Structural organization of casein mic icelle les concentrated la - PowerPoint PPT Presentation

Structural organization of casein mic icelle les concentrated la layer durin ing cross-flow ult ltrafil iltration Floriane Doudiès M. Loginov, N. Hengl, F. Pignon, N. Leconte, F. Garnier-Lambrouin, J. Pérez, L. Sharpnack, M. Granger-Delacroix, M. Belna, G. Gésan-Guiziou Paris Rennes UMR 1253 STLO INRA-Agrocampus Ouest FRANCE Joint Research Unit on Grenoble Science & Technology of Milk & Egg F-35000 Rennes, France

Milk ilk filtr filtration Skimmed milk: Soluble proteins Casein micelle Water, lactose… Ions Casein micelles are large globular aggregates of caseins with calcium phosphate, they are porous, deformable, compressible and dynamic particles (50-500nm) Micro- and ultrafiltration of skimmed milk are largely used in the dairy sector (≈ 40% of the membrane area installed in food sector) ultrafiltration  proteins concentration (cheese manufacture, standardization) microfiltration  proteins fractionation (high added value ingredients) 02

Membrane fou oulin ing by y cas asein in mic icell lles Bouchoux et al., Biophys. J., 2009 Transmembrane pressure ≈ 1 bar Cross-flow Increase of micelles concentration Membrane Permeate Gel with high concentration of casein micelles Formation of fouling gel layer: - limitation of the filtration performance reduces permeate flux, decreases permeate quality (low transmisson of soluble proteins) - difficulties of cleaning operation large consumption of water, detergents and energy… 03

Objective Th The structural l organiz izatio ion and behavi viour of f concentrated case sein in mice icelle lles in in fouli ling la layer duri ring cross ss-fl flow ultr ltrafil iltratio ion - to analyse fouling layer development during filtration step and redispersion during pressure relaxation step - to focus on the effect of temperature - to perform in situ Small-Angle X-ray Scattering (SAXS) cross-flow filtration 04

In-situ SAXS cross-flow filtration Scattered beam intensity, I (a.u.) 1000 100 10 1 0.1 0.01 0.001 0.01 0.1 1 10 Scattering vector, q (nm −1 ) Spatial resolution 20 µm Jin et al., J.Memb. Sci., 2014 05

SAXS by y cas asein mice icelle les in in static I(q=1nm -1 ) = 0.0132×C (g/L) 1000 Scattered beam intensity, I (a.u.) 1.2 100 1 10 Concentration↗ 0.8 1 I/Imax 0.6 0.1 0.4 0.2 0.01 0 0.001 0 100 200 0.0001 Casein concentration, C (g/L) 0.01 0.1 1 10 Scattering vector, q (nm −1 ) 06

SAXS an anal alysis of of fou oulin ling la layer Calibration curve Scattered beam intensity, I (a.u.) 1.E+03 10 3 Casein concentration, C (g/l) 1.E+02 300 Distance to membrane Fouling layer 1.E+01 10 1 20 µ m 1.E+00 200 1.E-01 10 −1 1.E-02 100 2000 µ m Initial suspension 10 − 3 1.E-03 1.E-04 0 0 100 200 300 0.1 1 0.05 0.5 0 100 200 300 Scattering vector, q (nm −1 ) Distance to membrane, z ( µ m) Filtration channel (side view) Retentate Concentration polarization layer Scattered X-ray intensity Distance z (µm) z Δ P Membrane x y Permeate 07

Quantification of of fou ouli ling la layer Accumulated mass Casein concentration, C (g/L) Casein concentration, C (g/L) of casein micelles 300 300 in fouling layer 200 200 C sol-gel 100 100 Gel thickness 0 0 Distance to membrane, z ( µ m) Distance to membrane, z ( µ m) 0 100 200 300 0 100 200 300 gel thickness (µm) Mass (g/m²) or Concentration of sol-gel transition: 12°C – 150 g/l 25°C – 174 g/l 42°C – 181 g/l (from Nöbel et al., Int. Dairy J., 2016) Time (min) 08

Filt Filtration protocol Suspension: 50 g/L of casein micelles in milk ultrafiltrate Temperature: 12, 25 or 42°C Filtration cycle: 2 steps Filtration Relaxation 150 min 55 min TMP, Crossflow rate, v = 10 cm/s crossflow rate TMP = 1,1 bar Crossflow rate, v = 3 cm/s TMP = 0,1 bar Time 09

TMP = 1.1 bar Filt Filtration step v = 3cm/s Filtration 150 min 60 500 Casein concentration (g/L) t0 450 50 25°C 400 42°C Mass (g/m 2 ) 40 350 12°C 300 30 250 12°C 200 20 150 25°C 10 100 42°C 50 0 0 0 50 100 150 0 200 400 Time (min) Distance to membrane z (µm) 200 Accumulated mass and gel thickness rise over Gel thickness (µm) 150 time 100 At 42°C , accumulation is faster and more important , gel is more concentrated and 12°C 50 thicker than at 12 or 25°C 25°C 42°C 0 0 50 100 150 10 Time (min)

TMP = 1.1 bar Filt Filtration kin kinetics v = 3cm/s 25 25 42°C 12°C 20 20 25°C Flux (L∙m −2 ∙h −1 ) 15 15 10 10 5 15 0 00 0 50 100 150 Time (min) Permeate flux decreases over time for each temperature With temperature decreasing , fouling layer less permeable Fouling rate and intensity due to the lower filtrate viscosity and higher filtrate flux 11

TMP = 0.1 bar Pressure rela laxation step v = 3cm/s and 10cm/s 60 12°C 25°C 42°C 50 25 40 Removed mass (g/m 2 ) 20 Mass (g/m 2 ) 30 15 10 20 5 10 0 Filtration Relaxation 0 10 20 30 40 50 0 Relaxation time (min) 0 100 200 Time (min) Relaxation step allowed to remove a part of polarized layer without using chemical products, ultrasound … But , relaxation time is comparable with accumulation time, relatively slow Removed mass rises with temperature 12

TMP = 0.1 bar Rela laxation v = 3cm/s and 10cm/s 250 12°C 25°C 42°C 200 Gel thickness (µm) 150 100 50 Filtration Relaxation 0 0 100 200 Time (min) Gel removal follows same trend as total accumulated matter removal: starts simultaneously with pressure decrease, at the very beginning of relaxation step At 12°C, less accumulation than at 42°C but it is removed with difficulty 13

Gel Ge l behaviour after pressure rele lease Osmotic Strong pressure 14.00 Example 25°C gradient pressure Casein concentration, C (g/l) 12.00 300 Time 10.00 Concentration 8.00 200 C sol-gel Liquid flux 6.00 4.00 100 Gel Sol Retentate 2.00 Gel swelling 0.00 000 0 100 200 300 Concentration Distance to membrane, z ( µ m) Simultaneous decreasing of gel thickness and concentration from beginning of relaxation Re-dispersion of sufficiently swelled part Fouling removal via gel swelling with C below C sol-gel and re-dispersion of external swelled part 14

Impact of Im of temperature on on gel l rela laxation 1 12°C 25°C Relative gel thickness 42°C 0.8 Limited gel removal at 12°C? 0.6 0.4 0 20 40 60 Relaxation time, min Concentration profiles during relaxation at different temperatures (same Y-axis scale) Casein concentration, g/L Casein Concentration, g/L Casein Concentration, g/L 500 500 500 400 400 400 25°C 300 12°C 300 300 42°C 200 200 200 100 100 100 0 0 0 0 100 200 300 0 100 200 300 0 100 200 300 Distance, µm Distance, µm Distance, µm 15

Three typ types of of fou ouli ling Schematic presentation of fouling layer − Calcium + Water phosphate Gaucheron, Reprod. Nutr. Dev., 2005 Cooling Hydrophilic brush Gel that Cooling Gel that Sol swells re-disperses but doesn't after swelling re-disperse Hydrophobic core Lower steric barrier Observed at moderate gel concentration (12°C) density – more open Not observed at highest concentration (42°C) surface for interactions → Nature of fouling (repulsive gel/attractive gel) (gelling)? depends on temperature 16

Con onclusions • In-situ SAXS cross-flow filtration allowed analysis of casein micelles fouling layer with an unique resolution of 20µm during filtration step and relaxation step • Fouling rate and fouling intensity (quantity of accumulated micelles and gel thickness) increase with temperature due to the lower filtrate viscosity and higher filtrate flux • Important part of fouling can be reduced by simple pressure relaxation • The fouling by casein micelles is removed through the swelling-dissolution mechanism • A limited efficiency of pressure relaxation at 12°C can be explained by transformation of repulsive gel (swells and dissolves) into attractive gel (swells but does not dissolve) • In the future: 1) local microstructure 2) rheological characterization of gels at different temperatures 3) study of cross-flow, time and transmembrane pressure effects on gel properties in fouling layer 17

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Cali alibration 25°C 1) Zero membrane placement 2) Calibration in static 1.E+03 Scattered beam intensity, I (a.u.) 176 g/L 1.E+02 3.E-04 1.E-03 transmitted intensity (u.a.) d(transmitted intensity)/dz Rise of 1.E+01 1.E-03 2.E-04 concentration 1.E+00 1.E-03 1.E-01 2.E-04 10 g/L 8.E-04 1.E-02 6.E-04 1.E-04 1.E-03 4.E-04 1.E-04 5.E-05 2.E-04 1.E-05 0.E+00 0.E+00 1.E-06 0 200 400 600 1.E-02 1.E-01 1.E+00 1.E+01 Distance to membrane z (µm) Scattering vector, q (nm −1 ) 1.2 1 Inox Slide 0.8 Feed canal I(q=1nm -1 ) = support view of 0.6 I/Imax 0.4 0.0132×C (g/L) cell 0.2 Membrane 0 0 100 200 120µm Width Casein concentration (g/L) 19

Cali alibration at t dif ifferent sc scatterin ing vectors 1.4 y = 0.0065x 1.2 R² = 0.9219 y = 0.0057x R² = 0.9991 1 0.8 y = 0.0053x I/Imax R² = 0.982 0.6 y = 0.0053x 0.4 q=0.08 R² = 0.9837 q=0.1 0.2 q=0.3 q=1 0 0 50 100 150 200 Concentration (g/L) 20