FOOD CHEMISTRY carbohydrates pectin gums carrageenan

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 Pectin Monomer: D-galacturonic acid, L-rhamnose Others: D-galactose, D-xylose, D-arabinose short side chain) Bonding: α-1,4 -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 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) 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 ESTERIFIED 70% SLOW SET – 50 - 70% ESTERIFIED Pectin Pectin gels (Jelly) 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 O C O- O C + + Ca -O Low methoxy pectin Alginate Alginate G M G, M Monomer: Bonding: β-mannuronic acid (M) α-L-guluronic acid (G) α-1,4/β-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 A) Ionic gums • Carrageenan Gums – 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 (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 34 Carrageenan: Properties -Most important red seaweed polysaccharides used by food industry -3 forms differ in sulfate ester -commercial products contain a mixture of 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: β -1,4/ α-1,3 kappa iota lambda 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 (ι, κ, and λ carageenan) • Functional Properties: pH independent thickening Double helix formation in κ or ι carageenan can lead to gelation – κ-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 ... • 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... 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... precipitation 14 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 • • • • •