Study Of Fabricated Rice And Systematic Model On Twin-screw Extruder

Twin-screw extrusion has been gradually applicated in fabricated rice because of its more stable processing capacity, higher automation than those of single-screw extrusion. However, there are still some drawbacks in the current research of producing fabricated rice or nutrient rice by twin-screw extrusion. These problems are unefficient extruding mode of twin-screw extrusion, unmature technology of rice molding and expansion of fabricated rice nutrition fortification.Thus, the present thesis is studied from the following aspect.The relationship between operation parameter, systematic parameter and objective parameter of twin-screw extruder has been set up; neuro network prediction model based on operation parameter was also set up, the residence time distribution of twin-screw extruder was studied, a die with rice shape hole has been designed,and the fabricated rice molding technical process has been optimized, a man-made nutrient rice with Mesona Blumes gum addtition has been developed and the physicochemical properties and its antioxidation capacity in vitro has been evaluated. The main conclusion was following like these:(1) During the fabricated rice processing, systematic parameters such as extrudates temperature, torque, pressure, SME, moisture content and product expansion ratio are obviously affected by the operation parameters of extrusion. Extrudates temperature, SME, product expansion ratio increased with the screw speed increment, while die pressure, torque and product moisture content decreased with screw speed increment. Increasing the moisture content of feed materials could obviously reduce extrudates temperature, torque, pressure, SME and product expansio ratio, the control of appropriate screw speed and feed moisture content is very significant for fabricated rice processing in energy saving and quality stablility.(2) In this study, expansion ratio of fabricated rice is 1.23±0.10, which is a relatively ideal processing condition of extruded fabricated rice. Expansion ratio of product increased with screw speed, feed rate and final barrel temperature increment, but decreased with feed moisture content increment. The predicted mathematic model of systematic parameter and expansion ratio of product was set up during fabricated rice extrusion by response surface methodolgy (RSM), which could provide reference to quality prediction and on-line control during fabricated rice processing. Within the operation parameters, the prediction model of RSM of ER, BD, DG, PV, FV and setback could be set up. These models can be used to provide reference for quality prediction and on-line automation control during fabricated rice processing. The appropriate RSM predicted model couldn't be set up for L, a, b,ΔE and WSI. Thus, there is necessary to find a more scientific and reasonable method for guiding the pratical production with a more proper model for each parameter.(3) In this study, MRT of rice extrusion is between 2.09-3.99min,σ2 is between 1.5-4.45min2, D/uL is between 0.081-0.255. The diffusion mathematic model belongs to the large scale diffusion model of mixed flow (D/uL>0.2). The influence of operation parameters on mean residence time (MRT) of extrudates within barrel is very significant, among them feed rate has the most significant effect on MRT. MRT of extrudates within barrel remarkably decreased with the feed rate increment. The appropriate mathematic regression model of operation parameter, MRT and RTD can be obtained by regression analysis.(4) In order to find a more scientifically sensible method, more appropriate model of each parameter could be set up to direct processing. The BP neuro network of PTW-24/250 experimental twin-screw extruder was built up. The systematic and objective parameters of fabricated rice could be predicted from operation parameters by this BP neuro network. The BP network is composed of 4 input neurons (screw speed, feed rate, moisture content of feed and barrel temperature), 1 hidden layer(36 neurons) and 18 output neurons including WAI, WSI, L, a, b, dE, PV, FV, setback, DG, BD, ER, M.C., MRT, TM-E3, P, M, SME. The systematic and objective parameters of fabricated rice extrusion could be well predicted by this network. On the basis of the network, friendly visual user interactive interface from Matlab GUI has been developed. This interface is very simple and convenient for user to predict systematic and objective parameters of fabricated rice through extrusion on PTW-24/25O experimental extruder.(5)Based on material flow and descriptive calculation of rice shape, combined with drawing of characteristic curve of screw speed and die, the special die with rice-shape hole has been designed. The die is used into the moulding and cutting experiment of fabricated rice. It was found that the shape of fabricated rice was very close to that of natural rice, which indicated that the design of such a die is very successful. The thousand seed weight and bulk density were taken as the quality level of fabricated rice and the screw speed (A),feed rate (B) and cutting speed (C) were taken as operation parameters. Prediction model of thousand seed weight of dry fabricated rice has been built up successfully through central combined design(CCD) of RSM, which provides a useful exploration for setting product standard of fabricated rice industry. Among them, TSW=45.06+0.88×A+9.24×B-6.33×C+2.1×AC-1.77×BC+1.03B2, R2=0.9429.(6) In order to expand the developing field of rice nutrient additives, Mesona Blumes gum as our traditional herbal resource was firstly added into rice flour, and then the physicochemical and antioxidant activities in vitro of nutrient rice extrudates were explored. The results indicated that ash content increased remarkably with MBG addition, protein content decreased but the influence was not very obvious, DG decreased firstly and increased lately, WAI and WSI always increased. Compared with rice flour, ER reduced, but with MBG addition, ER increased, BD reduced slightly and then increased. L*(lightness) decreased. a* (redness) and b*(greenness) firstly increased and then decreased, hardness increased firstly and then decreased. The phenol content of 15% MBG-rice extrudate 15.22μg/ml is the largest among the MBG-rice extrudates within the MBG addition levels. DPPH radical scavenging capacity of 15% MBG-rice extrudate is the strongest; IC50 concentration is 0.015μg/ml. Hydroxyl radical scavenging capacity of 10% MBG-rice extrudates is the strongest. There is no superoxide anion radical scavenging capacity of all MBG-rice extrudates. Ferrous ion chelating ability of 15% MBG-rice extrudates is the strongest. From above, it was concluded that MBG-rice extrudates is a potential antioxidant food.