| Summary: | 碩士 === 國立屏東科技大學 === 食品科學系 === 94 === The rice cake was the traditionally table delicacies that Chinese celebrated for the New Year , but make it complex. First polished glutinous rice soak , wet to rub , dehydrate , stir , finalize the design , drawing of patterns , then cool rice cake and cut it to become a piece of cake , keep and eat slowly . If want to steam outstanding , fragrant , flavor , available rice cake , every step should not be careless. Extrusion food technology was one of the advanced food technology in the 20th century , the extruder has many functions. Including sent, mix , rub rotating , compressing , shaping ,etc. Can not merely simplify process the tedious step of the tradition , even more there was economic effect produced in a large amount, it has already applied to the rice food of Chinese style and manufactured now, like vermicelli , cake of coagulated pig's blood used as a food .
In this study, the RTD (residence time distribution) and flow pattern of raw materials were mainly investigated in the single-screw extrusion processing of waxy rice flour and fructose for chunk rice-cake production. First , we used erythrosine as tracer to make the line curve examining of extruded chunk rice cake at different tracers concentrations. The influences of the two operation variables: screw speed (26、39、52 rpm ) and feed rate (6、9、12 kg/hr), were specifically studied. The high temperature and pressure in the process of extrusion would result in changes of the physicochemical properties of the raw materials, and these changes are functions of time. Therefore, it is an important subject to study the residence time distribution (RTD) of the raw materials in the extruder.
It was found that the mean residence time ranged from 365 to 671 sec, and increasing screw speed or feed rate would reduced the mean residence time. It is quite obvious that E(t) curves shifted to the left and sharp, represent screw speed increase that make supplies movement , and feed rate increased that it caused the filled degree increasing , when the screw speed and the feed rate were increased from 26 to 52 rpm and 6 to 12 kg/hr, respectively. Moreover, the E(t) curve had a long tail when the screw speed was 26 rpm which meant the mean residence time would be longer at lower screw speed. As far as the degree of influence is concerned, the mean residence time was more significantly affected by the feed rate.
As to the F(θ) curve, increasing screw speed or reducing feed rate result in the F(θ) curve near being vertical. The flow pattern of raw materials inside the extruder is close to plug flow, whereas increasing screw speed or reducing feed rate would increase the dispersion number. The dispersion number ranged from 0.0517 to 0.1503.
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