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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    • "The decrease in the setback could be also associated with the reduction in amylose content. Setback is a measure of starch retrogradation (Chiang and Yeh 2002). Therefore, lower setback value after fermentation implies a delay in retrogradation phenomenon in the final product. "
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    ABSTRACT: In the current study, effects of fermentation on physicochemical and functional properties of brown rice flour (BRF) were investigated. Fermentation conditions were optimized using response surface methodology to achieve moderate acidity (pH 5-6), specifically pH 5.5 of brown rice batter with time, temperature and yeast concentration as the independent variables. The results indicated that brown rice batter was well fermented to maintain pH 5.5 at optimum conditions of 32 °C for 6.26 h using 1 % yeast concentration. Fermentation at moderate acidity significantly increased the levels of protein, total ash, insoluble fiber, soluble fibre, minerals, phenolics, antioxidants, resistant starch, riboflavin, pyridoxine, nicotinic acid, γ-tocotrienol, and δ-tocotrienol. However, it reduced the contents of γ-oryzanol, γ-tocopherol, α-tocopherol, phytic acid, amylose and total starch. Foaming capacity, foaming stability, oil holding capacity, gelatinization temperatures, enthalpy and whiteness of BRF were increased after fermentation. In contrast, its swelling power, water solubility index, hot paste viscosity, breakdown, and setback significantly decreased. Microstructure of BRF was also influenced, where its starch granules released from its enclosed structure after fermentation. This investigation shows evidence that yeast fermentation modified the functionality of BRF and can be used as a functional food ingredient.
    Full-text · Article · Sep 2015 · Journal of Food Science and Technology -Mysore-
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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.
    Preview · Article · Apr 2014 · Food Structure
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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.
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