following ICC 110/1 and protein content following the Kjeldahl Method (EBC) (Anger, 2006). For the amylose content the colourimetric method of the Amylose/Amylopectin Assay Kit by Megazyme International Ireland, Bray, Ireland was used. 2.2. Sample preparation and experimental design In total, 25 starchegluten model dough systems (each 5.0 g) were prepared, based on five different starchegluten ratio and five
197
different distilled water levels in a full factorial design. The following starchegluten ratios were used: 92:8, 89:11, 86:14, 83:17, and 80:20. The starchegluten blend with the ratio of 86:14 reflects a realistic composition of starch and gluten in wheat flour (Goesaert et al., 2005). The other starch to gluten ratios are based in the narrow range below and above 14% gluten content. The amount of distilled water added to each starchegluten blend was 57.77, 60.78, 63.78, 65.58, and 69.11 g 100 g1 of total sample weight (based on 14% blend moisture content). The used water additions are derived from the solvent retention capacity (SRC) of the materials in accordance with AACC method 56-11 (AACCInternational, 2000): The SRC of starchegluten blends with the ratio 86:14 and 80:20 was determined to define the model dough adapted water addition and revealed a water absorption of 63.78 ± 1.46% (n ¼ 4) and 57.77 ± 2.28% (n ¼ 4), respectively. The further water additions correspond to the water absorption of wheat starch (69.11 ± 1.09% (n ¼ 4)) and for comparison of wheat flour type 550 obtained from Rosenmühle, Landshut, Germany (65.58 ± 0.11% (n ¼ 4)). The water addition of 60.78% corresponds to the mean of 57.77% and 63.78%. The water levels were chosen to enable a water addition comparable to the production of bakery products. Another reason was the quite equal distribution of the water levels for the experimental design. The model dough was mixed for 3 min in a Glutomatic system, which was specially modified for the sample preparation €ring, Nuber, Stukenborg, Jekle, & Becker, 2015). Since mixing has (Do a distinct effect on gelatinization properties (Mohamed & RayasDuarte, 2003) this mixing procedure and time was chosen for a standardization of the preparation. For the mixing, the metal sieve insert of the Glutomatic wash chamber was replaced with a metal insert without sieving functionality. Furthermore, the automatic washing after the mixing phase was deactivated. 2.3. Dynamic mechanical thermal analysis (DMTA) with oscillatory measurements Dynamic mechanical thermal analysis (DMTA) with oscillatory measurements was performed with an AR-G2 rheometer (TA instruments, New Castle, USA; software Rheology Advantage 5.7.2.0) using a Smart Swap Peltier plate temperature system with a 40 mm plateeplate geometry and a gap of 2000 mm. After placing the dough between the plates and adjusting the gap, the excess dough was trimmed with a spatula and the edges were coated with paraffin to prevent drying. The initial temperature was maintained at 30 C for all tests. The oscillation was carried out within the linear viscoelastic region of the sample at a constant strain amplitude (0.1% strain) as well as a constant frequency of 1 Hz. Equilibrium time before the test was set to 2 min, based on equilibrium in time sweep tests in pre-trials. After a oscillatory time sweep for 1 min at the initial temperature a heating step simulating the baking process from 30 C to 98 C with a temperature ramp of 4.25 C/min1 was performed. This heating rate was found in preliminary tests to be a realistic increase in temperature in dough during baking process. At the end of the heating step the temperature of 98 C was held for 3 min. The loss factor tan d and the complex shear modulus |G*| were recorded. The DMTA was performed with all combinations (in total 25) of the in 2.2 described starchegluten ratios and water addition levels. Analyses were performed in triplicate. 2.4. Determination of starch start gelatinization temperature The gelatinization process of starch can be easily monitored by the course of the dynamic moduli. During this process the complex shear modulus |G*| and the loss factor tan d show a pronounced maximum at different temperatures. While the maximum of |G*| is characteristic for the maximal structural hardening, the maximum
198
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
of tan d represents the highest viscous ratio and indicates the lowest structural stability. The increase of |G*| reflects the initiation of the gelatinization, when granule swelling occurs due to increased water absorption and leaching of amylose. Mathematically, the curvature of a curve is determined by the second derivative of the function and represents a change of direction. When the second derivative is greater than zero (f00 (x) > 0) the function graph is monotonically increasing. In this study the first positive maximum of the second derivative is defined as the temperature at which an increase of |G*| can be detected. Since the maximum of tan d is located in the area of the increase of |G*|, correlation analysis of the increase of |G*| with the maximum of tan d is carried out to reveal the possibility of determination of the onset gelatinization temperature in rheological measurements by the maximum of tan d. Thereby, the maximum value of tan d is determined by the intersection of the gradient of the function graph (first derivative) with x-axis (f0 (x) ¼ 0). 2.5. Statistics Statistical analysis was performed with the software Prism 6 (Version 6.01, GraphPad Software, Inc.). The results were analyzed using a linear regression analysis to determine the relationships between the variables, whereby the coefficient of determination R2 represents the degree of correlation. Two-Way-ANOVA was used to show a statistically significant difference between two independent variables and a dependent variable (5% significance level). 3. Results and discussion 3.1. Effect of different starchegluten ratios The effect of protein on starch gelatinization behavior was already investigated in several studies (Champenois et al., 1998; Li et al., 2007; Petrofsky & Hoseney, 1995). For a practical consideration of the results for dough systems there should be a) a starchegluten ratio in a realistic orientation, as in different wheat flours, b) a moisture content comparable to the intermediate dough, and c) a process derived heating ramp. Furthermore, a high resolution of starchegluten ratios is necessary to set up a quantitative dependency. These factors were considered in the experimental design. The results of the dynamic mechanical analysis combined with a temperature sweep (DMTA) with the exemplarily chosen water addition defined by the SRC of pure starch are presented in Fig. 1. All of the six model dough (starchegluten ratios of 100:0, 92:8, 89:11, 86:14, 83:17, 80:20) showed a significant increase of the complex shear modulus |G*| between 55 and 62 C, representing the onset of the starch gelatinization. Starch granules start to swell quickly, thus decreasing the content of free water in the surrounding matrix. Amylose leaches from the starch granules, causing another increase of viscosity due to a network formation. Between 65 and 69 C a maximum of the complex shear modulus occurs and the gelatinization reaches its maximal intensity since the starch granular structure starts to disintegrate and the crystalline structure melts. This is followed by a decrease of firmness up to 100 C (with exception of pure starch which showed a local minimum). This behavior describes the viscosity changes during gelatinization and is well known for starch containing materials. Additionally, Fig. 1 shows that the maximum firmness of the model dough decreases with increasing gluten content (up to 67%). Gluten could negatively affect the network formation of the leached amylose due to fault zones in this network (Champenois et al., 1998). Thus, the higher the gluten content the lower the peak of the complex shear modulus. In the context of starchegluten
Fig. 1. Complex shear modulus |G*| [Pa] and loss factor tan d [] of starchegluten model dough with different starchegluten ratios ( 100:0, 92:8, 89:11, 86:14, 83:17, 80:20) as a function of a temperature ramp (4.25 C min1). The water addition was exemplarily set to 69.11 g 100 g1 of the starchegluten blend, which reflects the SRC of starch. Results are shown as mean X ± standard deviation (n ¼ 3).
interactions which occur during gelatinization, this effect could be interpreted as the absence of covalent bonds between starch and gluten (Champenois et al., 1998; Martin, Zeleznak, & Hoseney, 1991). In the presence of new covalent bonds an increase of the firmness would have been expected. As well as the maximum firmness at the peak, the temperature at the onset of the firmness increase is highly dependent on the gluten content. This effect is not limited on gluten containing starch based foods but also on other protein containing starch based materials. In a milk-protein starch system a reinforcement of the starch granule structure in the presence of caseinates during heating was described. Kett et al. explained this effect with hydrophobic interactions between the caseinates and the starch granule surface (Kett et al., 2013). An interpretation of these facts leads to the assumption that a barrier by the proteins between the starch granules and the surrounding
Fig. 2. Correlation of the temperature at the maximum of tan d and the temperature at the onset of the increase of the complex shear modulus |G*|. Correlation coefficient of 0.97 and a slope of 0.977 ± 0.106.
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
199
liquid phase could lead to a limitation of water diffusion towards the starch granule during gelatinization. Since starch gelatinization is influenced by the water availability (Beck, Jekle, & Becker, 2011), a further explanation for the described behavior could be a competitive hydration of gluten and starch. The maximum of the complex shear modulus characterizes the maximum of the structure solidification. On the other side, the maximum of the loss factor tan d shows the highest viscos ratio of the samples and indicates the lowest structural stability. Another interesting fact is the coincidence in temperature of the maximum peak of the loss factor and the start of the increase of the complex shear modulus. The start of the increase of the complex shear modulus is referred to be the start of gelatinization (Vallons & Arendt, 2009). Thus, it would be interesting if the maximum of the loss factor tan d could be a tool to identify the start of the gelatinization.
Fig. 1). The value of the temperature increase is defined as the first positive maximum of the second derivative of the curve of the complex shear modulus. For pure starch this is 54.68 C. Fig. 2 compares the temperature at the maximum of tan d and the temperature at the onset of the increase of the complex shear modulus. A linear correlation shows a R2 of 0.97 (p ¼ 0.003) and a slope of 0.977 ± 0.106. Based on these results the maximum of tan d can be used to characterize the onset of the gelatinization in the current experimental conditions. Most of the analyses of gelatinization of starches and flours are performed in excess of water such as in an Amylograph or Rapid Visco Analyzer (Schirmer, Jekle, & Becker, 2015). Since these analyses are not comparable to real material conditions, the current method could be a valid tool to determine the start of gelatinization in dough systems. For a general significance these rheological properties should be examined with starches of different botanical sources.
3.2. Usage of the loss factor as a measure of gelatinization onset
3.3. Evaluation of dependencies at the gelatinization onset
In general, all experimental settings result in a solid state characteristic of the materials (tan d < 1). The maximum of the loss factor is calculated by the first derivative of the function of the temperature ramp. The loss factor reaches in this example its maximum at a temperature of 54.40 C (f0 (x) ¼ 0). Also, at this temperature the complex shear modulus increases rapidly (see
The loss factor is the ratio of the loss modulus to the elastic modulus and is in normal wheat dough between 0.34 (Jekle & Becker, 2011) and 0.46 (calculation based on the results) (Van Bockstaele, De Leyn, Eeckhout, & Dewettinck, 2008) at 30 C. Fig. 3A shows the maxima of tan d of the starchegluten model dough with different water additions as a function of the gluten
Fig. 3. A) Values of the maximum of tan d of starchegluten model dough with different water additions as a function of the gluten content (based on starchegluten blend). Results are shown as mean X ± standard deviation (n ¼ 3). B) Temperatures at the mean maximum of tan d of starchegluten model dough with different water additions as a function of the gluten content (based on starchegluten blend). Water additions are 57.77, 60.78, 63.78, 65.58, 69.11 g water 100 g1 of total sample weight (based on 14% mixture moisture content).
Fig. 4. A) Values of the maximum of |G*| of starchegluten model dough with different water additions as a function of the gluten content (based on starchegluten blend). Results are shown as mean X ± standard deviation (n ¼ 3). B) Temperatures at the mean maximum of |G*| of starchegluten model dough with different water additions as a function of the gluten content (based on starchegluten blend). Water additions are 57.77, 60.78, 63.78, 65.58, 69.11 g distilled water 100 g1 of total sample weight (based on 14% mixture moisture content).
200
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
content (based on starchegluten blend). The more gluten (the lower the starch ratio), the lower tan d gets and thus the higher the relative elastic part. This means a higher gluten content leads to a more elastic character at the onset of the gelatinization of a gluten containing starch matrix. This dependency is linear in a negative matter with a R2 of 0.81, 0.67, and 0.85 (p < 0.001) for 60.70, 65.58, and 69.11 distilled water 100 g1 of total sample weight, respectively. An addition of 57.77 and 63.78 g distilled water 100 g1 of total sample weight revealed no significant linear relation (p > 0.05). A Two-Way-ANOVA shows significant interactions between the gluten content and the water additions towards the tan dmax values (p ¼ 0.003). Thus, the amount of gluten has an impact on the viscous to elastic ratio of the glutenestarch model dough. Fig. 3B demonstrates the linear and positive dependency of the gluten content on the temperature at which dmax occurs. This is equal to the onset of the gelatinization. Gluten (in the amount of 8e20% in starch) delays the onset of the gelatinization by 7 C. However, water content has no significant effect (p ¼ 0.3) in these experiments. Further, a Two-Way-ANOVA reveals no significant effects of interactions between the starchegluten ratio and the water addition on the temperature at dmax. Before, two theories for the delayed gelatinization onset due to a varied gluten content (in the observed ratios) were discussed: a) a competitive hydration of the polymers, and b) a diffusion barrier effect located on the starch granule surface and thus a delayed diffusion of water into the starch granules. Taking the current results into account, it can be concluded that the competitive hydration of the polymers is not the main reason, since the water content has no significant effect. Thus, the barrier effects of gluten on the surface of the starch granules is the main reason for the delayed gelatinization onset. The competitive hydration seems to play a minor role. 3.4. Evaluation of dependencies at the gelatinization maximum The increase in firmness of the starch based material during
heating is based on the increased hydration of the starch granules and the gelling of the leached starch and its intra- and intermolecular hydrogen bonds (Chiotelli & Le Meste, 2002; Tamaki, Konishi, & Tako, 2011). The values for the maxima of the complex shear modulus (|G*|max) are presented in Fig. 4A. The variation of the gluten content in the starch matrix and the water addition reveals that gluten linearly and highly significantly decreases the gelatinization intensity of the starchegluten matrix R2 of between 0.91 and 0.98 (p < 0.001). The different water additions also have a significant effect. However, interactions between the starchegluten ratio and the water addition on |G*|max cannot be statistically detected. Fig. 4B shows the linear delay of the gelatinization maximum with increased gluten content. This means, that the gelatinization maximum occurs later and at a higher temperature. In contrast to the onset of the gelatinization, water has a significant effect on the temperature of |G*|max (p ¼ 0.01) in this case. Comparing the effect of gluten and water addition shows that gluten has twice the effect as water (based on a calculation w/w). In summary, the hydration properties seems to be a limiting effect for the maximum of the gelatinization. The role of the barrier effect around the starch granules can't be proven or disproven. However, due to the known strong structural disorientation of the starch granules during gelatinization a barrier effect seems to not be relevant in this process stage. Nevertheless, a structural weakening of the gluten in the whole matrix could be a supporting effect. 4. Conclusion In oscillatory rheological characterizations of wheat starch based materials during heating the maximum peak of the loss factor tan d can be a proper tool to easily specify the onset of the gelatinization. This seems to be valid at least in starchegluten ratios and water contents in wheat dough systems. The significance in all starch based materials has to be further investigated. The mechanistic context of this relation should also be addressed. The main aim of the study was the differentiation between the
Fig. 5. Schematic description of the barrier effect of gluten in a starchegluten model dough during heating and its effect on the delayed gelatinization onset.
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
possible interactions between wheat starch and gluten proteins during heating and the derived effect on the onset of gelatinization and the gelatinization maximum. It could be revealed that at the beginning of gelatinization gluten represents a layer around the starch granules forming a barrier for the increased hydration of the starch granules (see Fig. 5). Thus the diffusion of water into the starch granules is hindered and the gelatinization onset is delayed. The potential competition between the starch and gluten hydration seems to play a minor role, since an increased water content by 20% did not have a significant effect on the onset temperature. Focusing on the gelatinization maximum, this barrier effect becomes negligible and the hydration (affected by the increased available water amount) appears to play the major role. Further, a structural effect of gluten on the gelatinization intensity has to be discussed. Gluten could disturb the contact area between disintegrated starch granules during heating and thus hindering a network based on granuleegranule interactions. A second reason could be the weakening of the amylose network due to fault zones in the network structure (Champenois et al., 1998). The differentiation between these effects could be an interesting question for further experiments. In summary, it has again been proven that starch does not act as a simple filler in starchegluten model dough systems and that a simple and separated investigation of gluten and starch is not sufficient for the elucidation of the gelatinization behavior of starch based materials. References AACC International. (2010). Approved Methods of Analysis, 11th Ed. Method 56e11.02. Available online only. St. Paul, MN, U.S.A.: AACC International. Anger, H.-M. (2006). Brautechnische analysenmethoden. Band Rohstoffe. Selbstverlag der MEBAK. Beck, M., Jekle, M., & Becker, T. (2011). Starch re-crystallization kinetics as a function of various cations. Starch-Starke, 63, 792e800. Champenois, Y., Rao, M. A., & Walker, L. P. (1998). Influence of gluten on the viscoelastic properties of starch pastes and gels. Journal of the Science of Food and Agriculture, 78(1), 119e126. Chen, J.-s., Deng, Z.-y., Wu, P., Tian, J.-c., & Xie, Q.-g. (2010). Effect of gluten on pasting properties of wheat starch. Agricultural Sciences in China, 9(12), 1836e1844. Chiotelli, E., & Le Meste, M. (2002). Effect of small and large wheat starch granules on thermomechanical behavior of starch. Cereal Chemistry Journal, 79(2), 286e293. Considine, T., Noisuwan, A., Hemar, Y., Wilkinson, B., Bronlund, J., & Kasapis, S. (2011). Rheological investigations of the interactions between starch and milk proteins in model dairy systems: a review. Food Hydrocolloids, 25(8), 2008e2017. cassis, J., Sindic, M., & Deroanne, C. Delcour, J. A., Vansteelandt, J., Hythier, M. C., Abe (2000). Fractionation and reconstitution experiments provide insight into the role of gluten and starch interactions in pasta quality. Journal of Agricultural and Food Chemistry, 48(9), 3767e3773. € ring, C., Nuber, C., Stukenborg, F., Jekle, M., & Becker, T. (2015). Impact of arabiDo noxylan addition on protein microstructure formation in wheat and rye dough. Journal of Food Engineering, 154(0), 10e16. Doublier, J. L., Garnier, C., Renard, D., & Sanchez, C. (2000). Proteinepolysaccharide interactions. Current Opinion in Colloid & Interface Science, 5(3e4), 202e214. Eliasson, A. C. (1983). Differential scanning calorimetry studies on wheat starchdgluten mixtures: I. Effect of gluten on the gelatinization of wheat starch. Journal of Cereal Science, 1(3), 199e205.
201
Goesaert, H., Brijs, K., Veraverbeke, W. S., Courtin, C. M., Gebruers, K., & Delcour, J. A. (2005). Wheat flour constituents: how they impact bread quality, and how to impact their functionality. Trends in Food Science & Technology, 16(1e3), 12e30. Homer, S., Kelly, M., & Day, L. (2014). Determination of the thermo-mechanical properties in starch and starch/gluten systems at low moisture content e a comparison of DSC and TMA. Carbohydrate Polymers, 108, 1e9. Jekle, M., & Becker, T. (2011). Dough microstructure: novel analysis by quantification using confocal laser scanning microscopy. Food Research International, 44(4), 984e991. Jekle, M., & Becker, T. (2012). Effects of acidification, sodium chloride, and moisture levels on wheat dough: II. Modeling of bread texture and staling kinetics. Food Biophysics, 7(3), 200e208. Kett, A. P., Chaurin, V., Fitzsimons, S. M., Morris, E. R., O'Mahony, J. A., & Fenelon, M. A. (2013). Influence of milk proteins on the pasting behaviour and microstructural characteristics of waxy maize starch. Food Hydrocolloids, 30(2), 661e671. Koksel, F., & Scanlon, M. G. (2012). Effects of composition on dough development and air entrainment in doughs made from gluten-starch blends. Journal of Cereal Science, 56(2), 445e450. de Kruif, C. G., & Tuinier, R. (2001). Polysaccharide protein interactions. Food Hydrocolloids, 15(4e6), 555e563. Lindahl, L., & Eliasson, A.-C. (1986). Effects of wheat proteins on the viscoelastic properties of starch gels. Journal of the Science of Food and Agriculture, 37(11), 1125e1132. Li, J.-Y., & Yeh, A.-I. (2003). Effects of starch properties on rheological characteristics of starch/meat complexes. Journal of Food Engineering, 57(3), 287e294. 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(4), 1240e1247. Martin, M. L., Zeleznak, K. J., & Hoseney, R. C. (1991). A mechanism of bread firming. I. Role of starch swelling. Cereal Chemistry, 68(5), 498e503. Matignon, A., Moulin, G., Barey, P., Desprairies, M., Mauduit, S., Sieffermann, J. M., et al. (2014). Starch/carrageenan/milk proteins interactions studied using multiple staining and confocal laser scanning microscopy. Carbohydrate Polymers, 99(0), 345e355. Miller, K. A., & Hoseney, R. C. (1999). Dynamic rheological properties of wheat starch-gluten doughs. Cereal Chemistry, 76(1), 105e109. Mohamed, A. A., & Rayas-Duarte, P. (2003). The effect of mixing and wheat protein/ gluten on the gelatinization of wheat starch*. Food Chemistry, 81(4), 533e545. Navickis, L. L., Anderson, R. A., Bagley, E. B., & Jasberg, B. K. (1982). Viscoelastic properties of wheat flour doughs: Variation of dynamic moduli with water and protein content. Journal of Texture Studies, 13(2), 249e264. Petrofsky, K. E., & Hoseney, R. C. (1995). Rheological properties of dough made with starch and gluten from several cereal sources. Cereal Chemistry, 72, 53e58. Rosell, C. M., & Foegeding, A. (2007). Interaction of hydroxypropylmethylcellulose with gluten proteins: small deformation properties during thermal treatment. Food Hydrocolloids, 21(7), 1092e1100. Ryan, K. J., & Brewer, M. S. (2005). Model system analysis of wheat starch-soy protein interaction kinetics using polystyrene microspheres. Food Chemistry, 92(2), 325e335. Schirmer, M., Jekle, M., & Becker, T. (2015). Starch gelatinization and its complexity €rke, 67(1e2), 30e41. for analysis. Starch e Sta Schirmer, M., Zeller, J., Krause, D., Jekle, M., & Becker, T. (2014). In situ monitoring of starch gelatinization with limited water content using confocal laser scanning microscopy. European Food Research and Technology, 239(2), 247e257. Tamaki, Y., Konishi, T., & Tako, M. (2011). Gelation and retrogradation mechanism of wheat amylose. Materials, 4(10), 1763e1775. Vallons, K. J. R., & Arendt, E. K. (2009). Effects of high pressure and temperature on the structural and rheological properties of sorghum starch. Innovative Food Science & Emerging Technologies, 10(4), 449e456. Van Bockstaele, F., De Leyn, I., Eeckhout, M., & Dewettinck, K. (2008). Rheological properties of wheat flour dough and their relationship with bread volume. II. Dynamic oscillation measurements. Cereal Chemistry Journal, 85(6), 762e768. Yang, Y., Song, Y., & Zheng, Q. (2011). Rheological behaviors of doughs reconstituted from wheat gluten and starch. Journal of Food Science and Technology, 48(4), 489e493.
Contents lists available at ScienceDirect
Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd
Starchegluten interactions during gelatinization and its functionality in dough like model systems Mario Jekle*, Katharina Mühlberger, Thomas Becker €t München, Institute of Brewing and Beverage Technology, Research Group Cereal Process Engineering, Weihenstephaner Steig 20, Technische Universita 85354 Freising, Germany
a r t i c l e i n f o
a b s t r a c t
Article history: Received 21 May 2015 Received in revised form 6 October 2015 Accepted 8 October 2015 Available online xxx
Glutenestarch interactions are of specific importance during processing of cereal-based products. They become especially relevant during heating because of heat-induced changes within these biopolymers. A comprehensive characterization of the interactions during heating of the starchegluten model dough based on its mechanical behavior taking into account its raw material ratios and dough adapted water additions has yet to be achieved. Thus, the macrostructural characteristics with varying starchegluten ratios (92:8, 89:11, 86:14, 83:17, 80:20) in combination with different water additions (57.77, 60.78, 63.78, 65.58, 69.11 g water 100 g1 blend) was analyzed in dynamic oscillatory study during heating from 30 to 98 C. The delayed gelatinization onset (þ7 C) with increasing gluten content could be referred to a barrier effect of gluten around the starch granules with a hindered diffusion of water into the granules, since a competitive hydration was not significantly detectable. The decreased gelatinization intensity (67%) due to an increased gluten content showed a negligible effect of the barrier effect and a more competitive hydration between gluten and starch. A further reason can be weakening zones in the leached amylose network and a hindered granuleegranule interaction. Moreover, a simple possibility to identify the gelatinization onset in oscillatory tests by the derivative of the loss factor was defined. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Cereal Bread Gelatinization Rheology Baking Gluten denaturation DMTA
1. Introduction Interactions between biopolymers such as polysaccharides and proteins are of direct relevance to the macroscopic properties of many food matrices. They influence its functionality expressed by the rheological behavior, the stability, the texture, and the structure (Doublier, Garnier, Renard, & Sanchez, 2000; de Kruif & Tuinier, 2001). For this reason the interactions between polysaccharides and proteins have been studied in different fields of science and research for identifying functional properties (Considine et al., 2011; Koksel & Scanlon, 2012; Matignon et al., 2014; Navickis, Anderson, Bagley, & Jasberg, 1982; Petrofsky & Hoseney, 1995; Rosell & Foegeding, 2007; Ryan & Brewer, 2005). Among food matrices in particular, dough is a complex matrix of different, closely associated components. Induced by mechanical or thermal energy input, its polymers can be cross-linked creating the macroscopic structure through inter- and intramolecular forces. The matrix of (wheat) dough mainly consist of starch granules,
* Corresponding author. E-mail address: [email protected] (M. Jekle). http://dx.doi.org/10.1016/j.foodhyd.2015.10.005 0268-005X/© 2015 Elsevier Ltd. All rights reserved.
(gluten) proteins, lipids and arabinoxylans. The properties of these components shows a great variety due to its different growing, harvesting, and processing treatments, resulting in varying functionalities. Interactions between the components, which in consequence become visible in the viscoelastic characteristics, can be evaluated by macroscopic examination in dynamic oscillation measurements (Rosell & Foegeding, 2007). For a systematic analysis of different interactions model dough systems containing starch and gluten can be used. Thus the complexity of the real systems is reduced and relations between specific components can be analyzed. Dynamic rheological measurements of these kinds of model dough systems made with only starch and gluten already show that starch does not only act as an inert filler but interacts with gluten and is active in determining the viscoelastic behavior of systems (Champenois, Rao, & Walker, 1998; Miller & Hoseney, 1999; Petrofsky & Hoseney, 1995). Therefore, it is assumed, that not only the functionality of the single ingredients but rather the interactions between them influence the behavior of the matrix. The functionality of starch becomes specially dominant during the heating process (Jekle & Becker, 2012). Interactions between these polymers could also be rearranged. During heating the gelatinization of starch and the denaturation of gluten occurs due
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
to heat-induced conformational changes. The endothermic changes during the gelatinization of starch in the presence of gluten were already comprehensively investigated by Differential Scanning Calorimetry analyses (Delcour et al., 2000; Eliasson, 1983; Homer, Kelly, & Day, 2014; Mohamed & Rayas-Duarte, 2003). Furthermore, mechanical analyses of starch protein mixtures during heating were already conducted to investigate the interactions of starch and protein or gluten during heating: starch and meat protein during heating (Li & Yeh, 2003), starch and soy protein during heating (Li, Yeh, & Fan, 2007), gluten in already gelatinized starch gels (Lindahl & Eliasson, 1986), starch and gluten without a continuous recording of the changes due to the temperature (Yang, Song, & Zheng, 2011), starch and gluten (with different strength) mixtures (Chen, Deng, Wu, Tian, & Xie, 2010), and starch and gluten mixtures as dispersions in excess of water (Champenois et al., 1998). The last study was especially comprehensive in regard to the interactions. Since the high water content in this study varies from a typical dough system, a direct transfer of knowledge to dough based systems is hindered (Schirmer, Zeller, Krause, Jekle, & Becker, 2014). It is known that in starchegluten systems the hydration properties play a major role (Mohamed & Rayas-Duarte, 2003). However, since the water levels of the mentioned studies were fixed or even in excess water, this could be a limitation for some interpretations of interactions of starchegluten model systems in low water systems. From the mentioned studies above two main interactions between starch and gluten during heating are derived: a) a competitive hydration between the polymers during their structural changes, and b) a diffusion barrier by the gluten proteins located on the starch granule surface and thus a changed diffusion of water into the starch granules. In order to enable an elucidation of the interaction between starch and gluten a comprehensive characterization using a full factorial design of the macrostructural changes during heating of starchegluten model dough was conducted in this study. In the course of this, the raw-material ratios in wheat and dough adapted (and thus low) water additions were taken into account. In order to differentiate between the two main interactions different gluten and water additions were used in a full factorial design and in a dynamic mechanical thermal analysis (DMTA) the rheological properties complex shear modulus and loss factor were continuously examined during the heating and the following gelatinization. Since there is still no simple mathematical definition of the onset of starch gelatinization in rheological measurements, a further aim of this analysis was to define a quantitative determination of the start gelatinization temperature. 2. Materials and methods 2.1. Materials € ner Sta €rke, Wheat starch and gluten was kindly provided by Kro Ibbenbüren, Germany. Starch had a moisture content of 11.24 ± 0.50% (n ¼ 2), protein content of 0.24% (n ¼ 1) in the dry mass, and amylose content of 22.18 ± 0.13% (n ¼ 2). Gluten had a moisture content of 6.44 ± 0.39% (n ¼ 2) and protein content of 82.36% (n ¼ 1) in the dry mass. Moisture content was analyzed following ICC 110/1 and protein content following the Kjeldahl Method (EBC) (Anger, 2006). For the amylose content the colourimetric method of the Amylose/Amylopectin Assay Kit by Megazyme International Ireland, Bray, Ireland was used. 2.2. Sample preparation and experimental design In total, 25 starchegluten model dough systems (each 5.0 g) were prepared, based on five different starchegluten ratio and five
197
different distilled water levels in a full factorial design. The following starchegluten ratios were used: 92:8, 89:11, 86:14, 83:17, and 80:20. The starchegluten blend with the ratio of 86:14 reflects a realistic composition of starch and gluten in wheat flour (Goesaert et al., 2005). The other starch to gluten ratios are based in the narrow range below and above 14% gluten content. The amount of distilled water added to each starchegluten blend was 57.77, 60.78, 63.78, 65.58, and 69.11 g 100 g1 of total sample weight (based on 14% blend moisture content). The used water additions are derived from the solvent retention capacity (SRC) of the materials in accordance with AACC method 56-11 (AACCInternational, 2000): The SRC of starchegluten blends with the ratio 86:14 and 80:20 was determined to define the model dough adapted water addition and revealed a water absorption of 63.78 ± 1.46% (n ¼ 4) and 57.77 ± 2.28% (n ¼ 4), respectively. The further water additions correspond to the water absorption of wheat starch (69.11 ± 1.09% (n ¼ 4)) and for comparison of wheat flour type 550 obtained from Rosenmühle, Landshut, Germany (65.58 ± 0.11% (n ¼ 4)). The water addition of 60.78% corresponds to the mean of 57.77% and 63.78%. The water levels were chosen to enable a water addition comparable to the production of bakery products. Another reason was the quite equal distribution of the water levels for the experimental design. The model dough was mixed for 3 min in a Glutomatic system, which was specially modified for the sample preparation €ring, Nuber, Stukenborg, Jekle, & Becker, 2015). Since mixing has (Do a distinct effect on gelatinization properties (Mohamed & RayasDuarte, 2003) this mixing procedure and time was chosen for a standardization of the preparation. For the mixing, the metal sieve insert of the Glutomatic wash chamber was replaced with a metal insert without sieving functionality. Furthermore, the automatic washing after the mixing phase was deactivated. 2.3. Dynamic mechanical thermal analysis (DMTA) with oscillatory measurements Dynamic mechanical thermal analysis (DMTA) with oscillatory measurements was performed with an AR-G2 rheometer (TA instruments, New Castle, USA; software Rheology Advantage 5.7.2.0) using a Smart Swap Peltier plate temperature system with a 40 mm plateeplate geometry and a gap of 2000 mm. After placing the dough between the plates and adjusting the gap, the excess dough was trimmed with a spatula and the edges were coated with paraffin to prevent drying. The initial temperature was maintained at 30 C for all tests. The oscillation was carried out within the linear viscoelastic region of the sample at a constant strain amplitude (0.1% strain) as well as a constant frequency of 1 Hz. Equilibrium time before the test was set to 2 min, based on equilibrium in time sweep tests in pre-trials. After a oscillatory time sweep for 1 min at the initial temperature a heating step simulating the baking process from 30 C to 98 C with a temperature ramp of 4.25 C/min1 was performed. This heating rate was found in preliminary tests to be a realistic increase in temperature in dough during baking process. At the end of the heating step the temperature of 98 C was held for 3 min. The loss factor tan d and the complex shear modulus |G*| were recorded. The DMTA was performed with all combinations (in total 25) of the in 2.2 described starchegluten ratios and water addition levels. Analyses were performed in triplicate. 2.4. Determination of starch start gelatinization temperature The gelatinization process of starch can be easily monitored by the course of the dynamic moduli. During this process the complex shear modulus |G*| and the loss factor tan d show a pronounced maximum at different temperatures. While the maximum of |G*| is characteristic for the maximal structural hardening, the maximum
198
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
of tan d represents the highest viscous ratio and indicates the lowest structural stability. The increase of |G*| reflects the initiation of the gelatinization, when granule swelling occurs due to increased water absorption and leaching of amylose. Mathematically, the curvature of a curve is determined by the second derivative of the function and represents a change of direction. When the second derivative is greater than zero (f00 (x) > 0) the function graph is monotonically increasing. In this study the first positive maximum of the second derivative is defined as the temperature at which an increase of |G*| can be detected. Since the maximum of tan d is located in the area of the increase of |G*|, correlation analysis of the increase of |G*| with the maximum of tan d is carried out to reveal the possibility of determination of the onset gelatinization temperature in rheological measurements by the maximum of tan d. Thereby, the maximum value of tan d is determined by the intersection of the gradient of the function graph (first derivative) with x-axis (f0 (x) ¼ 0). 2.5. Statistics Statistical analysis was performed with the software Prism 6 (Version 6.01, GraphPad Software, Inc.). The results were analyzed using a linear regression analysis to determine the relationships between the variables, whereby the coefficient of determination R2 represents the degree of correlation. Two-Way-ANOVA was used to show a statistically significant difference between two independent variables and a dependent variable (5% significance level). 3. Results and discussion 3.1. Effect of different starchegluten ratios The effect of protein on starch gelatinization behavior was already investigated in several studies (Champenois et al., 1998; Li et al., 2007; Petrofsky & Hoseney, 1995). For a practical consideration of the results for dough systems there should be a) a starchegluten ratio in a realistic orientation, as in different wheat flours, b) a moisture content comparable to the intermediate dough, and c) a process derived heating ramp. Furthermore, a high resolution of starchegluten ratios is necessary to set up a quantitative dependency. These factors were considered in the experimental design. The results of the dynamic mechanical analysis combined with a temperature sweep (DMTA) with the exemplarily chosen water addition defined by the SRC of pure starch are presented in Fig. 1. All of the six model dough (starchegluten ratios of 100:0, 92:8, 89:11, 86:14, 83:17, 80:20) showed a significant increase of the complex shear modulus |G*| between 55 and 62 C, representing the onset of the starch gelatinization. Starch granules start to swell quickly, thus decreasing the content of free water in the surrounding matrix. Amylose leaches from the starch granules, causing another increase of viscosity due to a network formation. Between 65 and 69 C a maximum of the complex shear modulus occurs and the gelatinization reaches its maximal intensity since the starch granular structure starts to disintegrate and the crystalline structure melts. This is followed by a decrease of firmness up to 100 C (with exception of pure starch which showed a local minimum). This behavior describes the viscosity changes during gelatinization and is well known for starch containing materials. Additionally, Fig. 1 shows that the maximum firmness of the model dough decreases with increasing gluten content (up to 67%). Gluten could negatively affect the network formation of the leached amylose due to fault zones in this network (Champenois et al., 1998). Thus, the higher the gluten content the lower the peak of the complex shear modulus. In the context of starchegluten
Fig. 1. Complex shear modulus |G*| [Pa] and loss factor tan d [] of starchegluten model dough with different starchegluten ratios ( 100:0, 92:8, 89:11, 86:14, 83:17, 80:20) as a function of a temperature ramp (4.25 C min1). The water addition was exemplarily set to 69.11 g 100 g1 of the starchegluten blend, which reflects the SRC of starch. Results are shown as mean X ± standard deviation (n ¼ 3).
interactions which occur during gelatinization, this effect could be interpreted as the absence of covalent bonds between starch and gluten (Champenois et al., 1998; Martin, Zeleznak, & Hoseney, 1991). In the presence of new covalent bonds an increase of the firmness would have been expected. As well as the maximum firmness at the peak, the temperature at the onset of the firmness increase is highly dependent on the gluten content. This effect is not limited on gluten containing starch based foods but also on other protein containing starch based materials. In a milk-protein starch system a reinforcement of the starch granule structure in the presence of caseinates during heating was described. Kett et al. explained this effect with hydrophobic interactions between the caseinates and the starch granule surface (Kett et al., 2013). An interpretation of these facts leads to the assumption that a barrier by the proteins between the starch granules and the surrounding
Fig. 2. Correlation of the temperature at the maximum of tan d and the temperature at the onset of the increase of the complex shear modulus |G*|. Correlation coefficient of 0.97 and a slope of 0.977 ± 0.106.
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
199
liquid phase could lead to a limitation of water diffusion towards the starch granule during gelatinization. Since starch gelatinization is influenced by the water availability (Beck, Jekle, & Becker, 2011), a further explanation for the described behavior could be a competitive hydration of gluten and starch. The maximum of the complex shear modulus characterizes the maximum of the structure solidification. On the other side, the maximum of the loss factor tan d shows the highest viscos ratio of the samples and indicates the lowest structural stability. Another interesting fact is the coincidence in temperature of the maximum peak of the loss factor and the start of the increase of the complex shear modulus. The start of the increase of the complex shear modulus is referred to be the start of gelatinization (Vallons & Arendt, 2009). Thus, it would be interesting if the maximum of the loss factor tan d could be a tool to identify the start of the gelatinization.
Fig. 1). The value of the temperature increase is defined as the first positive maximum of the second derivative of the curve of the complex shear modulus. For pure starch this is 54.68 C. Fig. 2 compares the temperature at the maximum of tan d and the temperature at the onset of the increase of the complex shear modulus. A linear correlation shows a R2 of 0.97 (p ¼ 0.003) and a slope of 0.977 ± 0.106. Based on these results the maximum of tan d can be used to characterize the onset of the gelatinization in the current experimental conditions. Most of the analyses of gelatinization of starches and flours are performed in excess of water such as in an Amylograph or Rapid Visco Analyzer (Schirmer, Jekle, & Becker, 2015). Since these analyses are not comparable to real material conditions, the current method could be a valid tool to determine the start of gelatinization in dough systems. For a general significance these rheological properties should be examined with starches of different botanical sources.
3.2. Usage of the loss factor as a measure of gelatinization onset
3.3. Evaluation of dependencies at the gelatinization onset
In general, all experimental settings result in a solid state characteristic of the materials (tan d < 1). The maximum of the loss factor is calculated by the first derivative of the function of the temperature ramp. The loss factor reaches in this example its maximum at a temperature of 54.40 C (f0 (x) ¼ 0). Also, at this temperature the complex shear modulus increases rapidly (see
The loss factor is the ratio of the loss modulus to the elastic modulus and is in normal wheat dough between 0.34 (Jekle & Becker, 2011) and 0.46 (calculation based on the results) (Van Bockstaele, De Leyn, Eeckhout, & Dewettinck, 2008) at 30 C. Fig. 3A shows the maxima of tan d of the starchegluten model dough with different water additions as a function of the gluten
Fig. 3. A) Values of the maximum of tan d of starchegluten model dough with different water additions as a function of the gluten content (based on starchegluten blend). Results are shown as mean X ± standard deviation (n ¼ 3). B) Temperatures at the mean maximum of tan d of starchegluten model dough with different water additions as a function of the gluten content (based on starchegluten blend). Water additions are 57.77, 60.78, 63.78, 65.58, 69.11 g water 100 g1 of total sample weight (based on 14% mixture moisture content).
Fig. 4. A) Values of the maximum of |G*| of starchegluten model dough with different water additions as a function of the gluten content (based on starchegluten blend). Results are shown as mean X ± standard deviation (n ¼ 3). B) Temperatures at the mean maximum of |G*| of starchegluten model dough with different water additions as a function of the gluten content (based on starchegluten blend). Water additions are 57.77, 60.78, 63.78, 65.58, 69.11 g distilled water 100 g1 of total sample weight (based on 14% mixture moisture content).
200
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
content (based on starchegluten blend). The more gluten (the lower the starch ratio), the lower tan d gets and thus the higher the relative elastic part. This means a higher gluten content leads to a more elastic character at the onset of the gelatinization of a gluten containing starch matrix. This dependency is linear in a negative matter with a R2 of 0.81, 0.67, and 0.85 (p < 0.001) for 60.70, 65.58, and 69.11 distilled water 100 g1 of total sample weight, respectively. An addition of 57.77 and 63.78 g distilled water 100 g1 of total sample weight revealed no significant linear relation (p > 0.05). A Two-Way-ANOVA shows significant interactions between the gluten content and the water additions towards the tan dmax values (p ¼ 0.003). Thus, the amount of gluten has an impact on the viscous to elastic ratio of the glutenestarch model dough. Fig. 3B demonstrates the linear and positive dependency of the gluten content on the temperature at which dmax occurs. This is equal to the onset of the gelatinization. Gluten (in the amount of 8e20% in starch) delays the onset of the gelatinization by 7 C. However, water content has no significant effect (p ¼ 0.3) in these experiments. Further, a Two-Way-ANOVA reveals no significant effects of interactions between the starchegluten ratio and the water addition on the temperature at dmax. Before, two theories for the delayed gelatinization onset due to a varied gluten content (in the observed ratios) were discussed: a) a competitive hydration of the polymers, and b) a diffusion barrier effect located on the starch granule surface and thus a delayed diffusion of water into the starch granules. Taking the current results into account, it can be concluded that the competitive hydration of the polymers is not the main reason, since the water content has no significant effect. Thus, the barrier effects of gluten on the surface of the starch granules is the main reason for the delayed gelatinization onset. The competitive hydration seems to play a minor role. 3.4. Evaluation of dependencies at the gelatinization maximum The increase in firmness of the starch based material during
heating is based on the increased hydration of the starch granules and the gelling of the leached starch and its intra- and intermolecular hydrogen bonds (Chiotelli & Le Meste, 2002; Tamaki, Konishi, & Tako, 2011). The values for the maxima of the complex shear modulus (|G*|max) are presented in Fig. 4A. The variation of the gluten content in the starch matrix and the water addition reveals that gluten linearly and highly significantly decreases the gelatinization intensity of the starchegluten matrix R2 of between 0.91 and 0.98 (p < 0.001). The different water additions also have a significant effect. However, interactions between the starchegluten ratio and the water addition on |G*|max cannot be statistically detected. Fig. 4B shows the linear delay of the gelatinization maximum with increased gluten content. This means, that the gelatinization maximum occurs later and at a higher temperature. In contrast to the onset of the gelatinization, water has a significant effect on the temperature of |G*|max (p ¼ 0.01) in this case. Comparing the effect of gluten and water addition shows that gluten has twice the effect as water (based on a calculation w/w). In summary, the hydration properties seems to be a limiting effect for the maximum of the gelatinization. The role of the barrier effect around the starch granules can't be proven or disproven. However, due to the known strong structural disorientation of the starch granules during gelatinization a barrier effect seems to not be relevant in this process stage. Nevertheless, a structural weakening of the gluten in the whole matrix could be a supporting effect. 4. Conclusion In oscillatory rheological characterizations of wheat starch based materials during heating the maximum peak of the loss factor tan d can be a proper tool to easily specify the onset of the gelatinization. This seems to be valid at least in starchegluten ratios and water contents in wheat dough systems. The significance in all starch based materials has to be further investigated. The mechanistic context of this relation should also be addressed. The main aim of the study was the differentiation between the
Fig. 5. Schematic description of the barrier effect of gluten in a starchegluten model dough during heating and its effect on the delayed gelatinization onset.
M. Jekle et al. / Food Hydrocolloids 54 (2016) 196e201
possible interactions between wheat starch and gluten proteins during heating and the derived effect on the onset of gelatinization and the gelatinization maximum. It could be revealed that at the beginning of gelatinization gluten represents a layer around the starch granules forming a barrier for the increased hydration of the starch granules (see Fig. 5). Thus the diffusion of water into the starch granules is hindered and the gelatinization onset is delayed. The potential competition between the starch and gluten hydration seems to play a minor role, since an increased water content by 20% did not have a significant effect on the onset temperature. Focusing on the gelatinization maximum, this barrier effect becomes negligible and the hydration (affected by the increased available water amount) appears to play the major role. Further, a structural effect of gluten on the gelatinization intensity has to be discussed. Gluten could disturb the contact area between disintegrated starch granules during heating and thus hindering a network based on granuleegranule interactions. A second reason could be the weakening of the amylose network due to fault zones in the network structure (Champenois et al., 1998). The differentiation between these effects could be an interesting question for further experiments. In summary, it has again been proven that starch does not act as a simple filler in starchegluten model dough systems and that a simple and separated investigation of gluten and starch is not sufficient for the elucidation of the gelatinization behavior of starch based materials. References AACC International. (2010). Approved Methods of Analysis, 11th Ed. Method 56e11.02. Available online only. St. Paul, MN, U.S.A.: AACC International. Anger, H.-M. (2006). Brautechnische analysenmethoden. Band Rohstoffe. Selbstverlag der MEBAK. Beck, M., Jekle, M., & Becker, T. (2011). Starch re-crystallization kinetics as a function of various cations. Starch-Starke, 63, 792e800. Champenois, Y., Rao, M. A., & Walker, L. P. (1998). Influence of gluten on the viscoelastic properties of starch pastes and gels. Journal of the Science of Food and Agriculture, 78(1), 119e126. Chen, J.-s., Deng, Z.-y., Wu, P., Tian, J.-c., & Xie, Q.-g. (2010). Effect of gluten on pasting properties of wheat starch. Agricultural Sciences in China, 9(12), 1836e1844. Chiotelli, E., & Le Meste, M. (2002). Effect of small and large wheat starch granules on thermomechanical behavior of starch. Cereal Chemistry Journal, 79(2), 286e293. Considine, T., Noisuwan, A., Hemar, Y., Wilkinson, B., Bronlund, J., & Kasapis, S. (2011). Rheological investigations of the interactions between starch and milk proteins in model dairy systems: a review. Food Hydrocolloids, 25(8), 2008e2017. cassis, J., Sindic, M., & Deroanne, C. Delcour, J. A., Vansteelandt, J., Hythier, M. C., Abe (2000). Fractionation and reconstitution experiments provide insight into the role of gluten and starch interactions in pasta quality. Journal of Agricultural and Food Chemistry, 48(9), 3767e3773. € ring, C., Nuber, C., Stukenborg, F., Jekle, M., & Becker, T. (2015). Impact of arabiDo noxylan addition on protein microstructure formation in wheat and rye dough. Journal of Food Engineering, 154(0), 10e16. Doublier, J. L., Garnier, C., Renard, D., & Sanchez, C. (2000). Proteinepolysaccharide interactions. Current Opinion in Colloid & Interface Science, 5(3e4), 202e214. Eliasson, A. C. (1983). Differential scanning calorimetry studies on wheat starchdgluten mixtures: I. Effect of gluten on the gelatinization of wheat starch. Journal of Cereal Science, 1(3), 199e205.
201
Goesaert, H., Brijs, K., Veraverbeke, W. S., Courtin, C. M., Gebruers, K., & Delcour, J. A. (2005). Wheat flour constituents: how they impact bread quality, and how to impact their functionality. Trends in Food Science & Technology, 16(1e3), 12e30. Homer, S., Kelly, M., & Day, L. (2014). Determination of the thermo-mechanical properties in starch and starch/gluten systems at low moisture content e a comparison of DSC and TMA. Carbohydrate Polymers, 108, 1e9. Jekle, M., & Becker, T. (2011). Dough microstructure: novel analysis by quantification using confocal laser scanning microscopy. Food Research International, 44(4), 984e991. Jekle, M., & Becker, T. (2012). Effects of acidification, sodium chloride, and moisture levels on wheat dough: II. Modeling of bread texture and staling kinetics. Food Biophysics, 7(3), 200e208. Kett, A. P., Chaurin, V., Fitzsimons, S. M., Morris, E. R., O'Mahony, J. A., & Fenelon, M. A. (2013). Influence of milk proteins on the pasting behaviour and microstructural characteristics of waxy maize starch. Food Hydrocolloids, 30(2), 661e671. Koksel, F., & Scanlon, M. G. (2012). Effects of composition on dough development and air entrainment in doughs made from gluten-starch blends. Journal of Cereal Science, 56(2), 445e450. de Kruif, C. G., & Tuinier, R. (2001). Polysaccharide protein interactions. Food Hydrocolloids, 15(4e6), 555e563. Lindahl, L., & Eliasson, A.-C. (1986). Effects of wheat proteins on the viscoelastic properties of starch gels. Journal of the Science of Food and Agriculture, 37(11), 1125e1132. Li, J.-Y., & Yeh, A.-I. (2003). Effects of starch properties on rheological characteristics of starch/meat complexes. Journal of Food Engineering, 57(3), 287e294. 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(4), 1240e1247. Martin, M. L., Zeleznak, K. J., & Hoseney, R. C. (1991). A mechanism of bread firming. I. Role of starch swelling. Cereal Chemistry, 68(5), 498e503. Matignon, A., Moulin, G., Barey, P., Desprairies, M., Mauduit, S., Sieffermann, J. M., et al. (2014). Starch/carrageenan/milk proteins interactions studied using multiple staining and confocal laser scanning microscopy. Carbohydrate Polymers, 99(0), 345e355. Miller, K. A., & Hoseney, R. C. (1999). Dynamic rheological properties of wheat starch-gluten doughs. Cereal Chemistry, 76(1), 105e109. Mohamed, A. A., & Rayas-Duarte, P. (2003). The effect of mixing and wheat protein/ gluten on the gelatinization of wheat starch*. Food Chemistry, 81(4), 533e545. Navickis, L. L., Anderson, R. A., Bagley, E. B., & Jasberg, B. K. (1982). Viscoelastic properties of wheat flour doughs: Variation of dynamic moduli with water and protein content. Journal of Texture Studies, 13(2), 249e264. Petrofsky, K. E., & Hoseney, R. C. (1995). Rheological properties of dough made with starch and gluten from several cereal sources. Cereal Chemistry, 72, 53e58. Rosell, C. M., & Foegeding, A. (2007). Interaction of hydroxypropylmethylcellulose with gluten proteins: small deformation properties during thermal treatment. Food Hydrocolloids, 21(7), 1092e1100. Ryan, K. J., & Brewer, M. S. (2005). Model system analysis of wheat starch-soy protein interaction kinetics using polystyrene microspheres. Food Chemistry, 92(2), 325e335. Schirmer, M., Jekle, M., & Becker, T. (2015). Starch gelatinization and its complexity €rke, 67(1e2), 30e41. for analysis. Starch e Sta Schirmer, M., Zeller, J., Krause, D., Jekle, M., & Becker, T. (2014). In situ monitoring of starch gelatinization with limited water content using confocal laser scanning microscopy. European Food Research and Technology, 239(2), 247e257. Tamaki, Y., Konishi, T., & Tako, M. (2011). Gelation and retrogradation mechanism of wheat amylose. Materials, 4(10), 1763e1775. Vallons, K. J. R., & Arendt, E. K. (2009). Effects of high pressure and temperature on the structural and rheological properties of sorghum starch. Innovative Food Science & Emerging Technologies, 10(4), 449e456. Van Bockstaele, F., De Leyn, I., Eeckhout, M., & Dewettinck, K. (2008). Rheological properties of wheat flour dough and their relationship with bread volume. II. Dynamic oscillation measurements. Cereal Chemistry Journal, 85(6), 762e768. Yang, Y., Song, Y., & Zheng, Q. (2011). Rheological behaviors of doughs reconstituted from wheat gluten and starch. Journal of Food Science and Technology, 48(4), 489e493.