Fouling of membranes always takes place during concentartion or separation of liquid foods and fermentation broths. Membrane fouling not only decreases permeation flux but also sieving characteristics. Moreover, the extent of fouling affects greatly the efficiency of cleaning to be carried out after operation. In this review, we summarize the fouling mechanism and introduce some experimental results related to cleaning as well as fouling of the membrane.

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The membrane emulsification method, a new application technology of membrane properties, is described in relating with preparation characteristics of monodispersed food emulsions. For preparing o/w emulsions, the microporous membrane has to be hydrophilic to wet well with continuous (water) phase, and be hydrophobic for w/o emulsions. Commonly, dispersing phase (water or oil phase) is dispersed directly into continuous phase through a membrane with pressure. The emulsifying rate of this membrane emulsification system could not be high enough for preparing food emulsions, because the membrane had to be kept without wetting with the dispersing phase during emulsification processes. On the contrary, the emulsification rate was improved considerably by dispersing the preliminarily roughly emulsified emulsion as a dispersing liquid via membrane. The mean diameter and diameter distribution of emulsion particles depended on the mean pore size and pore size distribution of the membrane used, and the emulsifying conditions.

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In order to produce highly concentrated fruit juice, a pilot scale membrane system was developed by combining reverse osmosis units with another unit with loose reverse osmosis membrane (nanofiltration membrane). This system could concentrate apple juice up to 46.5% sugar concentration. The efficiency of the system was analyzed with a model derived from concentration polarization equation and membrane transport equation, and validity of the model was demonstrated. Then, based on the model, an industrial-scale process was designed.

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Membrane technologies such as reverse osmosis, ultrafiltration and electrodialysis have widely been applied to the fruit juice processing industries. The outlines of their development, application as well as the needs for technological inovation and the background in the filed of fruit juice processing technology are reviewed in this paper. Scientific and technological problems of application are also discussed.

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Falling in between reverse osmosis (RO) and ultrafiltration (UF), nanofiltration (NF) or loose RO, newly developed, is finding growing applications in the food industry which are reviewed.
It is one of the most important properties of NF membrane that makes some solutes pass through or not rejected. NF membrane rejects uncharged molecules due to size exclusion and charged components due to electrostatic interaction between charged membrane and them. A negative rejection coefficient of a more permeable ion than the same charged ions in a solution by NF can be observed due to the Donnan effect, maintaining electroneutrality. These characteristics of NF have been exploited in the food industry.
Applications of NF are summarized into five groups, as follows : 1) Desalination. 2) Concentration. Higher concentration of fruit juices by NF is established due to less different osmotic pressure across the membrane than RO. In the combination of 1) and 2), NF has been successfully applied into partial desalination and pre-concentration in the whey processing system of the dairy industry. 3) Fractionation due to size exclusion and/or electrostatic interaction has attracted researchers in separation of some oligosaccharides, amino acids and peptides from bio-products. 4) Decolorization. Color materials are easily rejected by NF. The lighter products from permeate of soy sauce or the imitated one have widened the soy sauce application area. 5) Taste modification. It was found that some unfavorable organoleptic materials in reconstituted skim milk are less rejected. The modified taste concentrate of it has been used for a non-fat milk product. A high grade ice cream, developed from NF concentrate of whole milk, gives us better taste due to less ash content of it and non-heat concentration.

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Improved thin-fim composite low pressure type reverse osmosis (RO) menbranes has been developed. The menbranes exhibits high salt and Organic materials rejection and high flux at low operating pressures. Low pressure type menbranes are classified into (1) high rejetion type RO menbranes and (2) loose RO (Nanofiltration) menbranes.
We will review the performance and aplications of resent low pressure type RO menbranes. The ultra-low pressure type RO membrane “ES10”, recently developed, exhibits up to 99.5% NaCl rejection, 95% isopropanol rejection and 30 m³/d (8-inch element) when tested at 0.75Mpa (107psi) and 25°C on 500 ppm solution.

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A phospholipid LB (Langmuir-Blodgett) film was prepared, and its electric potential and impedance were measured in order to evaluate its taste responses when it contacted several taste solutions. The results of impedance measurement showed that the resistance of the LB film increases by application of bitter substances, while only small changes were observed for the other taste qualities such as saltiness, sourness and umami. The changes in impedance of the membrane have no correlation with those in the membrane potential. The results may suggest that the impedance measurement is effective for detection of bitter substances, and also provide the important clue to the microscopic reception mechanism of “bitterness”.

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Microporous Neosepta membranes with relative porosity 56-62% and volume concentration of ionogenic groups (trimethylbenzyl-ammonium and sulfonic acid, 0.012-0.082 meq/ml) were used in the dialysis desalination of protein solution which contained immunoglobulin specific to horse-radish peroxidase. It was found that, if the pressure in the diffusate compartment lower than that in the dialysate compartment, the transition from the diffusion transport mechanism to the convection mechanism brought about not only the concentrating of the dialysate, but also the redistribution of proteins between the membranes and solutions. Up to 45-49% of Igs and 5-35% of accompanying proteins accumulated in the membrane phase, while their amount in the diffusate was 1-3% and 25-30%, respectively.

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Conventional RO element of spiral-wound type has no heat resistance. so application of this RO element is limited such as for food processing which does not require hot water sterilization.
New RO element can be poerated under the hot water sterilization (90°C) or high temperature and pressure opetation (60°C, 5 MPa) by modifing heat resistance.

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