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Continuous coagulation whey

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Figure 2. Flow scheme for the APV-SiroCurd process. (Reproduced with permission from Reference [18].

So far, the use of ultrafiltration for the production of semihard and hard cheeses is limited. Cheddar cheese, however, can be successfully made commercially from UF retentates by a process (APV-SiroCurd) developed in Australia [18]. In this process, the standardized and pasteurized milk is ultrafiltrated and diafiltrated giving a reteníate having the required solids, lactose and salt balance. Part of the reteníate is pasteurized and inoculated, mixed with the bulk retentate and rennet and coagulated [19], There is a certain whey drainage, which is not the case when fresh and soft cheeses are produced. A flow scheme for the cheddar cheese process is shown in Figure 2. The first commercial plant was commissioned in Australia in 1986, a second was installed in the USA in late 80'ies.

In many cases, traditional process technology must be modified when UF concentrates are used instead of milk. It is, for instance, very important to carefully adjust the mineral balance in order to obtain the correct rheological properties and taste in the final product. Ultrafiltration at the normal pH of milk often results in too high a calcium content in the final product, giving off-flavours and undesirable rheological properties.

3.1.5. Cheese brines

Another application of microfiltration is the removal of micro-organisms and fines from cheese brines. It has been shown that pathogenic bacteria such as Listeria are able to survive in cheese brine and that Staphylococcus sp. are able to grow even in a brine with a salt content up to 20% [20], Various methods of brine purification are used, the most common one being pasteurization, addition of NaOCl and kieselguhr treatment. Microfiltration is an interesting technique in this context since with this technique the bacterial content is reduced without changing the chemical composition of the brine. It has been shown that momentary heating of brine to 40-50 °C, immediately before the membrane filtration, causes precipitation of calcium phosphate complexes on the membrane as the solubility of these complexes decreases with increasing temperature [15]. This precipitation will cause heavy fouling of the membrane and will lead to a rapid and serious flux drop, more than cancelling out the improvement in flux due to the temperature. Thus, use of a filtration temperature close to the natural brine temperature is recommended. A temperature of 20 °C will minimize the need for cooling and change the mineral balance of the brine as little as possible during the filtration process [21],

3.1.6. Nanofiltration of whey

Lately, membranes with selectivity in the intermediate RO/UF cut-off range have been made available. Using this new class of modified, thin-film composite membranes, which has a high retention of low-molecular-weight organic substances and a fairly high salt permeation, it is possible to partially remove Na+, CI" and other monovalent ions from, for example, whey without a significant loss of lactose. The process, sometimes referred to as nanofiltration and sometimes to loose reverse osmosis or ultra-osmosis, is a very interesting alternative to ion-exchange and electrodialysis if moderate demineralization is required. One advantage of nanofiltration compared with the other two processes is that nanofiltration is quite a simple process through which partial demineralization and concentration can be obtained simultaneously (and in one step).

So far, very little work on the transport mechanisms in nanofiltration has been published. The salt permeability depends on the nature of the component as well as on the membrane itself. It is much higher for monovalent ions than for divalent ions. Increasing the NaCl content leads to a higher permeability of monovalent ions. At pressures in the range of 1.7-2.5 MPa, negative CI" retentions were obtained with sweet whey at volume reduction factors of more than two. The higher the volume reduction factor, the more negative the CI" retention [22],

Applications of nanofiltration in whey processing [23]:

* Concentration and partial demineralizing whey UF permeates prior to further processing into lactose and lactose derivatives.

* Converting "salt whey" to normal whey while solving a disposal problem.

* Preconcentration and partial demineralization of sweet whey to make 50% demineralization products or to act in sequence with ion-exchange or electrodialysis to produce 90% demineralized products.

* Partial demineralization and concentration of hydrochloric acid casein whey to convert it to a low-chloride "sweet whey".

* Partial deacidification and concentration of cottage cheese, fresh cheese (fromage frais), quarg and lactic acid casein wheys so as to convert them to "sweet wheys".

* Treating cheese brines solutions for reuse.

* Partial demineralization of lactose mother liquor (delactosed whey).

The partial demineralization of whey (or milk) UF permeates prior to the manufacture of lactose is reported to be employed commercially at three or four plants. The conversion of "salt whey" to sweet whey by NF is reported to be carried out in about 10-15 commercial plants with capacities ranging from 9 m3 to 22 m3 "salt whey" per day. Benefits are realized through the recovery of whey solids and a reduction in disposal costs [23].

3.2. Fruit juices and wine

3.2.1. Clarification

In juice processing, the process stream contains compounds such as pectins, cellulose, hemicellulose, starch and proteins, which cause an undesirable turbidity when the product is stored. It is thus necessary to clarify the juice. Since the late 1970's, ultrafiltration has been applied commercially for the clarification of different types of fruit juices. Most ultrafiltration plants have been installed for apple juice clarification, but commercial systems are also in operation for grape, pear, pineapple, cranberry and citrus juices. MF is now also used for the clarification of juices. Advantages of using membrane technology for the clarification are the following: a simplified and continuous process, shorter treatment times, lower personnel costs, reduced amounts of additives, increased efficiency, better colour, pasteurization unnecessary if the pore size is less than 0.2 jim.

One disadvantage is that the juice may exhibit turbidity when stored (past clouding). This phenomenon is ascribed to certain substances which can pass through the membrane.

Microfiltration is now used, to an increased extent, for the clarification of fruit juices and wines. In 1992, MF had replaced kiselguhr filtration in wine making in some 400 plants, producing 20-30% of the German wine. MF plants are small, typically less than 200 m2 in area.

3.2.2. Concentration

Fruit juices are concentrated in order to prolong their shelf-life and to minimize the cost of distribution and storage. Before retailing, the concentrated juice is diluted, pasteurized and packaged. Concentration normally takes place by means of vacuum evaporation in one or more stages. During this operation, many of the volatile aroma compounds (typically various organic substances such as esters, aldehydes, alcohols etc., which are present in very low concentrations, i.e., ppm levels) in the juice are lost in the vapour, resulting in reduced product quality. In order to maintain a high quality, aroma compounds must be recovered and added to the juice concentrate. For juices such as apple, pear and some berries, the vapour from the first of the evaporation stages is often taken to a distillation column where it is concentrated and cooled to a low temperature. The aroma concentrate is stored separately and then added to the diluted juice concentrate before pasteurization. On an industrial scale, such distillation techniques result in a very low yield. Also, the aroma compounds are treated at a relatively high temperature for quite a long time, which has a negative effect on the quality of the final product.

Pervaporation using hydrophobic membranes has showed to be a very interesting method for the recovery of aroma compounds from, for example, apple juice but also from beverages containing ethanol [24]. The possibility of using a low process temperature allows very gentle treatment and thus an improved flavour compared with aroma recovered by distillation. The process seems to have great commercial potential.

Bengtsson et al [24] obtained high enrichment factors, especially for esters and aldehydes, which are most important for e.g., apple flavour. When concentrating a natural aroma condensate from an apple juice concentration plant by pervaporation, a sensory study showed that the pervaporation permeate had a more natural flavour than the concentrate obtained conventionally at the plant (Alfa-Laval, Aroma Recovery Units (PAR)).

The mass transfer in the liquid feed can greatly affect the pervaporation process and it has been shown that the relative permeate composition of five different aroma compounds varies depending on the Reynolds number on the feed side. Operation with optimal feed flow conditions, i.e., a turbulent flow regime, can in some cases, such as for 2-methylbutanal, give a flux that is 10 times higher than the flux at the lowest feed flow (Re = 10). Although it might seem optimal to operate the pervaporation process under turbulent conditions in order to achieve maximum fluxes, other feed flow conditions might be optimal with respect to the sensory perception of the aroma concentrate produced. It is thus possible to control the relative composition, or in other words the flavour, of the aroma concentrate by a simple manipulation of the feed flow [25].

Reverse osmosis is used commercially for the concentration of different types of fruit juices. High aroma retention is reported using polyamide membranes. However, due to the osmotic pressure and/or the viscosity, traditional RO is used only as a preconcentration stage to reach 20-25 °Brix [26],

Separa Systems, a joint venture of the FMC Corporation and the Du Pont

Company, has developed a very interesting process, the "FreshNote System", mainly for the concentration of citrus juices [27]. In the first step, the juice is ultrafiltrated giving a clarified permeate stream and a low-volume retentate stream containing some soluble solids and all of the insoluble solids, pectins, enzymes, and the micro-organisms that would affect the stability of the concentrate. The permeate stream contains soluble compounds, particularly the sugars and the flavour and aroma compounds. The retentate is subjected to mild pasteurization which destroys enough of the micro-organisms to provide the necessary stability for the juice concentrate under typical storage conditions.

Apv Sirocurd
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Responses

  • Ted
    Who has advantages kieselguhr or ultrafiltration of apple juice?
    7 years ago

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