Study On The Effect Of Induced Electric Field Treatment On The Quality Of Kiwifruit Juice

As the main producer of kiwifruit in the world,China supplies a large amount of kiwifruit to the market every year,but the kiwifruit has a thin skin and juicy,which is prone to bacteria and spoilage during transportation and storage.Processing it into kiwifruit juice can digest a large number of kiwifruits,and can retains its original nutritional and flavor qualities to a certain extent.Sterilization is a necessary part of juice processing.Traditional thermal processing can easily cause the loss of nutrition and quality of juice due to too long processing time or high temperature.The new juice sterilization technology based on ohmic heating and pulsed electric field can effectively reduce the processing temperature and shorten the operation.Over time,it has gained certain development and industrial application in recent years.However,the use of metal plates in ohmic heating and pulsed electric field sterilization has risks such as plate corrosion and product contamination.The magnetically induced electric field(IEF)technology that does not rely on electrodes has attracted researchers'attention.In this study,a complete IEF processing system was built according to the working principle of the transformer,and the optimal conditions for IEF processing kiwifruit juice and the effect of non-thermal effects were studied,and the quality effects of kiwifruit juice after different processing methods and their effects during the storage period were compared.The main research contents are as follows:Determine the excitation voltage and heating tube flow rate for IEF treatment,and study the non-thermal effects of IEF treatment on this basis.When the excitation voltage was1400?1800 V,the current density of the kiwifruit juice in the treatment tube was 0.66?0.85A/cm~2,the conductivity was 4414.33?4917.00?S/cm,and the electric field intensity was172.56?221.00 V/cm.As the excitation voltage increased and the juice flow rate decreased,the survival rate of microorganisms,PPO activity,and POD activity in the juice were constantly decreasing.The optimal processing voltage and flow rate conditions were 1800 V and 6 m L/min.At that time,the total colonies,mold and yeast colonies were not detected,the PPO enzyme activity was reduced by 94.81%,and the POD enzyme activity was reduced by 92.69%.At 1800V,12 m L/min,and the treatment temperature is 62.3°C,the?-helix content of horseradish peroxidase(HRP)increased by 11.4%,the?-sheet content increased by 5.2%,and the irregular curl content increased 6.4%,the fluorescence intensity is also greatly enhanced,and its secondary structure and tertiary structure have produced significant changes(P<0.05),indicating that IEF could make the liquid food with low conductivity produce sufficient thermal and non-thermal effects.Compare the physical and chemical quality and sensory evaluation of fresh samples,UHT treatment,pasteurization,and IEF treatment to determine the storage conditions and quality changes.The results show that after different treatments,IEF-treated juice was the closest to the fresh.When stored at 4°C,the pasteurized and IEF-treated kiwifruit juice still met the requirements of commercial sterility on the 30th day.During stored at different temperatures,the pH,total soluble solids,total sugar and reducing sugar of the three processed juices all decreased to a certain extent.On the 30th day,the L~*value of kiwifruit juice treated with IEF dropped to 42.43,the a~*value rose to 2.23,the b~*value rose to 19.73,and the(35)E rose to 4.13.The(35)E of pasteurization and UHT treatment were 7.33 and 5.78,respectively;the total phenol content in kiwifruit juice after IEF treatment decreased to 111.76 mg GAE/100 g,and the flavonoid content decreased to 49.94 mg RE/100 g,the Vc content decreased o 93.82 mg/100g,the total phenol content on the 30th day of pasteurization and UHT treatment was respectively88.94 mg GAE/100 g and 114.15 mg GAE/100 g,the flavonoid content was respectively 32.16mg RE/100 g and 45.06 mg RE/100 g,the Vc content was 67.37 mg/100 g and 89.40 mg/100 g respectively.The relative content of volatile alcohol in the juice after IEF treatment increased to 21.09%,and the relative content of ester increased to 4.31%,the relative content of ketones did not change much,the relative content of aldehydes dropped to 66.19%,the relative content of alcohols in pasteurization and UHT treatment were 23.38%and 21.98%,and the relative content of esters were 11.33%and 6.35%,respectively.The relative content of ketones did not change much,the relative content of aldehydes was 55.28%and 65.22%.Through sensory evaluation,the comprehensive evaluation of color,appearance and aroma after IEF treatment is the closest to the fresh sample;and when stored at 25°C,only UHT-treated juice can be stored stably for 30 days.The storage period of IEF processed juice and pasteurized juice is shortened by 5 days,the color of juice,antioxidant active ingredients,and volatile flavor substances changed more significantly than those at 4°C.It can be seen that,as a new type of electric field treatment method that does not require an electrode plate,IEF has good commercial value.This research provides certain scientific guidance and theoretical support for the application of IEF in the field of kiwi juice processing.