Ultrafiltration, fruit juice

The removal of macromolecules by ultrafiltration has often been used in the production of clear fruit juices and wine (Girard and Fukumoto, 2000). This treatment removes both proteins and polysaccharides. Ultrafiltration through a 10,000 Da cut-off membrane has been shown to stabilize wines against haze formation (Flores, 1990). 

Figure 6.24 Ultrafiltration flux in apple juice clarification as a function of the volumetric feed-to-residue concentration factor. Tubular polysulfone membranes at 55 °C [27]. Reprinted from R.G. Blanck and W. Eykamp, Fruit Juice Ultrafiltration, in Recent Advances in Separation Techniques-III, N.N. Li (ed.), AIChE Symposium Series Number 250, 82 (1986). Reproduced by permission of the American Institute of Chemical Engineers. Copyright 1986 AIChE. All rights reserved...

Microfiltration, ultrafiltration, and nanofiltration are becoming standard in feed pretreatment for water desalination, wastewater treatment and fruit-juice concentration. 

A new process uses ultrafiltration to clarify fruit juices (see below). The advantage of this method is that flocculation and fining aids are no longer necessary which results in cost savings. To optimise the throughput it is however recommended to treat the juice enzymatically in order to reduce its viscosity. Properly applied, this process can work very economically. 

The concept of producing clarified fruit juice by a single pass of enzyme-treated fruit puree through a tubular, metallic ultrafiltration membrane system was recently described by Thomas et al. (5, 6). The process is known commercially as the Ultrapress process, since pressing and ultrafiltration are accomplished simultaneously (7). The metallic membrane ultrafiltration system is composed of sintered stainless steel tubes of varying diameters with membranes formed-in-place within the porous matrix of the tubes by deposition of various metallic oxides. Metallic oxides in combination with polymers are also possible. 

The concept of coupling reaction with membrane separation has been applied to biological processes since the seventies. Membrane bioreactors (MBR) have been extensively studied, and today many are in industrial use worldwide. MBR development was a natural outcome of the extensive utilization membranes had found in the food and pharmaceutical industries. The dairy industry, in particular, has been a pioneer in the use of microfiltra-tion (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) membranes. Applications include the processing of various natural fluids (milk, blood, fruit juices, etc.), the concentration of proteins from milk, and the separation of whey fractions, including lactose, proteins, minerals, and fats. These processes are typically performed at low temperature and pressure conditions making use of commercial membranes. 

Scheme of an integrated membrane process for the production of concentrated fruit juices. UF = ultrafiltration RO = reverse osmosis OD = osmotic distillation. 

Commercial pectinase Hollow-fiber ultrafiltration unit BMR Fruit juice processing 34... 

Ultrafiltration is used in many different processes at the present time. Some of these are separation of oil-water emulsions, concentration of latex particles, processing of blood and plasma, fractionation or separation of proteins, recovery of whey proteins in cheese manufacturing, removal of bacteria and other particles to sterilize wine, and clarification of fruit juices. 

In Section 9.1, Figure 9.1, we have seen that adjacent to a charged surface there is an excess of counterions and a deficit of co-ions. Both contribute to the neutralization of the surface charge. Let us now focus on the expulsion of the co-ions. The expulsion of co-ions implies a reduced volume available for electrolyte, or, in other words, there is an excluded volume with respect to the presence of electrolyte. This is known as the Donnan effect. For the same reason salt (= electrolyte) cannot penetrate in narrow capillaries and pores having charged walls. Based on this phenomenon, porous membranes that are permeable for water but not for salt may be used in reversed osmosis (also called ultrafiltration). Practical applications of reversed osmosis are found in, for example, the production of potable water from seawater, in hemodialysis using artificial kidneys, and in the concentration of solutions such as fruit juices. 

The amounts of pesticides passing from raw materials into fruit juices depend on the distribution of residues between the solid (skin or flesh) and liquid fruit portions. Moderately to highly lipophilic pesticides, such as parathion, captan, folpet or synthetic pyrethroids, usually pass to the raw juices only to a very limited extent. A further decrease of their contents may occur during operations such as clarification or ultrafiltration. The risk of infiltration of residues into the human food chain, however, exists when the solid waste with higher concentrations of pesticides is used as an animal feed. 

UF, Ultrafiltration 50-1000 A Separation of small molecules (inorganic compoimds, sugars, amino acids, small proteins) from macromolecules treatment of process water and whey clarification of fruit juices flood filtration in the kidney... 

Fruit juice processing is a major use for membrane filters, particularly for clarification (using microfiltration or ultrafiltration), concentration (using reverse osmosis) and deacidification (using electrodialysis). The clarification of apple juice by ultrafiltration is now an important process, whether making clear juice or natural (i.e. cloudy) ones. 

Rai R, Majumdar G. C., Das Gupta S., De S., Modeling the performance of batch ultrafiltration of synthetic fruit juice and mosambi juice using artificial neural network,/owmaZ of Food Engineering, 2005,71(3), 273-281. 

Apple, pear, orange and grape juices are all clarified by ultrafiltration. Ultrafiltration of apple juice is a particularly successful application. Approximately 200 plants have been installed, and almost all US apple juice is clarified by this method. In the traditional process, crude filtration was performed directly after crushing the fruit. Pectinase was added to hydrolyze pectin, which reduced the viscosity of the juice before it was passed through a series of decantation and... 

Process for the extraction of sugars from plants and fruits thereof, especially sugars from sugar beet and sugar cane, and inulin from topinambur, and the elimination of nonsugar matter from this extraction juice by means of ion exchangers or ultrafiltration... 

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