Pectin

Food applications of pectin?

Gelling agent - fruit jellies and jams Texture of processed fruits Thickening agent - viscosity of purees and juices Cloud stability in fruit juices

Two types of pectin gels?

High methoxyl (HM) pectin gel Low methoxyl (LM) pectin gel

Pectic acid?

overripe plant material

Pectin hydrolysis?

Acid pH Hydrolysis of glycosidic linkages & partial hydrolysis of methyl esters Neutral - Alkaline pH Pectinic acid: galacturonan with high methoxyl proportion (>50%)Unmethylated carboxylic groups are present as ionic state. Pectic acid: galacturonan with low methoxyl proportion (<50%)

Conformational structure of pectin?

C1 chair conformation, α-(1-4)-D-galacturonic acid units Three fold helical conformation OH, ester and COOH groups are in equatorial position Favourable for inter-molecular hydrogen and hydrophobic bonding.

Protopectin?

Immature plant material

Where is pectin found and what to they do?

Occurs in middle lamella. They give plants flexibility. Found rich in ripe fruits (not overripe fruits) Apple, peach, plum, grapefruit, orange

Low methoxyl pectin gel?

Only form gel in the presence of divalent cations (Ca2+) via cross-links by salt bridges Forms at higher pH (3.5 - 6.5) COOH group must be charged Addition of Ca2+ ions: reduce ionic repulsion Addition of sugar is not neededlow sugar jams and jellies (i.e. low caloric gels)

High methoxyl pectin gel?

Pectin 0.5-1.0% Contributes to the continuity of the structure. If juice is low in pectin, concentrate by boiling or add commercial pectin Peach pectin contains acyl groups, so form poor gel Citrus & apple form good gels Acid Neutralises -COO- charges & these lose water of hydration & become uncharged, thus allowing chains to approach one another, form H-bonds & junction zones. Contributes flavour and rigidity of structure. pH optimum is 3.2. If juice is low in acid, add lemon juice Sugar Sugar competes for water and strips it off pectin molecules allowing them to approach one another and form junction zones. COOH groups H-bonds with each other instead of water and high sugar conc. stabilizes this hydrophobic interaction

Chemical structure of pectin Polygalacturonan?

Polygalacturonan consisting of a linear chain of repeated α-(1-4)-D- galacturonic acids with methyl ester groups (predominant form of pectin)

Chemical structure of pectin Rhamnogalacturonan I?

Rhamnogalacturonan I: Some galacturonic acids are replaced by (1-2)- linked α-L-rhamnose which kinks the chain, thus preventing the extended chain

Chemical structure of pectin Rhamnogalacturonan II?

Rhamnogalacturonan II: Native pectin with highly irregular branches of arabinose, galactose, xylose, etc. Chain length and degree of methylation at C-6 depend on the source and processes used to extract pectins. Water soluble galacturonoglycans of varying methyl ester contents and degrees of neutralisation

Pectin is the collective name for......

Water soluble heteropolysaccharides

Pectin?

mature plant material

Pectinic acid?

mature plant material