Forward Osmosis Process For Nonthermal Concentration Of Cloudy Apple Juice

Cloudy apple juice is rich in nutrition and pleasant in flavor,which meets the needs of consumers for natural and healthy food product.Concentration is an important means to improve the quality of liquid food,prolong the shelf life and reduce the transportation cost.Comparing with clear apple juice,cloudy apple juice is rich in polysaccharides and other organic macromolecules,which is difficult to be concentrated by conventional methods.Forward osmosis(FO)is an emerging membrane technology which can be operated at ambient temperature and can avoid the disadvantage of thermal concentration which causes the loss of heat-sensitive components in the juice.Based on FO,this study explored the feasibility of cloudy apple juice concentrate produced by non-thermal FO,with emphasis on the influence of operating conditions on the application of FO in cloudy apple juice concentration and the study of fouling control strategy.The primary contents and results of this dissertation were as follow:The effects of different membrane orientations,different cross flow velocities,different solutes and different concentration of draw solution(DS)on water flux and reverse solute flux(RSF)during FO process were investigated.The orientation of the membrane can significantly affect the concentration polarization of FO process,and the concentration efficiency is higher when the active layer(AL)is toward the FS side.Increasing the crossflow velocity or concentration of DS can promote the water flux,but the RSF also increase.The osmotic pressure varies with different DS solute,and the RSF is closely related to the molecular size of the solute.The cleaning efficiency of water flushing,acid washing and alkali washing on FO membrane fouling were compared.The effect of alkali washing was similar to that of water flushing with high velocity,and both flux recovery rate was about 98%.After 3cycles of concentration-membrane cleaning operation,the flux recovery rate of FO was still above 90%.FO can achieve the required concentration without damaging the quality characteristics of apple cloudy juice.Compared with VE,FO can better retain the original color of cloudy apple juice.VE resulted in the decrease of the antioxidant capacity and the response value of aroma components of cloudy apple juice while FO can effectively preserve the biological active components and aroma substances of cloudy apple juice.Two types of FO membrane,i.e.,cellulose triacetate(CTA)membrane and thin film composite(TFC)polyamide membrane,were selected to concentrate cloudy apple juice,respectively.The effect of membrane characteristics on membrane fouling was investigated by water flux patterns and membrane surface morphology characterization.TFC membrane surface(AL)is more hydrophilic and has higher roughness than CTA membrane.More serious fouling phenomena on the surface of TFC membrane was observed,resulting in severe reduction of water flux.After hydraulic cleaning by water flushing,the flux recovery ratio of CTA membrane was 82.4%,and TFC membrane was 76.2%.The fouling layer is compacter on TFC membrane than CTA membrane.Membrane surface morphology could play a key role affecting the fouling during non-thermal concentration of cloudy apple juice by FO.The present study shows the great potential of FO in liquid food concentration.,investigates the key factors which affect the performance FO process for non-thermal concentration of cloudy apple juice,and further develops membrane fouling control strategy.The study provided a new technical option for the non-thermal concentration of cloudy apple juice,and promote the possible deployment of FO in food processing.