- Email: [email protected]
Effect of different pressure-soaking treatments on color, texture, morphology and retrogradation properties of cooked rice
LWT - Food Science and Technology 55 (2014) 368e373
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Effect of different pressure-soaking treatments on color, texture, morphology and retrogradation properties of cooked rice Yaoqi Tian a, b, Jianwei Zhao a, b, Zhengjun Xie a, b, Jinpeng Wang a, b, Xueming Xu a, b, Zhengyu Jin a, b, * a b
The State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi 214122, China Synergetic Innovation Center of Food Safety and Nutrition, Jiangnan University, Wuxi 214122, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 February 2012 Received in revised form 10 September 2013 Accepted 23 September 2013
The hydration of rice grain and the quality of cooked rice with the different pressure soaking treatments were estimated using Chroma meter (CM), Texture Profile Analysis (TPA), Scanning electron microscopy (SEM), and Differential Scanning Calorimetry (DSC). The results showed that the vacuum soaking and the high hydrostatic pressure (HHP) soaking increased the hydration degree of normal rice, while the hydration effect in waxy rice was increased only by the HHP treatment. The lightness (L*) and the color intensity (B) of cooked normal rice and waxy rice were significantly improved by the two treatments. The HHP soaking also generated the lower hardness, while the higher springiness and cohesiveness for cooked normal and waxy rice samples. These highlights were mainly attributed to the less amylose leaching and the smaller network channels formed between starch granules and other connection parts. Furthermore, the retrogradation of cooked normal and waxy rice was reduced by the HHP treatment. These findings suggest that the HHP soaking could be used for producing high-quality of cooked rice. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: High hydrostatic pressure Vacuum Soaking Cooked rice Quality
1. Introduction Soaking is an essential process to diffuse water inside rice grain and it improves the palatability of cooked rice. Many researchers reported that several physical changes occurred during soaking of rice grains at different time and temperatures (Chakkaravarthi, Lakshmi, Subramanian, & Hegde, 2008; Han & Lim, 2009; Yamakura et al., 2005). According to their findings, the high temperature soaking effectively generated better nutritional qualities and bio-functionality of cooked rice by hydrolyzing residual proteins to free amino acids like g-amino butyric acid and serine (Saikusa, Horino, & Mori, 1994; Yamakura et al., 2005). Nevertheless, the high temperature soaking often resulted in the loss of solids and increased the color of rice grains (Yamakura et al., 2005). High hydrostatic pressure (HHP) treatment is defined that packed food materials are treated by HHP (100e1000 MPa) in the vessel of the pressure unit at room temperature to achieve sterilization and material modification (Knorr, Heinz, & Buckow, 2006). HHP could only destroy the non-covalent bonds and retain the
color, aroma, flavor, and nutrition of foods (Balny, 2002; Knorr et al., 2006; Lullien-Pellerin & Balny, 2002). Yamakura et al. (2005) studied the effects of the soaking and the HHP treatment on rice quality by measuring pasting properties, loss of sugars and rice proteins, and protein solubility. The results demonstrated that the total sugar content increased and the change in internal structure of rice grain occurred during the HHP treatment. In addition, the HHP soaking could promote water penetration and increase the palatability of rice grain on the whole (Yamazaki, Kinefuchi, Yamamoto, & Yamada, 1996). However, published articles with respect to effects of the vacuum soaking and the HHP soaking on the qualities of cooked rice were very limited. The aim of this study, therefore, was to evaluate the effect of the two soaking treatments on the hydration effect of rice grains, the lightness and the color intensity, the texture, the internal microstructure, and retrogradation properties of cooked rice. The mechanism behind the improved quality by the HHP soaking was also discussed. 2. Materials and methods
* Corresponding author. The State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi 214122, China. E-mail addresses: [email protected] (Y. Tian), [email protected] (Z. Jin). 0023-6438/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2013.09.020
2.1. Materials Two rice varieties (normal rice and waxy rice) were purchased from Shandong Mei-Jing Rice Inc. (Shandong, China) in 2009 and
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373
stored at 15 C for use. The amylose contents of them determined by the spectrophotometric method (Hoover & Ratnayake, 2001) were 21.3% and 1.9%, respectively. All other chemicals and reagents were of analytical grade unless otherwise stated. 2.2. Rice soaking and cooking
369
Surrey, UK), as the method reported by Tian, Jin, Deng, Xu, and Zhao (2007). In brief, cooked rice was put on the sample table at the center of the probe in a flat form and compressed using a 2.5 mm diameter cylinder probe at a test speed of 0.5 mm/s and a control force of 10 g. The deformation level was 60% of original sample height and the partly broken rice was compressed again. This process was repeated at least 10 times for each sample using different rice grains and the mean value was collected for statistical analysis.
Twenty grams of rice grain with distilled water (140 g/100 g rice grain) were vacuum-packed in a food grade polyethylene film bag (Height and width, 18 cm 13 cm, Xincheng Packaging Materials Co., Suzhou, China) and soaked at 55 C for 30 min using a laboratory-scale high-pressure unit (UHPF-800MPa-3L, New hightech food machinery company, Baotou, China). Six film bags after the pre-soaking were further treated as follows. The working pressure for the first two film bags (one with normal rice grain and another with waxy rice grain) was increased at a rate of 100 MPa/ min, maintained at 300 MPa for 25 min, and then released at a rate of 150 MPa/min. The working pressure for second two film bags was increased at a rate of 100 MPa/min, maintained at 400 MPa for 25 min, and then released at a rate of 400 MPa/min. Here, the vessel temperature and the total time for increasing and releasing the high pressure were controlled to be 55 C and 5 min, respectively. The third two film bags of the presoaked samples were kept at 55 C using the HHP machine under atmospheric pressure for 30 min to prepare vacuum-soaking rice samples. Another two film bags with normal and waxy rice grains as the references were atmospheric pressure e packed in film bags and continuously soaked at 55 C using the HHP machine heating under atmospheric pressure for 60 min. Crucially, only two film bags (one with normal rice grain and another with waxy rice grain) each time could be treated using the HHP machine. The resultant film bags were cooked using a steam cooker (YJ308J 3L, Midea Group Co., Guangdong, China) for 18 min and kept warm for 5 min to obtain fresh rice samples with normally eating. The repeated trials were performed under the same soaking and cooking conditions.
As the method described in Section 2.2, the soaked rice grains were cooked by the steam cooker for 18 min and kept warm for 5 min to obtain fresh rice samples. These samples were stored at 4 C and relative humidity 75% for 0, 1, 3, 5, 7, 14, and 35 days to perform the retrogradation study. The retrograded samples (5 mg, 166.7 g water/100 g dry basis) were subjected to trituration and collected for thermal analysis. The enthalpy change was measured at a heating rate of 10 C/min from 30 C to 90 C using a DSC (Pyris 1, Pekin Elmer, MA, USA) under ultrahigh-purity nitrogen of 20 mL/ min. The same procedure was repeated 5 times for each sample. The retrogradation degree (DR) of the rice samples was calculated according to the following equation (Hu et al., 2011; Jouppila, Kansikas, & Roos, 1998):
2.3. Hydration of soaked rice samples
DRð%Þ ¼ ðDHt DH0 Þ=DHN 100%
The hydration degree of the soaked rice was determined as the procedure described by Chen et al. (2010). In brief, normal and waxy rice grains were packed and treated under soaking conditions detailed in Section 2.2 for 10, 20, 30, 40, 50, and 60 min, respectively. These samples were taken out the film bags at the designated time and immediately wrapped with filter paper to remove the surface water and dried in an oven at 105 C for 2 h to evaluate the moisture (g/100 g dry basis). 2.4. Color intensity and lightness of cooked rice The fresh cooked rice was immediately for color measurement using a Chroma meter CR-400 (Konica Minolta Sensing Inc., Osaka, Japan). Color coordinates for the extent of lightness (L*), redness/ greenness (þa*/a*), and yellowness/blueness (þb*/b*) were collected. The color intensity (B) was calculated using the following equation (Lamberts et al., 2006; Roy et al., 2008).
h 2 2 i1=2 B ¼ a* þ b*
(1)
2.5. Texture profile analysis (TPA) of cooked rice The fresh cooked rice was directly performed TPA analysis. The hardness, springiness and cohesiveness of cooked rice were measured using a texture analyzer (TA-XT2i, Stable Micro Systems,
2.6. Scanning electron microscopy (SEM) The cooked rice samples were immediately dried using a vacuum freeze dryer (ALPHA1-4, Marin Christ Inc., Osterode, Germany). After drying, they were stuck on a specimen holder using a silver plate and coated with a thin film of gold (10 nm) in a vacuum evaporator. The resultant specimens picked from the central endosperm of rice kernel were observed and photographed using a scanning electron microscope (Quanta-200, FEI Company, Eindhoven, Netherlands) at an accelerating voltage of 5.0 kV. 2.7. Retrogradation properties of cooked rice samples
(2)
where,
DH0 is the enthalpy change of the fresh rice sample, DHt is the enthalpy change (J/g) of the t-day retrograded rice sample, and
DHN is the enthalpy change of the 35-day retrograded rice sample. 2.8. Statistical analysis Statistical analysis was performed by using ORIGIN 7.5 (OriginLab Inc., Northampton, MA, USA). Data were expressed as means of at least triplicate and analyzed by a one-way analysis of variance (ANOVA). p value 0.05 was regarded as significant throughout the study. 3. Results and discussion 3.1. Hydration of soaked rice The present data showed that the HHP soaking, compared with the atmospheric pressure soaking, significantly increased the moisture content of normal rice grain from 40.94% to 44.4% (300 MPa) and 45.62% (400 MPa), respectively (Fig. 1a). This was well accorded with the results described by Yamakura et al. (2005). The increase in moisture indicated that water molecules could effectively penetrate into the peripheral portion of starch granules in rice grains under the high pressure, although the intact rice
370
a
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373 Table 1 Color parameters of cooked normal rice and waxy rice with different pressure soaking treatments.
50
Moisture content (g/100g dry basis)
45
Rice varieties
40
0.1 Cooked normal Vacuum 300 rice 400 0.1 Cooked Vacuum waxy 300 rice 400
35
30
25
15 0
10
20
30
40
50
60
Water soaking time (min) 55 50
Moisture content (g/100g dry basis)
68.7 72.5 74.7 76.2 69.2 72.8 75.8 76.5
b
0.9a 1.1b 0.9c 1.4c 1.3a 0.7b 1.1c 0.8c
7.8 6.4 5.8 5.6 6.7 5.8 5.3 5.1
b*
0.4f 0.3cd 0.3bc 0.4ab 0.3de 0.4abc 0.4ab 0.3a
B
13.5 11.8 10.3 9.7 12.5 10.9 9.8 9.4
0.3f 0.4de 0.4bc 0.4ab 0.3e 0.4c 0.5ab 0.4a
15.6 13.4 11.8 11.2 14.2 12.4 11.1 10.7
0.5f 0.4de 0.4bc 0.3ab 0.4e 0.3c 0.3ab 04a
a L*, the color lightness, þa*/a*; redness/greenness, þb*/b*, yellowness/blueness; and B, the color intensity. b Sample means with different lowercase letters in the same column are significantly different (p 0.05); the number of replications (n), n 8.
20
b
Pressure Color parametersa (MPa) L* a*
45 40 35 30 25 20
Production of lighter color rice is essential for the higher customer acceptability. The results showed that the color intensity and the lightness of cooked normal and waxy rice varieties were observed to be 15.6 and 68.7, and 14.2 and 69.2, respectively (Table 1). The lightness and the color intensity were dependant on the soaking pressures. Both of the vacuum soaking and the high pressure soaking could significantly increase the lightness and reduce the color intensity of cooked normal and waxy rice varieties. This result was probably attributed to a fact that the vacuum soaking reduced the enzymatic reaction occurring in rice by the less oxygen concentration. Furthermore, it was reported that the HHP treatment could inactivate the enzymes such as catalase and polyphenol oxidase present in rice (Knorr et al., 2006; Mabashi, Ookura, Tominaga, & Kasai, 2009). These results suggest that the HHP soaking improved the color lightness and the color intensity of cooked rice due to the inhibition of enzymatic browning by the less oxygen and the lower enzyme activity existing. 3.3. Texture properties
15 0
10
20
30
40
50
60
Water soaking time (min) Fig. 1. Moisture content (g water/100g dry basis) of (a) normal rice and (b) waxy rice with 300 MPa ( ), 400 MPa ( ), vacuum ( ), and atmospheric pressure ( ) soaking treatments during one hour. Number of replications (n), n 3.
starch granules were still present under 600 MPa (Hu et al., 2011). In addition, the vacuum-soaked normal rice had higher moisture than the atmospheric pressure-soaked one before 30 min, while after that, no significant difference in moisture was observed. This indicated that the vacuum soaking might cause wider channels between starch granules and benefit water incorporating due to a pressure difference occurring inside and outside of rice grain. For the vacuum-soaked waxy rice, the moisture content was significantly higher than that of the atmospheric pressure-soaked one during the whole soaking process (Fig. 1b). The HHP soaking also increased the moisture adsorbing and distributing in waxy rice grains. Nevertheless, there was no significant difference in moisture content for waxy rice soaked under different high pressures (300 MPa and 400 MPa). This might suggest that the sensitivity of waxy rice grains to high pressure was reduced after the grains were presoaked at 55 C for 30 min. 3.2. Color intensity and lightness analysis The color intensity of cooked rice has a negative effect on consumer acceptance and generates to a loss in market value.
The texture analysis data revealed that the cooked normal rice had higher hardness than the cooked waxy rice (Table 2). This was confirmed by a previous study, indicating that the hardness was positively correlated with the amylose contained in rice grain (Yu, Ma, & Sun, 2009). Rice with higher amylose content was liable to leach more into the cooking water and formed a coating film on rice grains to increase the hardness (Leelayuthsoontorn & Thipayarat, 2006). Amylose, on the other hand, was easier to retrograde and increased the hardness of the cooked rice in a short period. In addition, the hardness of cooked normal and waxy rice varieties was significantly reduced by the HHP soaking. This decrease might indicate that the HHP soaking could prevent amylose and amylopectin components leaching out, although it could decrease the crystallinity of starch granules (Hu et al., 2011). Springiness (length/ Table 2 Texture properties of cooked normal rice and waxy rice with different pressure soaking treatments. Rice varieties
Pressure (MPa)
Hardness (g)
Cooked normal rice
0.1 Vacuum 300 400 0.1 Vacuum 300 400
685.7 674.3 638.9 627.1 598.1 591.7 560.4 555.7
Cooked waxy rice
7.1da 8.6d 9.8c 8.4c 7.3b 6.5b 7.4a 8.5a
Springiness (length/length) 0.65 0.69 0.81 0.87 0.51 0.55 0.64 0.69
0.03b 0.04b 0.05c 0.04c 0.04a 0.02a 0.04b 0.05b
Cohesiveness (area/area) 0.54 0.55 0.63 0.64 0.73 0.75 0.87 0.91
0.04a 0.04a 0.03b 0.04b 0.04c 0.05c 0.04d 0.04d
a Sample means with different lowercase letters in the same column are significantly different (p 0.05); the number of replications (n), n 10.
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373
371
Fig. 2. SEM images of (a) cooked normal rice with atmospheric pressure soaking, (b) cooked normal rice with vacuum soaking, (c) cooked normal rice with 300 MPa high pressure soaking, (d) cooked normal rice with 400 MPa high pressure soaking, (e) cooked waxy rice with atmospheric pressure soaking, (f) cooked waxy rice with vacuum soaking, (g) cooked waxy rice with 300 MPa high pressure soaking, and (h) cooked waxy rice with 400 MPa high pressure soaking.
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373
length) is a measure of how much the gel structure is broken down by the initial compression. It is generally considered that a high springiness appears as a gel structure is broken into few large pieces during the first TPA compression, whereas low springiness results from a gel breaking into many small pieces (Huang, Kennedy, Li, Xu, & Xie, 2007). The high pressure soaking increased the springiness from 0.65 (atmospheric pressure) to 0.81 (300 MPa) and 0.87 (400 MPa) for cooked normal rice, and from 0.51 (atmospheric pressure) to 0.64 (300 MPa) and 0.69 (400 MPa) for cooked waxy rice. These results indicated that the macrostructure of cooked rice with the HHP treatment was broken into some large pieces during the first compression of the TPA test. The cohesiveness of cooked normal and waxy rice was significantly increased by the HHP soaking. This increase suggested that more compact network might be formed in rice under the high pressure soaking that could cause amylose and amylopectin redistributing in rice grains.
a
54 48
Degree of retrogradation (%)
372
42 36 30 24 18 12 6
0
3
3.4. Morphologic properties
3.5. Retrogradation properties The aging studies showed that the cooked normal rice with the HHP soaking had lower retrogradation degree than that with the atmospheric pressure soaking (Fig. 3a). The less retrogradation indicated that the HHP soaking inhibited the retrogradation process of cooked normal rice. Rice retrogradation was directly related to amylose leaching during cooking (Leelayuthsoontorn & Thipayarat, 2006). Hu et al. (2011) also reported that the HHP treatment (600 MPa) could retain the intact starch granules and prevent amylose leaching. The lower amylose leakage, therefore, only could generate a thinner film on rice grains and reduced the rapid retrogradation in a short period (Stolt, Oinonen, & Autio, 2001). Furthermore, long amylopectin chains might crystallize with amylose molecules to organize several adjacent clusters, thus resulting in less amylose leaching (Ong & Blanshard, 1995). However, there was no significant difference observed for cooked normal rice under the vacuum soaking and the atmospheric pressure soaking. This result indicated that the pressure difference
b
9
12
15
12
15
40 35
Degree of retrogradation (%)
The SEM images revealed that the cooked normal rice with the vacuum soaking and the HHP soaking had smaller cavities and larger connection parts compared to that with the atmospheric pressure soaking (Fig. 2aed). This result indicated that the soaking treatments under the vacuum and the high pressure conditions could prevent the microstructure damage of cooked normal rice and generate more network structure. The network formed could result in the higher springiness and cohesiveness, which were accorded with the results in Section 3.3. Furthermore, the soaking under the higher pressure (400 MPa) caused the holes smaller. The decrease in size demonstrated that a pressure difference outside and inside rice grains during soaking might retain the integrity of starch granules and only produce homogeneous channels between starch granules and other connection parts. For the cooked waxy rice, larger and more homogeneous channels were observed for soaking under the vacuum and the HHP treatments (Fig. 2eeh). This was attribute to a fact that the main component in waxy rice was amylopectin that was more sensitive to heat and pressure than amylose (Hu et al., 2011). The pressure difference, therefore, was easier to widen the channels for the soaked waxy rice grains. The channels could be swelled by heat air during cooking. These results suggest that the higher sensitivity of rice components to soaking pressure was responsible for generating the homogeneous network microstructure. This network might produce the lower hardness and the higher springiness of cooked waxy rice.
6
Storage time (d)
30 25 20 15 10 5 0 0
3
6
9
Storage time (d) Fig. 3. Retrogradation degree of (a) cooked normal rice and (b) cooked waxy rice with 300 MPa ( ), 400 MPa ( ), vacuum ( ), and atmospheric pressure ( ) soaking pretreatments. The number of replications (n), n 5.
produced under the vacuum condition did not have enough ability to redistribute starch granules and retain the integrity in normal rice. Comparing with the other soaking treatments, the HHP soaking significantly reduced the retrogradation of cooked waxy rice, while the inhibition effect was not significant between 300 MPa and 400 MPa high pressure soaking treatments (Fig. 3b). This result was partly confirmed by previous studies, indicating that waxy rice was more sensitive to the HHP treatment (B1aszczak et al., 2007; Stolt et al., 2001). Therefore, the lower high pressure (e.g. 300 MPa) was enough for soaking of waxy rice grains in this study. 4. Conclusions This work made it clear that the color, the texture, and the retrogradation properties were significantly improved by the vacuum soaking and the HHP soaking. The high quality of cooked rice was mainly attributed to the better water diffusion inside rice grains during high pressure soaking and the smaller network channels formed between starch granules and other connection sections. These findings suggest that the HHP soaking is one of advantageous techniques for cooked rice with better palatability.
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373
Future research should be performed to check if these results could be extrapolated to industrial scale to produce fresh cooked rice with a high quality. Acknowledgments This study was financially supported by the National Key Technology R&D Program for the 12th Five-Year Plan (Nos. 2012BAD37B02, 2012BAD37B01, and 2012BAD37B03). References Balny, C. (2002). High pressure and protein oligomeric dissociation. High Pressure Research, 22, 737e741. B1aszczak, W., Fornal, J., Kiseleva, V. I., Yuryev, V. P., Sergeev, A. I., & Sadowska, J. (2007). Effect of high pressure on thermal, structural and osmotic properties of waxy maize and hylon VII starch blends. Carbohydrate Polymers, 68, 387e396. Chakkaravarthi, A., Lakshmi, S., Subramanian, R., & Hegde, V. M. (2008). Kinetic of cooking unsoaked and presoaked rice. Journal of Food Engineering, 84, 181e186. Chen, G., Tian, Y., Jiao, A., Xu, B., Xu, X., & Jin, Z. (2010). Determination of the initial production conditions and steam cooking kinetics research for instant rice. Food and Fermentation Industries, 36(8), 36e40 [In Chinese]. Han, J. A., & Lim, S. T. (2009). Effect of presoaking on textural, thermal, and digestive properties of cooked brown rice. Cereal Chemistry, 86, 100e105. Hoover, R., & Ratnayake, W. S. (2001). Determination of total amylose content of starch. Current Protocols in Food Analytical Chemistry, E2.3.1eE2.3.5. Huang, M., Kennedy, J. F., Li, B., Xu, X., & Xie, B. J. (2007). Characters of rice starch gel modified by gellan, carrageenan, and glucomannan: a texture profile analysis study. Carbohydrate Polymers, 69, 411e418. Hu, X. T., Xu, X. M., Jin, Z. Y., Tian, Y. Q., Bai, Y. X., & Xie, Z. J. (2011). Retrogradation properties of rice starch gelatinized by heat and high hydrostatic pressure (HHP). Journal of Food Engineering, 106, 262e266. Jouppila, K., Kansikas, J., & Roos, Y. H. (1998). Factors affecting crystallization and crystallization kinetics in amorphous corn starch. Carbohydrate Polymers, 36, 143e149.
373
Knorr, D., Heinz, V., & Buckow, R. (2006). High pressure application for food biopolymers. Biochimica et Biophysica Acta, 1764, 619e631. Lamberts, L., De Bie, E., Derycke, V., Veraverbeke, W. S., De Man, W., & Delcour, J. A. (2006). Effect of processing conditions on color change of brown and milled parboiled rice. Cereal Chemistry, 83, 80e85. Leelayuthsoontorn, P., & Thipayarat, A. (2006). Textural and morphological changes of jasmine rice under various elevated cooking conditions. Food Chemistry, 96, 606e613. Lullien-Pellerin, V., & Balny, C. (2002). High-pressure as a tool to study some proteins’ properties: conformational modification, activity and oligomeric dissociation. Innovative Food Science and Emerging Technologies, 3, 209e221. Mabashi, Y., Ookura, T., Tominaga, N., & Kasai, M. (2009). Characterization of endogenous enzymes of milled rice and its application to rice cooking. Food Research International, 42, 157e164. Ong, M. H., & Blanshard, J. M. V. (1995). Texture determinants in cooked, parboiled rice. I: rice starch amylose and the fine structure of amylopectin. Journal of Cereal Science, 21, 251e260. Roy, P., Ijiri, T., Okadome, H., Nei, D., Orikasa, T., Nakamura, et al.. (2008). Effect of processing conditions on overall energy consumption and quality of rice (Oryza sativa L.). Journal of Food Engineering, 89, 343e348. Saikusa, T., Horino, T., & Mori, Y. (1994). Distribution of free amino acids in the rice kernel and kernel fractions and the effect of water soaking on the distribution. Journal of Agricultural and Food Chemistry, 42, 1122e1125. Stolt, M., Oinonen, S., & Autio, K. (2001). Effect of high pressure on the physical properties of barley starch. Innovative Food Science and Emerging Technologies, 1, 167e175. Tian, Y., Jin, Z., Deng, L., Xu, X., & Zhao, J. (2007). Study on the effect of vitamin D3-bcyclodextrin inclusion compound on the quality improvement in extruded nutrition-fortified rice. Food and Fermentation Industries, 33(12), 52e55 [In Chinese]. Yamakura, M., Haraguchi, K., Okadome, H., Suzuki, K., Tran, U., Horigane, A. K., et al. (2005). Effects of soaking and high-pressure treatment on the qualities of cooked rice. Journal of Applied Glycoscience, 52, 85e93. Yamazaki, A., Kinefuchi, M., Yamamoto, K., & Yamada, A. (1996). Physical properties and fine structure of grains of high pressure-treated rice after cooking. Review of High Pressure Science and Technology, 5, 168e178. Yu, S. F., Ma, Y., & Sun, D. W. (2009). Impact of amylose content on starch retrogradation and texture of cooked milled rice during storage. Journal of Cereal Science, 50, 139e144.
Contents lists available at ScienceDirect
LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt
Effect of different pressure-soaking treatments on color, texture, morphology and retrogradation properties of cooked rice Yaoqi Tian a, b, Jianwei Zhao a, b, Zhengjun Xie a, b, Jinpeng Wang a, b, Xueming Xu a, b, Zhengyu Jin a, b, * a b
The State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi 214122, China Synergetic Innovation Center of Food Safety and Nutrition, Jiangnan University, Wuxi 214122, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 February 2012 Received in revised form 10 September 2013 Accepted 23 September 2013
The hydration of rice grain and the quality of cooked rice with the different pressure soaking treatments were estimated using Chroma meter (CM), Texture Profile Analysis (TPA), Scanning electron microscopy (SEM), and Differential Scanning Calorimetry (DSC). The results showed that the vacuum soaking and the high hydrostatic pressure (HHP) soaking increased the hydration degree of normal rice, while the hydration effect in waxy rice was increased only by the HHP treatment. The lightness (L*) and the color intensity (B) of cooked normal rice and waxy rice were significantly improved by the two treatments. The HHP soaking also generated the lower hardness, while the higher springiness and cohesiveness for cooked normal and waxy rice samples. These highlights were mainly attributed to the less amylose leaching and the smaller network channels formed between starch granules and other connection parts. Furthermore, the retrogradation of cooked normal and waxy rice was reduced by the HHP treatment. These findings suggest that the HHP soaking could be used for producing high-quality of cooked rice. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: High hydrostatic pressure Vacuum Soaking Cooked rice Quality
1. Introduction Soaking is an essential process to diffuse water inside rice grain and it improves the palatability of cooked rice. Many researchers reported that several physical changes occurred during soaking of rice grains at different time and temperatures (Chakkaravarthi, Lakshmi, Subramanian, & Hegde, 2008; Han & Lim, 2009; Yamakura et al., 2005). According to their findings, the high temperature soaking effectively generated better nutritional qualities and bio-functionality of cooked rice by hydrolyzing residual proteins to free amino acids like g-amino butyric acid and serine (Saikusa, Horino, & Mori, 1994; Yamakura et al., 2005). Nevertheless, the high temperature soaking often resulted in the loss of solids and increased the color of rice grains (Yamakura et al., 2005). High hydrostatic pressure (HHP) treatment is defined that packed food materials are treated by HHP (100e1000 MPa) in the vessel of the pressure unit at room temperature to achieve sterilization and material modification (Knorr, Heinz, & Buckow, 2006). HHP could only destroy the non-covalent bonds and retain the
color, aroma, flavor, and nutrition of foods (Balny, 2002; Knorr et al., 2006; Lullien-Pellerin & Balny, 2002). Yamakura et al. (2005) studied the effects of the soaking and the HHP treatment on rice quality by measuring pasting properties, loss of sugars and rice proteins, and protein solubility. The results demonstrated that the total sugar content increased and the change in internal structure of rice grain occurred during the HHP treatment. In addition, the HHP soaking could promote water penetration and increase the palatability of rice grain on the whole (Yamazaki, Kinefuchi, Yamamoto, & Yamada, 1996). However, published articles with respect to effects of the vacuum soaking and the HHP soaking on the qualities of cooked rice were very limited. The aim of this study, therefore, was to evaluate the effect of the two soaking treatments on the hydration effect of rice grains, the lightness and the color intensity, the texture, the internal microstructure, and retrogradation properties of cooked rice. The mechanism behind the improved quality by the HHP soaking was also discussed. 2. Materials and methods
* Corresponding author. The State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, Wuxi 214122, China. E-mail addresses: [email protected] (Y. Tian), [email protected] (Z. Jin). 0023-6438/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.lwt.2013.09.020
2.1. Materials Two rice varieties (normal rice and waxy rice) were purchased from Shandong Mei-Jing Rice Inc. (Shandong, China) in 2009 and
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373
stored at 15 C for use. The amylose contents of them determined by the spectrophotometric method (Hoover & Ratnayake, 2001) were 21.3% and 1.9%, respectively. All other chemicals and reagents were of analytical grade unless otherwise stated. 2.2. Rice soaking and cooking
369
Surrey, UK), as the method reported by Tian, Jin, Deng, Xu, and Zhao (2007). In brief, cooked rice was put on the sample table at the center of the probe in a flat form and compressed using a 2.5 mm diameter cylinder probe at a test speed of 0.5 mm/s and a control force of 10 g. The deformation level was 60% of original sample height and the partly broken rice was compressed again. This process was repeated at least 10 times for each sample using different rice grains and the mean value was collected for statistical analysis.
Twenty grams of rice grain with distilled water (140 g/100 g rice grain) were vacuum-packed in a food grade polyethylene film bag (Height and width, 18 cm 13 cm, Xincheng Packaging Materials Co., Suzhou, China) and soaked at 55 C for 30 min using a laboratory-scale high-pressure unit (UHPF-800MPa-3L, New hightech food machinery company, Baotou, China). Six film bags after the pre-soaking were further treated as follows. The working pressure for the first two film bags (one with normal rice grain and another with waxy rice grain) was increased at a rate of 100 MPa/ min, maintained at 300 MPa for 25 min, and then released at a rate of 150 MPa/min. The working pressure for second two film bags was increased at a rate of 100 MPa/min, maintained at 400 MPa for 25 min, and then released at a rate of 400 MPa/min. Here, the vessel temperature and the total time for increasing and releasing the high pressure were controlled to be 55 C and 5 min, respectively. The third two film bags of the presoaked samples were kept at 55 C using the HHP machine under atmospheric pressure for 30 min to prepare vacuum-soaking rice samples. Another two film bags with normal and waxy rice grains as the references were atmospheric pressure e packed in film bags and continuously soaked at 55 C using the HHP machine heating under atmospheric pressure for 60 min. Crucially, only two film bags (one with normal rice grain and another with waxy rice grain) each time could be treated using the HHP machine. The resultant film bags were cooked using a steam cooker (YJ308J 3L, Midea Group Co., Guangdong, China) for 18 min and kept warm for 5 min to obtain fresh rice samples with normally eating. The repeated trials were performed under the same soaking and cooking conditions.
As the method described in Section 2.2, the soaked rice grains were cooked by the steam cooker for 18 min and kept warm for 5 min to obtain fresh rice samples. These samples were stored at 4 C and relative humidity 75% for 0, 1, 3, 5, 7, 14, and 35 days to perform the retrogradation study. The retrograded samples (5 mg, 166.7 g water/100 g dry basis) were subjected to trituration and collected for thermal analysis. The enthalpy change was measured at a heating rate of 10 C/min from 30 C to 90 C using a DSC (Pyris 1, Pekin Elmer, MA, USA) under ultrahigh-purity nitrogen of 20 mL/ min. The same procedure was repeated 5 times for each sample. The retrogradation degree (DR) of the rice samples was calculated according to the following equation (Hu et al., 2011; Jouppila, Kansikas, & Roos, 1998):
2.3. Hydration of soaked rice samples
DRð%Þ ¼ ðDHt DH0 Þ=DHN 100%
The hydration degree of the soaked rice was determined as the procedure described by Chen et al. (2010). In brief, normal and waxy rice grains were packed and treated under soaking conditions detailed in Section 2.2 for 10, 20, 30, 40, 50, and 60 min, respectively. These samples were taken out the film bags at the designated time and immediately wrapped with filter paper to remove the surface water and dried in an oven at 105 C for 2 h to evaluate the moisture (g/100 g dry basis). 2.4. Color intensity and lightness of cooked rice The fresh cooked rice was immediately for color measurement using a Chroma meter CR-400 (Konica Minolta Sensing Inc., Osaka, Japan). Color coordinates for the extent of lightness (L*), redness/ greenness (þa*/a*), and yellowness/blueness (þb*/b*) were collected. The color intensity (B) was calculated using the following equation (Lamberts et al., 2006; Roy et al., 2008).
h 2 2 i1=2 B ¼ a* þ b*
(1)
2.5. Texture profile analysis (TPA) of cooked rice The fresh cooked rice was directly performed TPA analysis. The hardness, springiness and cohesiveness of cooked rice were measured using a texture analyzer (TA-XT2i, Stable Micro Systems,
2.6. Scanning electron microscopy (SEM) The cooked rice samples were immediately dried using a vacuum freeze dryer (ALPHA1-4, Marin Christ Inc., Osterode, Germany). After drying, they were stuck on a specimen holder using a silver plate and coated with a thin film of gold (10 nm) in a vacuum evaporator. The resultant specimens picked from the central endosperm of rice kernel were observed and photographed using a scanning electron microscope (Quanta-200, FEI Company, Eindhoven, Netherlands) at an accelerating voltage of 5.0 kV. 2.7. Retrogradation properties of cooked rice samples
(2)
where,
DH0 is the enthalpy change of the fresh rice sample, DHt is the enthalpy change (J/g) of the t-day retrograded rice sample, and
DHN is the enthalpy change of the 35-day retrograded rice sample. 2.8. Statistical analysis Statistical analysis was performed by using ORIGIN 7.5 (OriginLab Inc., Northampton, MA, USA). Data were expressed as means of at least triplicate and analyzed by a one-way analysis of variance (ANOVA). p value 0.05 was regarded as significant throughout the study. 3. Results and discussion 3.1. Hydration of soaked rice The present data showed that the HHP soaking, compared with the atmospheric pressure soaking, significantly increased the moisture content of normal rice grain from 40.94% to 44.4% (300 MPa) and 45.62% (400 MPa), respectively (Fig. 1a). This was well accorded with the results described by Yamakura et al. (2005). The increase in moisture indicated that water molecules could effectively penetrate into the peripheral portion of starch granules in rice grains under the high pressure, although the intact rice
370
a
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373 Table 1 Color parameters of cooked normal rice and waxy rice with different pressure soaking treatments.
50
Moisture content (g/100g dry basis)
45
Rice varieties
40
0.1 Cooked normal Vacuum 300 rice 400 0.1 Cooked Vacuum waxy 300 rice 400
35
30
25
15 0
10
20
30
40
50
60
Water soaking time (min) 55 50
Moisture content (g/100g dry basis)
68.7 72.5 74.7 76.2 69.2 72.8 75.8 76.5
b
0.9a 1.1b 0.9c 1.4c 1.3a 0.7b 1.1c 0.8c
7.8 6.4 5.8 5.6 6.7 5.8 5.3 5.1
b*
0.4f 0.3cd 0.3bc 0.4ab 0.3de 0.4abc 0.4ab 0.3a
B
13.5 11.8 10.3 9.7 12.5 10.9 9.8 9.4
0.3f 0.4de 0.4bc 0.4ab 0.3e 0.4c 0.5ab 0.4a
15.6 13.4 11.8 11.2 14.2 12.4 11.1 10.7
0.5f 0.4de 0.4bc 0.3ab 0.4e 0.3c 0.3ab 04a
a L*, the color lightness, þa*/a*; redness/greenness, þb*/b*, yellowness/blueness; and B, the color intensity. b Sample means with different lowercase letters in the same column are significantly different (p 0.05); the number of replications (n), n 8.
20
b
Pressure Color parametersa (MPa) L* a*
45 40 35 30 25 20
Production of lighter color rice is essential for the higher customer acceptability. The results showed that the color intensity and the lightness of cooked normal and waxy rice varieties were observed to be 15.6 and 68.7, and 14.2 and 69.2, respectively (Table 1). The lightness and the color intensity were dependant on the soaking pressures. Both of the vacuum soaking and the high pressure soaking could significantly increase the lightness and reduce the color intensity of cooked normal and waxy rice varieties. This result was probably attributed to a fact that the vacuum soaking reduced the enzymatic reaction occurring in rice by the less oxygen concentration. Furthermore, it was reported that the HHP treatment could inactivate the enzymes such as catalase and polyphenol oxidase present in rice (Knorr et al., 2006; Mabashi, Ookura, Tominaga, & Kasai, 2009). These results suggest that the HHP soaking improved the color lightness and the color intensity of cooked rice due to the inhibition of enzymatic browning by the less oxygen and the lower enzyme activity existing. 3.3. Texture properties
15 0
10
20
30
40
50
60
Water soaking time (min) Fig. 1. Moisture content (g water/100g dry basis) of (a) normal rice and (b) waxy rice with 300 MPa ( ), 400 MPa ( ), vacuum ( ), and atmospheric pressure ( ) soaking treatments during one hour. Number of replications (n), n 3.
starch granules were still present under 600 MPa (Hu et al., 2011). In addition, the vacuum-soaked normal rice had higher moisture than the atmospheric pressure-soaked one before 30 min, while after that, no significant difference in moisture was observed. This indicated that the vacuum soaking might cause wider channels between starch granules and benefit water incorporating due to a pressure difference occurring inside and outside of rice grain. For the vacuum-soaked waxy rice, the moisture content was significantly higher than that of the atmospheric pressure-soaked one during the whole soaking process (Fig. 1b). The HHP soaking also increased the moisture adsorbing and distributing in waxy rice grains. Nevertheless, there was no significant difference in moisture content for waxy rice soaked under different high pressures (300 MPa and 400 MPa). This might suggest that the sensitivity of waxy rice grains to high pressure was reduced after the grains were presoaked at 55 C for 30 min. 3.2. Color intensity and lightness analysis The color intensity of cooked rice has a negative effect on consumer acceptance and generates to a loss in market value.
The texture analysis data revealed that the cooked normal rice had higher hardness than the cooked waxy rice (Table 2). This was confirmed by a previous study, indicating that the hardness was positively correlated with the amylose contained in rice grain (Yu, Ma, & Sun, 2009). Rice with higher amylose content was liable to leach more into the cooking water and formed a coating film on rice grains to increase the hardness (Leelayuthsoontorn & Thipayarat, 2006). Amylose, on the other hand, was easier to retrograde and increased the hardness of the cooked rice in a short period. In addition, the hardness of cooked normal and waxy rice varieties was significantly reduced by the HHP soaking. This decrease might indicate that the HHP soaking could prevent amylose and amylopectin components leaching out, although it could decrease the crystallinity of starch granules (Hu et al., 2011). Springiness (length/ Table 2 Texture properties of cooked normal rice and waxy rice with different pressure soaking treatments. Rice varieties
Pressure (MPa)
Hardness (g)
Cooked normal rice
0.1 Vacuum 300 400 0.1 Vacuum 300 400
685.7 674.3 638.9 627.1 598.1 591.7 560.4 555.7
Cooked waxy rice
7.1da 8.6d 9.8c 8.4c 7.3b 6.5b 7.4a 8.5a
Springiness (length/length) 0.65 0.69 0.81 0.87 0.51 0.55 0.64 0.69
0.03b 0.04b 0.05c 0.04c 0.04a 0.02a 0.04b 0.05b
Cohesiveness (area/area) 0.54 0.55 0.63 0.64 0.73 0.75 0.87 0.91
0.04a 0.04a 0.03b 0.04b 0.04c 0.05c 0.04d 0.04d
a Sample means with different lowercase letters in the same column are significantly different (p 0.05); the number of replications (n), n 10.
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373
371
Fig. 2. SEM images of (a) cooked normal rice with atmospheric pressure soaking, (b) cooked normal rice with vacuum soaking, (c) cooked normal rice with 300 MPa high pressure soaking, (d) cooked normal rice with 400 MPa high pressure soaking, (e) cooked waxy rice with atmospheric pressure soaking, (f) cooked waxy rice with vacuum soaking, (g) cooked waxy rice with 300 MPa high pressure soaking, and (h) cooked waxy rice with 400 MPa high pressure soaking.
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373
length) is a measure of how much the gel structure is broken down by the initial compression. It is generally considered that a high springiness appears as a gel structure is broken into few large pieces during the first TPA compression, whereas low springiness results from a gel breaking into many small pieces (Huang, Kennedy, Li, Xu, & Xie, 2007). The high pressure soaking increased the springiness from 0.65 (atmospheric pressure) to 0.81 (300 MPa) and 0.87 (400 MPa) for cooked normal rice, and from 0.51 (atmospheric pressure) to 0.64 (300 MPa) and 0.69 (400 MPa) for cooked waxy rice. These results indicated that the macrostructure of cooked rice with the HHP treatment was broken into some large pieces during the first compression of the TPA test. The cohesiveness of cooked normal and waxy rice was significantly increased by the HHP soaking. This increase suggested that more compact network might be formed in rice under the high pressure soaking that could cause amylose and amylopectin redistributing in rice grains.
a
54 48
Degree of retrogradation (%)
372
42 36 30 24 18 12 6
0
3
3.4. Morphologic properties
3.5. Retrogradation properties The aging studies showed that the cooked normal rice with the HHP soaking had lower retrogradation degree than that with the atmospheric pressure soaking (Fig. 3a). The less retrogradation indicated that the HHP soaking inhibited the retrogradation process of cooked normal rice. Rice retrogradation was directly related to amylose leaching during cooking (Leelayuthsoontorn & Thipayarat, 2006). Hu et al. (2011) also reported that the HHP treatment (600 MPa) could retain the intact starch granules and prevent amylose leaching. The lower amylose leakage, therefore, only could generate a thinner film on rice grains and reduced the rapid retrogradation in a short period (Stolt, Oinonen, & Autio, 2001). Furthermore, long amylopectin chains might crystallize with amylose molecules to organize several adjacent clusters, thus resulting in less amylose leaching (Ong & Blanshard, 1995). However, there was no significant difference observed for cooked normal rice under the vacuum soaking and the atmospheric pressure soaking. This result indicated that the pressure difference
b
9
12
15
12
15
40 35
Degree of retrogradation (%)
The SEM images revealed that the cooked normal rice with the vacuum soaking and the HHP soaking had smaller cavities and larger connection parts compared to that with the atmospheric pressure soaking (Fig. 2aed). This result indicated that the soaking treatments under the vacuum and the high pressure conditions could prevent the microstructure damage of cooked normal rice and generate more network structure. The network formed could result in the higher springiness and cohesiveness, which were accorded with the results in Section 3.3. Furthermore, the soaking under the higher pressure (400 MPa) caused the holes smaller. The decrease in size demonstrated that a pressure difference outside and inside rice grains during soaking might retain the integrity of starch granules and only produce homogeneous channels between starch granules and other connection parts. For the cooked waxy rice, larger and more homogeneous channels were observed for soaking under the vacuum and the HHP treatments (Fig. 2eeh). This was attribute to a fact that the main component in waxy rice was amylopectin that was more sensitive to heat and pressure than amylose (Hu et al., 2011). The pressure difference, therefore, was easier to widen the channels for the soaked waxy rice grains. The channels could be swelled by heat air during cooking. These results suggest that the higher sensitivity of rice components to soaking pressure was responsible for generating the homogeneous network microstructure. This network might produce the lower hardness and the higher springiness of cooked waxy rice.
6
Storage time (d)
30 25 20 15 10 5 0 0
3
6
9
Storage time (d) Fig. 3. Retrogradation degree of (a) cooked normal rice and (b) cooked waxy rice with 300 MPa ( ), 400 MPa ( ), vacuum ( ), and atmospheric pressure ( ) soaking pretreatments. The number of replications (n), n 5.
produced under the vacuum condition did not have enough ability to redistribute starch granules and retain the integrity in normal rice. Comparing with the other soaking treatments, the HHP soaking significantly reduced the retrogradation of cooked waxy rice, while the inhibition effect was not significant between 300 MPa and 400 MPa high pressure soaking treatments (Fig. 3b). This result was partly confirmed by previous studies, indicating that waxy rice was more sensitive to the HHP treatment (B1aszczak et al., 2007; Stolt et al., 2001). Therefore, the lower high pressure (e.g. 300 MPa) was enough for soaking of waxy rice grains in this study. 4. Conclusions This work made it clear that the color, the texture, and the retrogradation properties were significantly improved by the vacuum soaking and the HHP soaking. The high quality of cooked rice was mainly attributed to the better water diffusion inside rice grains during high pressure soaking and the smaller network channels formed between starch granules and other connection sections. These findings suggest that the HHP soaking is one of advantageous techniques for cooked rice with better palatability.
Y. Tian et al. / LWT - Food Science and Technology 55 (2014) 368e373
Future research should be performed to check if these results could be extrapolated to industrial scale to produce fresh cooked rice with a high quality. Acknowledgments This study was financially supported by the National Key Technology R&D Program for the 12th Five-Year Plan (Nos. 2012BAD37B02, 2012BAD37B01, and 2012BAD37B03). References Balny, C. (2002). High pressure and protein oligomeric dissociation. High Pressure Research, 22, 737e741. B1aszczak, W., Fornal, J., Kiseleva, V. I., Yuryev, V. P., Sergeev, A. I., & Sadowska, J. (2007). Effect of high pressure on thermal, structural and osmotic properties of waxy maize and hylon VII starch blends. Carbohydrate Polymers, 68, 387e396. Chakkaravarthi, A., Lakshmi, S., Subramanian, R., & Hegde, V. M. (2008). Kinetic of cooking unsoaked and presoaked rice. Journal of Food Engineering, 84, 181e186. Chen, G., Tian, Y., Jiao, A., Xu, B., Xu, X., & Jin, Z. (2010). Determination of the initial production conditions and steam cooking kinetics research for instant rice. Food and Fermentation Industries, 36(8), 36e40 [In Chinese]. Han, J. A., & Lim, S. T. (2009). Effect of presoaking on textural, thermal, and digestive properties of cooked brown rice. Cereal Chemistry, 86, 100e105. Hoover, R., & Ratnayake, W. S. (2001). Determination of total amylose content of starch. Current Protocols in Food Analytical Chemistry, E2.3.1eE2.3.5. Huang, M., Kennedy, J. F., Li, B., Xu, X., & Xie, B. J. (2007). Characters of rice starch gel modified by gellan, carrageenan, and glucomannan: a texture profile analysis study. Carbohydrate Polymers, 69, 411e418. Hu, X. T., Xu, X. M., Jin, Z. Y., Tian, Y. Q., Bai, Y. X., & Xie, Z. J. (2011). Retrogradation properties of rice starch gelatinized by heat and high hydrostatic pressure (HHP). Journal of Food Engineering, 106, 262e266. Jouppila, K., Kansikas, J., & Roos, Y. H. (1998). Factors affecting crystallization and crystallization kinetics in amorphous corn starch. Carbohydrate Polymers, 36, 143e149.
373
Knorr, D., Heinz, V., & Buckow, R. (2006). High pressure application for food biopolymers. Biochimica et Biophysica Acta, 1764, 619e631. Lamberts, L., De Bie, E., Derycke, V., Veraverbeke, W. S., De Man, W., & Delcour, J. A. (2006). Effect of processing conditions on color change of brown and milled parboiled rice. Cereal Chemistry, 83, 80e85. Leelayuthsoontorn, P., & Thipayarat, A. (2006). Textural and morphological changes of jasmine rice under various elevated cooking conditions. Food Chemistry, 96, 606e613. Lullien-Pellerin, V., & Balny, C. (2002). High-pressure as a tool to study some proteins’ properties: conformational modification, activity and oligomeric dissociation. Innovative Food Science and Emerging Technologies, 3, 209e221. Mabashi, Y., Ookura, T., Tominaga, N., & Kasai, M. (2009). Characterization of endogenous enzymes of milled rice and its application to rice cooking. Food Research International, 42, 157e164. Ong, M. H., & Blanshard, J. M. V. (1995). Texture determinants in cooked, parboiled rice. I: rice starch amylose and the fine structure of amylopectin. Journal of Cereal Science, 21, 251e260. Roy, P., Ijiri, T., Okadome, H., Nei, D., Orikasa, T., Nakamura, et al.. (2008). Effect of processing conditions on overall energy consumption and quality of rice (Oryza sativa L.). Journal of Food Engineering, 89, 343e348. Saikusa, T., Horino, T., & Mori, Y. (1994). Distribution of free amino acids in the rice kernel and kernel fractions and the effect of water soaking on the distribution. Journal of Agricultural and Food Chemistry, 42, 1122e1125. Stolt, M., Oinonen, S., & Autio, K. (2001). Effect of high pressure on the physical properties of barley starch. Innovative Food Science and Emerging Technologies, 1, 167e175. Tian, Y., Jin, Z., Deng, L., Xu, X., & Zhao, J. (2007). Study on the effect of vitamin D3-bcyclodextrin inclusion compound on the quality improvement in extruded nutrition-fortified rice. Food and Fermentation Industries, 33(12), 52e55 [In Chinese]. Yamakura, M., Haraguchi, K., Okadome, H., Suzuki, K., Tran, U., Horigane, A. K., et al. (2005). Effects of soaking and high-pressure treatment on the qualities of cooked rice. Journal of Applied Glycoscience, 52, 85e93. Yamazaki, A., Kinefuchi, M., Yamamoto, K., & Yamada, A. (1996). Physical properties and fine structure of grains of high pressure-treated rice after cooking. Review of High Pressure Science and Technology, 5, 168e178. Yu, S. F., Ma, Y., & Sun, D. W. (2009). Impact of amylose content on starch retrogradation and texture of cooked milled rice during storage. Journal of Cereal Science, 50, 139e144.