Study On Concentration And Non-thermal Sterilization Of Fingered Citron Juice

Fingered citron juice?FCJ?is nutritious with a lemon flavor and refreshing taste.After concentration of the FCJ,the volume of the FCJ decreased,as well as the costs of storage and transportation.As a result,harmful microorganisms in FCJ can be inhibited.Moreover,the shelf life of FCJ can be prolonged.Traditional methods of concentration and sterilization for fruit juice cause loss of volatile components and functional components thus leading the deterioration of quality.To solve these problems,four different methods of the concentration of FCJ were investigated,rheological properties of concentrated fingered citron juice were examined,the conditions of ultra-high pressure sterilization were optimized,the effects of ultra-high pressure sterilization and heat sterilization on the quality of concentrated fingered citron juice were compared and the shelf-life of the concentrated fingered citron juice were predicted.Critical parameters for the production of high quality concentrated fingered citron juice were provided.The main contents were as follows:1.Four methods including vacuum concentration,membrane concentration,freeze concentration and freeze-thaw concentration were used to concentrate FCJ.The concentration time,concentration efficiency and the retention rate of volatile components of these methods were compared.The results showed that both vacuum concentration and freeze-thaw concentration could reach the concentration requirements of fruit and vegetable concentrates in national standards and their concentration multiples were 7.78 and 6.78 respectively.Comparing with the results of vacuum concentration,freeze-thaw concentration could reserve volatile components of fingered citron juice more completely although the concentration efficiency of which is lower.Freeze-thaw concentration was found to be an ideal method for the production of concentrated fingered citron juice.2.The rheological properties of concentrated fingered citron juice prepared by freeze-thaw concentration were investigated.The differences in shear stress with shear rate,the influence of temperature and concentration effect on viscosity were evaluated.The results showed that the concentrated fingered citron juice belonged to Newtonian fluid.The variation of shear stress with shear rate could be fitted as a straight line after equation fitting.The combined effects of temperature and concentration on viscosity could be quantitatively characterized using the following formula:?=0.0003e^0.01Cexp(3060.5e^0.02C/RT),which provided theoretical basis for product control and equipment selection in the production of concentrated fingered citron juice.3.The conditions of ultra-high pressure sterilization were optimized through stress fatality curve of colony forming units and comparison of physicochemical indicators.Firstly,the effects of pressure and time on the indicators of colony forming units,coliforms,molds and yeasts were investigated respectively.Secondly,the residual curves of colony forming units under different pressures and time were fitted by linear equation.The test conditions were obtained to test the sterilization effect of ultra-high pressure sterilization.In the end,the condition of ultra-high pressure sterilization on concentrated fingered citron juice was optimized by comparing microbiological indicators and the retention rate of vitamin C.The results showed that the condition of ultra-high pressure sterilization which could achieve the microbiological indicators for beverages with a highest retention rate of vitamin C of 92%was 400 MPa,11 minutes.4.The sterilization effects and the implication on the quality of concentrated fingered citron juice of ultra-high pressure sterilization and pasteurization were compared.The results showed that both the ultra-high pressure sterilized and pasteurized concentrated juice can reach the requirements of microbiological indicators,while the ultra-high pressure sterilization could protect the flavor and color of the concentrated fingered citron juice.5.The main physicochemical indicators and sensory scores were used to evaluate the quality of concentrated fingered citron juice sterilized by ultra-high pressure during the storage time of 90 days.The accelerated shelf life experiment was selected to predict the shelf life of the concentrated fingered citron juice.The results showed that the quality of concentrated fingered citron juice gradually decreased during the storage time of 90 days.The shelf life was predicted to be 146¹52 days at storage temperature of 20?.