FOOD CHEMISTRY

1. FOOD CHEMISTRY BY DR BOOMINATHAN Ph.D. M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE), PDF (USA) PONDICHERRY UNIVERSITY IV lecture 10/August/2012

2. Goals • Pectin structure • Pectin ingredients • Applications of Pectin in food industry • Different Gum structure • Physico-chemical properties • Applications of Gums in food industry

3. Plant cell wall

4. Pectin

5. Pectin Pectin Monomer: D-galacturonic acid, L-rhamnose Others: D-galactose, D-xylose, D-arabinose short side chain) Bonding: -1,4 -gelling and thickening agents -bound to calcium in the middle lamella -bound to cellulose in the primary cell wall

6. Pectin • Pectic substances • Middle lamellae of plant cell walls • Functions to move H2O and cement materials for the cellulose network • Get PECTIN when you heat pectic substances (citrus peel etc. ) in acid • Not a very well defined material • Pectins from different sources may differ in chemical and functional details Pectin contains: • ~85% galacturonic acid • Some are esterified with methyl alcohol • DE = degree of esterification • 10-15% galactopyranose, arabinofuranose & rhamnose

7. Pectin • Most pectins have a DE of 50-80% • Young unripened plants/fruits have very • high degree of esterification  hard texture • Old ripened plants/fruits have • lower degree of esterification  softer texture • Food use A. Thickener - some use, but less common than gums B. Pectin gels are useful in making jelly and jams

8. Pectin Pectin gels (Jelly) 1. Regular sugar/acid gel • Pectin 0.2 - 1.5% • Low pH from 2.8 - 3.2 (suppresses ionization) - get less repulsion • Sugar (65 -70%) - causes a dehydration of pectin by competing for water through H-bonding • Get gel by charge, & hydration effect Undissociated at low pH  No repulsion RAPID SET - 70% ESTERIFIED SLOW SET – 50 - 70% ESTERIFIED

9. Pectin Pectin gels (Jelly) 2. Low methoxyl pectin gel • < 50% esterified • Get gel due to Ca2+ ion bridging • Avoid need for sucrose (diet foods) • Get gels over wide pH range • Gels tend to be more brittle & less elastic than sugar/acid gels

10. Low methoxy pectin

11. High methoxy pectin

12. Pectin gel forming mechanism

13. Pectin

14. Pectin Pectin and its characteristics: Example: Citrus juices • Normal juice - colloidal pectin - thickening • Pectin esterase - demethoxylates pectin --loss of thickening-- precipitation - due to H-bonding of COOH and Ca2+ bridging • Must heat juice to inactivate enzyme - causes dramatic flavor changes Pectin esterase Loss of precipitation

15. High Methoxy Pectin

16. Partially De-esterified Pectin at low pH

17. Partially De-esterified Pectin

18. Amidated Pectin

19. Pectin Esterase and Lyase

20. Polygalacturonase and Pectin Lyase

21. Pectins • Unbranched polymers of 200 - 1,000 Galactose units, linked b 1-4 Glucosidic bonds • Degree of esterification controls setting rate • >50% High Ester Pectins (HM) • <50% Low Ester Pectins (LM) • 70 - 85% (DE) = Rapid Set • 44 - 65% (DE) = Slow Set • Calcium required to gel LM Pectins • USES: • Amidated LM Pectins used to gel natural fruit preserves • High ester (HM) Pectins stabilize sour milk drinks - react with casein • Low ester (LM) Pectins used for milk gels

22. Gums • Plant polysaccharides (excluding unmodified starch, cellulose and pectin) that posses ability to contribute viscosity and gelling ability to food systems (also film forming) • Obtained from • Seaweeds • Seeds • Microbes • Modified starch and cellulose • All very hydrophilic • Water soluble • Highly hydrated • High hydration leads to viscosity = thickening and stabilizing effect • Also good gel formers • Some form gels on heating/cooling and in the presence of ions

23. Gums Properties depend on: • Size and shape • Ionization and pH • Interactions with other components

24. Gums Properties depend on: 1) Size and shape • Linear structures: • More viscous (occupy more space for same weight as branched) • Lower gel stability  get syneresis on storage (i.e. water squeezes out of the gel) • Branched structures • Less viscous • Higher gel stability  more interactions

25. Gums Properties depend on: 2) Ionization and pH • Non-ionized gums = little effect of pH and salts • Negatively charged gums • Low pH = deionization = aggregation  precipitation • Can modify by placing a strong acidic group on gum so it remains ionized at low pH(important in fruit juices) • High pH = highly ionized = soluble  viscous • Ions (e.g. Ca2+) = salt bridges = gels 3) Interactions with other components • Proteins • Sugars

26. Examples of gums and their applications A) Ionic gums Alginate From giant kelp Polymer of D-mannuronic acid and L-guluronic acid Properties depend on M/G ratio Highly viscous in absence of divalent cations pH 5-10 Form gels when: Ca2+ or trivalent ions pH is at 3 or less Used as an ice cream and frozen dessert stabilizer Also used to stabilize salad dressings Gums

27. Alginate

28. Alginate G M G, M Monomer:-mannuronic acid (M) -L-guluronic acid (G) Bonding: -1,4/-1,4

29. Pectin-Alginate image

30. Algin and Alginate • Polymers of Mannuronic and Galacturonic acids varying widely in ratios of the two acids • Viscosity of 1% solution ranges from 10 to 2,000 CP as a function of molecular weight and calcium ion content • Precipitates below pH 3.0 • Degrades above pH 6.5 • Forms gels with calcium ions - 0.5 to 1.0% calcium • Propylene glycol derivative improves stability to calcium and acid • Food functionality includes: • Water binding • Gelling • Emulsifying • Stabilizing

31. Propylene Glycol Alginate • Precipitate at low pH • Interaction with calcium ions • Some interaction with fat • "Slimy" mouthfeel can substitute for fat • Good foam stabilizer

32. Alginate Gels • Extrude into calcium bath • Use sodium alginate with a sparingly soluble calcium salt • Regulate calcium availability by regulating pH, sequesterant • Too much calcium gives grainy gels • Too slow release gives weak gels

33. Carrageenan

34. A) Ionic gums Carrageenan From various seaweeds Seven different polymers κ-, ι- and λ-carrageenan most important Commercial carrageenan is a mixture of these Polymer is sulfated Stable above pH 7 (is charged) Function Depends on salt bound to the sulfate group Na+ = cold water soluble and does not gel  provides viscosity K+ = produces firm gel Improves/modifies function of other gums Stabilizes proteins Interacts with milk/cheese proteins Gums

35. Carrageenan: Properties -Most important red seaweed polysaccharides used by food industry. -3 forms differ in sulfate ester -commercial products contain a mixture of 3 fractions -stabilize milk protein -water gel in low-calorie jams and jellies -thickeners/stabilizer (combine with other hydrocolloid)

36. Carrageenan Monomer: D-galactose (anhydro/sulfate) Bonding: -1,4/ -1,3 

37. Kinds of Carrageenan kappa iota

38. Kinds of Carrageenan lambda

39. Carageenan • Source: Seaweed gum • Structure: Linear D-galactopyranosyl chain with alternating 1,3 and 1,4 links.   Some residues have one or two sulfate ester residues.   Three broad types of repeating structure (i, k, and l carageenan) • Functional Properties: pH independent thickening. Double helix formation in k or i carageenan can lead to gelation. • k-carageenan is used in dairy foods

40. Carrageenans • Mixtures of nonhomogeneous polysaccharides • Galactans having sulfate half-ester groups attached to the sugar units • Extracted from red seaweeds • D-galactopyranosyl units joined with alternating (1 3)-a-D- and (1 4)-b-D-glycosidic linkages, with most sugar • units having one or two sulfate groups esterified to a hydroxyl group at carbon atoms C-2 or C-6

41. Carrageenans • Sulfate content-15 to 40% • Carrageenan products dissolve in water to form highly viscous solutions. • The viscosity is quite stable over a wide range of pH values because the sulfate half-ester groups are always ionized, even under strongly acidic conditions, giving the molecules a negative charge.