| Protein is a unique nutrient that performs important and diverse functions in our bodies, it is very important to make sure diet contains adequate amounts of protein. However, for patients with kidney disease, high protein absorption could interfere and aggravate the protein metabolism which increased renal workload, then accelerated progression of renal insufficiency and impaired kidney function; a restriction in dietary protein is beneficial in the prevention of renal insufficiency. So, how to develop a low-protein food has been an important research topic. Screw extrusion technology is an important method in many approaches to develop low-protein foods. In this study, we used Improved Extrusion Cooking Technology to product low-protein rice, the impact of process parameters on the physical and chemical properties were studied firstly, then using the texture properties of commercial rice as objective to determine the optimum process, finally, cooking techniques and eating quality were analyzed. The results were as follows:(1) low-protein texturized rice was product by Improved Extrusion Cooking Technology using rice starch as raw materials. Central factorial design was used to analyze product’s physical properties and texturized properties. The results showed that:the material moisture content, screw speed and barrel temperature affect the properties of produts to some extent, impact of temperature on the low protein texturized rice was more important. Elevated temperature increased the degree of gelatinization, the water absorption indices (WAI) and water solubility indices (WSI), the color, when the temperature increased from100℃to130℃, the dgree of gelatinization increased from63.87%to78.77%, the expansion rate increases rapidly from1.22to1.86, the color difference increases from2.35to4.14. WAI change range4.57-6.99g/g, WSI in between2.91%-8.08%; increase the moisture content can increase the WAI reduce the WSI; RVA map shows although the overall viscosity of low protein texturized is less than the raw starch, and still has a similar raw starch RVA profiles, that is, in low protein texturized rice had ungelatinized starch granuleds, starch granule degradation rate is relatively low(2) Texture is an important indicator of product quality, using the texture properties of commercial rice as objective to determine the optimum process:the material moisture content was35%, screw speed was30rpm, and barrel temperature (gelatinization zone temperature) was120℃. Under the conditions of this process, products had similar appearance and color with polished rice including clear crystal and compact structure, but had very low protein content, only0.43±0.01%%. So the products can meet the requirements of chronic kidney disease, aslo can restrict protein intake.(3) Cooking process and food quality results show:The levels of leached solids content and turbidity in soaking solution increased in the soaking process, resulting in some loss of nutrients, and the loss was greater as increased soaking time and soaking temperature. We determined the soak temperature was20-30℃, soaking time was30min. Amylase content, gel consistency and alkali spreading value of low protein rice were19.2±0.4%,52±3.5mm,5.2±0.3, respectively, which showed that low-protein texturized rice had slightly worse quality than the japonica and indica rice. Water absorption, volume expansion, iodine blue value and light transmission rate of low-protein cooking rice were92.2±3.5%,103.5±5.1%,0.22±0.03,70.4±2.3%, respectively, which displayed that it was superior to japonica rice and indica rice. In China, eating quality of rice is assessed to sensory evaluation, supplemented by physicochemical properties, so we carried out the sensory evaluation of rice sensory, the results consistented with the former, namely, the senses of the low-protein texturized rice was slightly worse than the japonica and indica rice, the integrated sensory score was69.3±1.3points, lower than the japonica and indica rice. |
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