Effect Of Ohmic Heating On Microbial Population, Enzyme Activity And Vitamin C Of The Kiwifruit Puree

With Kiwifruit delieiosa A. as the main raw material, this paper mainly research on effect of ohmic heating on microbial population, enzyme activity and vitamin C of the kiwifruit puree.This paper is composed of four parts:the first part studies on characteristics of Kiwi purees during ohmic heating. The relationship between conductivity and temperature was obtained.The second part include single factor test which can determine the best value of all single-factor or range and the second general rotation experiment. The first-order model and the two polynomial inactivation models of polyphenol oxidase and peroxidase in kiwifruit purees during ohmic heating was fit out and verified.The third part study on sterilization of ohmic heating for the kiwifruit purees. The various factors on the bactericidal effect and the optimal sterilization parameters were determined by the single factor test and the second general rotation design experiment. The last part study the effect of ohmic heating on the vitamin C degradation kinetics of kiwifruit purees and the apparent activation energy, and loss rules of vitamin C during ohmic heating kiwifruit purees was explored, and the model of vitamin C degradation was built. Conclusions can be summarized as follows:1.The relationship of voltage gradient and the heating temperature and the conductivity was obtained under different voltage gradient, the heating rate of kiwifruit purees increases with the increasing of voltage gradient, and a linear relationship was found. At the same voltage gradient, the kiwi purees heating rate increases with the rising of temperature; voltage gradient slightly affected on electrical conductivity of kiwifruit purees, but little effect on the conductivity curve coincide.2. The sensitivity of polyphenol oxidase and peroxidase in the ohmic heating system is:PPO> peroxidase.3. The inactivation process of polyphenol oxidase and peroxidase were in keeping with a dynamic model of passive dynamics, the measured RA and predicted RA have a good relationship. Two polynomial equations describe the effect of the field strength, heating time and heating temperature on the activity of polyphenol oxidase and peroxidase enzymes. The equation is:RA(PPO)=44.54694-10.84597t-3.70840V-11.05432T+0.62712t2-0.09767V2-0.5396 1 T2+0.33750tV-0.16250tT+0.31250VTRA(POD)=43.94455-17.25330t-4.60005V-20.88748T-0.02348t2+0.63059V2+0.20 633T2-0.38750tV+0.93750tT+1.16250VTIt can been seen that effect of the temperature on the polyphenol oxidase is the greatest, followed by heating time and field strength.4. The optimal process parameters for ohmic sterilization is temperature 80℃, time 30s, heating voltage 200V, the equation is as follows:Y1=3.57008-0.79394X1-0.52947X2+0.03501X3+0.34444X12+0.17827X22+0.04392 X32-0.03875X1X2-0.02375X1X3-0.00625X2X3Y2=2.68245-0.59820X1-0.37943X2+0.03402X3+0.25294X12+0.15218X2+0.02844 X32-0.04125X1X2-0.00875X1X3-0.00375X2X35. The relationship between heating temperature and vitamin C degradation reaction speed during ohmic heating process kiwifruit plasma was obtained, the higher the temperature, the faster degradation rate. And vitamin C degradation follow a degradation, consistent with a degradation model. The model is:...