Effects Of Processing Parameters On Indica Rice And Changes Of Rice Quality During Cooking

China is the largest country in production and consumption of rice in the world.Nowadays,people pay more and more attention to the quality of rice.The quality of cooked rice is highly related to the cooking conditions.Besides,the processing parameters of rice cooker,which is the main tool for cooking rice,have a significant impact on the quality of cooked rice,including appearance,nutrition and digestibility and internal structure.Therefore,10 representative processing models were selected to study the influence of processing parameters on quality and physicochemical properties of cooked rice.The change of indica rice during cooking was analyzed from three parts:the quality of indica cooked rice,the characteristic and structure during cooking.And different processing parameters were researched to find out the key parameter and their influence on the quality of cooked rice and the characteristic during cooking.Sensory evaluation was taken as the main method of evaluation,and physicochemical and instrumental analysis,such as Texture Analyzer,GC-MS,were used to compare the differences between indica rice cooked by different processing parameters.It was found that there were great differences in sensory quality of cooked rice with different processing parameters,especially the palatability and aroma.The palatability and aroma were further analyzed by Texture Analyzer and GC-MS.Hardness,cohesiveness and resilience were as the key indexs for the palatability evaluation and hexanal,nonanal,1-octen-3-ol and2-pentylfuran were as the key evaluation indexes for rice flavor.Partial least-squares regression analysis was used to analyze the influence of processing parameters of different rice cookers on sensory quality and key indexes of texture and flavor.Different processing parameters had different effect on the quality of rice.The time for water absorption was significantly and positively correlated with sensory indices of most rice,while V₂,t₄,t₅,T₁ and t₆ were negatively correlated.The increase of t₂ was beneficial to the better flavor and appearance of rice,but the increase of V₂ is not conducive to the uniformity of whole cooked rice,and the increase of t₄ was not conducive to obtain better appearance of cooked rice,and the increase of t₆ also affects the appearance of rice,especially the gloss.The changes of water absorption,iodine blue value,expansion ratio,gelatinization degree and reducing sugar of rice grains during cooking were determined by physicochemical methods,and the changes of proton relaxation signal and moisture migration of rice grain were studied by low field nuclear magnetic resonance?NMR?.Water absorption,swelling rate,iodine blue value and gelatinization degree gradually increased with cooking progress,and the absorption rate,swelling rate and gelatinization degree increased greatly during the water absorption stage.However,the index value of cooking characteristics with longer water absorption time is much smaller than others in water absorption and temperature increase stage.The rice with shorter boiling time and rice cooking time were with lower water absorption and expansion rate.During the cooking process,the intensity and relaxation time of T₂₂ continuously increase.A large amount of water was trapped as tectonic water and the binding of the protons and the macromolecules was reduced.The combined water signal of the cooking mode without the water absorption stage was slowly decreased,and the duration of water absorption stage was conducive to water distribution in rice while the boiling time was conducive to the increase of the water immersion degree.The effects of water absorption and boiling stages on thermal properties and structural changes of rice starch were analyzed by DSC,XRD and FTIR.In cooking process,the width of FTIR band changed,but no new absorption peak appeared and no absorption peak disappeared.The difference of cooking parameters could lead to the difference of starch macromolecule chain structure,but not chemical bond.During the water absorption stage,the FTIR diffraction pattern of rice starch maintained the A-type pattern,but the intensity and area of the diffraction peak decreased,and the crystallinity of starch decreased significantly.The cooking mode without water absorption stage,the temperature of starch gelatinization was obviously higher during cooking process,and the relative crystallinity of starch decreased rapidly in the pre-cooking stage.However,the gelatinization enthalpy value of the preheated rice was higher raw rice.