Effect of membrane length, membrane resistance, and filtration conditions on the fractionation of milk proteins by microfiltration
ABSTRACT We investigated the fractionation of casein micelles and the whey protein β-lactoglobulin (β-LG) of skim milk by crossflow microfiltration (0.1 μm) for the first time by a novel approach as a function of membrane length and membrane resistance. A special module was constructed with 4 sections and used to assess the effects of membrane length by measuring flux and β-LG permeation (or transmission) as a function of transmembrane pressure and membrane length. Depending on the position, the membranes were partly controlled by a deposit layer. A maximum for β-LG mass flow through the various membrane sections was found, depending on the position along the membrane. To study the effect of convective flow toward the membrane, membranes with 4 different intrinsic permeation resistances were assessed in terms of the permeation and fouling effects along the flow channel. From these findings, we derived a ratio between transmembrane pressure and membrane resistance, which was useful in reducing the effect of deposit formation and, thus, to optimize the protein permeation. In addition, the fouling effect was investigated in terms of reversible and irreversible fouling and, in addition, by differentiation between pressure-induced fouling and adsorption-induced (pressure-independent) fouling, again as a function of membrane length.
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ABSTRACT: The flux behavior of 0.8 and 0.5 mu m silicon nitride microsieves was studied in the pH range from 6 to 9 during microfiltration of milk protein dispersions supplemented with a mineral complex. The physicochemical properties of these dispersions were assessed by particle size distribution (PSD), zeta potential and rheological measurements. Microfiltration was carried out in a pilot cross-flow system where back pulsing was used. Results showed that increasing protein concentration from 30 to 90 g L-1 at pH approximate to 7 has a negligible effect on charge and PSD but increased viscosity and strongly reduced performance of both 0.5 and 0.8 gm microsieves. Adding minerals reduced further the 0.8 gm membrane flux and avoid filtration through the 0.5 mu m membrane, despite the fact that PSD was approximate to 0.3 mu m in all solutions. Raising the pH of dispersions at 9.0, which is higher than the isoelectric pH of both micelles and microsieves, drastically increased permeate flux of both membranes. Results from this work point out that even under quite high ionic strength conditions, the flux behavior of microsieves is mainly controlled by repulsive electrostatic protein-membrane interactions, hence, the pH of the dispersion and the membrane charge are critical when processing complex dairy products.Lebensmittel-Wissenschaft und-Technologie 12/2014; 59(2):827-833. DOI:10.1016/j.lwt.2014.06.057 · 2.47 Impact Factor
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ABSTRACT: This study investigates effects of ultrasound (US) on cross-flow ultrafiltration of skim milk by multi-scale characterization, using a custom designed “SAXS Cross-Flow US-coupled Filtration Cell”. The study of flow properties of casein micelle suspensions shows an evolution of their rheological behavior from Newtonian to shear-thinning until the emergence of yield stress with the increase of concentration (from 27 g L−1 to 216 g L−1). The concentration profiles during cross-flow filtration of skim milk have been revealed for the first time by real-time in-situ Small Angle X-ray Scattering (SAXS) measurement. Without any change of internal structure of casein micelles and membrane selectivity, the applied ultrasound (20 kHz, 2 W cm−2) leads to a significant increase of permeate flux arising from a disruption of concentrated layer. Varying the US intensity from 0.6 W cm−2 to 2.9 W cm−2 does not affect the US enhancement factor, which however depends on the feed concentration. In fact, increase of feed concentration induces the formation of highly cohesive fouling layer during filtration that the applied US could hardly disrupt. Results also suggest that the preventive US application mode is promising since formation of the reversible fouling layer was strongly limited in this mode.Journal of Membrane Science 11/2014; 470:205–218. DOI:10.1016/j.memsci.2014.07.043 · 4.91 Impact Factor
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ABSTRACT: As the cheese market faces strong international competition, the optimization of production processes becomes more important for the economic success of dairy companies. In dairy productions, whey from former cheese batches is frequently re-used to increase the yield, to improve the texture and to increase the nutrient value of the final product. Recycling of whey cream and particulated whey proteins is also routinely performed. Most bacteriophages, however, survive pasteurization and may re-enter the cheese manufacturing process. There is a risk that phages multiply to high numbers during the production. Contamination of whey samples with bacteriophages may cause problems in cheese factories because whey separation often leads to aerosol-borne phages and thus contamination of the factory environment. Furthermore, whey cream or whey proteins used for recycling into cheese matrices may contain thermo-resistant phages. Drained cheese whey can be contaminated with phages as high as 109 phages mL-1. When whey batches are concentrated, phage titers can increase significantly by a factor of 10 hindering a complete elimination of phages. To eliminate the risk of fermentation failure during recycling of whey, whey treatments assuring an efficient reduction of phages are indispensable. This review focuses on inactivation of phages in whey by thermal treatment, ultraviolet (UV) light irradiation, and membrane filtration. Inactivation by heat is the most common procedure. However, application of heat for inactivation of thermo-resistant phages in whey is restricted due to negative effects on the functional properties of native whey proteins. Therefore an alternative strategy applying combined treatments should be favored – rather than heating the dairy product at extreme temperature/time combinations. By using membrane filtration or UV treatment in combination with thermal treatment, phage numbers in whey can be reduced sufficiently to prevent subsequent phage accumulations.Frontiers in Microbiology 07/2013; 4:191. DOI:10.3389/fmicb.2013.00191 · 3.94 Impact Factor