Study On The Key Technology And Conditions Of Dehydrated Instant Rice Quality

Rice is one of Chinese most important and basic food. But cooking of rice istime-consuming, and is not easy to use, carry and store. Therefore, research and developmentof instant rice has great significance and good prospect in the modern society. Now there aresome quality problem for instant rice products, such as too long rehydrated time, unpalatabletaste and liability to aging. In this paper, the Northeast rice was chosen as material, and theeffects on the quality of the dehydrated instant rice were investigated through differentsoaking, cooking and drying conditions; and the food additives were determined for theirapplication in instant rice, in order to improve instant rice quality.The time and temperature of water soaking of rice would influence the moisture contentin rice, which affected the gelatinated rate of rice; and the time of cooking rice woulddetermine rice gelatinization immediately. From research results, the optimal technologicalconditions are: soaking at25℃for20min, which the moisture content in rice could be up to28.28%; cooking time15min, which the gelatinization rate could be up to87.20%.The four drying methods, the one-stage air drying, two-stage air drying, microwave andair combination drying, and freeze drying, had been investigated for their effects on instantrice quality, especially sensory evaluation and rehydration rate. The best technologicalconditions were obtained: the one-stage air drying,80℃for58min; the two-stage air drying,120℃for20min and80℃for11min; the microwave and air combination drying,464Wmicrowave drying for8min and80℃air drying for45min; and the lyophilization,–58℃for8h. From the sensory evaluation results, the quality of the instant rice through the freezedrying method was the best.The scanning electron microscopy (SEM) was used to examine the influence of thedrying methods on instant rice texture. The results showed: from the500×scanning electronmicroscope photographs, there were large numbers of holes on the surfaces of rice, except theone-stage air drying. From the1000×scanning electron microscope photographs, theinstant rice of air drying, whether the one-stage air drying or the two-stage air drying, hadhardly any hole inside rice; the instant rice of the microwave and air combination drying hadsome shallow holes inside; and there were the most intensive and the deepest holes inside thefreeze-drying rice, which was very favourable for instant rice rehydration.The food additives were also studied for their effects on rice quality and aging. Theresults showed:0.8%β-cyclodextrin and0.06%sodium carbonate could increase thegelatinization of rice, and0.4%citric acid and1.0%ethanol could improve the color and tasteof instant rice. Moreover,0.8%β-cyclodextrin could also prevent aging of instant rice.