FOOD CHEMISTRY

BYDR BOOMINATHAN Ph.D.

M.Sc.,(Med. Bio, JIPMER), M.Sc.,(FGSWI, Israel), Ph.D (NUS, SINGAPORE), PDF (USA)

PONDICHERRY UNIVERSITYIV lecture

10/August/2012

Goals

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

Plant cell wall

Pectin

PectinMonomer: D-galacturonic acid, L-rhamnoseOthers: D-galactose, D-xylose,

D-arabinose short side chain)Bonding: -1,4

Pectin

-gelling and thickening agents-bound to calcium in the middle lamella-bound to cellulose in the primary cell wall

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

~85% galacturonic acidSome are esterified with methyl alcoholDE = degree of esterification10-15% galactopyranose, arabinofuranose & rhamnose

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Pectin contains:

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 gumsB. Pectin gels are useful in making jelly and jams

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PectinPectin 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% ESTERIFIED8

PectinPectin 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

C

O

O

C

O

OCa+ +

- -

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Low methoxy pectin

High methoxy pectin

Pectin gel forming mechanism

Pectin

PectinPectin 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

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Pectin esterase

Loss of precipitation

High Methoxy Pectin

Partially De-esterified Pectin at low pH

Partially De-esterified Pectin

Amidated Pectin

Pectin Esterase and Lyase

Polygalacturonase and Pectin Lyase

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

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

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Gums

Properties depend on:1)Size and shape2)Ionization and pH3)Interactions with other components

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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

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Gums

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

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Properties depend on:

Gums

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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: 1. Ca2+ or trivalent ions2. pH is at 3 or less

– Used as an ice cream and frozen dessert stabilizer

– Also used to stabilize salad dressings

Alginate

G

M

G, M

Alginate

Monomer: -mannuronic acid (M)-L-guluronic acid (G)

Bonding: -1,4/-1,4

Pectin-Alginate image

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

Propylene Glycol Alginate

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

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

Carrageenan

Gums

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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

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)

CarrageenanMonomer: D-galactose (anhydro/sulfate)Bonding: -1,4/ -1,3

kappa

iota

Kinds of Carrageenan

lambda

Kinds of Carrageenan

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 (, , and carageenan)

• Functional Properties: pH independent thickening. Double helix formation in or carageenan can lead to gelation.– -carageenan is used in dairy foods

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

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.