Membrane separation

With the development of membrane separation engineering, microfiltration has been used in dairy industrial applications to insulate suspended atoms selectively ( Brans et al. , 2004 ; Vivekanand Vivekanand et al. , 2004 ) . By pull stringsing the filtration conditions, the separation of micellar caseins by size is considered a new powerful and realistic option to scale production up in the dairy industry.Like all other membrane separation processes, microfiltration is a pressure-driven separation technique which allows atoms larger than the membrane pore size evaluation retained by the membrane and the constituents with sizes smaller than the evaluation passing through the membrane. This enables casein micelles obtained by membrane microfiltration maintain their original construction and therefore hold better functional features than the traditional casein merchandises which requires the procedure of adding chemicals ( Al-Akoum et al. , 2002b ; Vivekanand Vivekanand et al. , 2004 ) .

In add-on, microfiltrate has a similar composing to sweet whey without caseinomacropeptide, phospholipoproteins ( Roe, 2001 ) and therefore is an ideal natural stuff for production of serum protein concentrates or isolates ( Saboya & A ; Maubois, 2000 ) .The efficiency of membrane separation technique depends on many factors, among them are the hydrodynamic parametric quantities regulating the procedure during filtration. It is good known that the fouling of microfiltration membranes will take to cut downing permeate flux and membrane selectivity ( Le Berre & A ; Daufin, 1996 ; Samuelsson et al. , 1997 ) . In the literature, there are several schemes available to get the better of a rapid fouling of microfiltration membranes, but the most popular manner against the fouling during the concentration of casein micelles from skim milk is to pull strings suited processing conditions, such as low unvarying transmembrane force per unit area ( UTP ) ( Sandblom, 1978 ) in combination with high cross flow speed ( Saboya & A ; Maubois, 2000 ) . In malice of that, a disadvantage of the unvarying transmembrane force per unit area system is the high energy demand of the pump to bring forth the flow crossing at both sides of the membrane.

Recently, efforts to get the better of the high operational cost of the permeate recirculation cringle of UTP systems while commanding fouling have resulted in gradient porousness and isoflux membranes, supplying the compensation to the force per unit area bead over the cross flow channel ( Brans et al. , 2004 ) .In add-on, the elements representing the membrane and its support besides play an of import function in regulating the separation of colloidal caseins. In the early 80s, research workers failed to utilize organic membranes ( polysulfone and polycarbonate ) in dairy industry due to inefficiency in footings of flux and selectivity and mechanical heat and chemical stableness ( Saboya & A ; Maubois, 2000 ) . Alternatively, ceramic membranes are considered the lone 1s that satisfy the demands of the applications in the dairy industry, such as long operational life, broad chemical and pH ( 0 – 14 ) compatibility and first-class thermic stableness ( Saboya & A ; Maubois, 2000 ; Baruah et al.

, 2006 ) . Besides, coiling lesion polymeric membranes have besides become available and supply a lower cost than ceramic membranes ( Zeman, 1996 ) ; nevertheless, they require a frequent replacing of membrane.Nowadays, there are many publications available covering with separation of native caseins from skim milk utilizing membranes with pore sizes from 0.05 to 0.5 µm ( Pierre et al. , 1992 ; Daufin et al. , 1993 ; Le Berre & A ; Daufin, 1996 ; Pouliot et al. , 1996 ; Samuelsson et al.

, 1997 ; Punidadas & A ; Rizvi, 1998 ; Tziboula et al. , 1998 ; Vadi & A ; Rizvi, 2001 ; Al-Akoum et al. , 2002a ; Al-Akoum et al. , 2002b ; Espina et al. , 2008 ; Lawrence et al.

, 2008 ; Espina et al. , 2009 ) . As to ceramic membrane systems, the literature advised that high crossflow speeds ( 3-7 m/s ) every bit good as high operating temperature ( 50-55oC ) should be used to minimise the boundary bed of concentration polarisation ; and therefore, to better the modification permeate flux rate ( Saboya & A ; Maubois, 2000 ; Brans et al. , 2004 ) . In a different survey of ultrafiltration of skim milk, Srilaorkul et Al. ( 1991 ) used polysulfone membrane with molecular weight cut-off at 25,000 Da to insulate and concentrate casein micelles in the retentate.

The writers showed the diminution in casein micelle size from 118 nanometers in control milk to 92 nanometers and 87 nanometer in the dressed ores at concentration factor ( CF ) of three and five, severally. However, the consequences are questionable since the sample readying process for measuring of atom diameter utilizing electron microscopy may modify the microstructure of casein micelles ( Karlsson et al. , 2007 ) .However, the bulk of issues merely concern about concentration instead than sized-fractionation of casein micelles from milk. Research by Punidadas & A ; Rizvi ( 1998 ) showed the efficiency of 0.

05 and 0.2 µm ceramic membranes to partition milk proteins into casein rich fractions but did non advert their sizes. Another afford to divide casein supermolecules utilizing different pore size membranes was besides made by Tziboula et Al ( Tziboula et al. , 1998 ) .

Skim milk was microfiltered at 45oC, at permeate flux rates of 300 or 450 l/m2 H, matching to the usage of ceramic membrane diameters of 0.8 and 1.4 µm.

Particle size measurings by photon correlativity spectrometry showed that at concentration ratio of 20 volumes of permeate: 1 volume of retentate, the mean micelle size in retentates was higher than that in permeates and in skim milk. However, although the diameter of micellar caseins in permeates diminished from 260 to 224 nanometers as membrane pore size decreased, the micelle dimension in the retentates seemed similar. What is more, Tziboula et Al. revealed the diminution of micelles larger than 700 nanometers in retentate collected from 0.

8 µm owing to the fouling of membrane. But, it is unsure if membranes mean diameters more than 0.8 µm are good to divide micelles one time the size of atoms scopes from 30 to 500nm, smaller than that of membrane ( Saboya & A ; Maubois, 2000 ) .

It is thought that choice of suited pore size and operating conditions may play of import functions in fractional process of casein micelles by size, nevertheless this is yet to be reported by experimentation.

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