Large Amplitude Oscillatory Shear (LAOS) analysis of gluten-free cake batters: The effect of dietary fiber enrichment

Journal Pre-proof Large Amplitude Oscillatory Shear (LAOS) analysis of gluten-free cake batters: The effect of dietary fiber enrichment

Esra Ozyigit, İsmail Eren, Seher Kumcuoglu, Sebnem Tavman PII:

S0260-8774(19)30510-2

DOI:

https://doi.org/10.1016/j.jfoodeng.2019.109867

Reference:

JFOE 109867

To appear in:

Journal of Food Engineering

Received Date:

11 June 2019

Accepted Date:

08 December 2019

Please cite this article as: Esra Ozyigit, İsmail Eren, Seher Kumcuoglu, Sebnem Tavman, Large Amplitude Oscillatory Shear (LAOS) analysis of gluten-free cake batters: The effect of dietary fiber enrichment, Journal of Food Engineering (2019), https://doi.org/10.1016/j.jfoodeng.2019.109867

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Journal Pre-proof Large Amplitude Oscillatory Shear (LAOS) analysis of gluten-free cake batters: The effect of dietary fiber enrichment Abbreviated title suggestion: Effects of dietary fiber enrichment on LAOS behaviors of gluten-free cake batters Esra Ozyigit1, İsmail Eren3, Seher Kumcuoglu2, Sebnem Tavman2 Seher Kumcuoglu [email protected] 1

Department of Food Engineering, Graduate School of Natural and Applied Sciences, Ege University, 35100 Bornova, Izmir, Turkey 2 Department of Food Engineering, Faculty of Engineering, Ege University, 35100 Bornova, Izmir, Turkey 3Department of Food Engineering, Faculty of Engineering, Manisa Celal Bayar University, 450140 Yunusemre, Manisa, Turkey Abstract The aim of this study is to investigate the effect of dietary fiber enrichment on nonlinear viscoelastic behavior of gluten-free cake batters by using Large Amplitude Oscillatory Shear (LAOS) analysis. Textural properties and specific volume of gluten-free cakes were also determined to investigate the possible correlations with LAOS parameters. Gluten-free cake batters were formulated by replacing buckwheat flour with two different dietary fiber sources, namely orange fiber (OF) and orange pomace powder (OPP) at five different levels (0%, 4%, %8, %12 and 16%). All gluten-free cake batter samples exhibited linear viscoelastic properties at small strain amplitudes but rheological properties enters the non-linear region by increasing strain amplitude. The Lissajous-Bowditch curves revealed that stored energy increased by increasing dietary fiber amount and gluten-free cake batters became more elastic in the nonlinear region. The normalized elastic Chebyshev coeffients (e3/e1) indicated the strain hardening behavior of cake batters at small strain amplitudes shifted to strain softening in the non-linear region. The e3/e1 and v3/v1 ratios as a function of strain amplitude indicated that non-linearity is more pronounced in the elastic component compared to the viscous component. The S and T values calculated at 50% strain amplitude showed strong correlation with water retention capacity, hardness and specific volume of gluten-free cakes enriched with OF whereas softer correlations were obtained for the OPP-containing ones due to elastic instability of the batters. Principal component (PCA) and hierarchical cluster analysis (HCA) were performed to provide basic graphical comparison of the differences/similarities between non-linear rheological properties of gluten-free cake batters by considering LAOS parameters. The viscoelastic properties of the cake batters containing 16% OPP were found to be suitable for high gas retention capacity since the highest cake specific volume was obtained. Keywords:Large Amplitude Oscillatory Shear (LAOS), Gluten-free batter, Dietary fiber, Lissajous-Bowditch curves, Orange fiber 1

Journal Pre-proof 1.Introduction The interest in gluten-free bakery products has been increasing in recent years due to the incidence of celiac disease and other gluten-based disorders (Matos and Rosell, 2011). Gluten-free diet is still the only indispensable treatment for celiac disease. However, there are still concerns about gluten-free diets because it is often characterized by an excessive consumption of energy, proteins, and fats, and a reduced intake of complex carbohydrates and dietary fibre (Fasano et al., 2003; Thompson et al., 2005). Also, the most of the gluten-free products are showed low mouthfeel and characterized by crumbly texture and humidty losses in markets (Arendt et al., 2002; Sinha N., 2007) The replacement of gluten from bakery products leads to these quality defects since it is the main structure-forming protein which provides the desired elastic characteristics to dough (Arendt et al., 2002; Bagley et al., 1998; Sicherer and Sampson, 2014), Therefore, there is an important need to reformulate gluten-free bakery products to have nutritional composition and quality characteristics equivalent with gluten containing counterparts (Gularte et al., 2012). Dietary fibre is the edible portion of plants which is resistant to digestion and adsorption in the human small intestine with complete or partial fermentation in the large intestine (Gelroth and Ranhotra, 2001;Sabanis et al., 2009). Besides its health-promoting effects which have been well documented by several researchers (Bazzano et al., 2003; Faivre and Bonithon-Kopp, 1999; Roehrig, 1988), fibre addition contributes to the improvement of the texture and sensory characteristics of gluten-free bakery products. Their water binding capacity, gel forming ability, texturizing and thickening effects play an important role on the rheological properties of glutenfree doughs and thus the final product quality (Gelroth and Ranhotra, 2001; Thebaudin et al., 1997). Several research attempts have been made on rheological characterization of gluten-free doughs and batters for different type of products such as gluten-free rice cakes (Turabi et al., 2008; Tsatsaragkou et al., 2015), gluten-free bread (Demirkesen et al., 2010; Torbica et al., 2010), gluten-free muffins (Matos et al., 2014) and cupcakes (Lebesi and Tzia, 2011). These studies have mainly focused on the small amplitude oscillatory shear (SAOS) rheology that provides information about the initial responses to stress and strain in sample and only applicable to the linear viscoelastic region (Joyner and Meldrum, 2016). However, many food process are showed nonlinear rheological properties (Ptaszek, 2015). Viscoelastic properties are defined by using elastic storage modulus (G') and viscous loss modulus (G") and both of these are independent of strain amplitude in the linear region. Moreover, sinusodial oscillatory stress response is observed in that region. The non-linear region has been formed beyond the SAOS by increasing oscillation strain. In the non-linear region, G' and G" became dependent of strain amplitude and sinusoidal stress waves are distorted. Consequently, G' and G" are no longer enough to determine viscoelastic properties of sample (Hyun et al., 2011). Therefore, there is a new attention on Large Amplitude Oscillatory Shear (LAOS) analysis to determine fundamental rheological properties of material in the non-linear region. LAOS analysis has been used successively for the characterization of non-linear viscoelastic properties of food foams (Ptaszek, 2015), hard wheat flour dough (Yazar et al., 2017), suspensions, emulsions and elastic networks (Duvarci et al., 2017). However,non-linear rheology of gluten-free cake batters enriched with dietary fiber has received less attention and 2

Journal Pre-proof the present paper focuses specifically on it. Therefore, the objective of this study is to investigate the effect of dietary fiber enrichment on non-linear viscoelastic behavior of glutenfree cake batters by using Large Amplitude Oscillatory Shear (LAOS) analysis. Also, textural properties and specific volume of gluten-free cakes were also determined to investigate the possible correlations with LAOS data. 2.Materials and methods 2.1. Materials Rice flour (Kenton, Ankara, Turkey), milk (Pınar Süt Mamulleri Sanayi A.Ş., Izmir, Turkey), pasteurized whole egg (Ipay A.,Ş., Turkey), sugar (Konya Şeker San. ve Tic. A.Ş., Konya, Ankara), shortening (Felda Iffco Gıda San. ve Tic. A.Ş., Izmir), vanillin and baking powder (Dr-Oetker Gıda San. ve Tic. A.Ş., Izmir) were purchased from the local markets. Orange fiber (OF) was obtained from Herba Food (Germany). Xanthan gum was purchased from Sigma-Aldrich (St. Louis, USA). Buckwheat seeds were obtained from Değirmen (Turkey) and ground to whole grain flour (250 µm) by using hammer mill (Armfield, UK). 2.2. Orange pomace powder production Orange pomace powder (OPP) was produced by using Santos No: 50 juice extractor (Santos SA, Lyon, France) and tray dryer (Armfield Ltd., Ringwood Hampshire, England) according to the Kırbaş et al. (2019) method. 2.3. Preparation of gluten-free cake batter and baking Table 1 illustrates the fundamental batter recipe and batter formulation containing rice flour and buckwheat flour in a ratio 80:20 was used as a control cake. Dietary fiber sources were added to the formulation in 4%, 8%, 12% and 16% by replacing buckwheat flour. Gluten free cake batter was prepared by using Kitchen Aid Mixer (St. Joseph, Mich., USA) with a wire whip attachment. Firstly, pasteurized whole egg was mixed for 4 mins at speed 6 (280 rpm), then sugar was added and mixing process further 3 mins at same speed. Then, shortening and milk were added to the mixture and mixed for 2 mins at speed 3 (135 rpm). Lastly, dry ingredients were added and mixed 1 min at speed 1 (60 rpm). Cake batters (80 g) were placed into silicon cake molds and baked in a convection oven for 35 mins at 180°C (Vestel, Turkey). After baking, cakes were taken from the molds and hold on at the room temperature for 1 h. Two different sets of experiments were carried out by duplicate for each cake recipe on different days.

Table 1. Gluten-free cake formulation 2.4. Properties of dry ingredients 2.4.1. Dietary fiber

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Journal Pre-proof The total, soluble and insoluble dietary fiber contents of orange pomace powder, orange fiber, buckwheat and rice flour were determined by the method of AOAC Method: 991.43 (AOAC, 1998). 2.4.2.Water retention capacity of flour blends Water absorption index (WAI) and water solubility index (WSI) were determined by the method of Choi et al. (2012) with slight modifications. According to this modification, obtained supernatant was dried in a hot oven at 105°C for 6 hours instead of overnight. 2.5. Properties of gluten-free cake batter 2.5.1. Rheological measurements Rheological properties of gluten free cake batter were determined by using TA DHR-3 (TA Instruments Inc., New Cattle, DE, USA) rheometer. Measurements were performed immediately after batter preparation by using parallel plate (40 mm diameter) with a gap height of 1 mm. LAOS tests were carried out 0.01- 300% strain range at constant frequency (10 rad/s) and by obtaining 40 different loops. All measurements were accomplished in the transition mode at 25°C. During the tests, elastic-viscous modulii, dynamic viscosity, Chebyshev coefficients and Lissajous curves data were collected. The rheological measurements were performed with two different sets of experiment and each set was carried out by duplicate. 2.5.2. Batter density The batter density was determined in duplicate by using Elcometer picnometer (Elcometer, Manchester, UK), that is a cup which consists of a 100 ml cylindrical container. The batter density was calculated by the ratio between the weight of the batter and the volume of the cup. 2.6. Properties of gluten-free cake 2.6.1. Specific volume The volume of the cakes were determined, after 1 h baking, by using AACC method 7210 (AACC, 2000) by means displacement of rapeseed. 2.6.2. Texture Profile Analysis In order to determine crumb texture of cakes, Gómez et al. (2007)’s method was modified and TA.XT Express Texture Profile Analyser (Stable Microsystems, Surrey, UK) was used. Hardness (N), springiness, cohesiveness and resilience of cakes were determined with “Texture Profile Analysis” double compression test (TPA). An aluminium 25 mm diameter cylindrical probe was used with a 10 N load cell. Samples were compressed to %50 penetration depth of original cake thickness at 2mm/s, with 30 s holding time between two compression. After 24 h of baking, cakes were cut into 40x40x15 mm and central part of the slices used for analysis. Ten measurements were done to determine texture properties of cake. 2.6.3. Scanning electron microscopy (SEM) analysis 4

Journal Pre-proof The microstructure of rice flour, buckwheat flour, dietary fiber sources and the baked cake samples determined by SEM analysis. Before the measurements, cake samples were cut into small particles and freeze-dried (Armfield, 158 FT 33, England) at -18°C. Analyzed performed by using a Quanto 250 FEG Scanning Electron Microscope (FEI Inc., Hillsboro, Oregon, USA) after coating with gold of all samples (Emitech K550X, France). 2.7. Data Analysis The effect of dietary fiber enrichment on LAOS data of gluten-free cake batters and cake quality parameters were determined statistically by means of variance analysis (ANOVA) at 95% confidence level. Statistical analysis of the experimental data were performed by using SPSS 22.0 software (IBM SPSS Statistics for Windows, Version 22.0. IBM Corp, Armonk, NY). All the results reported are an average of two replicates.When ANOVA indicated significant F values, Duncan’s multiple comprasion test was used to discriminate among the means. PCA analysis was applied to LAOS data of gluten-free cake batters by using SIMCA Software (Umetrics, Sweden) 14.1 Trial Version. PCA is a well-known multivariate statistical technique that is used to describe major trends in a group of data and to detect possible outliers (Birch et al. 2013). The principle of PCA is based on reducing the dimensionality of observed data to create new artificial variables named as principal components (PCs). A large portion of the variability is often described by a few PCs. The number of PCs should be increased until the balance between degree of fit (R2) and predictive ability (Q2). Result of PCA can be given in two complementary plots as scores and loading plots. By plotting the score plot it is possible to find how the observations are scattered and which of them clustered to differentiate principal grouping among observations. Loading plots are focused on variables to reveal which of the original variables are most important (Euerby & Petersson, 2003). In this study, classification of the dieatry fiber enriched gluten-free cake batters were performed separately by using LAOS parameters and the scores plot and loadings plot are employed. Hierachical Cluster Analysis (HCA) was also performed as a continuation of PCA to assess if, by using a different classification algorithm, it is possible to expect more sensitive sample classification. As with PCA, HCA is an unsupervised multivariate method, which evaluates the clustering tendency of samples through an iterative process which associates the samples by taking account of the chosen distance between samples and a linkage criterion according to which samples or clusters are merged (Viapiana et al., 2016). In this study Euclidean distance was checked as a distance similarity measure and Ward’s linkage for the dietary fiber enriched gluten free cake batters. 3.Results and discussion 3.1. Properties o dry ingredients 3.1.1. Dietary fiber

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Journal Pre-proof Total, soluble and insoluble dietary fiber content of flours and dietary fiber sources were investigated. The total dietary fiber (TDF) mass fraction of OPP and OF were 82.22/100g and 64.93/100g, respectively. Larrauri (1999) stated that, if dietary fiber source contain more than 50% TDF, these can be accepted as a rich source of dietary fiber. The TDF content of OF are in agreement with those reported by de Moraes Crizel et al. (2013) for orange fiber (63.6 g/100 g) and by Figuerola et al. (2005) for orange waste fiber (64.3 g/100 g). But TDF content of OPP was found higher than these results; and this may depend on the different cultivars, processing plan and maturation level of material. Insoluble dietary fiber (IDF) fraction higher than the soluble dietary fiber (SDF) fraction both orange pomace powder and orange fiber. Although, IDF contents of OPP and OF were found the largest fraction, these sources also consist high amount soluble dietary fiber (SDF). This statement have also been reported by Turksoy and Ozkaya 2011; de Moraes et al. 2013; Figuerola et al. 2005 for many other vegetable byproducts. The TDF mass fraction of buckwheat flour was 16.27/100 g (2.25/100 g IDF, 14.02/100 g SDF), which was higher than that reported by Bonafaccia et al. (2003) and Steadman et al. (2001) for different kind of buckwheat flour. According to Bonafaccia et al. (2003), these differences may depend on the varieties which was studied; also on growing conditions and milling methods. The lowest TDF mass fraction was found for rice flour with the value of 7.91/100 g (2.43/100 g .IDF, 5.52/100 g SDF). 3.1.2. Water retention WAI is used to determine the water absorption and swelling properties of the flour in relation to the consistency and structure of the food system. The WSI is used to determine starch degradation, and it defines free or released polysaccharide concentration from the granule by adding excess amount of water (Osundahunsi et al. 2003; Choi et al., 2012). The WAI results of rice flour, buckwheat flour, OF, OPP were found to be 2.99±0.06 g/g, 2.22±0.02 g/g, 7.28±0.46 g/g and 7.97±0.21 g/g, respectively. The WSI values of rice flour, buckwheat flour, OF, OPP were determined as 2.19±0.14 g/g, 6.83±0.08 g/g, 7.71±0.06 g/g, 1.82±0.30 g/g, respectively. Orange fiber sources, besides their calorie-lowering effect, are the functional ingredients that improve the structural properties of foods by affecting the viscosity due to high water absorption indexes.The WAI values were similar that reported for orange fiber (7.30 g/g) by Grigelmo-Miguel and Belloso (1999); but lower than the report of de Moraes Crizel et al. (2013) of orange fiber (8.71 g/g, 9.63). Lario et al. (2004) stated that increasing dimension of dietary fiber particles increased water absorption index of food. The differences between WSI values of OF and OPP can be attributed to their variety and production process. The WAI of mixture of dry ingredients ranged from 2.68 to 3.69 for OF samples and 2.68 to 3.90 for OPP samples with the highest in 16% OPP sample. The WAI of samples increased with an increase in dietary fiber level. OPP samples showed higher WAI properties as expected due to its high water absortion characteristics. Increasing amount dietary fiber source increased the WSI for OF samples from 3.54 to 5.07; but decreased for OPP samples from 3.54 to 1.09; that was expected due to high WSI level of OF. According to et al. (2001), high viscosity values could be obtain by using flour with higher WAI and lower WSI. 3.2. Rheological properties of gluten-free cake batter 6

Journal Pre-proof 3.2.1. Determination of the LAOS region by strain sweep test Strain sweeps results are shown in Fig. 1. The behavior of batter samples varied after certain strain value and entered non-linear region. All gluten-free batter samples indicated higher values for the storage modulus (G') than loss modulus (G") values at linear region where elastic behavior is dominant. As a general tendency for all samples, the nonlinearity began at almost 1% strain and the behavior of G' and G" has markedly differentiated. Results showed an increase in storage (G') and loss (G") modulii values with the addition of dietary fiber sources in the gluten-free batter. However, G' and G" values for OPP samples were found much more higher than OF samples. G' values of OF and OPP samples were ranged between 0-2000 Pa and 0-50000 Pa, respectively. G" values of OF and OPP samples were ranged between 0-800 Pa and 0-8000 Pa, respectively. G' and G" values were significantly affected by OPP enrichment with respect to control group, but the effect of OPP level was lower on G' and G" values. Matos et al. (2014) reported that addition of increasing amounts of protein sources led to an increase in storage and loss modulii values. Shevkani et al. (2015) stated that the rice cakes produced with protein isolate had higher storage modulus value than loss modulus. Fig. 1. Strain sweep plots of gluten-free cake batters as a function of dietary fiber level (0, 4, 8, 12, 16 % ) at 10 rad/s(a) OPP and (b) OF 3.2.2.General Lissajous Comparison The rheological response of gluten-free cake batters prepared with OPP and OF were determined as a function of strain amplitude in the non-linear region. LAOS tests were performed for different strain amplitudes (0.01-300%) at an angular speed of 10 rad/s and 23 of them were processed to produce the Lissajous-Bowditch curves in Fig. 2, Fig. 3 and Fig. 4. This enabled us to identify the onset of nonlinearity in the elastic stress and viscous stress functions by visual inspection prior to quantitative analytical analysis and compare the changes in nonlinear intracycle rheological behavior. Also, strain hardening/softening and shear thinning/thickening behaviors of the gluten free cake batters were described better in the nonlinear region. The addition of OPP and OF caused differences in viscoelastic behavior of cake batters.The stress values increased with increased dietary fiber level of cake batters and increased as the strain increased. 16% OPP and 16% OF samples had higher stress value than other samples, as expected. Linear viscoelastic region were identified by small loops in the middle of the Lissajous curves. Dietary fiber enrichment affect the loops and clockwise rotation was seen by increasing OPP and OF amount (Ng et al., 2011; Duvarci et al., 2017). By analysing and comparing the area from the stress curves at fixed strain, dissipated and stored energy could be defined. The dissipated energy is related with the projected area of the curves on the stressstrain , while stored energy is related with the projected area of the stress-strain rate curve (Lauger and Stettin, 2010; Duvarci et al., 2017). Fig. 2 represents that the stress response respect to strain rate increased by increasing OF and OPP amount; so, this means that stored energy of gluten-free batters were bigger at higher dietary fiber concentration.At this time, dissipated energy of gluten-free batters started to decrease by dietary fiber enrichment.

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Journal Pre-proof Fig. 2. The 3-D Lissajous curves for gluten-free cake batters at different strains between 0.01300%. 3.2.3. Comprasion of Elastic and viscous Lissajous-Bowditch curves The elastic component of stress in the form of normalized stress (𝜎 𝜎0) and normalized ' elastic stress (𝜎 𝜎 ) vs. normalized strain (𝛾 𝛾 ) are plotted in Fig. 3-a, Fig. 3-b and Fig. 3-c 0

0

for the gluten free cake batters including orange pomace powder (4-8% w/w), orange fiber (48% w/w) and lean cake batter as control sample, respectively. The linear viscoelastic response of the all cake batters at small strain amplitudes are found to be purely elliptical. On the other hand, increased strain amplitutes resulted in progressively wider and more distorted curves at the outer cycles. Hence, gluten free cake batters showed the expected transition from the response of a viscously-dominated fluid to an elastically-dominated gel.

Fig. 3. Lissajous-Bowditch curves for the elastic component of the gluten-free flour dough samples a) OPP b) OF c) Control. The addition of OPP and OF to cake batter formulation lead narrower loops in the stress responses as compared to control sample at all concentrations. This implies that OPP and OF enrichment significantly affected the microstructure of the gluten free cake batter and resulted in a more elastic behaviour. Sabanis et al. (2009) also reported the synergistic interaction of fibre with starch and proteins to promote the formation of a more stable structure for gluten free bread doughs. The elastic component (red lines) showed smoother lines (less non-linearity) at all strain amplitudes (higher number of cycles) for the cake batter formulations enriched with OF. It is seen in Fig. 4 that increased concentrations of OF decreased the non-linearities in the elastic component which corresponds to ideal elastic solid (Hookean) behaviour. Strain hardening was observed by a clockwise turn in the elastic component of the stress response as the OF concentration increased from 4% to 8%. The rehological behaviour of the OPP added cake batters becomes more complex as the strain amplitude increases. The elastic component of the stress shows both strain-stiffening at moderate strains and also strain-softening characteristics at very high strains, which may be an indication of structural weakning. The viscous Lissajous–Bowditch curves (normalized stress (𝜎 𝜎0) and normalized '' viscous stress (𝜎 𝜎0) vs. strain rate (𝛾 𝛾0) also supported the rheological behavior defined by the elastic component (Fig. 4). In contrast to the elastic perspective, the outer loops represent the linear region and the inner loops represent the non-linear region (Yazar et al, 2017).

Fig. 4. Lissajous-Bowditch curves for the viscous component of the gluten-free flour dough samples a) OPP b) OF c) Control The nonlinear behavior of samples were also examined quantitatively by using storage and loss moduli values. Ewoldt et al. (2008) defined specific ranges for elastic and viscous modulus to 8

Journal Pre-proof interpret nonlinear behavior of samples. Interpretation of nonlinearities in elastic and viscous moduli can be summarized by means of G'L G'M and 𝜂'L 𝜂'M. The minimum strain modulus ( G'M) and the large strain amplitude modulus (G'L) are defined by the slope of the tangent at minimum strain (𝛾 = 0) and the slope of the secant at maximum strain (𝛾 = 𝛾0), respectively. These parameters are used to define elastic moduli in LAOS (Ewoldt et al., 2008). Large-rate dynamic viscosity (𝜂'L) and minimum-rate dynamic viscosity (𝜂'M) are the instantaneous viscosity coefficients which are defined by the viscosity at the largest (𝛾 = ± 𝛾0) and smallest shear-rates (𝛾 = 0), respectively (Ewoldt et al., 2008). The ratio of G'L to G'M defined the nonlinear elastic behavior (<1 strain softening; >1 strain hardening); while the ratio of the 𝜂'L to 𝜂'M defined the non-linear viscous behavior (<1 shear thinning; >1 shear thickening). LAOS results for all batter samples are shown in Fig. 5. At lower strain, all batter samples showed elastic dominant behavior. These results were in agreement with Lissajous curves where the elliptical shape and linear viscoelastic behavior was observed clearly. As the strain increased, cake batter samples start to show non-linear viscoelastic properties. Approximately at 1-100% strain range, samples showed strain hardening behavior, while increasing strain caused to decrease G'L G'M values and samples behavior shifted to strain softening. The effect of OPP addition on G'L G'Mvalues were more significant at lower strains than OF addition. The 𝜂'L 𝜂'M ratio were lower than 1 for all samples and exhibited shear thinning behavior. Fig. 5. The variation of G'L G'M and 𝜂'L 𝜂'M with respect to strain of gluten-free cake batters at different (a) OPP and (b) OF levels (0, 4, 8, 12, 16%).

3.2.4. Chebyshev Harmonics Analysis As previously discussed, by analysing the Lissajous curves, it can be seen that all samples showed linear viscoelastic properties at small strain amplitudes, but increasing strain caused to transition on behavior of samples and cakes showed viscous dominant behavior in the beginning of non-linear region and than turn into elastically-dominated form.This was consistent result because of the viscous modulus values are higher than the elastic modulus values for first Chebyshev coefficients. (Cho et al., 2005). Chebyshev coefficients provide more detailed information on nonlinear behavior of the material. The coefficient en and vn represent the elastic and viscous Chebyshev weighting coefficients, respectively. The subscript n denotes the order of Chebysev coefficients and higher order (n: odd) Chebysev coefficients are used to determine the material’s nonlinearity. The third order Chebysev coefficients are predominantly used to define material’s behavior in the nonlinear region (Ewoldt et al., 2008). Also, the evaluation of the ratio of third order Chebysev coefficients (e3 , v3) to first order Chebysev coefficients (e1 , v1) gives an information about material’s intacycle behavior in the nonlinear region (Ewoldt et al., 2008). By evaluating the Chebyshev coeffients of the batters, it is observed clearly that behavior of the e1 and v1 values of samples changed. In this study, a certain strain value was 9

Journal Pre-proof chosen for examination of nonlinear properties of material. The Chebyshev coefficients of the selected strain value for batters are shown in Fig. 6. The values of v1 are higher in comparison to the values of e1, but e1 values are not zero. Consequently, the gluten free batter samples also exhibited elastic behavior as well as dominant viscous behavior. Similarly, Ptaszek (2015) interpreted the elastic and viscous behavior of the material by using e1 and v1 values of the samples. It is reported that the v1 values were higher by comparing the e1 values at a certain amplitude level for egg foam samples so that samples showed viscous dominant behavior.

Fig. 6. Chebyshev harmonics of gluten free cake batters in function of strain amplitude at γ0=50%. Fig. 6. illustrates that dietary fiber enrichment caused to increase in the Chebyshev coefficient values of samples. Moreover, the Chebyshev coefficients decrease rapidly and then disappear. Therefore, it is better to use Chebyshev coefficients by normalizing against the first one for further analysis. Normalized elastic and viscous Chebyshev harmonics in the function of the strain amplitude are shown in Fig. 7. According to 3th Chebyshev harmonics, all samples showed linear elastic and viscous properties between 0.01-1% strain amplitude. The e3/e1 values for the control and 4% OF samples were positive until 60% strain amplitude (γ0), which is indicated that samples show strain hardening. However, at higher strains, e3/e1 values were lower than zero and samples behavior shifted to strain softening. Thus, batters with increased amounts of OF exhibited strain hardening behavior in a wide range while the range of strain softening properties decrease. On the other hand, extention of the positive range of elastic e3/e1 values increased compared to control sample with use of OF and OPP; but, there were no significant differences between samples which containing different amount OPP. The e3/e1 values of OPP samples showed that behavior of all samples were strain hardening until 100% strain except 12% OPP and 16% samples. Results of that sample were negative behind the 100% strain value, after these strain, e3/e1 values of all samples were below zero and indicates strain softening. In general, v3/v1 values of all samples are below zero after 0% strain value. Subsequently, the values of v3/v1 decrease until they reach the lowest value, than they start to increase. This pattern is the same for all samples, but it occurs at different strain amplitude of each sample. All batter samples indicated shear thinning behavior within the range of strain from 0% to 300%.

Fig. 7. Normalized Chebyshev coefficients of gluten free cake batters as a function of strain amplitude at γ0=50%,a) OPP b) OF.

3.2.5. Batter density 10

Journal Pre-proof The batter density values of gluten free cake batters for different concentrations of OF and OPP, were presented in Table2. All samples showed significant differences (p<0.05) compared to the control and the increase in amount of OF decreased batter density of cake batters. The highest cake batter was obtained with control sample. Thus, OF and OPP amount lead to increase in air incorporation during mixing and decrease in density. Consequently, we expected the specific volume of cakes should be increased by decreasing batter density. Masoodi et al. (2002) and Sreenath et al. (1996) reported that the addition of fibers or fiber enriched ingredients in cake batters decrease the density of batters. The same effect was reported by Baixauli et al. (2008), when using resistant starches in cake formulation. Table 2. Density of gluten-free cake batters 3.3. Properties of gluten-free cake 3.3.1. Specific volume Dietary fiber enrichment increased the specific volume of gluten-free cakes with respect to control sample (p<0.05) (Table 3). The cake with the highest specific volume was 16% OPP sample. According to obtained results, OPP increased specific volume of cakes higher than OF due to its high water retention capacity. But, there was a slight reduction for a cake which contains 12% orange fiber. Relationship of OF and buckwheat flour concentrations may be caused this reduction due to their specific properties like water retention capacity. Similar results were also found by Al Sayed and Ahmed (2013), in which used water melon rinds and melon powders as dietary fiber sources increased specific volume of cakes by increasing dietary fiber level. Also, Lebesi and Tzia (2011) reported that preparation of cakes with dietary fibers which determined from wheat, corn, barley and oat lead to increase of specific volume of cakes. Final volume and texture properties of baked cakes directly related with the amount of air incorporated into batter. Air incorporation during mixing can be good when the appropriate batter density and viscosity of batters are supplied. When the consistency of batters is low, air cannot be preserved during mixing and baking, and low volume cakes are produced. Also higher consistency levels caused to limitation of batter expansion (Gόmez et al.,2007). Singh et al. (1995) stated that volume and specific volume of cakes increased by increasing amount of dietary fiber sources.

Table 3. Specific volume of gluten-free cakes. 3.2.2. Texture Profile Analysis Table 4 illustrates the effect of dietary fiber enrichment on the textural properties (hardness, springiness, cohesiveness, resilience) of gluten free cakes. Dietary fiber addition and its level significantly (p<0.05) affected the textural properties of cakes. Dietary fiber sources addition decreased hardness value of cakes in relation to control sample except 16% OPP sample. 16% OPP sample showed the highest hardness value. Lebesi and Tzia (2011) was reported that hardness values of cakes decreased; and cakes became softer by replacing wheat flour with dietary fiber sources (wheat, corn, barley, oat) in cake preparation. Also, dietary fiber 11

Journal Pre-proof addition affected the cake volumes and hardness values inversely proportional. In general, the specific volume has an opposite tendency according to the crumb hardness (Gómez et al. 2010). Same results were obtained for gluten free cake samples, dietary fiber enrichment increased the specific volume of cakes and while cakes became softer respect to control sample. The springiness values of cakes changed in a range from 0.93 to 0.99; however, there was no significant differences between samples (p>0.05). Cohesiveness and resilience values of cakes were affected significantly by adding dietary fiber sources (p<0.05); and 8% OF sample showed the highest cohesiveness and resilience values. After this fiber amount, springiness, cohesiveness and resilience values of cakes decreased by increasing dietary fiber level. Gómez et. al (2011) stated that cohesiveness and resilience values of cake samples decreased by increasing dietary fiber sources in cake formulations. Table 4. Texture profile analysis results of gluten-free cakes. 3.2.3. SEM images Macro- and microstructures of materials can be examined by using with SEM images at high resolution. Scanning electron micrographs of OF, OPP, buckwheat and rice flour are given in Fig. 8 with 2500x magnification. According to micrographs, rice flour particles have an irregular structure; but, buckwheat flour particles are round and showed more uniform distribution than rice flour particels. On the other hand, micrographs of dietary fiber sources showed more rough particles than round particles. It is thought that, this differences in particle distribution lead to increase water absorption capacity of materials. It can be seen from the images, orange pomace powder granules are the most rough particles and have the highest water absorption capacity according to WAI analysis, as it was expected. This conclusion is in agreement with the results of water retention capacity analysis of flour blends. Consequently, replacement of buckwheat flour with dietary fiber sources in formulation leads to an increase viscosity of batter because of high retention capacity. Also, porosity, volume and texture properties were affected by replacement. The results of SEM analysis on cake crumbs with different formulation are given in Fig. 8. According to these micrographs, increasing dietary fiber level in formulation decreased porosity of cakes. This can be seen more clearly in the samples prepared with orange pomace powder, due to higher water retention capacity. Fig. 8. Scanning electron micrographs (x100) of gluten-free cakes a. Cakes containing OF, b. Cakes containing OPP, c. Control; Numbers 1, 2, 3 and 4 indicate dietary fiber concentration at 4% ,8%, 12%, 16%, respectively. 3.4. Correlation of LAOS data with cake properties In the current study, correlations between strain hardening (S)-shear thickening (T) ratios and selected cake properties were evaluated. Strain hardening (S) and shear thickening (T) behavior are determined by the interperation of the relationship between G’M,G’L, 𝜂’L and 𝜂'M. The stiffening ratio (S) is given by 𝑆 ≡ (𝐺ˈ𝐿 ― 𝐺ˈ𝑀)/𝐺ˈ𝐿 and the shear thickening ratio is calculated by 𝑇 ≡ (𝜂ˈ𝐿 ― 𝜂ˈ𝑀)/𝜂ˈ𝐿 (Ewoldt et al., 2008). The analysis were performed in a wide 12

Journal Pre-proof strain range, so one strain value in nonlinear region for all batter samples was chosen to use in examination. The correlation between S-T and selected cake properties were investigated at 50% strain. The batter viscosity values are directly related water binding capacity of dry ingredients in the batter formulation. On the other hand, water solubility of dry ingredients also affects the batter viscosity. The amount of free water, that is available to promote the motion of particles in batters, reduces by increasing in water binding capacity of ingredients; as a result, high apparent viscosity values are found (Ronda et al.,2011). Other authors obtained high batter viscosity values by using flours which have high water absorption and low water solubility index (Bryant et al., 2001). Accordingly, thickening ratios (T) obtained from dynamic viscosity values of batter in the nonlinear region could be associated with water retention capacity of dry ingredients. The correlation between S-T values of batters and water retention indexes was showed positive high correlation for OF samples. Correlation coefficients were found R2:0.83 and R2:0.86 for between S and WAI - WSI, respectively. For T values of batters; correlation coefficients were found R2:0.83 and R2:0.86 for WAI and WSI, respectively. This means that, dry ingredients with high water retention indexes increased batter viscosity values so thickening ratio (T) in the nonlinear regime. But, it was obtained good correlation between LAOS data and water retention indexes of cakes enriched with OPP.

Fig. 9. Correlations between LAOS parameters and water retention indexes (WAI and WSI) of gluten-free flour blends. In addition, we investigated the relationship between hardness values of cakes and S-T values of batters. For samples containing OF; S (R2:0.97) and T (R2:0.94) were negatively correlated with hardness at 50% strain. On the other hand, hardness of cakes were positively correlated with T (R2:0.76) for cakes that contains OPP, but correlation coefficient was too low for S (R2:0.22) for OPP samples. As stated in previous sections, OPP samples showed instable elastic properties compared to OF samples; and correlation between S were found lower, as expected. Correlations between the specific volumes and S-T values of cakes were also evaluated. Highly good correlation for OF samples with S (R2:0.84) and T (R2:0.81) was observed; however, lower correlation coefficients were obtained in the case of using OPP for cake enrichment; and were found 0.41 and 0.32 for S and T, respectively. Similarly, Melito et al. (2013) examined the relationship between nonlinear rheological properties and textural properties of whey protein isolate/K-carrageenan gels. At different frequencies, G'L/G'Mvalues were negatively correlated with compressibility and also positively correlated with cohesiveness. Also, Yazar et al. (2017) investigated that correlations between LAOS parameters and gluten-free bread properties and G'L and G'M values showed good correlation with bread volume.

13

Journal Pre-proof Fig. 10. Correlations between LAOS parameters and the gluten-free cake hardness and specific volume. 3.5 Multivariate statistical analysis of LAOS data Multivariate statistical evaluation of the dietary fiber enrichment on rheological behavior of gluten-free cake batters was performed by PCA and HCA considering the LAOS parameters. Loading and score plots of PCA (R2:0.98) were given as a biplot (Fig 11.). Thus, it was possible to understand that LAOS parameters are affected by using different amount of dietary fiber and source of it. The first principal component (P1) can explain 57.4% of the total variability in the data whereas the second principal component (P2) 40.7%. Regarding the plot, there is a clear seperation between OF and OPP samples with the effect of P1. In addition, control group distinguished from both OF and OPP samples by the effect of P2. It is also seen that, there were four different groups and the use of OF and OPP affect the rheological behavior of batters, obviously. LAOS parameters (G'L G'M, e3/e1, S and 𝜂'L 𝜂'M, v3/v1, T) clustered on different sides of the loading plot which means that they are negatively correlated. It should be noted that G'L G'M, e3/e1, S and 𝜂'L 𝜂'M, v3/v1,T define the elastic and viscous behavior of the batters, respectively. Therefore, OPP samples exhibitied more elastic behavior while OF samples were more viscous.

Fig 11. Biplot of principal component analysis for LAOS parameters of gluten-free batters (different colours indicate different groups of gluten-free batters). 4.Conclusion The effect of dietary fiber enrichment on non-linear viscoelastic behavior of gluten-free cake batters were evaluated by LAOS method and correlated with cake quality parameters such as specific volume, hardness and water absorbtion index. It was found that the addition of OF and OPP significantly affected the viscoelastic properties of the cake batters and improved the quality of gluten-free cakes. The stress response of cake batters and its projections on the strain and strain rate planes were utilized as a primary evaluation of the non-linear behavior by means of 3-D Lissajous-Bowditch curves. The onset of non-linearity was observed by distortion in the shape of the stress response and the non-linearity of elastic and viscous components of stress at different strain amplitudes. A Type II LAOS behavior (strain hardening) was observed by the upward turn of stress responses at large strains which was more evident at high dietary fiber levels. Strain hardening can be associated with the formation of complex microstructures and nonlinear elastic network due to interaction of dietary fiber with gluten-free proteins and starch molecules. Quantitative analysis of the non-linear viscoelastic behavior were performed by using the elastic modulus (G'L ,G'M), the dynamic viscosity (𝜂'L,𝜂'M) and the 3th harmonic data of Chebyshev coefficients(e1, e3, v1, v3). Similarly, the elastic modulus values revealed that all gluten-free cake batters showed the ideal viscoelastic properties at low strain amplitudes. 14

Journal Pre-proof However, strain softening behavior was observed at increased strain amplitudes due to large deformations and higher harmonics. Chebyshev coefficients were found to be increased as the OF and OPP levels increased in the batter formulations. The e3/e1 values of the OPP containing batters were found to be positive for a larger range of strain amplitudes as compared to OF samples. Also, the negative values of v3/v1indicated a shear thinning behavior for all the samples at strain amplitudes between 0-300%. The correlations between LAOS parameters (S and T values) and cake properties (specific volume, hardness) and water retention capacity of flour blends were also investigated. The S and T values correlated well with water retention index, cake hardness and specific volume of the OF added batters whereas softer correlations were obtained for the OPP-containing cake batters due to elastic instability. However, the viscoelastic properties of the cake batters containing 16% OPP were considered to be the best in terms of gas retention, as the highest cake specific volume was achieved. The e3/e1 and S values were the most distinct LAOS parameters for rheological fingerprinting of the complex non-linear behavior observed in OPPcontaining cake batters. PCA results were plotted to see the efficiency of each LAOS parameters on gluten-free batter classification with respect to OF and OPP samples. The use of different source and amount of dietary fiber caused to differentiation on rheological properties of batters. PCA has been found extremely useful statistical approach for categorization of samples by using LAOS parameters. Finally, it is concluded that the addition of dietary fiber significantly altered the nonlinear viscoelastic behavior of gluten-free cake batters and LAOS analysis could be used successfully to improve product quality by providing an in-depth perspective on characterization of the structural differences.

Acknowledgements This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) [Grant No. 215O227]; the Ege University Scientific Project Commission [Grant No. 2016 BIL 009]. References AACC. (2000). Approved methods of the AACC, 10th ed., St. Paul, MN: American Association of Cereal Chemists (Method 72-10). Al-Sayed H.M., Ahmed, A.R. (2013). Utilization of watermelon rinds and sharlyn melon peels as a natural source of dietary fiber and antioxidants in cake. Annals of Agricultural Sciences, 58(1), 83–95. https://doi.org/10.1016/j.aoas.2013.01.012. AOAC Official Methods of Analysis. (1998). Method 991.43, total, soluble, and insoluble dietary fiber in foods. Association of Official Analytical Chemists International, Gaithersburg. Arendt E. K., O’Brien C.M., Schober T., Gormley T.R., Gallagher E. (2002). Development of gluten-free cereal products. Farm and Food, 12, 21–27. http://hdl.handle.net/10197/6892. 15

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Journal Pre-proof Author contribution Esra Ozyigit: Conceived of the presented idea, do the experiments, evaluate the results, performed the calculations, wrote the manuscript. İsmail Eren: Evaluate the results, performed the calculations, wrote the manuscript. Seher Kumcuoglu: Conceived of the presented idea, evaluate the results, performed the calculations, wrote the manuscript. Sebnem Tavman: Conceived of the presented idea, evaluate the results, wrote the manuscript.

Journal Pre-proof HIGHLIGHTS 

Effect of different dietary fiber addition on rheological properties of cake batters was investigated.



Rheological characterization of gluten-free cake batters were carried out by LAOS analysis.



Quality properties of cakes were also determined to investigate correlation with LAOS data.

Journal Pre-proof Table 1 Gluten-free cake formulation Ingredients (g) Rice flour Buckwheat flour Dietary fiber source Pasteurized whole egg Sugar Shortening Milk Baking powder Vanillin Gum

Dietary fiber (%) 8% 12% 80 80 12 8

Kontrol 80 20

4% 80 16

16% 80 4

0

4

8

12

16

80

80

80

80

80

80 25 120 6 1

80 25 120 6 1

80 25 120 6 1

80 25 120 6 1

80 25 120 6 1

0.5

0.5

0.5

0.5

0.5

Table 2. Density of gluten-free cake batters Dietary fiber source Orange fiber Sample Control

Orange pomace powder Density (g/ml) 1.103±0.42bA 1.103±0.42aA

4%

1.052±0.001aA

1.074±0.003aA

8%

1.055±0.004aA

1.086±0.004aA

12 %

1.052±0.000aA

1.099±0.022aA

16 %

1.058±0.001aA

1.084±0.002aA

Different letters in the same column (a, b, c, d) and line (A, B, C, D) indicate significant differences between means (p<0.05).

Journal Pre-proof Table 3. Specific volume of gluten-free cakes

Sample Control

Dietary fiber source Specific volume (cm3/g) Orange pomace Orange fiber powder a 1.58±0.04 1.58±0.04a

4%

1.65±0.1abA

1.87±0.03bB

8%

1.79±0.05cB

2.06±0.07cC

12 %

1.73±0.06bcC

2.22±0.11dD

16 %

1.78±0.034cE

2.52±0.10eF

Different letters in the same column (a, b, c, d) and line (A, B, C, D, E, F) indicate significant differences between means (p<0.05).

Table 4. Texture profile analysis results of gluten-free cakes

Orange fiber

Orange pomace powder

Sample

Hardness (N)

Springiness

Cohesiveness

Resilience

Control

13.2±1.60a

0.95±0.02a

0.70±0.27a

0.33±0.01ab

4%

11.85±1.43bA

0.96±0.01aE

0.70±0.02aA

0.32±0.09bE

8%

10.12±0.86cB

0.99±0.14aC

0.73±0.02bB

0.34±0.01aC

12 %

9.43±1.22cC

0.97±0.08aD

0.71±0.03aD

0.32±0.01bB

16 %

9.39±0.69cE

0.93±0.021aA

0.69±0.01aE

0.31±0.01cA

Control

13.2±1.60bc

0.95±0.02a

0.70±0.27bc

0.33±0.01b

4%

11.42±0.36aA

0.95±0.01aE

0.72±0.01cB

0.36±0.01cF

8%

12.28±0.86abC

0.95±0.01aC

0.70±0.01bC

0.34±0.009bC

12 %

12.16±0.78baD

0.94±0.01aD

0.67±0.02aE

0.33±0.01abB

16 %

13.81±0.89cF

0.94±0.01aB

0.65±0.02aF

0.31±0.01aA

 Different letters in the same column (a, b, c, d) indicate significant differences between means (p<0.05). Different letters in the same column and same dietary fiber concentration indicate significant differences between means (p<0.05).