Study On Quality Changes And Storage Characteristics Of Frozen Fried Rice Under Dry Steaming Process

Yangzhou fried rice is one of the famous classic Huaiyang dishes,which is widely used in banquets in China’s culinary industry,with fresh and fragrant taste,distinctive rice grains,and crystal clear under the wrapping of egg liquid,which is called "gold covered silver" in the industry.At present,the development of China’s prefabricated dishes industry is rising rapidly,Yangzhou fried rice as the most widespread Huaiyang cuisine naturally in the research and development of prefabricated dishes to bear the brunt.At present,food factories have a more complete fully automated process and assembly line for making frozen fried rice,but after being put on the market,problems such as aging of fried rice and sensory gap with Yangzhou fried rice slowly emerge.Therefore,this paper adopts the rice made by dry steaming process to make frozen fried rice,and take this as the research object to explain the feasibility and advantages of dry steaming process from the scientific point of view,and then analyzes the influence of different reheating processes on the nutritional quality of frozen fried rice,and finally analyze the storage characteristics and establish and verify the shelf life model for frozen fried rice.The main findings are as follows:Firstly,the response surface optimization of the multiple soaking stages of the dry steaming process was carried out by selecting three factors:primary cold soaking time,hot soaking time and secondary cold soaking time for a single-factor test,and the Box-Behnken test design and response surface optimization were carried out according to the results.Finally,the parameters of the optimal multiple soaking stages were determined as 30 min for primary cold soaking time,2.4 min for hot soaking time,25 min for secondary cold soaking time,and finally 50 min for dry steaming maturation.Second,the basic nutrients,color,starch digestibility characteristics,stage aging during storage at 4℃,volatile flavor substances,textural characteristics,microstructure,freezable water content,and sensory quality were determined and compared.The results showed that the differences of basic nutrients between rice and fried rice of different cooking processes were mainly in moisture,the internal microstructure of rice of dry steaming process was more severely damaged due to multiple soaking process,the moisture loss was more serious when fried,starch easily formed starch-lipid mixture with fat,and had certain hardness and chewiness,while rice and fried rice made by traditional cooking process had the lowest glycemic index(eGI),better sensory score and nutritional health effects,and the required visual effect of grainy and gold-covered-silver for Yangzhou fried rice.In addition,the flavor substances of the rice from the three cooking processes were different,and there were almost no common substances,which indicated that the rice from each of the three cooking processes had its own characteristics.In the staged aging experiment,the aging rate of the rice and fried rice made by the dry steaming process was the lowest in terms of both enthalpy(ΔH)and starch digestion characteristics,which could solve the current concerns of food factories about the regeneration and quality of frozen fried rice.Subsequently,fried rice made by the dry steaming process was frozen and reheated in different ways(Water bath,Microwave,Back to the pot)to determine its starch digestion characteristics,protein digestion characteristics,free amino acid fraction,free fatty acid fraction,and volatile flavor substances.The results showed that the nutritional quality of frozen fried rice improved after reheating,among which,water bath reheating had the highest SDS content and the highest final release of free amino acids during digestion,microwave reheating had the highest RDS and RS,and the fastest release of free amino acids during digestion in the gastric phase;reheating in the pot had the lowest eGI,but its final release of free amino acids during digestion was the least.There was no significant change in the free fatty acid composition of fried rice between the three reheating methods,but the changes in aromatic presenting amino acids and flavor substances among the free amino acids were very obvious,and the highest amount of flavor substances were detected in the reheated fried rice with 2-pentyl furan,which had good flavor.Finally,the storage characteristics of frozen fried rice were investigated by measuring pH,color,acid value(AV),water activity(Aw)and peroxide value(POV)at-15,-20 and-25℃every 5 d.The Arrhenius equation was used to predict and validate the shelf life by linearly fitting a one-level kinetic equation model based on peroxide value.The results showed that there was no significant change in the color of fried rice during storage at different temperatures,pH and Aw showed a decreasing trend and the rate of decrease was faster the higher the storage temperature,and AV and POV values kept increasing,and the higher the storage temperature the faster the increase.The results of shelf life study showed that the predicted shelf life of frozen fried rice stored at-15,-20 and-25 were 107,119 and 131 d.which were close to the actual shelf life of 103,125 and 139 d,and the errors were-3.88%,4.80%and 5.76%,respectively,with small errors and reliable models.In conclusion,the dry steaming process of frozen fried rice has lower regeneration rate,better sensory quality and better flavor than traditional frozen fried rice,and is suitable for reheating in the reheat mode,which provides scientific guidance and theoretical basis for further large-scale industrial production.