Microfiltration (0·1 μm) of milk: effect of protein size and charge

Abstract

Microfiltration (MF) of milk with a ceramic membrane (0·1 μm mean pore diam.) for the separation of casein micelles from soluble proteins was studied. Experiments were performed at constant flux density (J=65 or 75 l h−1 m−2) and wall shear stress (τw=100 or 110 Pa) with milks containing particles and solutes with different sizes and charges, produced by physicochemical change (heat and mechanical treatment, pH, ionic strength, addition of ions). Membrane separation performance was limited by the build up of a cake with characteristics that depended on the size of particles and soluble proteins. Best performance (higher permeability and whey protein transmission) was obtained with milk containing fat on the one hand and calcium phosphate on the other. An optimal value of the particle size was found, close to 0·5–3·0 μm; above this separation performance decreased. In addition, the present study confirmed that the transfer of charged solutes is the consequence of both size and ionic exclusion. Better performance was achieved with higher ionic strength (1 M).

Limiting flux in skimmed milk ultrafiltration: impact of electrostatic repulsion due to casein micelles

“…• Addition of CaC12 up to 50 mmol L-~ did not lead to a significant change in micelle size distribution, but the addition of 100 mmol L-1 induced a micelle aggregation (without any precipitation) and therefore a sharp increase in micelle size. No measurements were performed for the addition of NaH2PO4, but aggregation of micelles due to calcium phosphate bridges between caseins (containing both phosphate groups and calcium) probably occurred as for CaC12 additions [ 12].…”

Microfiltration of skim milk using polymeric membranes for casein concentrate manufacture

“…Of critical importance is the size of the casein micelle, which can range from 0.01 to 0.3 m [18], relative to that of the membrane pores (typically 0.1 or 0.2 m). Micelle size is strongly correlated with the ionic calcium concentration and thus decreases with the addition of citrate and increases with the addition of calcium and phosphate [8].…”

“…Kentish). [2,5,8,[10][11][12][13][14][15][16]. There is very little scientific literature regarding the use of polymeric membranes in this application.…”

“…The casein concentrated retentate is used for cheesemaking [5,6], resulting in an increased cheese yield compared with standard skim milk [7]. The permeate provides an "ideal" whey [7,8] that is a much better feed for purifying serum proteins than cheese whey [9].…”

On the origin of flux dependence in pH-modified skim milk filtration

“…This concept was earlier proposed on a hydrodynamics background and mainly described in microfiltration and UF of model solutions (latex, silicates, etc.) designed for the purpose [2,16,32], and has also been shown successful for the filtration of milk products [13,14,17,18,[33][34][35]. Globally, these works mainly concerned parametric studies of hydrodynamics conditions of filtration, highlighting flux variations and sometimes those of retentions [13,14,17,[33][34][35].…”