Research And Development Of Rice Cooking Device Based On Ohmic Heating

Rice is one of the food crops because it is rich in carbohydrates and proteins,as well as many trace elements needed by the human body.When rice is steamed by traditional heating method,both fire heating or electric wire heating must transfer heat to rice and water through the heating vessel,thus causing heat loss.Meanwhile,the heating method has the problems of uncontrollable heating,non-uniform heating and burnt rice,which affects the quality of rice.Ohmic heating have some advantages such as heated evenly,no parching,simple equipment,energy saving,heating fast.Therefore,to design a rice cooking device based on ohmic heating and to evaluates the temperature control performance of the device.The factors affecting the effect of ohmic heating and cooking rice were explored.To explore and optimize the preparation process of ohmic heating and cooking rice.Finally,compared with the traditional heating method to improve the cooking quality and save the cooking energy.The main research results are as follows:(1)Design and manufacture of rice cooking device based on ohmic heating.The rice cooking device is composed of hardware structure and circuit system,in which the circuit system is divided into control circuit and frequency conversion circuit.The device is mainly divided into two functional areas:control area and heating area.The control area is composed of power switch,fan,control panel,control system and frequency conversion system.The heating area is composed of heating tank,electrode,temperature sensor and power coupler.(2)To evaluate the temperature control performance of the rice cooking device based on ohmic heating,and to discuss the changes of current,voltage,power and conductivity in the process of cooking rice.According to the heating temperature curve,the heating fitting equation has a high fitting degree with the actual temperature increase curve(R~2>0.99),and the heating rate error is no more than 1.2%.The maximum temperature difference in the insulation process is 1.2℃,and the temperature difference is less than 0.5℃ after the insulation is stabilized.The device control system has a good control effect on the heating rate of ohmic heating and the insulation temperature.In the heating phase,the current gradually increases and the voltage gradually decreases.In the phase of insulation,the voltage and current show a half sine attenuation trend.The electric conductivity increases gradually in the heating stage,but decreases gradually in the insulation stage,and the larger the water-meter ratio is,the higher the electric conductivity is.(3)The effects of water-to-rice ratio,soaking temperature and soaking time on water content of rice,electric conductivity of water-to-rice mixture,initial heating rate,cooking energy consumption and rice quality were studied.The results showed that the higher the soaking time and soaking temperature,the higher the moisture content and electrical conductivity of the rice,and the faster the ohmic heating speed under the same voltage.The larger the ratio of water to rice during soaking and cooking,the more energy consumed,the higher the water absorption rate and expansion rate of rice,but the hardness,stickiness and springiness of rice decreased,which had no effect on the color of rice.Moreover,the higher the soaking temperature and the longer the soaking time,not only will not reduce the cooking quality of rice,but also can save energy and accelerate the softening of rice.(4)Cooking experiment and comparison of rice with self-made ohmic heating equipment and rice cooker were carried out.The results showed that the expansion rate and water absorption rate of rice could be increased by using ohmic heating method and increasing water-to-rice ratio,and the rice hardness could be reduced.At the same time,the energy required for cooking rice by ohmic heating was about 25% of that of traditional heating.In terms of the uniformity of heating,there is a large temperature difference in the food of the two heating methods.In traditional heating,the rice is too hard and yellow due to local overheating,while the hardness and color value of the rice heated by ohmic are even.(5)The effects of ohmic heating conditions on the hardness,stickiness,springiness,shewiness and food quality of rice were investigated by Box-Behnken method,and a regression model was established.The order of influence on hardness is:heat preservation time,heat preservation temperature,heating rate;The order of influence on the score of stickiness,springiness and food quality is:heat preservation temperature,heat preservation time and heating rate;The order of influence on shewiness is:heat preservation temperature,heating rate and heat preservation time.Among them,when the ohmic heating condition is set to the heating rate of 7.4℃/min,the heat preservation temperature is 98℃,and the heat preservation time is 22 min,the rice quality score is the best.Moreover,the physical value has a significant influence on the score of rice taste quality,which can be used to evaluate the score of rice taste quality and simplify the method of rice taste evaluation.Appropriately increasing the frequency of the power supply is helpful to reduce the electrode corrosion phenomenon.