starch update 2013: the 7 - thaiscience.info for thaiscience/article/2/10030364.pdf · effect of...

Starch Update 2013: The 7th International Conference on Starch Technology

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O-STARCH-22

Effect of frozen storage on structure and properties of roti dough supplemented with rice bran

Khanittha Muadiad* and Piyarat Sirivongpisal

Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University,

Hat Yai, Songkhla, 90112 Thailand *Corresponding author; E-mail: [email protected]

Abstract

Effects of frozen storage on structure and properties of roti dough supplemented with rice bran were investigated. Roti dough was frozen at -18oC by air blast freezing and stored at -18oC for 0, 28, 56, 84 days. This study presented that frozen storage affected on structure of dough matrix. During frozen storage, frozen roti dough showed changing of protein structure that the amount of β-sheet and random coil significantly increased and decreased (p<0.05), respectively, while α-helix and β-turn no significantly changed. The resistance to extension of frozen roti dough significantly decreased (p<0.05) while extensibility significantly increased (p<0.05) with increasing frozen storage time. The creep compliance curve of frozen roti dough exhibited the combination of elastic and viscoelastic behavior, which could be fitted by the 4-element Burger model. In addition, the instantaneous elastic modulus (G0) of frozen roti dough significantly decreased (p<0.05) during frozen storage which indicates a decrease in the elastic properties and lower recoverability. The freezable water of frozen roti dough analyzed by DSC significantly increased (p<0.05) during frozen storage time.

Keywords: Roti dough, frozen storage, rhelological properties 1. Introduction Roti, a flat unleavened bread prepared from specific ingredients are involved (flour, water, salt, sugars and fat), is the common food in southern part of Thailand which a lot of Muslim people and around the world its consumption is increased. About 85–90% wheat consumption in India is in the form of chapati and its culinary preparations such as tandoori roti, nan, paratha and poori (Gujral and Gaur, 2002). Demand for products that can combine both a high nutritional value and a good shelf life is steadily increasing, new perspectives in the bakery industry appeared with the use of alternative flour mixes or the use of ingredients that could influence the following: dough structure, sensory attributes and storage stability. However, it is well known, that roti has a short shelf life so immediately to eating after cooked. This means that numerous undesirable physicochemical changes, normally called by the ‘‘staling”, occur in a relatively short time. Extending the shelf life of roti is a challenge as the demand for ready to cooked products is high. Considering this need, freezing was used, which increases the energy consumption, nevertheless it is widely applied due to its convenience. Freezing and frozen storage may cause deleterious effects on rheological properties and structural behavior changes occur in roti dough and finished products. Several studies have shown the report of non-yeast frozen dough, and identified factors influencing the quality of bread produced from frozen dough without fiber (Angioloni et al., 2008; Leray et al., 2010; Ribotta et al., 2003; Yadav et al., 2009; Yi and Kurr, 2009). However, reports on storage study of frozen flat breads dough supplemented with fiber are scanty, and no scientific study is available on frozen roti dough supplemented with rice bran. Therefore, the present study on the changes in textural and sensory quality of ready-to-cook frozen roti


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dough during storage was undertaken. The aim of this research work was to evaluate the effects of frozen storage on structure and rheological properties of frozen roti dough supplemented with rice bran 2. Materials and Methods 2.1 Materials

Defatted rice bran from Thai Edible Oil Co., Ltd., Bangkok Thailand, was dried in a hot air oven at 60oC until the moisture content was less than 10%. The other raw materials used were wheat flour, magarine, milk, eggs, salt and sugar, which were obtained from a local market in Hat Yai, Songkhla, Thailand. 2.2 Dough preparation Roti doughs were prepared using ingredients such as wheat flour, rice bran (9 %), eggs, milk, water and salt. They were mixed to be homogeneous and proofed for about 2 hours at 80%RH. After proofing, roti dough was sheeted into a 140 mm diameter and approximately 2 mm thick. Fresh roti dough before freezing (control) was analyzed as in section 2.4 to 2.8. 2.3 Freezing and storage condition

Each piece of roti dough was covered on the surface with a polyethylene sheet. Then 10 pieces of roti dough were stacked vertically on the aluminium tray. After that they were frozen in air blast freezer at -18◦C. Sample temperature was measured by thermocouples connected to a data logger. Freezing was completed when the core temperature of roti dough reached -18◦C. 10 pieces of roti dough were packed in polyethylene bag. They were stored at -18 ◦C for 0, 28, 56 and 84 days. Frozen roti doughs were thawed by microwave before being analyzed as in section 2.4 to 2.8. 2.4 Microstructure of roti dough

Microstructure of fresh dough and frozen roti dough with different storage time were analysed by using Scanning Electron Microscope (SEM) with magnification of (1000X). 2.5 Infrared measurement

The secondary structure of gluten network for fresh dough and frozen roti dough with different storage time was investigated using Fourier transform infrared (FT-IR) spectroscopy. The protocol used in this study has been previously described by Meziani et al. (2011). The amide III band (1200-1350 cm-1) deconvolution provide various peaks and frequencies correspond to: α-helix (1330-1295 cm-1), β-turn (1295-1270 cm-1), random coil (1270-1250 cm-1) and β-sheet (1250-1220 cm-1) (Cai and Singh, 1999). 2.6 Dough extensibility The resistance to extension and extensibility of fresh dough and frozen roti dough with different storage time were measured by Texture analyzer equipped with Kieffer Extensibility (Stable Micro Systems, UK., 1995). 2.7 Creep and creep recovery

Creep and creep recovery fresh dough and frozen roti dough with different storage time were carried out at constant stress, (σ = 100 Pa) for 100 s and allowing strain (γ) recovery in 400 s after removal of stress. Creep data was described with creep compliance parameters, J(t) (Pa-1) = γ/σ. Compliance curve data of roti doughs were analysed by the Burgers model (Dolz et al. 2008; Garcia-Loredo et al. 2013) as following equation.


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(1)

Where J(t) (Pa-1) represents the overall compliance at any time, G0 (Pa) is the

instantaneous elastic modulus, G1 (Pa) is the retared elastic modulus, η0 (Pa.s) represents the retared viscosity and η1 (Pa s) is the terminal viscosity,

2.8 Freezable water

Freezable water of fresh dough and frozen roti dough with different storage time was analysed using Differential Scanning Calorimetry (DSC). A method applied from Leray et al. (2010). The ice melting enthalpy (H) was obtained by integrating the ice melting peak located at about 0 ◦C on the thermogram. The quantity of freezable water (%) was calculated by dividing the ice melting enthalpy (J/g product) by the latent heat of ice fusion (L= 333 J/g) and multiplying by 100. 2.9 Statistical analysis

All samples were compared with a complete randomize design (CRD). Analysis of variance (ANOVA) was performed and means comparisons were carried out using Duncan’s Multiple Range Test (DMRT). 3. Results and Discussions 3.1 Microstructure of roti dough Microstructure of fresh and frozen roti dough was investigated by SEM as showed in Figure 1. The microstructure of the fresh roti doughs (Fig. 1a) show continuous matrices of the gluten network and embedding of two types of starch granules (large and small) in gluten network. This result agrees with previous study that described fresh dough as continuous matrix with starch granules to be scattered (Ribotta et al. 2004; Yi and Kerr 2009). The frozen roti dough was quite damaged after frozen storage (Figure 1b - Figure 1c). The microstructure of frozen roti dough showed more damaged when increasing frozen storage time. The microstructure of frozen roti dough after frozen storage for 84 days (Fig. 1c) showed the gluten strands appeared more porous, discontinuous and thinner than that of frozen roti dough at 42 days. This could attribute to ice crystals growing during storage and then promoting to damage the gluten matrix (Baier-Schenk et al., 2005; Zounis et al., 2002). Figure 1 Scanning Electron Micrograph (SEM) at 1000X of fresh (a) and frozen roti dough during frozen storage at -18 ◦C for 42 (b) and 84 (c) days. G: gluten and S: starch granule

(a) (b) (c)

G

S

G S

G S


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3.2 Secondary structure of gluten proteins Secondary structure of gluten protein dough was investigated by FT-IR at amide III region (1200-1350 cm-1) as showed in Figure 2. The various peaks and their frequencies correspond to: -helix (1330–1295 cm-1), -turn (from 1295-1270 cm-1), random coil (1270–1250 cm-1) and -sheet (1250-1220 cm-1) (Cai and Singh, 1999). These results showed highest peak at the range of -sheet (1250-1220 cm-1) indicated that the secondary structure of gluten is subjected by -sheet conformation. This agrees with Meziani et al. (2011) who reported that gluten proteins mainly contained -sheet conformation (around 70%). Furthermore, -sheet of frozen roti dough significantly increased (p<0.05), while random coil significantly decreased (p<0.05) with increasing frozen storage time (Table 1). This probably due to during freezing, water diffuses and migrates to form ice crystals lead to interrupt the organized hydrogen bonding system that stabilizes the protein structure, therefore hydrophobic and hydrophilic regions of proteins are exposed to a new environment (Santos-Yap, 1996). Table 1 Conformational changes in the secondary structures of amide III band of fresh and frozen roti dough during frozen storage at -18°C for 28, 56 and 84 days.

Secondary structure (%) Storage time (day) -helix -sheet -turn random coil

fresh 4.61 ± 0.40b 65.89 ± 0.50a 3.54 ± 0.17a 25.60 ± 0.26d

0 3.34 ± 0.78a 67.31 ± 0.25b 3.33 ± 0.38a 22.21 ± 0.27c

28 3.25 ± 0.95a 68.21 ± 0.89b 3.28 ± 0.56a 21.81 ± 0.56c

56 3.07 ± 0.09a 71.18 ± 0.81c 3.27 ± 0.17a 19.78 ± 0.78b

84 3.12 ± 0.48a 72.56 ± 0.35d 3.26 ± 0.14a 18.41 ± 0.98a

Note: Each value is mean of triplicate ± SD. The different superscript letters under the same column are significantly different (p<0.05)

Figure 2 Absorbance Fourier transform infrared spectroscopy (FTIR) spectrum of the 1200–1350 cm-1 region (amide III band) of fresh and frozen roti dough during frozen storage time at -18 C for 28, 56 and 84 days. Infrared bands at 1330–1295 cm-1 ( -helix), 1295–1270 cm-1 ( -turns), 1270–1250 cm-1 (random coil) and 1250–1220 cm-1 ( -sheet).


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3.3 Textural properties Figure 3 shows the resistance to extension and extensibility of fresh and frozen roti dough. The resistance to extension of dough is a representative to the ability of the dough to retain gas and dough extensibility is a representative to handling characteristic of dough (Rosell et al., 2001). Frozen roti dough showed the resistance to extension significantly decreased (p<0.05), while the extensibility significantly increased (p<0.05) with increasing frozen storage time. This result indicates deterioration in the quality of gluten by ice crystals formation during freezing and recrystallization during frozen storage (Inoue and Bushuk, 1992).

Figure 3 Resistance to extension and extensibility of fresh dough and frozen roti dough during frozen storage time at -18 °C for 28, 56 and 84 days. 3.4 Viscoelastic properties Creep and recovery are temporary tests in an instantaneous stress. The system deformation per unit stress is called compliance as showed in Figure 4. The creep compliance curve of fresh and frozen roti dough exhibited a typical viscoelastic behavior combination of elastic and viscous components, which could be fitted by the 4-element Burger model. Frozen roti dough significantly decreased (p<0.05) in the instantaneous elastic modulus (G0) and retarded elastic modulus (G1) during frozen storage time (Table 2) which indicates a decrease in the elastic properties and lower recoverability of dough by ice crystal formation during frozen storage. This agrees with previous studies showed the G' decrease during frozen storage (Angioloni et al., 2008; Ribotta et al., 2004).


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Figure 4 Creep compliance and creep recovery of fresh and frozen roti dough during frozen storage at -18 oC for 28, 56 and 84 days. All samples were measured at 25 ◦C and strain at 100 Pa. Table 2 Creep parameter of fresh and frozen roti dough during frozen storage at -18 ◦C for 28, 56 and 84 days.

ideal elastic viscoelastic viscosity Storage time

(days) G0(Pa) x 104 G1(Pa)x104 1(Pa.s)x105 (Sec) N(Pa.s) x 106

fresh 4.56 ± 0.12c 1.40 ± 0.10c 3.33 ± 0.26c 23.68 ± 0.21b

3.35 ± 0.19c

0 4.27 ± 0.77c 1.39 ± 0.15c 3.26 ± 0.42c 23.33 ± 0.26b

3.26 ± 0.20c

28 3.13 ± 0.02b 0.82 ± 0.07b 1.91 ± 0.14b 23.17 ± 0.28b

2.62 ± 0.25b

56 2.85 ± 0.22ab 0.74 ± 0.16b 1.60 ± 0.26b 21.76 ± 1.10a

2.26 ± 0.30b

84 2.30 ± 0.15a 0.50 ± 0.09a 1.10 ± 0.15a 20.94 ± 0.74a

1.75 ± 0.27a

Note: Each value is mean of triplicate ± SD. The different superscript letters under the same column are significantly different (p<0.05) 3.5 Freezable water Freezable water of fresh and frozen roti dough was investigated by DSC as showed in Table 3. Frozen roti dough significantly increased (p<0.05) in�H comparing with fresh roti dough and with increasing frozen storage time. In addition, freezable water of frozen roti dough increased to 42.26% when frozen storage time increase from 0 to 84 days. This increasing in freezable water was attributed to the deterioration of gluten network as a result of ice crystals formation during freezing and recrystallization of ice crystals during frozen storage time, inducing to the separate of water from the other components of the dough (Sharadanant and Khan, 2003).


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Table 3 Enthalpy of ice melting (�H) and freezable water of fresh and frozen roti dough during frozen storage at -18◦C. (moisture content: fresh roti dough: 34.83%)

Storage time (days)

�H (J/g)

Freezable water (% of total water)

fresh dough 43.31 ± 0.61a 37.29 ± 0.53a

0 48.29 ± 0.63b 42.79 ± 0.56b

28 51.69 ± 0.42c 45.80 ± 0.37c

84 83.64 ± 0.87d 74.11 ± 0.77d Note: Each value is mean of triplicate ± SD. The different superscript letters under the same column are significantly different (p<0.05) 4. Conclusion Increasing storage time of frozen roti dough supplemented with rice bran leads to decrease in the qualities of roti dough. Changing of protein structure (β-sheet and random coil) and increasing of freezable water of frozen roti dough during frozen storage seems to be the responsible of the quality loss. Furthermore, decreasing the resistance to extension and the instantaneous elastic modulus (G0) but increasing the extensibility time indicate a decrease in the elastic properties and lower recoverability of frozen roti dough during storage time. Acknowledgements

The authors would like to express their sincere thanks to Prince of Songkla University for supporting Government Budget fund. References Angioloni, A., Balestra, F., Pinnavaia, G. G. and Rosa, M. D., Small and large deformation

tests for the evaluation of frozen dough viscoelastic behavior. J.Food Eng. 2008, 87, 527–531.

Baier-Schenk, A., Handschin, S., von Schonau, M., Bittermann, A.G. et al., In situ observation of the freezing process in wheat dough by confocal laser scanning microscopy (CLSM): formation of ice and changes in the gluten network. Cereal Sci. 2005, 42, 255–260.

Cai, S. and Singh, B. R., Identification of b-turn and random coil amide III infrared bands for secondary structure estimation of proteins. Biophys. Chem. 1999, 80, 7-20.

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Meziani, S., Jasniewski, J., Gaiani, C., Ioannou, I. et al., Effects of freezing treatments on viscoelastic and structural behavior of frozen sweet dough. J. Food Eng. 2011, 107, 358–365.

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