The Study Of Process And Eating Quality For Instant Rice With Un-soaked Cooking

Instant rice is a class of staple food convenience food, which has been developed rapidly on the basis of the development of national economy and the quickening pace of life. There are many types of instant rice, and the low-temperature sterile rice represents the future direction of instant rice. Presoaking rice in water for 1-1.5 h before cooking is traditionally practiced in the production of low-temperature sterile rice at present, which reduced the cooking time as well as brought many problems, such as, the production cycle became longer, the rate of finished products declined, and the energy consumption and pollution increased. In order to solve these problems, we propose a new production method to produce instant rice—un-soaked cooking, which can not only improve these problems but also improve the eating quality and extend the shelf life. The ultimate purpose of this project is to produce low-temperature sterile rice using a new method, which is to combine the washing-free rice processing equipment with the low-temperature sterile rice production equipment, and this new production method is expected to be applied to the current production of various types of instant rice.Firstly, impacts of presoaking on rice physicochemical properties before cooking were studied. The results showed that the content of reducing sugar and total amino acids in soaking solution increased during presoaking period, and between them there were Maillard reactions which would affect the eating quality of cooked rice. The Sulfur-containing amino acids content also increased, which would affect the flavor of cooked rice. And the levels of turbidity and leached solids content in soaking solution also increased, which would affect the yield of cooked rice. In addition, the color value (L*,a*,b* and△E) of rice would be changed significantly during presoaking period, which would affect the color acceptance of cooked rice. In short, the higher the presoaking temperature, the longer the presoaking time, the greater impact on rice quality.Secondly, the initial production conditions and steam cooking kinetics for instant rice were studied. The initial production conditions we obtained from experiments were that about 1h was needed for complete water absorption at 20℃in trap water, and the quantity of rice and water required for producing 200 g rice were about 75 g and 125 g, respectively. The end point of cooking was identified by using parallel glass plate method, and under atmospheric conditions of steam cooking, the cooking time of presoaked rice (PR) and un-soaked rice (UR) were about 18 min and 26 min, respectively. Results from steam cooking kinetics study showed that both PR and UR were in line with the first-order kinetics equation during the steam cooking process, and two cooking rate constants were observed for cooking of PR, while in the case of UR three cooking rate constant were observed, and at the various stages during cooking the cooking rate constants were different.Thirdly, the physicochemical properties and eating quality of fresh un-soaked instant rice were studied. Results from the flavor compounds study showed that a total of 48 components in un-soaked cooked rice (UCR) were identified, including hydrocarbons (31 kinds), alcohols (6 kinds), aldehydes (4 kinds), ethers (1 kind), esters (3 kinds) and other components (3 kinds). While in the case of presoaked cooked rice (PCR), a total of 45 components were identified, including hydrocarbons (30 kinds), alcohols (3 kinds), aldehydes (5 kinds), ethers (2 kinds), esters (3 kinds) and other components (2 kinds). Among of these components, the main flavor compounds were attributed to all kinds of non-hydrocarbon compounds, the proportions of these non-hydrocarbon compounds in UCR were more than those in PCR, which indicated that presoaking treatment would greatly affect the flavor of cooked rice. Results of sensory evaluation indicated that the flavor, color and taste of UCR were much better than PCR, while the shape and palatability of UCR were a little worse than PCR, and the total score of sensory evaluation of UCR was higher than PCR.Then, the physicochemical properties and eating quality of un-soaked instant rice during storage were studied. In the low-temperature storage, results of the physicochemical properties study showed that total acid values and textural properties (hardness, adhesiveness and springiness) of both UCR and PCR were changed greatly in 0-3 days, while in 3-30 days the changes occurred slowly, and these changes were mainly caused by the aging of starch. Results of sensory evaluation for 30-day storage cooked rice indicated that the flavor, color and taste of UCR were better than PCR, while the shape and palatability of UCR were a little worse than PCR, and the total score of sensory evaluation of UCR was a little higher than PCR. Further, when compared with the fresh un-soaked instant rice, the results indicated that the flavor, taste and palatability of both UCR and PCR were declined dramatically, while the color and shape of both UCR and PCR were declined slightly, it revealed that storage would seriously affect the flavor, taste and palatability of the cooked rice.At last, we accounted for the cost of the un-soaked cooking process with washing-free rice (new process). The results showed that the difference of the total direct production cost between new process and original process (presoaked cooking process with ordinary rice) followed the following formula (x—the increment of cooking time, the unit: min): y=[(36＋x)／288×14020±4877.5]-6820=3505 x/72-190(0≤x﹤8) (0≤x﹤8) This indicated that the cost would decrease when the increment of cooking time less than 4 min and the cost would increase when the increment of cooking time more than 4 min, and the cost would increase 48.7 RMB/ton with each additional 1 min.