Research On Lethal And Sublethal Effects Of Pulsed Electric Field Treatments On Saccharomyces Cerevisiae In Chinese Rice Wine

Pulsed electric field (PEF) technology is a new non-thermal processing technology with the advantages of low-temperature processing, food quality retaining, and energy saving. Rice wine is a kind of wine with rich nutrition and mellow taste. Zhejiang Shaoxing yellow rice wine is the oldest and most representative of yellow rice wine products. The purpose of our research was to investigate the lethal and sublethal effects of pulsed electric field treatments applied to Saccharomyces cerevisiae suspended in rice wine (Zhejiang Shaoxing). Moreover, we aimed to detect the structural changes of Saccharomyces cerevisiae by the observation of the scanning electron microscope and atomic force microscopy.The main contents and results of this research were as follows:(1) According to the growth of microorganisms on selective and nonselective medium, the inactivation effect induced by PEF treatments increased with the increasing of treatment intensity. For example, the inactivation rate increased by 1.3 log CFU/mL with the electric field strength increased from 6 kV/cm to 15 kV/cm and the maximum percentage of cells sublethal injured was 12.51%. The inactivation rate increased by 0.7 log CFU/mL with the treatment time increased from 90μs to 180μs, the maximum percentage of cells sublethal injured was 9.25%. Compared with cells untreated, Saccharomyces cerevisiae cells treated by PEF was influenced by the storage time significantly. The inactivation rate was increased by 0.5 log CFU/mL with the longest storage time of 210 min. According to the results obtained from all treatments, the percentage of cells sublethal injured was less than 15%.(2) The permeability of cell membrane was decreased by PEF treatment. The inactivation effects of PEF treatments showed the same trend according to the results obtained from the measurement of flow cytometry. Similarly, the bactericidal effects of PEF treatment increased with the increasing of treatment intensity. The proportion of sub-lethal damage cells was in the range of 7% to 12%.(3) According to the two/three-dimensional diagram of cells treated by PEF collected using atomic force microscope, it can be found that the yeast cells treated by PEF of a considered strength became smaller and the height decreased. According to the observation of Saccharomyces cerevisiae structure by scanning electron microscope, concave shape of the cells treated by PEF were observed. In addition, a certain proportion of the cells were sunken, wrinkled or became fragmented after PEF treatments.