| Rice is the main food of human beings.Processed rice,due to the loss of protection from the husk,is easily affected by internal and external factors during storage,resulting in losses.It is highly susceptible to spoilage due to moisture,heat,oxygen,insects,mold,and other factors,leading to increased acidity,decreased viscosity,poor quality,and even loss of edible value.Previous studies on microwave treatment of rice have mostly focused on modifying starch,and there has been no relevant research on the use of microwave stabilization treatment in rice storage.Therefore,this article takes fresh rice as the experimental material and obtains the optimal process through response surface experiments.The rice is treated using a continuous tunnel microwave drying and sterilization line.From the perspective of rice structure analysis,starch structure,and protein oxidation degree,the influence of microwave treatment on the storage quality and microstructure of rice is explored,It has been proven from both quality and structure that microwave stabilization treatment can improve the storage stability of rice.The main research findings are as follows:1.According to three factors,namely,different microwave processing power(800,1200,1600,2000,2400 W),different transmission speeds of microwave equipment(1,2,4,6,8 cm/s),and different thickness of rice laid flat on the conveyor belt(0.2,0.4,0.6,0.8,1.0 cm),the hardness,elasticity,and taste value of rice color difference,texture characteristics were measured,and the highest taste value and the highest hardness elasticity within the range were analyzed to reduce the impact of color difference,Combining single factor experiments and response surface analysis,it was found that the optimal process optimization parameters for microwave treatment on rice quality are set power of 1140 W(actual power of 1105 W),microwave equipment conveyor belt flow rate of 4.8 cm/s,and rice thickness of 0.6 cm laid flat on the conveyor belt.At this time,the maximum expected function value is 0.92.2.Microwave treatment can improve the storage stability of rice in terms of quality.Use a continuous microwave device to treat rice,explore the impact of microwave treatment on the quality of stored rice,and analyze the appearance quality,cooking,texture,gelatinization,rheological and thermodynamic properties of stored rice after microwave treatment.The results showed that the changes in moisture content,fatty acid value,amylose content,and taste value of stored rice after microwave stabilization treatment were the same as those of untreated rice.The decrease in moisture content was slower than that of untreated rice,and there was almost no change in fatty acid value and taste value.The increase in amylose content was relatively small,and the overall hardness and chewiness showed an upward trend,while the overall elasticity,adhesion,and resilience showed a downward trend,After 180 days of storage,the hardness and chewiness of microwave treated rice were lower than those of untreated rice,and the elasticity was higher.Among them,the hardness of microwave treated rice increased by 732 g,and the hardness of untreated steamed rice increased by832 g.The overall water absorption rate and expansion rate show an upward trend,while the amount of dry matter in steamed rice soup shows a downward trend,with almost no changes in water absorption rate,expansion rate,and dry matter quality;The valley viscosity,final viscosity and peak viscosity of Rice noodles after microwave treatment and untreated showed an upward trend,which was larger but not significant than that of untreated Rice noodles.The disintegration value and retrogradation value of Rice noodles after microwave treatment also slightly increased.The energy storage modulus was slightly higher than that of untreated rice noodles,and the loss modulus was slightly lower.Compared with untreated rice,the microwave stabilized rice gel has almost no change in low-temperature storage,and the microwave stabilized rice is higher in room temperature storage.3.Microwave treatment can effectively maintain the structure of rice.In response to the changes in the structure of rice and the spatial distribution of starch proteins in rice,the structure of rice grains stored under microwave treatment was analyzed using stereomicroscopy,scanning electron microscopy(SEM),optical microscopy(LM),laser confocal microscopy(CLSM),and biological transmission electron microscopy(TEM)to explore the impact of rice microstructure on rice quality.Observation under a stereoscopic microscope revealed cracks,incomplete particles,matte surface,and blackening of the rice head after storage.After microwave treatment,the stored rice remains relatively intact in shape,with a gray white head,while the untreated head has turned black,indicating an inedible state.SEM can observe that the surface of rice grains after 180 days of storage is not a smooth structure.The degree of starch depolymerization in rice after microwave treatment is lower than that in untreated rice.The starch particles in untreated rice are severely depolymerized,and under LM,there is severe deformation in the morphology of starch particles.There are many irregular particles,and the starch particles are clustered together in a dispersed distribution.CLSM observation found that after 180 days of storage at room temperature,the arrangement of protein and starch in rice treated with microwave was relatively neat compared to untreated rice.However,the degree of starch dispersion was enhanced,and the protein content increased and aggregated.TEM observation of the ultrastructure showed that the color of the protein gradually turned gray after storage,and the starch binding of untreated rice became more dispersed.It was clearly visible that the starch cracks,small protein bodies,and some proteins had already been bound together,And the protein body is smaller.4.Microwave treatment can reduce the degree of changes in rice starch structure and protein oxidation.Regarding the structure of rice starch and protein,SEM,Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),and small angle Xray scattering(SAXS)were used to analyze the structure of rice starch and protein stored under microwave treatment.SEM observed that microwave stabilization treatment resulted in lower dispersion of rice compared to untreated treatment,The infrared absorption spectrum reflects that the position and shape of the absorption peak of rice starch after microwave stabilization treatment are similar to those of the control group,with no new characteristic peaks or disappearance of absorption peaks.Moreover,the absorbance ratio at 1047/1022 cm-1 after microwave stabilization treatment is higher than that of the untreated group.The XRD diffraction pattern shows no new peaks or significant position shifts,and the crystallinity of rice starch treated with microwave treatment after 180 days of storage at room temperature decreases slightly by 3.3%,The crystallinity of untreated rice starch decreased by 4.7%,and SAXS showed that the absorption intensity of microwave stabilized stored rice starch was higher than that of untreated stored rice starch;After microwave stabilization treatment,the carbonyl content was lower than that of untreated rice protein.After 180 days of storage at room temperature,it increased by 124.43% and 118.58%,respectively.After 180 days of storage at room temperature,it decreased by 42.40% and 38.73%,respectively.FTIR showed that the carbonyl content in rice protein treated with microwave and untreated rice protein increased by 124.43% and 118.58%,respectivelyα-The helix content decreased by 0.46% and 1.12% respectively,indicating that microwave stabilization has a stabilizing effect on the starch and protein structure of rice,reducing the degree of structural changes during storage. |
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