The Killing Method Of Osmotolerant Yeast From Concentrated Apple Juice By Radio Freguency

China is the world's largest producer of concentrated apple juice,Chinese concentrated apple juice exports accounted for more than half of the world trade volume.The security of concentrated apple juice makes great concern of the international community.At present,Chinese concentrated apple juice exported to Europe often lead to trade disputes and quality issues due to osmotolerant yeasts contamination.Looking for a safe and efficient method to kill the osmotolerant yeasts in concentrated apple juice become the urgently solved key technical problems for industry.This article used Z.rouxii as model microorganism,which make great threat to concentrated apple juice,studied the influence of different factors on Z.rouxii killing under the RF heating treatment,systematically discussed the killing effect of RF and water bath,and compared the influence of juice quality,this study also achieved the best sterilization process and sterilization dynamics model,made a preliminary study to sterilization mechanism.The research provides a theoretical basis for further study on the RF heating sterilization and its application in killing osmotolerant yeasts in concentrated apple juice in industry.The main research results are as follows:(1)The temperature rising curve is liner when apple juice was heated by RF,and the heating temperature is more evenly distributed during RF heating.Meanwhile,the polar plates'spacing,juice volume and juice concentration can significant impact the speed of temperature rising speed.(2)The RF heating time,polar plates' spacing,juice volume and juice concentration can significant impact the sterilization effect(P<0.01).The optimized parameters were determined by response surface experiment and they were as follows:polar plates'spacing of 110 mm,juice volume of 45 mL and heating time of 70 s.Under this optimal condition,at least a reduction of logarithm value of 6 for viable count of Z.rouxii could be achieved.(3)RF sterilization kinetics is "S" shape,and it conform to Log-Logistic model.The changes of polar plates' spacing,juice concentration and model microorganism can not influence the sterilization kinetics model.(4)A reduction of logarithm value of 6 for viable count of Z.rouxii could be achieved after 70,120 and 110s RF heating for juice concentration of 70,40 and 11.5 °Brix,respectively.However,water bath would cost at least 300s to achieve the same sterilizing effect.Therefore,the RF heating can faster sterilize the Z.rouxii in apple juice than traditional water bath,and furthermore,its impacts on the quality and flavor of apple juice were less than water bath treatment.(5)RF heating can not cause the Z.rouxii cell surface rupture and the contents leakage,the main cause of death is its thermal effect to proteins,enzymes,nucleic acids and other substances degeneration to loss vitality.Therefore,even if the non-thermal effects of RF sterilization is presence it must also be very weak.