Effects Of Combined Ultra-high Pressure And Thermal Treatment On Physicochemical Properties And Proteins Of Rice Flour

Ultra-high pressure technology is more widely applied in food.As a kind of cold sterilization technology,it destroys less on food nutrition,which give food materials better sensory quality than heat treatment,and the application of ultra-high pressure in food are generally combined with heat treatment to sterilize,keep fresh or improve the texture of food.The major ingredients in rice are starch and protein,and they both have an important impact on the properties of rice flour.Knowing the changes of starch,protein and physicochemical properties of rice flour,can provide a theoretical basis for the application of this technology in food processing.Therefore this research takes the maize as the study object,studying the effect of ultra-high pressure combined with thermal treatment on physical properties and granule structure of rice flour and to reveal the relationship between treatment conditions and physicochemical properties.Also to explore the effects of combined ultra-high pressure and thermal treatment on the extraction rates and the structure of rice protein.The specific research contents and results are as follows:1.Effects of combined ultra-high pressure and thermal treatment on the physical properties of rice flour.The light transmittance of rice flour treated by combined ultra-high pressure and thermal treatment were significantly lower than the native rice flour.The iodine blue value increased significantly after combined ultra-high pressure and thermal treatment.The solubility and swelling of rice flour improved obviously under the suitable treatment conditions.The gelatinization of rice flour increased significantly along with the rising of pressure,pressure-holding time,temperature and the amount of water.Designing the orthogonal test program of the three main factors and determine the best combination.The results of orthogonal experiments indicated that under the same pressure holding time,the amount of water has the greatest effect on the gelatinization followed by temperature and pressure.Correlation analysis showed that both temperature and pressure-holding time were positively correlated with iodine blue value,theamount of water had obviously positive correlation with iodine blue value(p<0.01),the light transmittance was negatively correlated with pressure(p<0.05),and significantly negatively correlated with pressure holding time,temperature and the amount of water(p<0.01).Swelling was positively correlated with solubility and light transmittance,but negatively correlated with iodine blue value.2.Effects of combined ultra-high pressure and thermal treatment on granule structure of rice flour.X-ray diffraction studies showed that the combined ultra-high pressure and thermal treatment converted native rice flour(A-type pattern)to a B-type pattern.The FT-IR analysis showed that there was no new chemical bond or group and most of the original groups still exist.The proportion of crystallization region decreased first and then increased with the rising of pressure,pressure-holding time,temperature or the amount of water.The SEM analysis showed that the granules of rice flour became smaller when treated by 200 MPa to 300 MPa for 15 min or 600 MPa for 5min.When the pressure-holding time was 25 min or the temperature was 60? or the amount of water was 55%,the rice granules presented irreversible loss of the particle structure and showed viscous gel-like appearance.3.Effects of combined ultra-high pressure and thermal treatment on the extraction rates of rice protein.Different pressures(200,400 and 600MPa)were used to treat rice at45 ?.Four protein isolates including albumin,globulin,gliadin and glutelin were extracted from rice,and the effect of pressure on extraction rates of four protein isolates were studied.The results indicated that the order of the contents of four protein isolates was as follows: glutelin(81.12%)> globulin(7.49%)> gliadin(6.52%)> albumin(4.87%).After combined ultra-high pressure and thermal treatment,the extraction rates of four protein isolates improved.The extraction rates of albumin and glutelin reached maximum at200 MPa,the extraction rates of gliadin and glutelin reached maximum at600 MPa.4.Effects of combined ultra-high pressure and thermal treatment on thestructure of rice glutelin.The FT-IR analysis showed that combined ultra-high pressure and thermal treatment induced a significant decrease in the contents of ?-sheet and?-helix.Loss of ordered structure gradually transformed into disordered structure.Correlation analysis showed that the content of ?-sheet was obviously negatively correlated with pressure(p<0.05),and significantly negatively correlated with temperature or pressure holding time(p<0.01).The content of ?-turn was obviously positively correlated with pressure(p<0.05),and significantly positively correlated with pressure-holding time(p<0.01).The content of ?-helix was obviously negatively correlated with temperature(p<0.05).The content of random coil was obviously positively correlated with pressure(p<0.05),and significantly positively correlated with temperature(p<0.01).The ultraviolet spectral analysis showed that the structure of rice glutelin changed and the molecule chain stretched after combined ultra-high pressure and thermal treatment.The SEM analysis showed that glutelin had loose structure after combined ultra-high pressure and thermal treatment.The results of this paper indicated that suitable treatment conditions improved the solubility and swelling of rice flour,which might contribute to improve the taste of extruded rice products.Additionally,after combined ultra-high pressure and thermal treatment,the extraction rates of albumin,globulin,gliadin and glutelin improved,and the content of ordered structure in glutelin decreased,which might favors the dissolution of glutelin,and the utilization of rice protein in functional food can be increased.