Different Microstructures of Binary Gels for Food Applications

7/29/2019 Different Microstructures of Binary Gels for Food Applications

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DIFFERENT

MICROSTRUCTURES OFBINARY GELS FOR FOOD

APPLICATIONS

Marcela Jarpa

PhD Student

Supervisor: L. Chen


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PROTEINS & POLYSACCHARIDES

Proteins and polysaccharides play a key role in

the structure formation and stabilisation of food

systems.

http://www.siskiyous.edu/

http://www.mn.uio.no


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Protein/polysaccharide interactions and

systems

Below Above


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Protein-Polysaccharide gels

Gels have been classified in three types :

I. Interpenetrating networks (incompatibility)

II. Phase-separated networks (incompatibility)

III. Coupled networks (compatibility)


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I. Interpenetrating networks (IPN)

An Interpenetrating gel comprise two or more

independent polymer networks.

Individual polymer networks interact with eachother through topological entanglement.

Interlocked structures by crosslinks


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Basic synthesis methods for IPN

Adapted from Sperling, L. H. (1994)"Interpenetrating Polymer

Networks: An Overview."

A. Sequential IPN

B. Simultaneous IPN


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Whey protein/ Locust Bean Galactomannan

(WPI/LGB)(Monteiro et al.,2005)

Objective:

Study the influence of the molecular mass ofgalactomannan on whey protein gelation.


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Method


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Results

A. The effect of LBG on

11% WPI solution WPI solutions at 11% do not

gel.

Addition of galactomannan of

any Mw at low

concentration, does not

change the microstructure

(phase separation).

Addition of galactomannan of

higherMwand concentration

(0.7%), forms an incipient IP

gel.

WPI 11% WPI 11% + LBG LMw

WPI 11% + LBG HMw(0.7%)


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Results

B. The Effect of LBG on 14%WPI Gels.

Addition of medium rangeMwgalactomannan changesthe microstructure (phase

separation) at lowconcentration.

Increasing thepolysaccharidesconcentration and/orMwpromote gel formation at

lower temperature. Greaches higher values as

the polysaccharideconcentration and/orMwincrease

WPI 14% WPI 14% + LBG MMw

WPI 14% + LBG HMw(0.7%)


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Conclusions

Differences in the molecular weight of the

polysaccharide have a significant influence on the

gel microstructure.

At 11% WPI, below the gelation threshold of theprotein alone, the presence of the non-gelling

polysaccharide induces gelation to occur.

At higher protein concentration, the main effect ofthe polysaccharide was a re-enforcement of the

gel.


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Protein-Polysaccharides gels





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II. Phase-separated network

Consist of a gel matrix filled with particulateinclusions.

Some degree of demixing occurs prior to gelation.First and second component network will beseparated spatially.

Bigger polymer concentration


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Synthesis Method

Incompatibility between polymers

One component gel faster than the second one.

The second one aggregates within the pores of

the supporting network


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Gelatin / Dextran(Butler et al. 2003)

Objective:

Study the microstructure formation and

evolution in a gelatin/dextran mixture, over arange of temperatures.


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Method


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Results

Small-Angle Light Scattering and Turbidity The kinetics of phase separation depends on

temperature.

At temperatures below 18 C, the gelation kinetics

is sufficiently rapid to trap the structure as soon asthe phase separated morphology formed.

At temperatures above 20 C , the gelation is

slower, allowing a coarsening process for long

periods of time: There was a time-delay of up to tens of minutes

between reaching the quenched temperature and

the onset of phase separation.


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Results

Polarimetry

optical rotation at the onset of phase separation

in the delayed samples demonstrate the coil

to helix transition in gelatin occurs attemperatures below about 30 C.

Also suggest, that a certain degree of helix

formation was required to trigger phaseseparation.


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Results

Confocal Laser Scanning Microscopy.

Evolution of the

microstructure in a

sample held at

26C for 26,29,41,and 62 min.

1 2

3 4


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Conclusions

Depending on temperature, the formed gel will have

a very clear droplet morphology (over 20C), or a

typical diffuse morphology of early stages of phase

separation (below 18C). The time-delay phenomenon demonstrated the

phase separation only occurred once a certain

amount of ordering of the gelatin molecules is

achieved.


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Protein-Polysaccharides gels





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III. Coupled networks

Defined as those in which chains of different

polymers interact directly to form the network.

Large attractive interaction between the

components Junction zones


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Junction zones

Tolstoguzov,V. (2003). Food Hydrocolloids 17,1-23.

Schematic representation of the

complexing between oppositely charged

polymers

Compactness of protein-

polysaccharide complexes


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-Lactoglobulin/ Xanthan Gum(Laneuville et al, 2006)

Objective:

Determine the mechanism and kinetics of the

electrostatic gelation of native -lg/ xanthan

gum mixtures in aqueous solution.


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Method

Gel


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Results

The higher protein concentration, the faster

structuration process, and the weaker gels.

The lower the pH at high protein concentration, the

weaker the gel after an optimal ph.

Phase contrast micrographs of the microstructure of-lg/xanthan gum gels for (a) r=2, (b)r=5, and (c)

r=15


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Results

Best results for-lg/Xhantan gum ratio: 2and 5

Evolution of the storage () and loss () modulus during gelation forlg/xanthan gum mixtures at

(a) r=2 and (b)r=5. The dotted lines indicate the gelation time. The acidification curves () and the

IEP oflg (pH 5.1)(*) are also presented.


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Results

Soluble complexes Interpolymeric

complexesCluster-cluster

aggregation

Gel

Polysaccharides: coils

Proteins: circles

A two-step mechanism for gel formation.

Step 1 Step 2pH


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Results

The total biopolymer concentration at which

gelation was obtained was extremely low (0.1

wt %) compared to the usually tested

concentrations for protein-polysaccharide mixedgels (4-12 wt %).

The gel is formed without applying any

treatment to denature the protein (e.g. heating,

enzymatic hydrolysis)


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Conclusions

A two-step mechanism for gel structuration

is proposed.

The -lg/xanthan ratio had an important

effect on the reaction rate and the stability

of the gels.


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SUMMARY

Three main gel structures could be form when

protein and polysaccharides are mixed in

aqueous solution: IP, Phase-separated, and

Coupled networks. The different structures depending on the nature

and strength of interactions between polymers

and, also, depend on their properties.

Polymer gelling properties are impacted by

presence of other polymers in the medium,

sometimes producing synergistic effects.


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SUMMARY

In mixed gels, usually, the minimum concentration

of gelation is lower than those of solutions of both

individual gelling agents

The control of gelation process in binary gelsallows the formation of a wide range of

microstructures and different applications.


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Applications

Creation of tailor-made structures for

specific food applications:

Surimi based products, meat replacers, dairy

products, fat replacers, heat sensitive foods,

and microencapsulation.


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References Butler, M. F. & Heppenstall-Butler, M. (2003). Delayed Phase Separation in a Gelatin/Dextran Mixture

Studied by Small-Angle Light Scattering, Turbidity, Confocal Laser Scanning Microscopy, and Polarimetry

Biomacromolecules , 4, 928-936

Clark, A.H. (2000). Biopolymer gelation - The structureproperty relationship. Gums and Stabilisers for the

food industry, 10,

De Kruif, C. G., & Tuinier, R. (2001). Polysaccharide protein interactions. Food Hydrocolloids, 555-563.

Jones, O., Lesmes, U., Dubin, P., & McClements, D. (2010). Effect of polysaccharide charge on formation

and properties of biopolymer nanoparticles created by heat treatment of B-lactoglobulin-pectin complexes.

Food Hydrocolloids, 374-383.

Laneuville et al. (2006).Gelation of Native -Lactoglobulin Induced by Electrostatic Attractive Interactionwith Xanthan Gum.Langmuir, Vol. 22, No. 17.

Monteiro, S.,Claudia Tavares, Dmitry V. Evtuguin, Nuno Moreno, and J. A. Lopes da Silva (2005). Influence

of Galactomannans with Different Molecular Weights on the Gelation of Whey Proteins at Neutral pH.

Biomacromolecules, 6, 3291-3299

Neirynck, N. et al. (2007). Influence of pH and biopolymer ratio on whey proteinpectin interactions in

aqueous solutions and in O/W emulsions. Colloids and Surfaces A: Physicochem. Eng. Aspects, 99-107.

Sperling, L. H. "Interpenetrating Polymer Networks:An Overview." In Interpenetrating Polymer Networks,

Edited by Klempner, 3-38. Washington, DC: American Chemical Society, 1994.

Tolstoguzov, V. (2003). Some thermodynamic considerations in Food Formulation. Food Hydrocolloids

17,1-23.

Turgeon, S., & Laneuville, S. (2009). Protein+Polysaccharide and Complexes: From Scientific Background

to their Application as Functional Ingredients in Food Products. In I. T. Edited by: Stefan Kasapis, Modern

Biopolymer Science. (pp. 327-363). London: Elsevier.


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Acknowledgement

Dr. L. Chen (supervisor)

Dr. F. Temelli and Dr. T. Vasanthan (committee members)

THANK YOU!

Documents

Different Microstructures of Binary Gels for Food Applications