| Under the background of present applied technology for juice processing and under the target to develop concentrated juice with high nutritional quality by industrialization of membrane clarification, separation and concentration, the experiments of pilot-scaled ultrafiltration for clarification, reverse osmosis for preconcentration, membrane distillation for concentration,osmotic distillation for concentration are respectively carried out for different kinds of juice. Main results achieved in this research as follows:UF process was carried out using a single tubular PVDF membrane system (Koch C(?)r.).The experiments mainly investigated effects of operative conditions in terms of pressure, temperature, feed flow rate, volume concentration ratio (VCR) on the permeate flux; and the rentention of nutrient in UF juice was determined. The results showed the permeateflux could be increased by increasing the transmembrane pressure or the axial flow rate. At fixed feed velocity, the permeate flux increased initially with TMP and leveled above 85 KPa. At fixed TMPs, flux increased with high feed velocity. The results showed that flux decreased with operating times as by increasing the VCR, due to gel formation. The permeate flux of carrot juice through the same UF membrane was higher than those of kiwifruit juice and orange juice, since the latter have suspended more solids and viscosity. The optimum conditions for the clarification of blood orange juice were feed flow rate 800 l/h and transmembrane pressure 0.85 bar at 20℃, The optimum conditions for the clarification of carrot juice and kiwifruits juice were the same (T = 25.0 ℃; TMP = 85 kPa, Qf = 800 L/h). Suspended solids, including cloud and pectin were removed from juice, juice serum had a clear amber color with no measurable turbidity. The recovered soluble solids and organic acid were almost 100% in all permeate juices, while UF led to degradation of Hydroxycinnamic, anthocyanins, ascorbic acid and flavonoids with losses of 10%, 15%, 15%, and 10%, respectively. In comparison with fresh juice, the UF retentate showed 2.5% reduction of the TAA, 8% reduction of the TAA was observed in the concentrated juice, while pasteurization led to 23% reduction of the TAA.Reverse osmosis trials were carried out in a pilot scale equipment, using Composite polyamide membrane with 99% NaCl rejection at low temperature(20℃). A clarified carrot juice at around 6.3g kg-1 of total soluble solids were pre-concentrated to 13.6 g kg-1, the average evaporating flux obtained was 8.0L h-1m-2 at 2.5MPa transmembrane pressures while clarified blood orange juice at around 12.4g kg-1 of total soluble solids were preconcentrated to 21.4 g kg-1, with permeate fluxes 5.1L h-1m-2 at 3.5Mpa transmembrane pressures. The results indicated that the permeate flux was mainly depended on the transmembrane pressures, and it decreased with the increase of juiceconcentration due to membrane fouling and concentration polarization. Membrane distillation trials were carried out using flat and plate PVDF membrane to inspect the effects of operating conditions on the permeate flux and feasibility of concentrating juice. The results indicated that fluxes are higher in the membrane distillation than in the reverse osmosis, at high concentrating ratio. Because of this main advantage, membrane distillation has a great potential to concentrating fruit juices. Regarding process of membrane distillation, the flux gradually increases with an increase of feed juice temperature for each flow rate at a constant inlet temperature of cooling water (20V) and increase with a decrease of the cooling water. Lower temperature differences led to lower flux, while the increase of flow rate and UF pretreatment of orange juice could improve the permeate flux. It is observed that PVDF membrane used in the experiment has very good rejection and retention of orange juice compounds such as soluble solids; sugars ang organic acids, but vitamin C decreased by 42.1%.The potential and suitability of OD for concentrating citrus, kiwifruit and carrot juice after UF pretreatment has been studied. OD membrane contactors were operated with a slightly higher pressure on the shell (feed) side of the module than the lumen (strip) side, so that the pressure difference across the membrane at all points in the contactor is greater on the shell side for avoiding the leakage of the brine strip into the product and not vice versa. The study indicated that the use of UF for pulp and suspended solids removal prior to the OD process provided an equivalent operating characteristics, and an increase of the permeate flux in OD process could be obtained from UF pretreatment of the juice. The clarified juices were concentrated to above 60°Brix, using a Liqui-Cel membrane contactor with 1.4 m2 of membrane areas. The results showed that the permeate flux decreased gradually with a decrease of osmotic agent concentration and an increase of juice concentration, since the vapor pressure difference between feed juice and osmotic agent (CaCl2) decreased. It was observed that OD flux decay was more attributable to the reduction of the stripper concentration at a low TSS of the feed juice, while it mainly depends on viscous polarization (juice viscosity) when juice concentration values reached higher than 40 °Brix, because of the sharp increase of the juice viscosity, in compared with RO process, the rather low permeate flux was obtained in OD process, but it only slightly decreased over that concentration range.The stability of the antioxidant activity (TM) during juice processing is of interest since they play an important role in reducing the risk of free radical related oxidative damage associated with a number of diseases. Changes in ascorbic acid, phenolics and total antioxidant activity during membrane processing of blood orange juice were evaluated. The results showed that the content of these antioxidant compounds besides anthocyanins and ascorbic acid remains almost the same as...
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