Study On The Synergistic Effects Of Radio Frequency Combined With Antibacterial Agents On The Quality Of Typical Prepared Foods And Related Mechanism

During the processing and storage of prepared foods,the continuous biochemical reactions in the food matrix can easily lead to quality deterioration,which greatly limited the quality and shelf life of prepared foods.Although the conventional sterilization technology(high pressure steam)effectively ensures the microbiological safety of prepared foods,the color,flavor and texture of prepared foods are usually and greatly compromised.In this research,novel mild pasteurization methods which used green physical technology(radio frequency)in combination with biological antibacterial agent(ε-polylysine)and chemical antibacterial agent(zinc oxide nanoparticles)were performed to overcome the shortcomings of quality degradation of prepared foods caused by conventional sterilization technique.Three typical raw foodstuffs(edible mushroom,vegetable and poultry meat)were selected for the applicability evaluation of radio frequency combined with antibacterial agents.Based on the research of three raw foodstuffs,single-component prepared food((pan-fried chicken breast)and multi-component prepared foods(Kungpao chicken,stir-fried chicken with mushroom and pepper)were selected as research materials.The applicability and effects of radio frequency combined with antibacterial agents on typical prepared foods were systematically studied and compared with conventional high pressure steam sterilization.The related mechanism was clarified and shelf life model was established.The objective of the present study is to provide new idea and theoretical basis for the industrialization of prepared foods.The specific results are as follows:Firstly,E.coli,which is commonly found in foods during processing,transportation and storage,was selected in the present research.The synergistic effects of radio frequency combined with antibacterial agents were comprehensively evaluated by analyzing the residual bacteria amount,cell membrane permeability and leakage of ultraviolet absorbing substances of E.coli after pasteurization,and the related inactivation mechanism was clarified by the above mentioned analysis combining with scanning electron microscopy and confocal laser scanning microscopy.The results showed that radio frequency combined with ε-polylysine and zinc oxide nanoparticles contributed to the increased structural damage of E.coli,increased permeability of cell membrane,increased leakage of intracellular material and aggravated cell damage.The results of the inactivation kinetic study showed that the modified Gompertz model had higher correlation coefficients and model evaluation parameters,which indicated that the modified Gompertz model was more suitable and accurate for the radio frequency combined with antibacterial agents pasteurization than the first-order kinetic model and Weibull model.According to the experimental results,the electrode gap was set as 20 mm,the radio frequency heating time was set as 20 or 30 min,the concentration of ε-polylysine was set as 0.25 g/kg and the concentration of zinc oxide nanoparticles was set as 0.04 g/kg,respectively.Secondly,three typical raw materials of Cordyceps militaris(edible mushroom),green pepper(vegetable)and chicken breast(poultry meat)were pasteurized using different methods.The synergistic effects of radio frequency combined with antibacterial agents on the total microbial load,color,texture,cordycepin content,ascorbic acid content and thiobarbituric acid reactive substances content were evaluated.The results showed that radio frequency combined with ε-polylysine and zinc oxide nanoparticles caused significant higher reduction in total microbial load than those of radio frequency treated samples,and caused minor changes in cordycepin content,ascorbic acid content,thiobarbituric acid reactive substances content,color and texture in the samples.The penetration depths of radio frequency combined with antibacterial agents on the three prepared foods were much greater than the thickness of the corresponding packages,which indicated good heating uniformity during pasteurization.Thirdly,based on the results of previous research,the applicability of radio frequency combined with ε-polylysine on the pan-fried chicken breast was evaluated.The quality change of prepared chicken breast and the mechanism after pasteurization were analyzed by combining electronic tongue and scanning electron microscopy.The results showed that radio frequency combined with ε-polylysine resulted in uniform temperature distribution,good penetration depth(59.13～66.29 cm)in pan-fried chicken breast,and there was no edge effect during pasteurization.Moreover,radio frequency combined with ε-polylysine maintained the original quality(color,texture and taste)of pan-fried chicken breast compared with the conventional high-pressure steam sterilization.However,conventional high-pressure steam sterilization not only greatly reduced the umami taste of pan-fried chicken breast by up to 33.45%,but also severely damaged the tight network structure of myofibrillar,which might be the main reason for the deterioration in taste and texture of prepared chicken breast.Fourthly,the typical multi-component Chinese prepared food,Kungpao chicken,which composed of chicken breast,carrot,pepper,cucumber and mushroom,was prepared.And the applicability of radio frequency combined with zinc oxide nanoparticles on Kungpao chicken was evaluated.The results showed that radio frequency combined with zinc oxide nanoparticles could effectively reduce the total microbial load in Kungpao chicken,and there was uniform temperature distribution during pasteurization without edge effect.The results of hierarchical cluster analysis and principal component analysis of the e-nose data indicated that the flavor of Kungpao chicken after radio frequency combined with zinc oxide nanoparticles pasteurization was close to that of the unpasteurized sample.Radio frequency combined with zinc oxide nanoparticles pasteurization caused increases in thiobarbituric acid reactive substances content by 18.82%～31.92%,however,the conventional high-pressure steam sterilization caused sharp increase by 95.68%.The conventional high-pressure steam sterilization greatly damaged the cell structure and the water status of the chicken,while radio frequency combined with zinc oxide nanoparticles maintained the fluidity of water protons and water distribution in cell,which contributed to good texture after pasteurization.Fifthly,based on the previous study,the applicability and synergistic effects of radio frequency combined with composite antibacterial agent consisting of ε-polylysine(0.20 g/kg)and zinc oxide nanoparticles(0.03 g/kg)were evaluated by applying it to the typical multicomponent Chinese prepared food,stir-fried chicken with mushroom and pepper.The results showed that radio frequency combined with composite antibacterial agent effectively improved the bactericidal efficiency of stir-fried chicken with mushroom and pepper,resulted in lower thiobarbituric acid reactive substances content and higher ascorbic acid content by shortening the pasteurization time.Radio frequency combined with composite antibacterial agent resulted in uniform temperature distribution during pasteurization without edge effect.The relative content of aldehyde and alcohol compounds were high in stir-fried chicken with mushroom and pepper.The total relative content of aldehyde compounds initially increased to 32.65% during the first 20 min of pasteurization and then decreased to 27.70%,meanwhile the total relative content of alcohol compounds gradually decreased from 22.83% to 14.38%.The changes of aldehyde and alcohol compounds elucidated the reason that the flavors of samples treated by conventional high pressure steam are different from samples without pasteurization.Finally,accelerated storage tests were conducted on the three kinds of typical prepared foods for the establishment of shelf-life model based on thiobarbituric acid reactive substances content,and the shelf-life model showed good accuracy of prediction with lower errors.The qualities changes during storage indicated that radio frequency combined with antibacterial agents could effectively control the microbial load in the prepared foods,and the total microbial load did not exceed the maximum limit during 270 d storage at 4°C.Compared with the samples treated by conventional high-pressure steam,the overall sensory scores of prepared foods treated by radio frequency combined with antibacterial agents were closer to 0 d.By comprehensive comparison of the qualities changes during storage,radio frequency combined with antibacterial agents pasteurization could maintained the original quality of the prepared foods.It could effectively extend the shelf life of prepared foods up to 270 d at 4°C.On the other hand,three kinds of prepared foods showed the best quality within 180 d of storage.