Inactivation Of Saccharomyces Cerevisiae By High Pressure Homogene Ous-assisted High Pressure CO₂

Heat inactivation is commonly used in the food industry,however it usually causes some quality decline of thermal unstable food such as color,taste and texture changes,therefore,it's necessary to develop non-thermal inactivation technology.High pressure CO₂ and high pressure homogeneous inactivation are two of non-thermal inactivation techniques,a lot of studies have shown that its application in fruit and vegetable juice drinks inactivation has achieve significant bactericidal effect.So,the two techniques were combined to provide a new type of food inactivation technology so that it can strengthen bactericidal effect and receive a better application.According to the working principle and characteristics of high pressure homogenization-assisted high pressure CO₂ sterilization technology,the sterilization test device was successfully built.The complex food matrix is simplified as a CO₂-water mixture,the phase equilibrium theory was used to analyze the CO₂ phase characteristics during high pressure homogenization-assisted high pressure CO₂ sterilization.The results showed that if the treatment temperature is not lower than 15? and the pressure is in the range of 0²00 bar,the CO₂ hydrate will not be produced,which could ensure the safe operation.A two-stage cooling scheme was proposed to solve the problem of temperature rise during sterilization.The test results showed that this scheme could meet the requirement of non-thermal sterilization.The strain was tested with Saccharomyces cerevisiae ATCC9763,and its suspension was used as the research substrate.The CO₂ pressure,homogenization pressure,treatment time and temperature on the bactericidal effect of high pressure homogenization-assited high pressure CO₂ were systematically studied.The results showed that the bactericidal effect of high pressure homogenization-assited high pressure CO₂ was better than that of single sterilization method,and the synergistic bactericidal effect was gradually increased with the increase of CO₂ pressure,homogenization pressure,temperature and the extension of time.Six kinds of nonlinear curve dynamics models were used to fit the sterilization kinetics data.The results showed that CO₂ pressure and high pressure homogenization pressure had a great effect on sterilization,and the lethal kinetic characteristics showed a two-stage lethal curve.The results of model fitting showed that the six nonlinear curve dynamics models had good fitting degree,but their fitting accuracy was not the same: Peleg Type B > Peleg Type A > Biphasic > Modifid Gompertz > Weibull > Modifid Logistic.The mechanism of high pressure homogenization-assisted high pressure CO₂ sterilization was revealed by the study of cell size,leakage of important intracellular substances,cell external morphology and cell membrane permeability.The results showed that the crushing capacity of high pressure homogenization was the strongest,and the disruption of the cells treated with high pressure CO₂ was very weak,and the disruption ability of high pressure homogenization-assisted high pressure CO₂ was between the two ways.The cells treated with high pressure CO₂ were less stained by PI;almost no cells treated with high pressure homogenization were stained by PI;after high pressure homogenization-assisted high pressure CO₂,the number of cells stained by PI was increased significantly with the increase of treatment time.Combining the bactericidal effect of three kinds of sterilization methods,the sterilization mechanism of high pressure homogenization-assisted high pressure CO₂ technique was obtained: on one hand,the Saccharomyces cerevisiae was killed by high pressure homogeneous mechanical crushing;on the other hand,CO₂ is more easily to enter the intact cells to change the cell physiological state leading to cell death,so its bactericidal ability is much higher than high pressure homogenization sterilization or high pressure CO₂ sterilization.