Pasteurisation Of Escherichia Coli Suspension And Pineapple Juice Using Radio Frequency Heating

Pasteurisation technology is one of the important technologies of food engineering. It is often the key process to decide food safety, nutrition and flavor quality. Thus, pasteurisation technology is closely related to the human health, utilization efficiency of food resources and commercial value of product. Radio frequency(RF) is a new type of pasteurisation method with the characteristics of deep heating penetration, good heating uniformity and high heating speed. In recent years, RF pasteurisation has become a hot research topic at home and abroad,studies on RF pasteurisation gradually increased.Escherichia coli was selected as the research object in this paper, which was a common and typical harmful microorganism in food. First, E.coli suspension was made by the sodium chloride solution of different conductivity to study the factors that could affect RF pasteurisation, pasteurisation kinetics of RF heating was also studied. Thereby changing the suspension system, E.coli was inoculated into fresh pineapple juice, and then experiment researched the pasteurisation function and kinetics of juice by RF heating. The results were as follows:(1) Heating uniformity of E. coli suspension and pineapple juice in centrifuge tube by RF treating was better. It can be observed by a plan view and side view of temperature distribution, more uniform temperature distribution in the radial and height direction, near the edge of the container temperature lost due to radiating.(2) Heating curve of E.coli suspension and pineapple juice showed a linear trend.Electrode gap, conductivity, height, pH value significantly affect the heating and pasteurisation rate by RF heating. Heating up fast and bactericidal effect for electrode gap115 mm, heating rate and pasteurisation rate were gradually reduced with the electrode gap increasing. Effect of conductivity on heating and pasteurisation rate was first increased and then reduced, heating and pasteurisation rate were the fastest and best for conductivity close0.1S/m. Heating rate and pasteurisation rate were increased with the height increasing. Low pH value could significantly enhance E.coli bactericidal effect by the same time.(3) The inactivation curve of E. coli suspension and pineapple juice was reverse "S" type,which was not comply with the Linear kinetics. Weibull model, Log-Logistics Model and Dose-Response model could all fit the inactivation curve well. The fitness of the three models were evaluated by using a series of indices including Accuracy Factor(Af), Bias Factor(Bf),Root Mean Square Error(RMSE) and the correlation coefficient(R2). Log-logistic model provided the best fitness.(4) Dielectric constant and dielectric loss factor of pineapple juice decreased with increasing frequency at a fixed temperature. However, different trends at fixed frequency, the dielectric constant decreased with increasing temperature, loss factor increased with increasing temperature.(5) Physicochemical properties and color of pineapple juice were studied, based on achievement completely pasteurisation by RF treatment and heat treatment separately. The results showed that soluble solids content, pH, total acidity, conductivity had no significant change in both RF treatment and heat treatment(P>0.05), for Vc content and color, RF treatment was better than the heat treatment.