Effect of Soaking on Wet-milling of Rice

National Taiwan University, Graduate Institute of Food Science and Technology, 59, Lane 144, Keelung Road, Section 4, Taipei, Taiwan
Journal of Cereal Science (Impact Factor: 2.09). 01/2002; 35(1):85-94. DOI: 10.1006/jcrs.2001.0419


Soaking is an essential step in wet-milling of rice flour. The effects of soaking duration and temperature (5 and 25 °C) on the properties of rice flour have been investigated. The uptake of water by rice kernels increased with temperature and reached a plateau at about 30–35%. Protein, lipid, and ash leached out during soaking. The moisture content after soaking appeared to be a key factor on loosening the structure of rice kernels, which resulted in the production of small particle flours with little starch damage. The particle size of flours did not alter the gelatinisation temperature (Toand Tp) in DSC thermograms. Small particle and low lipid content flours appeared to have high peak viscosity measured by RVA. The change in microstructure of rice kernels during soaking was also examined by SEM.

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    • "In this stage, starch gelatinization would also be responsible for suddenly decreased overall and surface firmness between 85 8C and 100 8C as shown in Fig. 3. Changes in leached material amount in grain–water mixture during cooking are shown in Fig. 4. Leached material amount measured between 30 8C and 50 8C, and 70 8C and 85 8C was not significantly different, however the amount at 70 8C was significantly higher than at 50 8C (approximately 1.5 times; P < 0.05). Chiang and Yeh (2002) reported that endosperm tissue softening during soaking progressed with water absorption and elution of soluble proteins, lipids, and minerals from rice grains, which should be appeared as the amount at 30 8C and 50 8C. Hanashiro, Ohta, Takeda, Mizukami, & Takeda (2004) also reported that carbohydrate elution become lager between 55 8C to 70 8C, which should be connected with leached material increase between 50 8C to 70 8C. "
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    ABSTRACT: Textural-related property including histological tissue structure changes in rice grain (Oryza sativa L.) during cooking process was investigated in this study. Forty grams of polished grain were added to 60. ml of water, and cooked using the Japanese style cooking method. Rice grains were removed at 30, 50, 70, 85, and 100. °C during cooking, and moisture content, overall firmness, surface firmness, and histological tissue structures were examined. The leached material amount in cooking water at each temperature was also measured. Results showed moisture content in rice grains linearly increased from 70. °C to 100. °C, while moisture remained almost constant at from 30. °C to 50. °C. The overall firmness almost linearly decreased from 30. °C to 85. °C and decreased from 85. °C to 100. °C significantly, though no significant difference in surface firmness change between 70. °C and 85. °C was found. The leached material amount increased approximately 1.5 times between 50. °C and 70. °C. Voids in the cooked grains were generated between 85. °C and 100. °C, where gelatinization and morphological changes in grain shape, with histological cell wall disruptions occurred. The results shown in this study indicate that structural tissue properties, i.e. cell wall properties, are one of the important factors responsible for the textural-related properties of cooked rice grains.
    Food Structure 04/2014; 1(2):164–170. DOI:10.1016/j.foostr.2013.10.003
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    • "Recently, however, ultrafine rice powder down to 500 mesh has gained attention and rice flour utilization is explored in many new products (Kum, 2010). Characteristics and quality of rice flour are influenced by many factors such as rice cultivar (Han et al., 2012), preprocessing method (Chiang and Yeh, 2002; Kim and Kim, 1995), milling method (Choi et al., 2006; Lee & Lee, 2006b) and equipment (Kum et al., 1993a; Park et al., 1988), and particle size distribution (Kum and Lee, 1999; Park et al., 2006). It is now generally accepted that particle size distribution and degree of damaged starch are the two key factors affecting the physicochemical properties of rice flour and in turn the suitability of the flour for specific application. "
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    ABSTRACT: Background: The Korean government launched a project in 2008, where the amount of rice used as raw ingredient in rice-based foods in 2012 was planned to increase up to 10% (470,000 ton) of the total rice production through developing various new rice-based processed foods and their commercial manufacturing technology. Among the four major rice-based processed foods, rice cakes and noodles need rice flour as their main raw ingredient. Technology in rice flour utilization and manufacturing is far behind than the technology pertinent to wheat flour in many subject areas. Purpose: This review aims to provide information on rice flour utilization and manufacturing with some fundamental subjects in the area of size reduction. Results: A variety of food items including bread, noodle, cake, cookie, muffin, pre-mix, beverage, vinegar, surimi, and artificial meat have found rice flour as their raw ingredient. Rice bread made out of 100% rice flour has been developed and is now sold in retail stores. Various noodle products made from rice flour are also on the market. Issues on product definition and labeling regulation about rice flour content of the products were explored. Generalized grinding equations available in the literature were seldom used in practice; instead, it has been a general practice to develop empirical equations from test milling data. Introductory remarks on three popular particle size measurement methods (sieving, Coulter counter, light diffraction) were explained. Mathematical expressions frequently used to describe particle size distribution and to correlate cumulative quantity of particles with particle size were represented. Milling methods used in producing rice flour were described along with their advantages and disadvantages. Because of their profound effect on functional properties of the rice flour, four rice flour milling equipments used at both laboratory experiments and commercial manufacturing plants were discussed.
    06/2013; 38(2). DOI:10.5307/JBE.2013.38.2.103
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    • "Rice flour is used to produce many kinds of food and desserts such as noodles, breakfast cereals, unleavened breads, snack food items, crackers, candies and baby foods (Bao and Bergman , 2004). Generally, there are three methods used to prepare rice flour: wet grinding, semidry grinding, and dry grinding (Chiang and Yeh, 2002). Wet grinding is a traditional method used to prepare rice flour and incorporates five distinctively consecutive processes: soaking, adding excess water during grinding, filtering, drying, and sieving; this process includes the use of many machines and much manpower. "
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    ABSTRACT: This study attempted to replace the wet grinding process of rice with a freeze grinding process. The freeze grinding process involved soaking the rice samples in liquid nitrogen before grinding in a dry grinding machine. Three different types of grinders (hammer mill, roller mill, and pin mill) were used in both the freeze and the dry grinding processes. Wet grinding resulted in significantly (P < 0.05) smaller average particle size and a lower percentage of damaged starch than the alternative methods of grinding. Freeze grinding, especially using the hammer mill significantly reduced both the average particle size and the damaged starch content. Moreover, freeze grinding produced a higher yield after sieving in comparison with dry grinding using an identical grinder. In particular, freeze grinding with the hammer mill gave a significantly higher yield after sieving than dry grinding with the hammer mill. The wet grinding process had the significantly highest specific energy consumption (13,868 kJ/kg) due to the large consumption of electrical energy by the many machines in the process. The energy consumption of freeze grinding was similar to dry grinding. Consequently, the freeze grinding process was a viable alternative to the traditional wet grinding process.
    Journal of Food Engineering 06/2011; 104(4):632-638. DOI:10.1016/j.jfoodeng.2011.02.001 · 2.77 Impact Factor
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