Non-Food Uses of Polysaccharides

Transcription

1 Non-Food Uses of Polysaccharides John Mitchell

2 Acknowledgements Fundamentals of Hydrocolloid Technology Course ( ) Rob Winwood Colin Melia Steve Harding Pete Williams EPNOE

3 Polysaccharides and Applications Xanthan gum Pharmaceutical applications Gaviscon Hydrophilic matrix tables Gelatin replacement for hard capsules Hydroxypropycellulose Thermoplastic extrusion for drug delivery Breast Implants The future

4 Xanthan gum

5 Xanthan (E415) Extracellular polysaccharide from Xanthomonas campestris b-(1 4)-D-glucopyranose backbone with side chains of -(3 1)- a-linked D-mannopyranose-(2 1)-b-D-glucuronic acid-(4 1)- b-d-mannopyranose on alternating residues. Molecular weight Intrinsic viscosity 5000ml/g from:

6 Tertiary Structure: Conformation Zones Zone A: Extra-rigid rod: schizophyllan Zone B: Rigid Rod: xanthan Zone C: Semi-flexible coil: pectin Zone D: Random coil: dextran, pullulan Zone E: Highly branched: amylopectin, glycogen Slide: Courtesy of Steve Harding

7 Viscosity of 0.3% Xanthan Gum solution in standardised tap water. 100 Viscosity (Pa s) Shear Rate (1/s) Pseudoplastic flow! Slide Courtesy of Rob Winwood

8 Advantages Very high low shear viscosity Allows particles to be suspended but fluid to be easily pumped Cling to surfaces Ordered (helical) cellulose backbone gives high stability against degradation

9 At Low Concentration Xanthans Can Destabilise Suspensions Through Depletion flocculation

10 Xanthan Gum - Industrial Applications Liquid cleaners Paints and pigments Construction chemicals Oil well drilling Ceramics Mineral Suspensions Latex Emulsions Fire foams Fertilizers/Pesticides Liquid polishes (car care) Adhesives Carpet Printing Inks Foundry Core Washes Slide courtesy of Rob Winwood

11 Gaviscon Active ingredient low molecular weight low guluronate alginate Gels on the top of the stomach contents forming a raft which prevents reflux. Acid or calcium gel?

12 Stomach Raft to Treat GI Reflux

13 Alginate (E400-E404) Source: Brown seaweeds (Phaeophyceae, mainly Laminaria) Linear unbranched polymers containing b(1 4)-linked D-mannuronic acid (M) and a(1 4)-linked L-guluronic acid (G) residues Not random copolymers but consist of blocks of either MMM or GGG or MGMGMG

14 Different types of alginates different properties e.g. gel strength Polyguluronate: - gelation through addition of Ca2+ ions egg-box Polymannuronate less strong gels, interactions with Ca2+ weaker, ribbon-type conformation Alternating sequences disordered structure, no gelation

15 Gaviscon containing 10% low molecular weight alginate is an excellent mixer

16 Extended release Hydrophilic matrices Viscous surface layer Diffusion/erosion Percolation thresholds Erodes in GI tract Commonly used HPMC, HPC, alginates, xanthan, other gums. Slide courtesy of Colin Melia

17 Extended release Hydrophilic matrices Dry Matrix Initial Wetting Expansion of Gel Layer Gel Layer Hydration Slide courtesy of Colin Melia Insoluble Drug Tablet Erosion Soluble Drug Diffusion through gel layer

18 HARD GELATIN CAPSULES CAN GELATIN REPLACED BY POLYSACCHARIDES?

19 Pin Dipping Process

20 Gelatin Replacement Features Required Low viscosity at high concentrations Weight of dry material on pin and drying time critical Ability to gel and melt/dissolve in a specific temperature range Gel on the pin Melt in the stomach Mechanical properties of dried capsules (flexible rather than brittle) to survive high speed handling Acceptability as a food and pharmaceutical material

21 For biopolymer mixtures at high concentrations phase separation is the rule rather than the exception. Low concentrations of gelling polymer may form inclusions within high concentrations of the matrix. Such a structure will not gel on the pin Matrix polymer Gelling polymer

22 Summary of patent example WO A 20% pullulan, 0.12% gellan Heat to 75OC to totally dissolve polysaccharides Dipped at 60OC Hard transparent capsule Totally disintegrated in deionised water at 37O C in 75 minutes

23 Why pullulan? Linear polysaccharide Polyglucan 3 glucose units linked by α 1-4 linkages as in amylose (maltrotriose) each maltotriose unit linked α 1-6

24 Tertiary Structure: Conformation Zones Zone A: Extra-rigid rod: schizophyllan Zone B: Rigid Rod: xanthan Zone C: Semi-flexible coil: pectin Zone D: Random coil: dextran, pullulan Zone E: Highly branched: amylopectin, glycogen Slide Courtesy of Steve Harding

25 Movement around bonds: from: /water/hydro.html

26 How does structure relate to mechanical properties of dry film??

27 Hydrodroxypropylcellulose (hpc) Molar degree of substitution greater than 3 Food allowed Thermoplastic

28 Extrusion Increased increase in extrusion as a way of encapsulating drugs (has some advantages over spray drying) hpc has been extensively used Patent on using to hpc sometimes in combination with starch to reform plant materials

29 Breast Implants Hpc gel within a silicon rubber shell has been used Effect of irradiation used to sterilise the implant on rheology of gel important.

30 Relevance of Oscillatory rheometry Measure structural changes in gels E.g effect of irradiation on hpc gels Follow changes with temperature Effect of drugs on thermal association of hydroxypropylmethyl cellulose Predicting gelation on cooling of pin dipping formulations Follow changes with time Predict physical instability in stored liquids systems

31 A challenge for Europe Papers published in Carbohydrate Polymers by region 60 % of Total Western Europe 30 Asia 20 US and Canada South America Year In % of published papers were from Asia

32 Carbohydrate Polymers Citations For Papers Published in 2007 and 2008 Keyword Composite Ant-bacterial, microbial, viral Drug delivery Chitosan Alginate Food Cellulose Starch Pectin Citations per publication Number of publications

33 Polysaccharides Are Clever Molecules (Carmen Boeriu)