| With the acceleration of the pace of life and the improvement of the material level,the consumer's demands for instant foods(such as instant porridge)and product quality are becoming higher and higher.Extrusion cooking compound instant porridge made full use of broken rice resources,broken rice and other nutritive raw materials are made into an instant porridge via extruding,ripening and granulating processing technology.It has good flavor and tastes with less nutrition loss,and easy to be digested and absorbed by the human body,and facilitate the storage.The study aims o to improve the monotonic nutritional structure of people's daily staple food,and improve the utilization rate of grain resources and the economic benefits of grain processing enterprises.In this study,broken rice was used as the main raw material with glutinous rice,corn,millet,yam powder,milk powder,egg yolk powder,etc,which were used to produce compound instant porridge by the twin-screw extrusion cooking method.The rehydration of the product during hot water brewing and the eating quality of the product after rehydration are the key to extrusion cooking instant porridge foods.The effects of soybean protein isolate(SPI),molecular distillation monoglyceride(GMS)and light calcium carbonate(CaCO3)as quality improver on the quality of porridge were studied,and the optimum improved formula was obtained by orthogonal optimization test.The effect of extrusion process parameters on the quality of instant porridge was also studied,and the ranges of process parameters were determined.The optimal process parameters were determined by response surface optimization design.In addition,the nutritional composition and physicochemical properties of the cereal raw materials before and after extrusion cooking were compared and studied.Finally,the variation of quality of instant porridge under different packaging conditions was studied.The study might provides a theoretical basis for the development and application of extruded compound cereal instant porridge.The main conclusions are as follows:(1)Through studying extrusion cooking compound porridge with different content of SPI,GMS,and CaCO3,the results showed that all three quality improvers can improve the quality characteristics of the product.The univariate test results showed that the sensory score is highest when the SPI,GMS,and CaCO3 are added at4%,0.1%,and 0.3%,respectively.Orthogonal experiments are carried out using the comprehensive sensory score of fuzzy mathematics as the evaluation index.The results showed that the order of importance of the modifier on sensory quality is:GMS>CaCO3>SPI,and the best quality modifier formula is SPI 6%,GMS 0.05%,CaCO30.3%.SEM observation showed that the improved product had a complete porridge structure with loose porosity.The improver significantly improved the quality of extrusion cooking instant porridge and the improved porridge has better rehydration ability and better taste.(2)The study showed that the material moisture content,screw speed,and extrusion temperature have great effects on the bulk density,microstructure,gelatinization degree,water absorption index,water solubility index,rehydration time,and sensory quality of the porridge.The extruded parameter ranges are determined by single factor test,that is material moister 13%-15%.screw speed 32-40 Hz,and extrusion temperature 120-140?.The Box-Behnken test design and response surface analysis method were used to optimize the moisture content,screw speed,and extrusion temperature of the extruded material.The results showed that the main order of each factor was moisture content>extrusion temperature>screw speed,and the best process parameters are material moisture content 13%,screw rotation 35 Hz,and extrusion temperature 135?.The optimal process is verified experiment,the agreement rate between the experimental value and the theoretical value reaches102.18%,which further indicates that the optimized process parameters obtained by the optimization are reliable.(3)Through a comparative study of the nutritional composition and physical and chemical properties of the mixed cereal flour before and after extrusion cooking,which proved that the content of raw starch and crude fat was significantly reduced after the extrusion cooking treatment;the crude protein content was basically unchanged,and the measured amino acid content was reduced;total dietary fiber,soluble dietary fiber and insoluble dietary fiber contents are increased;starch and protein digestibility were significantly improved in vitro digestion trial.Both water solubility index and water absorption index significantly increased after extrusion cooking;the L*of the instant porridge decreased,and the a*and b*values significantly increased.The microstructure of material have changed,the surface is rough with cracks and micropores were observed by scanning electron microscopewere.The differential scanning calorimetry analysis shows that the T_o?T_p?T_c of the extruded samples are all reduced,and the?H is reduced;The fourier transform infrared spectroscopy the analysis shows that the spectrum is basically the same before and after extrusion,which indicating that extrusion cooking did not change the chemical groups.(4)The effects of different packaging on quality of porridge during storage period are studied.Results showed PE packaging with desiccant has the best effect on controlling the moisture content and maintaining the rehydration rate of the instant porridge at 25?.PE packaging with desoxidant has the best inhibitory effect on microorganism.The cfu meets the food safety standards during the experimental storage period,and no coliform bacteria are detected.There is no significant difference between PE packaging with desiccant and PE packaging with desoxidant on the sensory quality of porridge.In summary,the addition of deoxidizers and desiccants can extend the shelf life of instant porridge and provide a certain theoretical support for extruded food manufacturers. |
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