Research On The Inactivation Process And Kinetic Of High Hydrostatic Pressure(HHP) And Its Microwave Combined Method Of Soft-packing Food

High hydrostatic pressure(HHP)is one of the cold inactivation methods using high pressure(>100 MPa)to kill the microorganisms in food.Compared with the thermal inactivation method,HHP process treats at room temperature,which can guarantee the food safety and meanwhile avoid the damage of flavor,taste and nutrient caused by high temperature.Currently,researches about HHP was mainly focused on liquid food,while still limited in solid food.The research on the influence factors of inactivation results and their mechanisms is still not sufficient.The development and exploration of HHP combined method is also not enough.Based on these situations,this paper studied the inactivation rule of escherichia coli,saccharomyces cerevisiae and penicillium citrinum under HHP treatment in room temperature,established and optimized the inactivation kinetic model of the three kinds of microorganisms,analyzed the effect of different food compositions on the results of HHP treatment.Furthermore,the inactivation efficacy of HHP-microwave combined method and its application in different food were also discussed.The main research contents and results are as follows:(1)Modification and optimization of the HHP inactivation kinetic modelE.coli,S.cerevisiae and P.citrinum suspension were treated by different HHP process,the inactivation rule and kinetic of different microorganisms in pressure raising and pressure holding stage were studied,results showed the inactivation effect increased with the rising of pressure and treatment time during the two stages.Based on the effect of pressure raising stage,the weibull model and the log-logistic model were modified by adding parameter characterize the initial inactivation quantity of the pressure holding stage.Results showed the modified models had higher accuracy and could express the real condition of HHP inactivation in pressure holding stage.Kinetic analysis of the pressure raising and holding stage found log-logistic model was more accurately in explaining the HHP inactivation rule in the whole pressure raising-holding stage compared with weibull model.Based on the weibull model and the log-logistic model of pressure holding stage and pressure raising-holding stage,the relationship between pressure and the other model parameters was discussed to optimize and simplify the models.Results showed the two optimized models had high accuracy and could be used to characterize the effect of pressure continuous changing on the inactivation results.(2)Research on the effect of food composition on HHP inactivation resultsStudied the HHP inactivation effects of microbial suspension contained saccharides,acids,fatty acid and protein.Results showed the inactivation ability of HHP process significantly enhanced with the increase of acids content(low p H),while the existing of protein decreased the inactivation effect remarkably.Saccharides weakened the inactivation slightly,while the effect of polysaccharide was more than disaccharide and monosaccharide.Content of fatty acid played few role to the inactivation results.Based on the observation results of different microorganisms in acids and protein suspension after HHP treatment by transmission electron microscope and scanning electron microscope,the mechanism of acids and protein effect was preliminary discussed.Existing of acids intensified the cell wall damage and broken degree of E.coli and S.cerevisiae,while P.citrinum and some S.cerevisiae still appeared surface deformation and wrinkle.However,the existing of protein decreased the broken and deformation degree of all the microorganisms.The function of membrane was more likely to be effected by HHP under acidic condition,furthermore,the activity of protein and enzyme was easier distoried,and ultimately led the death of the microorganisms.The cell wall damaged and deformation of microorganisms were slightly after HHP in protein suspension.Protein can protect the microorganisms from high pressure and help their reactivation because of the high nutrient.Empirical inactivation models including acids and protein parameters of different microorganisms were established based on Box-Behnken design method and Design Expert software.The models had a high accuracy and could be used to predict the HHP inactivation results.(3)Research on the HHP-microwave combined inactivation methodApplied microwave treatment to promote the inactivation ability of HHP process.Results showed,combined with microwave post processing could significantly enhance the inactivation effect of HHP process,and control samples' temperature in a low range.Based on the observation results of different microorganisms after combined treatment by transmission electron microscope and scanning electron microscope,the mechanism of combined method was preliminary discussed.After combined treatment,the cell wall broken degree of E.coli and S.cerevisiae was increased,while P.citrinum and some S.cerevisiae still appeared surface deformation or wrinkle.Microwave can promote the cell wall and membrane damage caused by HHP,break the inner reaction equilibrium,cause protein denaturation,disturb the growth and metabolism of microorganisms.Empirical inactivation models of HHP-microwave combined method of different microorganisms were established based on Box-Behnken design method and Design Expert software.The variance analysis showed the effects of pressure,pressure holding time,microwave density and microwave processing time on inactivation results were significant,pressure was the most significant parameter and microwave density was the second,while pressure holding time was the last.Therefore,the inactivation efficiency of combined method could be promoted by shortening the pressure holding time when process optimization.(4)Application analysis of HHP-microwave combined inactivation method on boiled bamboo shoots and Tai Lake whitebaitApplied HHP-microwave combined method to inactive microorganisms in boiled bamboo shoots and Tai Lake whitebait,process optimization results showed combination process of high pressure 378 MPa for 3 min with microwave density 20 W/g for 35 s and high pressure 600 MPa for 3 min with microwave density 19.4 W/g for 39 s could eliminate all the microorganisms in bamboo shoots and whitebait respectively.Empirical inactivation models of HHP-microwave combined method were obtained based on the inactivation effects of the two products,variance analysis showed the significance of pressure holding time was lower than other parameters for low pressure resistance microorganisms.Inactivation efficiency of combined method could be promoted by reducing pressure holding time.Comparison of the effects of HHP,microwave and HHP-microwave process with equivalent inactivation ability on the qualities of the two products found that,the sensory and texture quality,vitamin c content of boiled bamboo shoots were reduced after combined treatment as well as the moisture,soluble protein and free amino acid content of whitebait,the reduction degree was slightly more than these qualities after HHP treatment but much less than these qualities after microwave treatment.Furthermore,combined method cost less time than HHP treatment and had much higher inactivation efficiency.Therefore,the HHP-microwave combined method was suitable for the inactivation of boiled bamboo shoots and Tai Lake whitebait.