Microfiltration of Raw Whole Milk to Select Fractions with Different Fat Globule Size Distributions: Process Optimization and Analysis

Set-up of the microfiltration (MiFi) system. The electromagnetic flow meters, pumps, and temperature and pressure gauges are connected to the digital control platform where process run data is stored and exported.

Fat transmission (Tr, ♦), fat content in the permeate (C_P, □) and modal diameter (d_mod) of the milk fat globules in the permeate (○) and in the retentate (●), as a function of the shear stress at the wall τ_w, at volume reduction factor=4, permeation flux=1,041 L/h per m², and 50°C. Error bars represent standard deviations.

Influence of permeation flux (J_p) and volume reduction factor (VRF) on fat transmission (Tr), permeate fat concentration (C_P) and retentate fat concentration (C_R) at shear stress at the wall=80Pa, 50°C: (– –♦– –) Tr at J_p=1,041 L/h per m²; (—♦—) Tr at J_p=1,350 L/h per m²; (—♦—) Tr at J_p=1,875 L/h per m²; (– –□– –) C_P at J_p=1,041 L/h per m²; (—□—) C_P at J_p=1,350 L/h per m²; (—□—) C_P at J_p=1,875 L/h per m²; (– –■– –) C_R at J_p=1,041 L/h per m²; (—■—) C_R at J_p=1,350 L/h per m²; and (—■—) C_R at J_p=1,875 L/h per m².

A) Fat globule size distribution in raw whole milk (—), and in the following fractions obtained at shear stress at the wall (τ_w)=80Pa, 50°C, permeation flux (J_p)=1,041 L/h per m²: (– –○– –) permeate at volume reduction factor (VRF)=4; (—○—) permeate at VRF=16; (– –●– –) retentate at VRF=4; (—●—) retentate at VRF=16. B) Influence of the ratio J_p.VRF/τ_w (expressed in m/h per Pa) on the modal diameter (d_mod) of milk fat globules in the permeate (○) and in the retentate (●) obtained from raw whole milk with d_mod=3.7±0.2μm. Trend line for fat globule diameter in the permeate: d_mod=2.10×(J_p·VRF/τ_w) + 2.83; R²=0.82. Trend line for fat globule diameter in the retentate: d_mod=5.46×(J_p·VRF/τ_w) + 4.16; R²=0.84.

Evolution of the transmembrane pressure (TMP) and modal diameter of the native milk fat globules (d_mod) during long runs of the crossflow microfiltration process with nominal membrane pore size of 5μm: TMP (□) and d_mod (○) during the collection of small milk fat globules in the permeate at permeation flux (J_p)=1,041 L/h per m², volume reduction factor (VRF)=4, and shear stress at the wall (τ_w)=80Pa; (■) TMP and d_mod (●) during the collection of large milk fat globules in the retentate at J_p=1,475 L/h per m², VRF=15, and τ_w=80Pa.

Particle size distributions of milk fractions with different sizes of fat globules obtained by the microfiltration process operated at 50°C using various nominal membrane pore sizes and different hydrodynamic conditions. (—) Raw whole milk; (– –○– –) permeate obtained with nominal membrane pore size=2μm, volume reduction factor (VRF)=3, shear stress at the wall (τ_w)=45Pa, permeation flux (J_p)=417 L/h per m²; (—○—) permeate obtained with nominal membrane pore size=2μm, VRF=2.5, τ_w=45Pa, J_p=417 L/h per m²; (– –●– –) retentate obtained with nominal membrane pore size=2μm, VRF=3, τ_w=45Pa, J_p=417 L/h per m²; (—●—) retentate obtained with nominal membrane pore size=12μm, VRF=25, τ_w=80Pa, J_p=1,458 L/h per m² followed by a 13-volume diafiltration with skimmed milk for 10min at 350 L/h to enhance milk fat globule fractionation while maintaining the composition of the continuous phase. Inserts show polarized light micrographs of creams obtained from the milk fractions (scale bar represents 10μm).

Firmness of rennet milk gels containing 150 g/kg of fat in the form of native milk fat globules of various sizes (d_mod = modal diameter of the native milk fat globules), measured as the penetration shear stress at 13mm depth using a universal testing machine equipped with a 90° cone moving down at 60 mm/min.