Effects Of Pulsed Electric Field Pretreatment On Processing Characteristics Of Fresh-cut Lotus Root Slices

Lotus root is a common aquatic root vegetable in China,and it is popular among consumers because of its crisp taste and rich nutrition.However,the most part of lotus root sales is mostly dominated by fresh consumption,and total processing consumption accounted for an extremely low proportion in the market scale.It is an excellent sale strategy to make various kinds of ready-to-eat snacks from fresh-cut lotus root to promote the rural revitalization.Currently,blanching is usually used as the pretreatment method of lotus root,though to some extent to achieve initial pickling purpose and enhance mass transfer,but there is still a problem of high energy consumption and low efficiency,severely limit the expanding industry development of lotus root,failed to give full play to the important value of agricultural products in the country revitalization.Hence,we aimed to use pulsed electric field(PEF)to pretreat the fresh-cut lotus root slices.By this method,it is worth to evaluate that the processing method and the products quality would be improved.The main research contents and results are summarized as follows:(1)Effects of pulsed electric field pretreatment parameters on removing reducing sugar in fresh-cut lotus root slicesIn order to evaluate the effects of pulsed electric field pretreatment on enhancing the mass transfer capacity of pretreated lotus root slices,the reducing sugar content(Y)was studied with different combinations of pulsed electric field parameters(electric field strength A,electric field frequency B and processing time C).First of all,the electric field parameters were determined by the single factor experiment,and select the optimum parameters with the help of a Box-Benhnken response surface design methods for the experiment of three factors and three levels,according to the test results of fitting out of the electric field on the impact of parameters on reducing sugar content in multiple linear regression model.The influence level of each factor and the accuracy of the model were determined by ANOVA.The results indicated that all the factors showed significantly effects on the reducing sugar content,and the prediction model was:Y=1.59-0.45×A-(9E^-04)×B-0.05×C+0.26×A²+(1.3E^-06)×B²+(1.78E^-03)×C²,R² of the model is 0.92.According to F test in the variance analysis,the order of influence factors in the model was as follows:processing time>electric field strength>frequency,which was consistent with the results of response surface analysis.The optimal processing parameters in this study were as follows:electric field strength1.43 k V/cm,frequency 180 Hz and processing time 21 s.With this pretreatment,the reducing sugar content was the lowest,which was 0.61 mg/g.(2)Effects of pulsed electric field pretreatment on mass transfer kinetics of pickled lotus root slicesIn order to investigate the effects of pulsed electric field pretreatment on pickling process and final quality of lotus root,the mass transfer process was studied by kinetic models and the flavor quality was evaluated by sensory evaluation.The moisture content,Na Cl content and total weight changes of lotus root slices were determined during pickling process,and the mass transfer kinetic model was applied to establish the content changes of each component.The effective diffusion coefficients of samples in different groups were calculated by Fick's second law to determine the Na Cl transfer process in pickling process.At last,the pickling degree and surface microstructure of samples were combined to evaluate the effects of pulsed electric field on pickling process.The results indicated that the permeability of pretreated lotus root slices was significantly enhanced,resulting in stronger water loss and Na Cl absorption than those of control.The kinetics model with little error could accurately predict the changes of component content in pickling process.Besides,the mass transfer(k2,2.38)and diffusion coefficient(De,1.742 E^-6)of pretreated groups were higher than those of control(k2=1.79,De=9.506E^-7),leading the system reached osmotic equilibrium in a shorter term.In conclusion,pulsed electric field has positive effects on processing and quality of pickled lotus root slices.(3)Effects of pulsed electric field pretreatment on frying quality of lotus root slicesIn order to evaluate the effects of pulsed electric field pretreatment on quality of fried lotus root slices,the changes of physicochemical properties and quality of fresh-cut lotus root slices after pretreatment and frying were studied by comparing with the blanching pretreatment group(80°C,3 min)and the control group.The quality changes including cell viability,microstructure,texture,oil content and browning index were evaluated.The results showed that the microstructure of lotus root was seriously damaged with pulsed electric field pretreatment,and leading the decrease of cell viability and cutting force.For fried samples,the pretreatment also decreased the oil content(15.0%)and acrylamide content(25.9%),improving the browning index and crispness.It was shown that the pulsed electric field technology could be used as a pretreatment method in the production and processing of fried lotus root and similar products,which could not only save production resources and reduce energy consumption but also further improve the processing technology and product quality.In this study,pulse electric field was used as a pretreatment method for processing fresh-cut lotus root slices,which was applied to the production of pickled and fried lotus root slices.The results showed that it can effectively play a positive effect of traditional thermal-processing,greatly reduce the energy consumption,avoid the waste of resources,significantly optimize the production process,improve the quality of the final product,and is expected to be used as a practical pretreatment method in the production and processing of lotus root or similar products.