Process Optimization And Applied Basic Research Of Forward Osmosis System Based On Fruit Juice Concentration

To increase juice shelf life and save juice storage and transportation costs,the commercial juices are generally concentrated from raw products.Nowadays,the multistage vacuum evaporation technology is most commonly used for juice concentration,but the concentration process often causes severe nutrition loss.Forward osmosis(FO)has been widely used for juice concentration with lots of advantages,such as potential high concentration products,low operation pressure and temperature.However,the absence of suitable draw solutions,severe internal concentration polarization(ICP)and membrane fouling are significant obstacles to hinder the practical applications of FO.Therefore,in this work,a series of food preservatives were systematically investigated as draw solutes in the FO system.The direct contact ultrasonic-assisted FO system also was developed to enhance the efficiency of juice concentration.The key research contents and results of this work are as follows:(1)Exploration of food preservatives as draw solutes in the FO process for juice concentrationThe lack of suitable draw solutes is a significant obstacle hindering the practical application of FO for juice concentration.In this work,a series of food preservatives were systematically investigated as draw solutes in the FO system.By careful evaluation of these preservatives,we selected 4 M sodium diacetate(SDA)as one model of draw solution to concentrate grape juice in a 72-h continuous FO test.The concentrated grape juice with 5.14 folds was obtained with no loss of the titratable acidity and the vitamin C content.Moreover,the SDA accumulation in the concentrated product was only 2.0±0.1 g/kg,which was below the safety limit(0.5 g/kg,the Food and Agriculture Organization(FAO))after proportional dilution.Our findings demonstrate the application potential of the food preservative draw solutions for juice concentration in the FO.(2)Construction of direct contact ultrasonic-assisted FO system for fruit juice concentrationThe performance of FO process for juice concentration is severely hindered by the ICP and membrane fouling.In this study,a direct contact ultrasonic-assisted FO system was developed to alleviate ICP and membrane fouling.The effects of key parameters on the performance of this FO system were studied,including the continuous versus pulsed ultrasonic operation mode,ultrasonic frequency and power,and membrane orientation.The application of ultrasound at the optimal parameters(40 k Hz,60 W,1min on/1 min off)significantly reduced the ICP of the FO membrane and increased its water flux by 20% during juice concentration.In addition,the direct contact ultrasonicassisted FO system could mitigate the water flux decline of the FO membrane and the foulants accumulation on the membrane surface.Therefore,the direct contact ultrasonic-assisted FO system has a promising prospect for juice concentration.In conclusion,we have developed an efficient FO system for juice concentration by screening the food preservative draw solutions and optimizing the operating parameters of the direct contact ultrasonic-assisted FO set-up,which can effectively increase the water flux of the FO membrane and the juice concentration efficiency.This work provides some insights for the development of FO system for juice concentration.