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

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

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

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

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

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

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

Low methoxy pectin

High methoxy pectin

Pectin gel forming mechanism

Pectin

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

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

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

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

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

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

Alginate

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

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 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)

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

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

Kinds of Carrageenan lambda

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

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.