29C-20 |
Effect of preheating treatment temperature on rheological properties of rice milk |
P. N. DIAS, Dept. of Food Science, University of Arkansas, 2650N, Young Avenue, Fayetteville, Fayetteville, AR 72704, J. F. C. Meullenet, Dept. of Food Science, Univ. of Arkansas, 2650 N. Young Ave., Fayetteville, AR 72704-5585, and T. A. Howell, Jr., Food Science, University of Arkansas, 2650 N. Young Avenue, Fayettville, AR 72704. Rice milk, which has been used as a milk substitute, is conventionally processed from whole grain brown or white rice kernels. Since starch is the major component in rice milk, gelatinization of starch by preheating treatment is required in establishing proper texture and quality of the product. The differences in gelatinization temperatures among different rice types (long medium and short grains) and milling fractions (brown, and polished) influence the flow behavior of rice milk. Consequently, our objective was to investigate the rheological properties of rice milk processed from brown and polished rice of "Wells" (long grain) and "Bengal" (medium grain) cultivars as influenced by different preheating treatment temperatures. Rice milk samples were subjected to a programmed shear rate (0 to 400 1/s in 200 s) using a rotational viscometer. The resulting flow curves indicated that rice milks that received a preheating treatment at the gelatinization temperature showed a Newtonian behavior. However, rice milk behaviors were shear thickening and shear thinning, at temperatures below and above the gelatinization temperature, respectively. The DSC onset temperatures of brown and polished rice of Wells were 80 °C and 78 °C, respectively. Rice milks, heat-treated at 80 °C for 10 min, showed Newtonian behavior with viscosity values of 0.001 Pas and 0.002 Pas for the brown rice and polished rice, respectively. Brown and polished rice made from Bengal rice had onset temperatures of 71 °C and 72 °C, respectively. Rice milk from Bengal showed a power law behavior with flow behavior indices (n) of 0.76 and 0.75 and consistency coefficients of 0.05 and 0.16 Pasn, respectively, for brown and polished rice, treated at 80 °C. Because the flow properties of rice milk are affected by preheating treatment temperatures, processors should choose the appropriate preheating treatment temperature as a function of the gelatinization temperature of the raw material (i.e. rice), to meet the desired quality standards.
Session 29C, Food Engineering: Rheology and texture
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