Technology Of Instant Rice Congee And Mechanism Of Its Gelatinization And Retrogradation

Instant rice congee (IRC) is one kind of new instant food. At present, the technology and mechanism of IRC is few reported at home and abroad. In this experiment, the optimal process route of IRC was established through the study of various process units with the high-quality nonglutinous rice. Besides, the gelatinization and retrogradation mechanism of IRC was further explored by the methods of rapid visco-analyser (RVA), differential scanning calorimeter (DSC), x-ray diffraction (XRD), scanning electron microscopy (SEM) and so on. The results were summarized as follows:The optimal process route of IRC was: nonglutinous rice→roasting→cooking in boiling water→cooking by slow fire→soaking and enzymolysis→dispersing→steaming→drying→product. The optimal process parameters were as follows: First, the high-quality nonglutinous rice was roasted for 15min by a slow fire until the craquelure appeared on its surface, then boiled for 2min and cooked by slow fire for 10min. Next, the rice was soaked inα-amylase solution (100U/100g rice) at 50℃for 30min. The enzymolysised rice was drained and steamed for 15min, then washed with cold water quickly. Afterwards, the rice was dispersed with 3% dispersion liquid composed of 10% ethanol, 5% sucrose fatty acid ester, 85% distilled water. Finally, the IRC was gotten by freeze - hot air drying, including 3 circles of freezing at -20℃for 1h and drying at 160℃for 5min firstly, and then hot air drying at 80℃for 2h. The rehydration time of IRC made by this process was 4.5min. The taste and organizational status of rehydrated IRC could be improved by adding 2% of potato starch, 0.07% of CMC, 0.02% of the rice flavor, 2% sugar.The the process of IRC can be divided into three stages. The first stage is the rice gelatinization stage, from roasting to slow fire cooking. At this stage, rice rapidly absorbed water and heat, began to expand. The hydrogen bonds between molecules of rice starch were destroyed gradually by the high energy of heat and water, and the starch crystal structure collapsed to amorphous. In the process, rice starch viscosity rised constantly, and the organizational structure of rice changed into expansion and central hollow from the former uniform and dense tissue. The second stage is the rice swelling stage, from soaking and enzymolysis to steaming. At this stage, rice starch had gelatinized completely, and was hydrolyzed into oligosaccharides, result in which the viscosity dropped significantly. Rice orgnization became fluffy and was full of pores and cracks through soaking and was steaming. The third stage is the rice partial retrogradation stage, from discreting to drying. At this stage, due to water lossing and temperature lowering, starch molecular motion slowed down, moved closer to each other, and combined with hydrogen bonds, forming recrystallization. As the freeze - hot air drying effect, only a small part of this phenomenon occurred. After drying, rice organization began tightening, and appeared hollow in center and irregular pores on surface.