Influences Of Processing Technology On Properties And Microstructure Of Rice

Instant rice is a staple food which is produced by large-scale industrial production and only requires simple cooking or can be directly consumed but has consistent taste with the ordinary rice.Instant rice is produced through immersion,cooking,drying,sterilization and other processes.These processing methods change the microbial colony and microstructure of rice and result in increased retrogradation rate,swelling ability change,poor rehydration and other problems.This paper studies the microbial colony changes,builds the best parameters of rice immersion,microwave heating and cooking and characterizes the microstructural changes before and after the processing with SEM,XRD,FT-IR,DTA,TGA and other methods,thereby exploring the retrogradation characteristics,swelling ability and rehydration characteristics of rice.The results were as follows:(1)In the processing methods of instant rice,the immersion process can better maintain the rice flavor,but the increase in rice water content will also cause the significant growth of the microbial colonies and the rise of retrogradation rate.The results showed that with the prolongation of immersion time,the total number of microbial colonies increased rapidly and after 7 days of immersion,the total number of microbial colonies exceeded the standard and the growth rate of mold and yeast was obviously smaller than that of bacteria.With the increase of immersion time and temperature,the water content in rice increased.The rice retrogradation rate was positively correlated with water content.In the practical production and application of instant rice,the optimum process parameter was to soak it at 25? for 60 min.To examine the reason for the increase of retrogradation rate,the microstructure of rice was characterized,it was found that the microstructures of rice surface and profile were dented and adhered,the crystal structures remained as Type-A,but since the water flows into the internal structure of rice,the number of hydrogen bonds in rice changed,the relative crystallinity decreased then tended to be steady,the starch molecules tended to be ordered,thereby enhancing the retrogradation of starch.(2)In the processing methods of instant rice,microwave heating process has the effect of rapid expansion and sterilization,but excessive microwave thermal effect will change the rice swelling ability and affect the body's absorption of nutrients.The results showed that the swelling ability will improve with the increase of water content,and swelling ability will first improve then decline with the increase of microwave power.In the practical production and application of instant rice,Soaking time is 60 minutes;microwave heating for 10 min at 464 watts will achieve the best microwave treatment process parameters.In order to study the change reason of swelling ability,we do characterization on the rice both before and after microwave treatment;it is found the dimple phenomena on the microstructure of rice starch.The crystal structure belongs to type A;and under the microwave thermal effect,the internal structure of starch would be broken.The binding ability of reducibility hydroxyl and water is rising.The number of hydrogen bonds in rice is decreasing.The relative crystallinity declines and becomes steady comparing with before treatment.Starch molecular stability is increasing,and swelling ability is stronger.(3)In the processing methods of instant rice,The cooking process can save the rice nutrition and improve the flavor,but the change of the cooking conditions can also cause nutritional loss,sensory quality decline and other problems.The results showed that undulate change with the ratio of rice to water and cooking time,and the optimum process parameters were the ratio of rice to water of 1:7 and the cooking time of 7 min.To study the reasons for the changes of rehydration characteristics and characterize the microstructure of rice,it was found that the surface and profile microstructure of rice showed sponge-like structure.Under the cooking process,with the rise of temperature,starch-lipid complex gradually formed,the crystallization area was destroyed,the relative crystallinity decreased and water entered the starch,resulting in hydrogen bond fracture between the starch molecules and promoting the rehydration characteristics to show wave changes under the dual function of temperature and water.