Scholarly article on topic 'Evaluation of viscoelastic properties and air-bubble structure of bread containing gelatinized rice'

Evaluation of viscoelastic properties and air-bubble structure of bread containing gelatinized rice Academic research paper on "Agriculture, forestry, and fisheries"

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Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — Mario Shibata, Junichi Sugiyama, Chia Ling Tsai, Mizuki Tsuta, Kaori Fujita, et al.

Abstract The impact of addition of gelatinized rice porridge to bread has been investigated on loaf volume, viscoelastic properties and air-bubble structure. We prepared four variety of bread: bread containing rice porridge (rice porridge bread), bread containing gelatinized rice flour (gelatinized rice flour bread), and wheat flour and rice flour breads for references. Instrumental analyses the bread samples were carried out by volume measurement of loaf samples, creep test and digital image analysis of crumb samples. Rice porridge bread showed the maximum specific volume of 4.51cm3/g, and even gelatinized rice flour bread showed 4.30cm3/g, which was larger than the reference bread samples (wheat and rice flour breads). The values of viscoelastic moduli of gelatinized rice flour bread and rice porridge bread were significantly smaller (p < 0.05) than those of wheat flour and rice flour breads, which indicates addition of gelatinized rice flour or rice porridge to bread dough encouraged breads softer. Bubble parameters such as mean air- bubble area, number of air-bubble, air-bubble area ratio (ratio of bubble area to whole area) were not significantly different among the bread crumb samples. Therefore, the bubble structures of the bread samples seemed to similar, which implied that difference of viscoelasticity was attributed to air-bubble wall (solid phase of bread crumb) rather than air-bubble. This study showed that addition of gelatinized rice to bread dough makes the bread with larger loaf volume and soft texture without additional agents such as gluten.

Academic research paper on topic "Evaluation of viscoelastic properties and air-bubble structure of bread containing gelatinized rice"

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ProcediaFoodScience 1 (2011) 563 -567

Procedía

Food Science

11th International Congress on Engineering and Food (ICEF11)

Evaluation of viscoelastic properties and air-bubble structure of bread containing gelatinized rice

Mario Shibataa , Junichi Sugiyamaa, Chia Ling Tsaib, Mizuki Tsutaa*,

Kaori Fujita , Mito Kokawa , Tetsuya Araki

aNational Food Research Institute, 2-1-12 Kannondai, Tsukuba-shi, Ibaraki, 305-8642, Japan bThe University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan

Abstract

The impact of addition of gelatinized rice porridge to bread has been investigated on loaf volume, viscoelastic properties and air-bubble structure. We prepared four variety of bread: bread containing rice porridge (rice porridge bread), bread containing gelatinized rice flour (gelatinized rice flour bread), and wheat flour and rice flour breads for references. Instrumental analyses the bread samples were carried out by volume measurement of loaf samples, creep test and digital image analysis of crumb samples. Rice porridge bread showed the maximum specific volume of 4.51 cm3/g, and even gelatinized rice flour bread showed 4.30 cm3/g, which was larger than the reference bread samples (wheat and rice flour breads). The values of viscoelastic moduli of gelatinized rice flour bread and rice porridge bread were significantly smaller (p < 0.05) than those of wheat flour and rice flour breads, which indicates addition of gelatinized rice flour or rice porridge to bread dough encouraged breads softer. Bubble parameters such as mean air-bubble area, number of air-bubble, air-bubble area ratio (ratio of bubble area to whole area) were not significantly different among the bread crumb samples. Therefore, the bubble structures of the bread samples seemed to similar, which implied that difference of viscoelasticity was attributed to air-bubble wall (solid phase of bread crumb) rather than air-bubble. This study showed that addition of gelatinized rice to bread dough makes the bread with larger loaf volume and soft texture without additional agents such as gluten.

©2011Publishedby ElsevierB.V.Selectionand/orpeer-review under responsibilityof11thInternationalCongress on Engineering andFood(ICEF 11) ExecutiveCommittee.

Keywords: rice bread: gelatinization; porridge; air-bubble structure; viscoelastic property

* Corresponding author. Tel.: +32-66-32-85-27 E-mail address: mizukit@affrc.co.jp.

2211-601X © 2011 Published by Elsevier B.V. Selection and/or peer-review under responsibility of 11th International Congress on Engineering

and Food (ICEF 11) Executive Committee.

doi:10.1016/j.profoo.2011.09.085

1. Introduction

Recently, making bread containing rice flour (rice flour bread) have been suggested as a newly method to make use of excessive rice in Japan. However, the quality of rice flour bread has been reported to be inferior to that of wheat flour bread, because its dough expansion is lower and the texture is harder than wheat flour bread. Okunishi[1] reported that adding cooked rice to bread dough could make high-quality bread with high volume and soft texture. One of the differences between rice flour and cooked rice is the degree of gelatinization. Several process patents are registered about manufacturing of bread by adding gelatinized rice (gelatinized rice flour, or rice porridge) to bread dough. Thus, adding gelatinized rice or rice to bread dough would have a possibility to effect texture, or physical properties of bread. However, no scientific data has not been reported about relationship between gelatinization of rice and bread quality.

The objective of this study is to investigate the effect of addition of gelatinized rice porridge on bread qualities of loaf volume, viscoelastic properties and air-bubble structure.

2. Material and Methods

Bread containing cooked rice porridge (rice porridge bread), gelatinized rice flour (gelatinized rice flour bread), wheat flour (wheat flour bread) and rice flour (rice flour bread) were prepared. Table 1 shows the ingredients of bread samples. In this study, substitution ratio of rice flour and rice to wheat flour in each sample was defined as 15 % of all the amount of flours (or cereal). Gelatinized rice flour was made by adding of water to rice flour and then heated by using microwave oven for 5 minutes. Meanwhile, rice porridge was made with rice cooker. They were mixed with other ingredients after cooled to room temperature.

Table 1. Ingredients of bread samples

unit: g

Ingredients WFB RFB GRFB RPB

Wheat flour 1000 850 850 850

Rice flour 150 150

Rice 150

Water (mixed with gelatinized rice flour or rice) 586 546

Water (mixed with ingredients) 690 690 104 144

Sugar 60

Salt 20

Skimmed milk 20

Shortening 50

Dry yeast 10

WFB: wheat flour bread, RFB: rice flour bread, GRFB: gelatinized rice flour bread, RPB: rice porridge bread

The breads were made based on straight method. Ingredients except shortening were mixed by use of bread mixer (KTM-10, Kanto Kongouki Industrial Co., Ltd., Tokyo, Japan). After adding shortening, the dough was mixed until its temperature reached to 27 °C. Next, the dough was fermented in a dough conditioner (NS-D923FA, Matsushita Electric Industrial Co., Ltd., Osaka, Japan) at 27C in 75 % RH for 80 minutes. After the dough was divided into 420g X4 and rounded, floor time (27 C, 75 %RH, 25 minutes) was ensured in the dough conditioner prior to rolling of the doughs into thickness of 4.5 mm by use of a molder (WR-01, Oshikiri Machinery Ltd., Kanagawa, Japan). The rolled doughs were set in pans and fermented in a proofer (toku hoiro, Tokura Shoji Co., Ltd. Shiga, Japan) at 38 C in 85 %RH for about

50 minutes (The end of fermentation was defined when the surface of the dough reached to the rim of the pan.). Finally, the doughs were baked for 20 minutes at 200°C in a convection oven (739 Shop Oven, Revent International AB, Vasby, Sweden). After the baking, the loafs were released and cooled for 1 hour at room temperature.

The loaf volume were measured by laser volume measurement unit (Selnac-WinVM2100A, Astex Corp., Tokyo, Japan), and then heights and the specific volumes of loaves were obtained (n = 4). After the measurements, loaves were stored in polyethylene bags to minimize dehydration. Following measurements were performed 1 day after the baking.

Loaf samples were sliced into thickness of 2 cm by a pan slicer (A-70, Hakura Seiki Co., Ltd., Tokyo, Japan). Cubic samples of 2x2x2 cm were cut from the slices with an ultrasonic cutter (USC-3305-2, Yamaden Co., Ltd, Tokyo, Japan) for the subsequent viscoelastic and air-bubble image measurements.

The bread samples were provided to creep tests using creep meter (RE2-33005S, Yamaden Co., Ltd, Tokyo, Japan) with the condition: loading weight 0.1 N, measurement time 2 minutes, 55 mm diameter of circle plunger. The compression direction was defined as the directions vertical to the sliced surface. The specimens were stored in closed plastic case to avoid their dehydration. Viscoelastic properties of the bread specimens was obtained by applying the equation (1) based on the four-element Voigt model as shown in Figure 1 to the time-strain curves obtained by the creep test. The analysis was carried out using a statistical software JMP 7 (SAS Institute. Inc., NC, USA).

e: strain, t: time, a0: stress, E0; instant elasticity, Ex: retardation elasticity, nv. retardation viscosity, nN: permanent viscosity

Next, the surface of the samples were scanned using a flatbed image scanner (GT-X970, SEIKO EPSON Corp., Nagano, Japan) with a 150 dpi resolution, and then the acquired 16-bit gray-level images were saved in TIFF format without any image compression. During the measurement, the specimens were covered with a ceramic case to protect from an external light. Square area of 10.1 mmx10. 1 mm (60x60 pixel) of the samples were selected for air-bubble image analysis. The detection of air-bubble was performed using the thresholding method based on the previous study [2]. Three air-bubble parameters such as mean air-bubble area, number of air-bubble, air-bubble area ratio (ratio of bubble area to whole area) were quantified. The digital image processing was carried out by Matlab 2010a software (Mathworks Inc., Massachusetts, U.S.).

E0: instant elasticity,

E^ retardation elasticity retardation viscosity nN: permanent viscosity

Fig.1. Four-element Foigt model

3. Results and Discussion

Figure 2 shows loaf height and specific volumes of bread samples. Rice porridge bread showed the maximum height and specific volume of 13. 0 cm and 4.51 cm3/g, respectively. Gelatinized rice flour bread also showed 4.30 cm3/g, which were larger than rice flour bread. All the samples did not show caving, and keep their shape after baking.

Figure 3 represents viscoelastic moduli of the crumb samples. In the viscoelastic moduli except retardation viscosity, significant differences were identified between two groups: (wheat flour bread and rice flour bread) and (gelatinized rice flour bread and rice porridge bread). In the retardation viscosity, the modulus of rice porridge bread was smaller than those of wheat flour and rice flour breads, though significant difference was not identified between those of gelatinized rice flour and wheat flour bread. This indicated that elasticity and viscosity of rice porridge bread were smaller than those of wheat flour and rice flour breads, thus, rice porridge bread has softer texture than them. In addition, though gelatinized rice flour bread might have similar viscoelastic properties to wheat flour bread, it was confirmed that the gelatinized rice flour bread was more similar to rice porridge bread.

Figure 4 shows air-bubble parameters of the crumb samples. All the parameters (mean air-bubble area, number of air-bubble, air-bubble area ratio) were not significantly different among the bread crumb samples. Thus, the air-bubble structures of the bread samples seemed to be similar, which implied that the difference of viscoelasticity could resulted from mechanical property of air-bubble wall (solid phase of bread crumb) rather than the air-bubble structure (the water content of the samples were almost the same: 45 %).

Thus, it was confirmed that the breads containing gelatinized rice flour or rice porridge have higher dough expansion and softer texture than usual without additional ingredients such as gluten.

The reason why that the breads containing gelatinized rice flour or rice porridge had high dough expansion might be that (1) gelatinization of rice flour or rice encouraged water absorption of wheat flour and then gliadin and glutenin, which contained in wheat flour, with sufficient water formed gluten smoothly, and (2)while gelatinized starch by baking complemented structure of gluten, gelatinized rice flour and rice porridge might extended and made structure which captured air-bubbles.

<u 12 JS

WFB RFB

WFB RFB GRFB RPB

Fig.2. Loaf height and specific volumes of bread samples (*p < 0.05, WFB: wheat flour bread, RFB: rice flour bread, GRFB: gelatinized rice flour bread, RPB: rice porridge bread)

« 11 P4

WFB RFB GRFB RPB

tf 45 P4

WFB RFB GRFB RPB

WFB RFB GRFB RPB

WFB RFB GRFB RPB

Figure 3 Viscoelastic moduli of crumb samples (*p < 0.05, E0: instant elasticity, Ei: retardation elasticity, ni: retardation viscosity, nN: permanent viscosity, WFB: wheat flour bread, RFB: rice flour bread, GRFB: gelatinized rice flour bread, RPB: rice porridge bread)

4. Conclusion

To investigate the effect of addition of gelatinized rice porridge on bread qualities, loaf volume, viscoelastic properties and air-bubble structure of the bread samples were measured.

Rice porridge bread showed the maximum specific volume among others. The viscoelastic moduli of gelatinized rice flour bread and rice porridge bread were significantly smaller (p < 0.05) than those of the other breads, which indicate the addition of gelatinized rice could make the bread texture soft. The air-bubble structures of the bread samples were almost similar. This study showed that the addition of gelatinized rice to bread dough makes the bread with larger loaf volume and also good texture without improving additive such as gluten.

References

[1] Okunishi.T. Bread made from cooked rice and wheat flour blend. Journal of the Japanese Society for Food Science and Technology 2009; 56: 424-428.

[2] Shibata, M., Sugiyama, J., Tsuta, M., Fujita, K., Sugiyama, T., Kokawa, M., Araki, T., Nabetani, H. and Sagara, Y. Development of measurement for bubble structure of bread using image scanner, Journal of the Japanese Society for Food Science and Technology 2010; 57: 243-250.

Presented at ICEF11 (May 22-26, 2011 - Athens, Greece) as paper EPF645.