【作者】 苏学素；

【导师】 陈宗道；

【作者基本信息】 西南农业大学 ， 农产品加工与贮藏工程， 2005， 博士

【摘要】 本文以血橙汁、猕猴桃汁、胡萝卜汁为原料,利用现代膜分离技术(超滤、反渗透、膜蒸馏、渗透蒸馏)对上述果蔬汁进行了澄清和浓缩实验研究,分析了不同操作条件对膜渗透通量的影响,探讨了膜清洗再生方法,并考察了不同膜过程对果蔬汁营养成分和总抗氧化能力的影响;以膜基提取(membrane-based extraction)方法为基础,首次采用手性冠醚为手性选择剂,对蛋氨酸外消旋体混合物进行拆分,主要结果如下: (1)聚偏氟乙烯膜(PVDF)对血橙汁澄清效果良好,对糖、酸截留较低,吸光率小于4%,管式组件抗污染能力强,适用于固形物含量高、粘度大的柑桔汁种类;按照总循环模式对跨膜压力、轴向流速和温度对膜透过速率的影响进行了实验研究。结果发现,透过速率随跨膜压力或轴向流速的增加而增加,在进料流速一定时,透过速率开始随跨膜压力增大而增加到85kPa到一个极限值临界压力TMPlim,在固定跨膜压力的情况下,透过速率随进料流速的增加而增大。由于凝胶层的形成,透过速率随时间的延长,体积浓缩比的增加而减小。相同条件下PVDF膜澄清胡萝卜汁的渗透速率大于血橙汁和猕猴桃汁。以批次浓缩方式澄清血橙汁的最佳操作参数为压强=85kPa,温度=20℃,进料速率=800 L/h。澄清胡萝卜汁最佳操作参数为压强=85kPa,温度=25℃,进料速率=800 L/h。澄清猕猴桃汁最佳操作参数为压强=85kPa,温度=25℃,进料速率=800 L/h。超滤膜在保留血橙汁抗氧化成分方面,对维生素C和花青素类成分的保存率约为85%左右,对几种酚酸及类黄酮组分(除槲皮素外)的保存率均在90%以上。同未杀菌的血橙原汁相比,巴氏杀菌汁的TAA损失率为23%,而超滤澄清汁仅为10%左右,主要与维生素C和花青素损失有关。 (2)反渗透浓缩血橙澄清汁的适宜条件为T=20°C,TMP=3.5MPa,血橙澄清汁从12.4°Brix浓缩到浓度为21.4°Brix后,平均渗透通量为5.0L/m~2.h。反渗透浓缩胡萝卜澄清汁的适宜条件为T=20°C;TMP=2.5MPa。胡萝卜澄清汁从6.3°Brix浓缩到浓度为13.6°Brix,平均渗透通量为8.0L/m~2.h后,其浓缩果汁色泽和风味均保持良好,因此可用反渗透法预浓缩果汁,先除去大部份水,然后再用膜蒸馏或渗透蒸馏法进一步浓缩到60°Brix以上。污染膜经自来水冲洗30min,再在40℃和跨膜压力0.5 MPa的条件下,用0.1%NaOH循环清洗60min,清水冲洗后膜通量基本得到恢复。 (3)采用平板疏水性PVDF微孔膜,对膜蒸馏法浓缩甜橙汁的可行性及工艺过程特性进行了研究。结果表明,该法浓缩橙汁是可行的,尤其在浓缩倍数高的情况下,膜通量透速率显著高于反渗透过程。从过程机理来看,膜通量随膜两侧温度差的增大呈指数规律上升;在温度差相同的情况下,膜通量随热侧温度的升高呈线性规律上升。此外,提高热侧果汁和冷水侧的进料速率,可提高物料剪切力,使传质系数增大,增大膜通量;而随着果汁浓缩度的提高,膜通量下降。导致膜通量下降的主要原因是果汁粘度增大和蒸汽压下降。超滤处理果汁能增大膜蒸馏通量,这可能是超滤降低或除去了果胶等物质,因而降低果汁粘度(原汁相对粘度为1.92,更多还原

【Abstract】 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更多还原