Effect of Roasting on Physicochemical Properties of Rice Flours

• Main Authors: CHANG, WEI-SHOW, 張惟琇
• Other Authors: CHANG, YUNG-HO
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/qsz5kr

碩士 === 靜宜大學 === 食品營養學系 === 106 === This study investigated the effect the moisture content of milled rice (13, 15, & 20%), sand temperature ( 180, 200, 220, & 240 oC) and roasting time (30, 60, & 90 seconds) on the physicochemical properties of obtained rice grains (TK 9 & TCS 17) and its flour after roasted. The results showed that the rice grains became opaque after roasted, and their color was more yellow-orangeish with increase in sand temperature or roasting time, but became in their moisture content. Under the same condition of moisture content and roasting time, the damaged starch content of rice flour increased with increasing the sand temperature. The rice grains of TK 9 & TCS 17 with 15% moisture content were characterized by the damaged starch content of 5.0% and 18.8%, respectively, after being roasted at 180 oC for 30s. With the temperature being increased to 240 oC, the damaged starch content of the corresponding rice grains was increased to 33.3% and 40.7%, respectively. The peak viscosity, hot paste viscosity and final viscosity of roasted TK 9 rice flour decreased with decreasing the moisture content of rice grains but with increasing. The hot paste viscosity and final viscosity were both higher than raw rice when the rice moisture content was higher than 15% and roasted at 180 oC. For TCS 17, the peak viscosity, hot paste viscosity and final viscosity were decreased after the roasting treatment. With on increase in sand temperature, decreases in the To,Tp, Tc & H of roasted TK 9 & TCS 17 flours were observed, accompanied by the increases in their degrees of gelatinization. After roasting of TK 9 and TCS 17, the onset temperature, peak temperature, conclusion temperature, and enthalpy of gelatinization were decreased with the increase of sand temperature. In the same moisture content and roasting time, the degree of gelatinization of TK 9 and TCS 17 increased with the increase of temperature. TK 9 and TCS 17 contained 20% moisture content, the gelatinization degree of rice roasting at 180 oC for 30 seconds was 3.5% and 39.0%, the gelatinization degree of rice roasting at 13% moisture content when heating at 240 oC for 90 seconds was 59.3%, 82.2%. The solubility of raw TK 9 flour was 10.14%. After roasting treatment, the solubility of rice flour was lower except with the treatment at 240 oC for 90 s. The solubility of raw TCS 17 rice flour was 7.50%. After roasted at the temperature of 180-200 oC, of the flour was lowered. However, with increasing the sand temperature, the solubility slightly of the flour increased. The swelling factors of raw TK 9 and TCS 17 rice flour were 17.48 and 10.98, respectively. After roasting treatment the swelling factors of the flours were lowered, and the decreasing extent was intensified by increasing the roasting time. Contribution ratio analysis showed that the peak viscosity, hot paste viscosity and final viscosity of roasted TK 9 rice flour were greatly influenced by the moisture content of starting rice grains, while their damaged starch contents, thermal properties and solubility were greatly influenced by the sand temperature. For TCS 17, the damaged starch content, final viscosity, thermal properties and solubility of were significantly affected by sand temperature.