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There is little information concerning the fractionation by microfiltration (MF) of casein micelles and immunoglobulins plus other minor whey proteins with ceramic gradient membranes. The order of transmission was α-lactalbumin (α-La, 2.3 nm)> β-lactoglobulin (β-Lg; 4.2 nm)>IgG (10.7 nm)> lactoperoxidase (8.2 nm)> IgA (18.1 nm)> IgM (23.8 nm)> lactoferrine > blood serum albumin (7.8 nm), irrespective of the applied transmembrane pressure (0.6–3 bar) and equal to 55% > 50% > 47% > 41%>39% > 32% > 22% > 19%. Including preconcentration, it was possible to obtain 90% of the initial IgG, IgA and IgM within 85, 119, and 160 min, based on 1 m2 of membrane area and 50 L of skim milk volume. The long-term process exposure at 50 °C did not affect α-La and IgG but β-Lg (3–5% denaturation), which, however, was selectively retained by the MF. In conclusion, MF is not only suitable for fractionation of the major whey proteins and caseins, but also for the minor and far bigger immunoglobulins.

Milk protein fractionation for casein/whey protein separation by microfiltration in diafiltration mode was investigated using washing waters differing in pH, calcium content and ionic strength. Properties of the deposit layer and process efficiency were assessed as functions of diafiltration progress and deposited layer structures were analysed. Results were compared with findings obtained in crossflow mode with a gradual change from milk to diafiltration medium. Deionised water as well as softened water induced a significant increase of deposited casein layer hydration, thereby increasing flux levels and separation efficiency. Dependent on water hardness, tap water was found to induce fewer changes to the deposit hydration and process performance indicating less change of casein micelles. These findings are consistent with the generic colloidal behaviour of casein micelles as previously determined through laboratory experiments. Therefore, waters with a certain degree of hardness could be recommended as the most suitable diafiltration medium not requiring pre-treatment.

Compared to tubular membranes, spiral-wound membranes (SWM) cannot be operated at very high crossflow velocities due to mechanical instabilities of the module. We therefore applied a novel approach using custom-made microfiltration SWM modules to study the effects of crossflow velocities beyond the level currently applicable for commercial SWM. First, we used a modified industrial SWM (0.96 m) to measure flux and protein permeation spatially resolved within the limits of crossflow conditions applied in routine operation (maximum ΔpL of 1.3 bar). Secondly, we applied a short SWM (0.24 m) to assess the effect of extreme crossflow velocities with a corresponding ΔpL of up to 2.8 bar m−1. The goal was to investigate the effects of deposit formation reduced to the minimum, and thus, to measure the theoretically achievable improvement of flux and protein permeation even though this is currently not practicable. As key result, we found a critical crossflow velocity up to which a significant increase of protein mass flow could be achieved; beyond which, however, no further reduction in filtration resistance caused by deposit formation was observed. The filtration became independent of the transmembrane pressure. Based on these findings, more rigid modules could potentially improve the performance of SWM.

Existing works on the influence of spatial effects on flux and permeation of proteins in microfiltration (MF) have focused on ceramic membranes. There is little information on spiral-wound membranes (SWMs). Since the inner core of a SWM is practically inaccessible by non-destructive techniques, three different prototypes were constructed in this study to optimize suitability for the investigation of spatial effects on filtration performance. To measure the pressure drop, shortened SWMs 0.25, 0.50, and 0.75 times the length of a standard industrial SWM (0.96 m) were designed. Second, a sectioned membrane (0.96 m) with separated compartments on the permeate side was constructed to analyze spatial effects on flux and protein permeation along the flow path of a SWM. Three different features characterized this sectioned module: sectioned permeate pockets, a sectioned permeate collection tube, and sectioned permeate drain and measurement systems. Crossflow filtration experiments showed that these modifications did not alter the filtration performance compared to an unmodified control SWM. Thus, it can be applied to assess spatially-resolved filtration performance in SWMs. The third prototype designed was a test cell with accessible flat sheet membranes and spacer material, as in SWMs. The flow path in this test cell was designed to match the characteristics of the channels between the membrane sheets in a standard SWM as closely as possible. The flow path length and the combination of membrane material and spacer architecture were the same as in the control SWM. This test cell was designed to assess the effects of length and processing conditions on the formation of a deposit layer. The combined results of these test modules can yield new insights into the spatial distribution of flux, permeation of target components, and deposit formation.

The use of bioactive bovine milk immunoglobulins (Ig) has been found to be an alternative treatment for certain human gastrointestinal diseases. Some methodologies have been developed with bovine colostrum. These are considered in laboratory scale and are bound to high cost and limited availability of the raw material. The main challenge remains in obtaining high amounts of active IgG from an available source as mature cow milk by the means of industrial processes. Microfiltration (MF) was chosen as a process variant, which enables a gentle and effective concentration of the Ig fractions (ca. 0.06% in raw milk) while reducing casein and lactose at the same time. Different microfiltration membranes (ceramic standard and gradient), pore sizes (0.14&ndash, 0.8 &micro, m), transmembrane pressures (0.5&ndash, 2.5 bar), and temperatures (10, 50 &deg, C) were investigated. The transmission of immunoglobulin G (IgG) and casein during the filtration of raw skim milk (&lt, 0.1% fat) was evaluated during batch filtration using a single channel pilot plant. The transmission levels of IgG (~160 kDa) were measured to be at the same level as the reference major whey protein &beta, Lg (~18 kDa) at all evaluated pore sizes and process parameters despite the large difference in molecular mass of both fractions. Ceramic gradient membranes with a pore sizes of 0.14 &micro, m showed IgG-transmission rates between 45% to 65% while reducing the casein fraction below 1% in the permeates. Contrary to the expectations, a lower pore size of 0.14 &micro, m yielded fluxes up to 35% higher than 0.2 &micro, m MF membranes. It was found that low transmembrane pressures benefit the Ig transmission. Upscaling the presented results to a continuous MF membrane process offers new possibilities for the production of immunoglobulin enriched supplements with well-known processing equipment for large scale milk protein fractionation.