Inactivation Mechanism Of Temperature-pressure Synergistic Treatment On Hanseniaspora Opuntiae

The growth and reproduction of yeasts are two major factors contributing to the microbial spoilage of berry products.However,yeasts are generally capable of a relatively strong resistance to the environment due to the protective effect of the cell wall,which means they are elusive to be completely killed by the conventional sterilization method.In recent years,although the emerging ultra-high pressure sterilization technology has a good ability to kill yeasts,the sterilization effect cannot meet the demand of industrial production when it comes to the high sugar solution with high viscosity.On the other hand,the escalating processing pressure and holding time not only pose damaging threaten on the equipment,but also increase the energy consumption,which is not conducive to the development of industrialization.Therefore,this thesis initially focused on inactivating the Hanseniaspora opuntiae by the method of co-treatment of temperature and pressure and selected the best process parameters of sterilization.In addition,this research mainly probed into the mechanism concerning inactivation of the yeast associated with co-treatment from multiple perspectives.The main results were as follows:(1)The optimal growth temperature of Hanseniaspora opuntiae was 28 ?,and there was no significant effect of high temperature treatments on its the pressure sensitivity.The yeast in the suspension could be completely lethal(lethal rate>61g)under the best sterilization condition(300MPa/300s+55 ?/120s).(2)The permeability of the cell membrane of Hanseniaspora opuntiae saw an increase trend as the treatment temperature was rising,whereas it significantly increased more after the ultra-high pressure treatment,which may cause the rupture or perforation and eventually the death of the bacteria.Both treatments were able to substantially enhance the permeability of the cell membrane,meanwhile leading to a large amount of leakage of nucleic acids and proteins existing in the cells.Furthermore,through the electron microscopy,it showed that high temperature could disintegrate the organelles of the bacteria and ultra-high pressure had a strong ability to destroy the cells in terms of the structure of membrane and the leakage of intracellular substances.(3)Compared with the high pressure treatment,the high temperature treatment had a more significant effect on reducing the activity of intracellular ATPase in C.Hanseniaspora opuntiae.Additionally,the different types and contents of secondary structure of proteins demonstrated various changes subjected to different treatments.Specifically,ultra-high pressure treatment could more effectively and significantly destroyed the bacterial DNA;With regard to the mitochondrial membrane potential,temperature treatment had no significant effect,while the ultra-high pressure treatment contributed to an obvious decline.(4)The expressions of different genes in Hanseniaspora opuntiae after each treatment were analyzed by the RNA-Seq technique.Overall,the gene expression adjusted upwards and downwards to different extent in response to environmental changes,where the most changeable expression was related to cell membranes.More importantly,the meiosis and the autophagy of Hanseniaspora opuntiae were heavily affected by both treatments.