1. PONDICHERRY UNIVERSITY
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 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 Pectin contains: 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 (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 % ESTERIFIED
SLOW SET –
% 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 ,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)
% (DE) = Rapid Set
% (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 2) Ionization and pH 3) Interactions with other components
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. Gums A) Ionic gums Examples of gums and their applications 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

27. Alginate

28. Alginate G M G, M Monomer: -mannuronic acid (M)
Because of their heat stability, alginate gel are often used in preference to some thermoreversible gelling system
-excellent thickening properties/stabilizing capabilities
-At low pH, it gel or precipitate, can not be used as a stabilizer to products; fruit juices, salad dressing
-May use glycol alginate; carboxyl groups were esterified.
-propylene glycol alginate acts as emulsifier/emulsion stabilizer (bear foam)
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 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. Gums 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

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
-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)
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.