Research And Analyses On Influence Of Heating Rate And Soaking Temperature On Qualities Of Rice

How to improve the eating quality of rice has been the goal pursued by people for a long time.There have been many researches and applications about adjusting the cooking procedures of rice cookers to improve the eating quality of rice.However,few studies have been done on the heating rate of rice cookers and the physic-chemical properties of rice during cooking.The basic theoretical depth is not enough.For this purpose,in view of the existing problems of current study,this paper firstly optimized the correlation analysis and regression equation model of rice eating quality,which made the evaluation system more scientific and convenient.On this foundation,the influence and mechanism of heating rate and soaking temperature on the eating quality and physicochemical properties of rice were studied,which would provide a theoretical basis for improving the eating quality and cooking process of rice.The results of sensory evaluation score,texture characteristic and gelatinization characteristic were processed by data scaling and log transformation.Then the correlation analysis and regression equation were established based on the above parameters.The results showed that the processed data could eliminate or reduce the orders of magnitude differences caused by instruments and measurement methods,providing a possibility for the sensory evaluation of the universality of regression equation.After data processing,the multiple linear regression equations between the sensory evaluation scores and instrumental analysis of rice were as follows:sensory viscosity=-0.438×regeneration value-0.812×cohesiveness-7.688e^-8;sensory elasticity=-0.477×viscosity-0.580×cohesiveness+5.648e^-8;sensory soft hardness=-0.577×cohesiveness-0.940×final viscosity+8.257e^-8.The effects of different heating rates on the textural properties of cooked rice were studied.The results showed that the higher the heating rate,the more uneven the water distribution of rice grain.The greater the degree of surface damage of rice grain,the more starch leached out.With the increase of heating rate,the hardness of both japonica rice and indica rice increased,however,the stickiness of japonica rice decreased and indica rice increased.The appearance of cooked rice showed that the rice grains swelled with the absorption of water.The surface of rice grains was looser when heated at the heating rate of600 W,which was helpful to improve the eating quality of cooked rice.The condensability of cooked rice is minimum when heated at 600 W.Combining the regression equation of sensory evaluation,the results showed that the optimal heating rate was 600 W.A higher or lower heating rate than 600 W would have a negative impact on the eating quality of rice.The changes of physic-chemical properties of rice at different heating rates and the mechanism was explored.The results showed that the physic-chemical properties of rice during cooking were initially affected by the distribution of water and gelatinization of starch in rice and were later influenced by the migration rate of water from the surface to the inner area of rice.The higher the heating rate,the greater the influence.The peak temperature and enthalpy value of rice were higher when heated at the higher heating rates.During the rice cooking process,the structural water content gradually increased,and the combined water content first increased and then decreased.When heated at 300 W,the iodine blue value and reducing sugar content increased with the cooking time,while these values first increased and then decreased at 600 W and 900 W.Meanwhile,the iodine blue value and reducing sugar content of japonica rice were higher than that of indica rice.The effects of soaking temperature on the textural and physicochemical properties of rice were studied.The results showed that the hardness and cohesion of rice soaked at 40°C were lower than that at 60°C,while the stickiness and water content of cooked rice were much higher.The appearance of rice showed that the rice grains after soaking were easier to absorb water and swell,and the surface of rice grains was looser.After soaking at 40°C for 20 min,the cooked rice at a heating rate of 600 W had the best eating quality.The physicochemical properties of rice showed that soaking at 40°C was benefit for the water absorption of rice grain,while a high soaking temperature at 60°C could provide more energy for the molecular movement,resulting in the leaching of soluble substances,such as short-chain amylose and reducing sugar.