RECENT DEVELOPMENTS UNDERSTANDING DISSOLUTION OF PROTEINACEOUS DEPOSITS. Ruben Mercadé-Prieto

Transcription

1 RECENT DEVELOPMENTS UNDERSTANDING DISSOLUTION OF PROTEINACEOUS DEPOSITS Ruben Mercadé-Prieto 1 1

2 Introduction Fouling Dairy fouling in pasteurization Milk heating in a PHE SS DLC-SS Patel et al. J Food Eng (2013) 116:413 Barish et al. Food Bioprod Proc (2013) 91:352

3 Introduction and Cleaning Removal of milk proteins form stainless steel surfaces in heat exchangers NaOH solution How cleaning of protein deposits occurs? Li et al. Colloids Surfaces B: Biointerfaces (2013) 107:198

4 Alkali dissolution of whey protein gels (by 2009) Boundary layer Swollen layer NaOH penetration NaOH solution Whey Gel 1. NaOH Diffusion into the gel 4. Diffusion throughout the (acid-base reactions) swollen layer 2. Swelling 5. External mass transfer 3. Chemical reactions through the boundary layer (breakdown the gel matrix, denaturation)

5 Outline Better understand swelling of protein hydrogels (Equilibrium and dynamic) Expand dissolution knowledge of whey protein gels to other protein systems (Egg white, Soy proteins and BSA) Other research to understand better dissolution 5

6 Microstrucuture of Protein Hydrogels Lefevre & Subirade. Biopolymers (2000) 54:578 Low salt ph <<>> pi More organized aggregation Strands Transparent gels High salt ph ~pi Random aggregation Dense large particles Opaque gels BSA initial gel 0.5 M NaOH solution NaOH penetration zone 6

7 Swelling of protein hydrogels - Microstructure 2 different microstructure using 2 protein systems Not equal gelation conditions Diff. Proteins Roughly comparable microstrucure Stranded (transparent) Particulate (opaque) 7

8 Swelling of protein hydrogels - Equilibrium Opaque Egg white 8

9 Equilibrium swelling stranded gels Q Volumetric swelling ratio Q ph Dissolution 40 WPI Threshold (DT) transparent Egg white transparent 0.01M [NaCl] 0.06M 0.01M 0.06M 1M [NaCl] DT * Very similar swelling profiles Existence of dissolution threshold (DT), yet specifics different. Swelling increase can be understood considering the net charge in proteins and ionic strength. 10 1M [NaOH] 9

10 Flory-Rhener swelling model for protein gels 1/Q [NaCl] + [NaOH] Ionic strength Theoretical net charge in a protein (at given ph) Assume amino acid composition: WPI like Lg, Egg white like Ovalbumin (OVA) Asp, Glu & -COOH His Cys -NH 2 Tyr Lys Arg Ser & Thr N k WPI N k Egg white Works OK! (bit surprising for egg white) pk a

11 Flory-Rhener swelling model for protein gels 1/Q Flory-Huggins interaction parameter system Offset (Perfect mixing, ideal chains (random walk)) 11

12 Flory-Rhener swelling model for protein gels 1/Q Crosslinking density e =0.30±0.02 mol L -1 e constant in nondissolution conditions Offset e =0.25±0.014 mol L -1 (Need mechanical characterization to confirm values) 12

13 Flory-Rhener swelling model for protein gels Summary stranded (transparent) gels Like polyampholyte polymers What about particulate (opaque) gels? 13

14 Equilibrium swelling particulate gels ph WPI opaque0.01m 60 Very similar swelling profiles Q Q Egg white opaque How? Why? 0.06M DT [NaCl] 1M [NaOH] * 0.01M 0.06M 1M * * [NaCl] * DT Existence of dissolution threshold (DT), yet specifics different. Swelling increase cannot be understood considering the net charge in proteins and ionic strength. 14

15 Equilibrium swelling particulate gels Microphase separation: protein rich (particles) and solvent rich areas Swelling? 0.1 M NaCl 0.5 M NaCl WPI 44.5 g/l, ph ~7 at 68.5 C for 20 h Verheul and Roefs J. Agric. Food Chem. (1998) 46:

16 Swelling particulate aggregates WPI particulate aggregates made in 0.15 M NaCl No evidence of swelling only breakup 16

17 Swelling particulate aggregates Egg white particulate aggregates (no extra salt) No evidence of swelling only breakup 17

18 Swelling particulate aggregates Size particulates stable (ph, NaCl) Size particulates decrease Macroscopic Particulate Gels do not swell Macroscopic Particulate Gels do swell Swelling of particulate gels is due to the partial destruction of the protein rich particles (e.g. decrease e ) Solvent increase would occur mainly in the solvent rich areas 18

19 Equilibrium swelling particulate gels Q Q ph WPI opaque Egg white opaque DT [NaOH] * * * * DT Between ph main interactions destroyed are non-covalent (hydrophobic, H-bonds, electrostatic, etc.) Biomacromolecules (2007) 8:1162 More stable at high [NaCl] Food Hydrocolloids (2009) 23:1587 WPI gels non-covalent interactions are the key stabilizing crosslinks inhibiting dissolution: ph Threshold Biomacromolecules (2007) 8:469 In Egg white disulfide crosslinks should be cleaved for dissolution [NaOH] > 0.1 M 19

20 Monitoring Dynamic Swelling - MRI Magnetic Resonance Imaging (MRI) Together with Dr. Xin Jin Swelling of WPI gels University of California at Davies Pure diffusion model Use mass data! J. Food. Eng. (2011) 106:53 Quantification of [WPI] from MRI data (intensity & T 2 ) unclear Oztop et al. J. Food. Sci. (2010) 75:E508 20

21 Monitoring Dynamic Swelling - Fluorescence Preliminary data Protein staining with RITC Rhodamine B isothiocyanate Very large focal depth Collect ~all vertical florescence Intensity should decrease as 2D swelling 21

22 Monitoring Dynamic Swelling - Fluorescence 1 Volumetric swelling ratio Q Fluorescence intensity ratio (I/I0) M NaCl 0.05M NaCl Diameter ratio (D/D0) 3 h 1 D 2 D 3 D Need equilibrium swelling experiments for better calibration 22

23 Monitoring Dynamic Swelling - Fluorescence 1 D WPI gel Make gels inside 2 mm cuvettes Fluorescence intensity min 120 min 1000 min Initial fluorescence ph 11 No NaCl Only swelling No dissolution Q > Arbitrary Horizontal Distance (mm) 23

24 Dissolution protein Gels All protein hydrogels dissolve in the same way than whey ( Lg) gels? General mechanisms? 24

25 Dissolution BSA gels vs Lg Concentration BSA (g/g) BSA 0.1 M NaOH Dissolution rate R (g/m2s) R o -Lactoglobulin Time (s) Time (s) Concentration BSA (g/g) BSA R start 0.5 M NaOH R end Dissolution Rate (g/m 2 s) Time (s) Time (s) 25

26 Dissolution BSA gels vs Lg Dissolution rate (g/m 2 s) BSA R start R o R end [NaOH] (M) -Lactoglobulin (or whey mixtures) R o R end E a (kj/mol) ~40 > >55 Effect of dissolution temperature 26

27 Dissolution Egg White Gels Egg white (Agro Campus Ouest, Rennes, France) Amount of protein dissolved (g m -2 ) C 0.1 M NaOH R o 1.5 M NaOH Dissolution rates ~0.005 g m -2 s Time (s) DissolutionrateR o (gm -2 s -1 ) OVA ph C OVA ph [NaOH] (M) E a at M NaOH of kj/mol Effect of dissolution temperature 27

28 Dissolution Egg White Gels Dissolution in the presence of NaCl (hinder swelling) Amount protein dissolved (g m -2 ) WPI WPI gel 0.1 M NaOH 0.3 M NaCl 63 C 0.02 R start R start Egg white gel R end M NaOH M NaCl C 79.5 C 79.5 C Time (s) Time (s) Dissolution rate (g m -2 s -1 ) Amount protein dissolved (g m -2 ) Egg white R end Dissolution rate (g m -2 s -1 ) 28

29 Dissolution Egg White Gels Dissolution rate (g m -2 s -1 ) Rstart 0.3M NaCl Rend 0.3M NaCl Rstart 0.7 M NaCl Rend 0.7 M NaCl No NaCl 0.3 M NaCl WPI 0 M NaCl [NaCl] At 0.1 M NaOH 0.7 M NaCl Dissolution rate (g m -2 s -1 ) Rstart 0.3M NaCl Rend 0.3M NaCl Rstart 0.7M NaCl Rend 0.7M NaCl No NaCl 0 M NaCl Egg white WPI Temperature ( C) Swelling is very important! (Stabilization non-covalent interactions?) Egg white Temperature ( C) Dissolution temperature Swelling is not key! 29

30 Dissolution Soy Protein gels SPI - Mixture of many proteins 22 C E a ~60 kj/mol Similar than Egg white gels but much faster! 30

31 Equilibrium swelling of Soy Protein gels Volumetric swelling ratio 1:1 mixture of glycinin and -conglycinin 31

32 Dissolution Soy and Egg white Protein gels Egg white (OVA) dissolution gels seem to be limited by the alkaline cleavage of disulfide bonds OVA 4 SH 1 S S SPI gels normally are not extensively disulfide crosslinked (few free SH groups) -elimination reactions could be so important because destruction of large SS proteins like glycinin -conglycinin subunits SPI Glycinin subunits 32

33 Mechanical properties hydrogels Mechanical cleaning? Erosion? Pure chemical cleaning Cleaning in a pipe Mechanical properties of hydrogels during dissolution? Mercade-Prieto and Chen. AIChEJ. (2006) 52:792 33

34 Mechanical properties hydrogels Stable swelling equilibrium conditions [NaCl] aq 4mm WPI gel 0.1 M NaCl G E = 15.3 kpa Loading Loading + Relaxation µm [NaCl] / M Swelling ratio SR (mean ± SD) a ± swelling b ± 0.02 shrinkage c ± 0.02 shrinkage Number of tests G E / kpa 15 a ±3 32 b ±5 36 c ±7 e,eff /moll Rubber elasticity 34

35 Poroviscoelasticity FEM - Relaxation Max S/E = 0.2 d = 0.1 R/t 0 = 0.33 g VE1 0.1 = Misses Stress Each frame limits Pore pressure 35

36 Mechanical properties hydrogels - Relaxation (F(t) - F( )) / (F E - F( )) Exp. 3 PE 0.4 PE BC1 0.3 Exp. 3 PVE 0.2 Optim. PVE BC2 0.1 Residuals E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 F PVE ) F E PE =( 1 j=1 N VE g VEj)( 1 2(1 d )) Poroelasticity D = 9.3x10-9 m 2 s -1 Poroviscoelasticity D = 4.9x10-9 m 2 s -1 g VE1 = 0.10 VE1 = 6 s 36

37 Experimental results Poroviscoelasticity [NaCl] / M D / 10-9 m 2 s a ±2 3.2 ab ± b ± 1.1 g VE a ± b ± ab ± 0.04 VE1 / s 13 a ±6 12 a ±5 11 a ±4 d 0.21 a ± b ± c ± 0.3 Av. MSE 1.1x10-4 a 6.5x10-5 b 7.8x10-5 ab D ~ self diffusivity of free water (~2x10-9 m 2 s -1 ) Similar viscoelastic parameters Key parameter affected by swelling was the drained Poisson ratio d (auxetic material?) 37

38 Mechanical properties hydrogels Need to miniaturize - Microindentations Proven using AFM (Soft Matter (2012) 8:3393) Probe 45 µm 20 µm Force (µn) Melamine-Formaldehyde microcapsule 500 Rupture Contact probe microcapsule Contact probe surface Displacement (µm) 38

39 Mechanical properties hydrogels Need to miniaturize - Microindentations Gel High precision nanostage Force transducer Indenter probe Much faster relaxations Multiple measurements in one gel Plenty of data Better statistics Large indenter size range (10 µm 1 mm) Separate poro & viscoelasticity Measure surface mechanical properties Local Rupture & Failure properties? Measurements during dissolution? 39

40 Q Understanding swelling dissolution threshold ph M Dissolution 40 WPI Threshold (DT) transparent Q Threshold? [NaOH] Soluble WPI aggregates 68.5 C 2 24 h ph >11.5 Room temp. * ~7-9 wt% Modulus (Pa) 10 1 Viscous modulus ph Viscous modulus Elastic modulus ph Time(s) Elastic modulus G max ~[WPI] 28 Gel like Liquid like Check Zhao Lei poster for more info! 40

41 Conclusions Dissolution mechanisms of protein hydrogels vary significantly Better understanding of swelling Insitu measurements undergoing dissolution (swelling, mechanics, etc.) 41

42 Acknowledgments Françoise Nau (INRA) Students Li Hui Boris Koutzenko Joaquim Lopez Hu Wei Weiji Liu Zhao Lei Maud Coignaud Funding from Jiangsu province 42