1. Polysaccharides 11

2. 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 & apple pomace) in acid
Not a very well defined material
Pectins from different sources may differ in chemical and functional details
~85% galacturonic acid
Some are esterified with methyl alcohol
DE = degree of esterification
10-15% galactopyranose, arabinofuranose & rhamnose

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

4. 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 - 70% ESTERIFIED
SLOW SET % ESTERIFIED

5. 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

6. Pectin Pectin and quality problems Example: Cloud in citrus juices
Normal juice - colloidal pectin - cloud
Pectin esterase - demethoxylates pectin get loss of cloud - precipitation - due to H-bonding of COOH and Ca2+ bridging
Must heat juice to inactivate enzyme - causes dramatic flavor changes

7. Cellulose Most abundant organic compound on the planet
Plant cell wall component
Gives tensile strength to cell wall
Very high molecular weight insoluble polymer of glucose
-1-4 glycosidic bonds
These bonds give cellulose a very rigid straight parallel chain that has extensive H-bonds
v.s.

8. Cellulose
Hydrogen
Bond

9. Cellulose Properties Crystalline regions have very tight H-bonding
Insoluble in water
No effect on viscosity (why?)
Little access to hydrolytic reagents and enzymes
Very tough texture
Not digestible by humans
-1-4 glycosidic bonds
Pass through digestive system
Contributes no calories
Dietary fiber
Possibly lower cholesterol
Improve bowel movements

10. Cellulose Uses in foods Can improve function slightly by heating
Unmodified cellulose is made from wood pulp or cotton (dry powder)  very cheap
Minimal effect on viscosity
Added as "fiber" (breads and cereals)
Non-caloric bulk (no flavor, color etc)
Very little effect in foods
Can improve function slightly by heating
Small number of H-bonds break
Slight swelling, softening
Only slightly soluble in water
No change in digestibility

11. Cellulose
Cellulose can be modified to dramatically improve its function and use:
Microcrystalline cellulose (MCC)
Prepared by partial acid hydrolysis
Non-crystalline regions are penetrated by acid and cleaved to release the crystalline regions
Crystalline regions combine to form microcrystals
Still insoluble (all crystalline)
Limited food uses:
Stabilizes emulsions
Absorbs oils & syrups
Dry mixes - keeping them free-flowing

12. Cellulose Two main products of MCC Powdered MCC Spray dried MCC
Forms aggregated porous/sponge-like microcrystals
Uses:
Flavor carrier
Anticaking agent in powders and cheese

13. Cellulose Colloidal MCC
Mechanical energy applied after hydrolysis to rip microcrystals apart to form small micro-aggregates
Water dispersible – similar function as food gums
Food uses:
Foam and emulsion stabilizer
Pectin and starch stabilizer
Fat and oil replacement

14. Cellulose B) Methyl cellulose
Cellulose treated with alkali to swell fibers and then methyl chloride is introduced:
Get methyl ether group O CH 2 OH
OCH 3 1]
NaOH
2] CH Cl

15. Cellulose Unique results: “Soluble” in cold water
Methyl ether group breaks H-bonding
Solubility  as temperature 
Heating dehydrates the cellulose and hydrophobic methyl ether groups start to interact
Viscosity increases and methyl cellulose forms a gel
Becomes soluble again on cooling

16. Cellulose Food uses: Thermogelation properties Fat replacer
Fat/oil barrier in batters for deep fried food applications
The cellulose gels on heating and prevents fat uptake
Holds moisture in food during thermal processing
Acts as binder during thermal processing
Fat replacer
Methyl ether groups gives it fat-like properties
Emulsion and foam stabilizer
Due to increased viscosity (thickening effect)
Film forming ability (e.g. water soluble bags)

17. Cellulose C) Carboxymethyl cellulose (CMC)
Cellulose treated with alkali
to swell fibers and then
chloroacetic acid is
introduced:
Get carboxymethyl ether
group O CH 2 OH
1] NaOH
2] ClCH
COOH CO -
pH DEPENDENT

18. Cellulose Food use: Major use: non-digestible fiber in dietetic foods
Hot and cold water soluble
Weak acid  properties affected by pH due to carboxyl group
COOH  COO-
Negative charge leads to repulsion between CMC making it a good thickening and stabilizing agent
repulsion = viscosity

19. Cellulose Food uses (cont.) Common stabilizer in ice cream
Retards ice crystal formation
Foam stabilizer
E.g. commercial meringues
Tends to interact with proteins due to charge, increasing their viscosity & solubility
Used to stabilize milk proteins in milk
Can form gels and films between pH 5-11

20. 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

21. 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

22. Gums 2) Ionization and pH 3) Interactions with other components
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

23. Gums 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

25. 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

26. Gums B) Non-ionic gums Guar gum and Locust bean gum
No effect of pH and ions (salts) since they are uncharged
Guar gum has galactose side-groups on every other mannose unit (2:1) while locust bean gum does not have uniform distribution (4:1)

27. Gums B) Non-ionic gums Guar gum and Locust bean gum
Guar gum produces: soluble in hot/cold water; very viscous solutions at 1% and gels and films at 2-3%; thixotropic
Ground meats, salad dressings and sauces……
Locust bean gum: Soluble at 80/90oC; very viscous solutions; Synergist with xanthan gum or carrageenan
Binder in luncheon meat products and used in frozen desserts

29. Guar gum uses Ice creams: Smooth creamy texture
Bakery products: Texture, moisture retention
Noodles: Moisture retention, machine runnability
Beverages: Body, mouth feel
Meat: Binder, absorb water
Dressings: Thickener, emulsion stabilizer

30. Gums
Gum arabic
One of the oldest known gums, from the bark of Acacia trees in the Middle-East and N- Africa
Very large complex polymer
Up to Dalton (varies greatly with source)
Glucuronic acid and galactose main building blocks
Rhamnose and arabinose in minor amounts
Very expensive compared to other gums but has unique properties

33. Gums Properties of gum arabic Readily dissolves in water
Colorless and tasteless solutions of relatively low viscosity
Can go up to 50% w/w
Newtonian behavior <40%
Pseudoplastic behavior >40%
Can manipulate solution viscosity of gum arabic by changing pH
Low or high pH = low viscosity
pH 6-8 = higher viscosity

34. Gums Applications of gum arabic
Gum candy (traditional hard “wine gums”) and pastilles
Retards sugar crystallization
Coating agent and binder
Ice cream and sherbets
induces and maintains small ice crystals
Beverages
foam and emulsion stabilizer
used in beverage powders (e.g. citrus drink mixes) to maintain and stabilize flavor (encapsulates flavors)
Bakery and snack products
Lubricant and binder

35. Gums C) Branched ionic gums Xanthan
Produced by Xanthomonas a microbe that lives on leaves of cabbage plants
Cellulose backbone with charged trisaccharide branches
Branching prevents gelation
Very viscous due to charged branches
Expensive ingredient

36. Gums Xanthan is widely used due to unique function
Soluble in hot and cold water
Very high viscosity at low concentrations
Has pseudoplastic properties
viscosity decreases when it is poured or agitated (shear-thinning)
Viscosity is independent of temperature (10-95°C) and pH (2- 13)
High freeze-thaw stability
Compatible with most food grade salts

37. Gums Xanthan is widely used due to unique function
Ideal for emulsions excellent in fat-free dressings due to viscosity, pseudoplasticity and smooth mouth feel
Excellent food stabilizer
Good for thermally processed foods
Expensive!