Effects And Mechanism Analysis Of ZnO Nanoparticles Combined Radio Frequency Pasteurization On The Quality Of Chinese Typical Dishes

Prepared dishes mainly include meat,vegetables,fungi and algae.Because of the relatively short development time of prefabricated foods,industrialized production and standardized management are still very limited.The occurence of excessive microbial and unqualified products is more likely to happen.High-temperature and high-pressure sterilization technology is a traditional sterilization technology used in the food industry.Although the sterilization effect is very good,but the severe textural damage to food is unexpect.In the view of this problem of food degradation caused by high-temperature sterilization,this thesis considers three typical texture of single product from color matching,nutritional value and taste:crisp fruits and vegetables（carrots）,sticky meat（pork）,gum edible algae（Nostoc sphaeroides）and two kinds of typical dishes（Twice-cooked pork and Yuxiang shredded pork）as research material,developed a novel method of ZnO nanoparticles combined radio frequency（ZNCRF）pasteurization.We systematically carried out relevant research and hoped to clarify the relevant mechanism of ZNCRF influence on the quality of dishes while solving problems.The relevant mechanism of the influence of ZNCRF on the quality of dishes provides suitable processing techniques for the maintenance of the flavor of Chinese typical dishes.Pathogenic bacterium（Listeria monocytogenes）widely found in the food and food processing environment was selected as the research object.The mechanism of ZNCRF pasteurization and the cytotoxicity of Zn O nanoparticles were evaluated.The results showed that the ZNCRF synergistic treatment resulted in a significant decrease of Na⁺/K⁺-ATPase activity,which resulted in the destruction of the ion homeostasis inside and outside the cell membrane.The inorganic salt ions and nucleic acid substances in the cell abundant leaked and eventually led to the death of the bacteria.ZnO nanoparticles have no cytotoxicity in the range of mass fraction of 0.01 g/kg⁰.05 g/kg.Although the permeability of the bacterial cell membrane was the largest when the ZnO nanoparticles concentration increased to 0.05 g/kg,but the growth rate slowed down significantly.There was no significant difference in the concentrations of inorganic salts and intracellular UV absorbing material leakage between0.04 g/kg and 0.05 g/kg of ZnO nanoparticles.In this experiment,we chose 0.04 g/kg（ZnO nanoparticles concentration）for pasteurization.Fragile vegetables（carrots）,sticky meat（pork）,and edible algae（Nostoc sphaeroides）were selected as the research subjects.Firstly,the sterilization effect of three kinds of sterilization methods（Nano zinc oxide,radio frequency,and ZNCRF pasteurization）was compared.Then,under the premise of satisfying the bactericidal effect,the effects of different sterilization conditions on the quality of dishes were compared.The mechanism was analyzed by scanning electron microscopy.The results showed that with the increase of the amount of ZnO nanoparticles,the antibacterial effect was enhanced.The bactericidal effects of the 0.04g/kg and 0.05 g/kg Zn O nanoparticles were not significantly different.Taking into account the principle of choosing the minimum amount of bactericidal effect,this experiment further proved that the selection of ZnO nanoparticles concentration of 0.04 g/kg is appropriate for pasteurization.From the perspective of bactericidal effect,ZNCRF pasteurization is better than radio frequency sterilization alone or ZnO nanoparticles alone.From a quality point of view,after the sterilization conditions are satisfied,the influence factors of ZNCRF synergistic pasteurization on the quality lies in the time of synergistic sterilization.Based on the previous studies,we mixed pork and carrot as a meat-vegetable complex system.The effect of ZNCRF synergistic pasteurization on the quality of dishes was studied.The mechanism of quality change from the microscopic perspective was analyzed by FTIR spectrometer.The results showed that ZNCRF synergistic pasteurization is a moderate degree heat treatment,and the effect on sensory,carotenoid content,unsaturated fatty acid and texture of meat-vegetable compound system is smaller than that of high pressure steam（HPS）sterilization.Within 10 min of ZNCRF synergistic pasteurization,α-helical structure content of samples did not change and decreased by 7.22%at heating 20 min.While theα-helical structure content of HPS sterilization samples decreased by 14.36%.At the same time,the random coil content of ZNCRF synergistic pasteurization 20 min samples increased by 6.48%,while that of the HPS sterilization samples increased by 18.94%.With the increase of bactericidal intensity,the content ofβ-sheet in the secondary structure of pork myofibrillar protein decreased from 50.29%to 44.14%.Choosing the typical dish Twice-cooked pork as the research object,we evaluated the effectiveness and applicability of ZNCRF synergistic pasteurization.The mechanism of quality change was analyzed by using electronic nose and gas chromatography-mass spectrometry（GC-MS）technology.The results showed that,the sensory and flavor characteristics of the Twice-cooked pork samples pasteurized by ZNCRF 10 min and 20 min were similar to the unsterilized samples.GC-MS results showed that with the increase of bactericidal strength,the main volatile flavor compounds aldehydes in the Twice-cooked pork samples decreased significantly,which clarifyed the reason of flavor characteristics of ZNCRF 30 min and HPS samples far from the control samples.Choosing the typical dish Yuxiang shredded pork as the research object,we evaluated and compared the effects of ZNCRF synergistic pasteurization and HPS sterilization on the color,flavor and taste of Yuxiang shredded pork dishes.The electronic tongue measurement,GC-MS and Low-field nuclear magnetic resonance（LF-NMR）technology were used to analyze the mechanism of changes in color,aroma,and taste.The results showed that the Yuxiang shredded pork had sufficient homogeneity in the case of ZNCRF synergistic pasteurization,which could ensure effective bactericidal effect and had little effect on color,flavor characteristics,taste substances and water distribution.The contents of heterocyclic compounds（representative flavor compounds of Yuxiang shredded pork）decreased by 35.10%and 55.62%,respectively,with ZNCRF synergistic pasteurization for 30 min and HPS sterilization.The aldehydes and heterocyclic compounds of samples pasteurized by ZNCRF for 20 min only caused a decrease of 7.66%and 7.82%.LF-NMR imaging further demonstrated that different degrees of heating damaged the cell membrane and tonoplast membrane of the sample,leading to the loss of water in the cytoplasm(T₂₂).With increasing bactericidal strength,more water was lost.By analyzing the changes of microbiological parameters,combined water content,sensory quality,color,and texture over time of ZNCRF synergistic pasteurizing dishes at different storage temperatures,a shelf life model of combined water content was established.The storage stability of two kinds of typical dishes（Twice-cooked pork and Yuxiang shredded pork）was studied.The results showed that the shelf-life model based on changes of combined water content can predict quickly and reliably the shelf life of two typical dishes.The dishes pasteurized by ZNCRF still have good sensory acceptance when refrigerated（4°C±1°C）for 8 months.