Study On Apple Pectin Extraction And Auxiliary Extraction Equipment Based On Radio Frequency Field

As the second largest fruit in production,apple plays a important role in agricultural trade and processing.Apple peel pomace(AP),a by-product in apple juice processing,is rich in pectin.As a high-value compound,pectin is widely used in food,chemical,pharmaceutical and other industries.AP is the second largest commercial pectin source after citrus peel.Acidic hot water is commonly used to extract pectin in industry,however it leads to high energy consumption,pectin degradation and environmental pollution.The quality and yield of pectin are directly related to its extraction methods.As an efficient process strengthening technology,radio frequency heating is a potential technology for extracting pectin.In this study,apple pomace was used as material for radio frequency assisted extraction conducted on 2.4 k W 27.12 MHz 50 Ω RF heating system.The main research contents and results are as follows:(1)The study of dielectric properties with apple pectin extraction system.The effects of frequency,temperature,liquid-solid ratio(LSR)and p H on the dielectric properties with apple pectin extraction system were studied.With increasing frequency of electromagnetic wave,the dielectric constants with the extraction system gradually decreasd,and the loss factor first decreased and then increased.With increasing temperature,the dielectric constants of the extraction system gradually decreased and the loss factors increased at 27 MHz.Both of dielectric constants and loss factors decreased at 2450 MHz.When frequency was at 27 MHz,the dielectric constants and loss factors of extraction system increased with the increasing LSR at lower levels of solvent p H,and the dielectric constants and the loss factors decreased with the increasing LSR at high levels of solvent p H.When frequency was at 2450 MHz,the dielectric constants increased and the loss factors decreased with the increasing LSR.The dielectric constants and loss factors of extraction system decreased with the increasing solvent p H.The empirical models of dielectric properties related to temperature,p H and LSR with apple pectin extraction system were established,and the penetration depth of electromagnetic wave energy was calculated for apple pectin extraction system at 27 and 2450 MHz.The results showed that the penetration depth of RF energy was significantly greater than that of microwave under the same extraction system.(2)Process optimization of radio frequency assisted extraction(RFAE)with apple pectin.With pectin yield(PY)used as the response value,a single factor test was designed to obtain the optimal level of LSR.Extraction temperature,holding time and solvent p H were selected as the test factors,and response surface(BBD)with three factors and three levels was designed to obtain the optimal process conditions of apple pectin with RFAE.The pectin extraction kinetics with RFAE,microwave assisted extraction and conventional extraction were studied under same conditions The results showed that the optimal level of LSR was 25 m L/g,and optimal conditions of apple pectin with RFAE were 88 °C of extraction temperature,19 min of holding time and 2.2 of solvent p H.Predicted and verified PY was 11.70% and 11.01 ± 0.35% respectly under same conditions.Both were close,which indicated that the regression model could predict the PY well.The PY with RFAE was similar to that of microwave assisted extraction,but both were significantly higher than that of conventional extraction.(3)The quality study of apple pectin.Under same conditions(the same extraction temperature,holding time and solvent p H),The physicochemical properties and structural characteristics of pectin with RFAE were studied,including esterification degree,galacturonic acid content,total phenol content,antioxidant activity,color values,thermal properties,FTIR,XRD,NMR and SEM.The results showed that different extraction methods had no effects on the structural characteristics of apple pectin,but apple pectin with RFAE was superior to microwave assisted extraction and conventional extraction in esterification degree,galacturonic acid content,ABTS scavenging ability,color values,thermal stability and other physical and chemical properties.Therefore,compared with microwave assisted extraction and conventional extraction,the quality of apple pectin with RFAE was better under same extraction conditions.(4)The design of auxiliary extraction equipment with apple pectin.Based on the27.12 MHz 50 Ω parallel polar plate radio frequency heating system,a experimental auxiliary extraction equipment was designed.The overall design schemes of the equipment were first determined,and the continuous flow extraction scheme was selected.The equipment was mainly composed of peristaltic pump,liquid storage vessel,liquid collection vessel,conveying pipeline and extraction vessel.The working principle of the equipment was explained.Then the main components were designed.BT100 S peristaltic pump was selected.The inner diameter of pump tube was 3.2 mm.COMSOL Multiphysics 5.6software was used to simulate and optimize the parameters of the extraction container.The optimized container parameters were as follows: the fluid inlet and outlet were located on the same side of the extraction container,the inner diameter of the container was 40 mm,and the depth of the container was 100 mm.The test was completed after the assembly of the equipment was completed,.The test results showed that the equipment could be used for RF continuous extraction pectin from AP.