PECTIC SUBSTANCES, PECTIN AND FOOD GUMS

This is a presentation on pectic substances and gums. It covers all 4 types of pectic substances - protopectin, pectinic acid, pectin and pectic acid as well as their inter-conversion. The process of gel formation and types of pectin are also mentioned in detail. It also contains different types of food gums - guar gum, locust bean gum, agar, algin, carrageenans and mucilage. It also mentions the common physical, chemical and rheological properties of pectin and gums along with their applications.

1. PECTIC SUBSTANCES, PECTIN AND GUMS SREE NANDANA S F OOD SCIENCE & TECHNOLOGY KUFOS

2. PECTIC SUBSTANCES Protopectin, Pectinic acid and Pectic acid . Complex carbohydrates which occur in, or are prepared from plants. Linear polymers of D- Galacturonic acid joined by α(1,4) glycosidic linkages Some carboxyl group esterified with methanol Cross planar glycosidic linkages gives a twisted ribbon structure Found mainly in primary cell wall . Abundant in soft tissues like rinds of citrus fruit and sugar beet pulp.

3. 1. Protopectin A high molecular-weight methylated galacturonic acid polymer Insoluble in water Cannot form gel Converted to water dispersible pectin by heating in boiling water Found in immature fruits

4. 2. Pectinic acid A polymeric form of methylated galacturonic acid . Formed by enzymatic hydrolysis of protopectin as a fruit ripens. Dispersible in water and can form gels . High-molecular-weight pectinic acids are known as pectins.

5. 3. Pectic acid A shorter-chain derivative of pectinic acid that is formed as fruit overripens. No methyl esterified carboxyl groups . Enzymes, such as polygalacturonase and pectinesterase, cause depolymerization and demethylation of the pectinic acid, respectively. Complete demethylation of pectinic acid yields pectic acid, which is incapable of gel formation.

6. Conversion Protopectin Pectin Galacturonic acid Pectin / Pectinic acid Pectic acid Protopectinase Hydrolysis Pectinase Hydrolysis and De-esterification Protopectin is the parent substance . Protopectin - water insoluble precursor of pectin . Pectin - >75% of carboxyl groups methylated Pectinic acid - <75% of carboxyl groups methylated Pectic acid - no methyl esterified carboxyl groups. Pectinesterase Complete De-esterification

7. PECTIN High molecular weight pectinic acids . Linear polymers of D- Galacturonic acid joined by α(1,4) glycosidic linkages with some carboxyl group esterified with methanol. In fruits, keeps the walls of adjacent cells together. Helps ripening fruits remain firm and keep their shape. When fruits overripen, pectin is broken down making it soft. Degree of esterification - 60% in apple pulp to 10% in strawberries.

8. Based on degree of esterification, pectin can be classified as: HM Pectin (Degree of esterification – above 50%) LM Pectin (Degree of esterification - below 50%)

9. Low Methoxy (LM) Pectin Forms gels in low to moderate sugar levels . More free carboxyl groups that forms cross-links with divalent ions like Ca²⁺ . Resultant 3D network can trap liquid to form gels. Form gel in presence of divalent ions without sugar or acid . High Methoxy (HM) Pectin Less free carboxyl groups to form cross-links with divalent ions. Can be made to gel with the addition of sugar and acid . Exhibit thermal reversibility i.e., gel to sol transition with temperature. Commonly used to form pectin jellies .

10. Gel Formation A pectin gel - water held in a 3D network of pectin molecules Usually forms ‘sol’, under right conditions form a ‘gel’ Pectin is hydrophilic - presence of –OH group and –COO- groups. Water binds to both these groups. Negative charge and attraction for water keeps the molecules apart. To form gels, forces keeping the molecules apart should be reduced. Attraction for water molecules - reduced Attraction for each other - increased. Achieved by addition of sugar and acid .

11. Sugar competes for water . Decrease pectin-water attraction. Acids reduces pH (for gel formation, pH<3.5). Ionized and unionized forms of carboxylic acids exists in equilibrium. -COOH + H2O -COO¯ + H3O⁺ Addition of acid - equilibrium is shifted to left. Ionization of carboxylic acid - depressed Charge on the pectin molecules - reduced . Pectin molecules no longer repel each other. Pectin molecules align and interact at specific regions ( junction zones ). Regions not involved in junction zones ( pockets ) entrap water. Forms a 3D network.

12. Physical Properties Appearance – White or light brown powder Odour - Odourless or slightly sweet Taste - Tasteless or slightly bitter Texture - Powder: Fine or coarse; Gel: Firm or soft (depend on the conditions) Melting Point - No distinct melting point. Decomposes at very high temperature. Solubility - Water: Soluble, forms viscous solutions Organic solvents: Insoluble or partially soluble Hygroscopicity - Absorbs moisture from the air Refractive Index - 1.3-1.5

13. Chemical Properties Degree of Esterification (DE) - 20-90% Acetyl Content - 1-10% Methoxy Content (MC) - 5-15% Galacturonic Acid Content - 60-90% pK a Value (Acid Dissociation Constant) - 3.5-4.5 - indicates pectin's acidic nature Gelation - able to form gels Stability - relatively stable over a wide pH range (2.5-7.5).

14. Rheological Properties Viscosity - High (increases with concentration; decreases with temperature). Non-Newtonian behavior - Viscosity decreases with increasing shear rate. Thixotropy - Viscosity decreases over time under constant shear rate; recovers at rest. Creep behavior - Pectin gels deform over time under constant stress. Relaxation behavior - Pectin gels release stress over time after deformation. Temperature dependence – Increased temperature reduce viscosity & gel strength. pH dependence - Optimal gelation occurring at pH 2.5-4.5. Sugar dependence - Increased sugar concentration enhance gel strength.

15. Uses Jams, jellies, ice cream, and yogurt drinks – thicken and stabilize. J uices and soft drinks - improve texture , especially when the sugar content is low Used to make edible films and coatings for food packaging Reduce low-density lipoprotein  (LDL) levels, hence lower cholesterol levels A good source of dietary fiber S low the passage of food through the intestine, relieving diarrhea

16. GUMS Complex hydrophilic carbohydrates with thousands of monosaccharide units Galactose - common monosaccharide Glucose – usually absent Called hydrocolloids (size and affinity for water) When added to water, form ‘sol’. Highly branched thus unable to form gels Trap high amount of water within their branches Highly viscous - unable to move freely without being tangled They are soluble fibre .

17. Food gums are mainly of 6 types:- Guar Gum Locust Bean Gum Agar Algin Carrageenan Mucilage

18. Guar Gum Ground endosperm of seeds from the guar plant Main component is galactomannan . Highest viscosity among any natural or commercial gum. Used in milk products, baked goods, meat etc. In canned soup – thickener and stabilizer.

19. Locust Bean Gum Carob gum or carob bean gum A vegetable gum extracted from the seeds of carob tree. Main component is galactomannan. Mainly used in baked goods and diary products. Used to sweeten food and as a chocolate substitute.

20. Agar Extracted from sea weed ( red and brown algae ). Composed of g alactan , a polysaccharide of polymerized galactose . Two components - agarose and agaropectin. Agarose responsible for gelling properties. Agaropectin responsible for viscous properties.. Used as a solid medium in microbiological applications, thickener in ice cream etc.

21. Algin Obtained from brown algae. Alkaline extraction of brown algae Sodium salt of alginic acid . Colour – white to yellowish brown Commonly used in food industry as a stabilizer, thickener, emulsifier etc.

22. Carrageenans Extracted from sea weeds . Sulphonated galactans having sulphate group instead of hydroxyl groups in some places. Used as stabilizer in dairy products, thickener in desserts etc. Used in beer to remove haziness due to proteins.

23. Mucilage A thick, gluey substance produced by plants and some micro-organisms. A polar glycoprotein and an exopolysaccharide . Made of sugars and uronic acid linked by glycosidic bonds. In plants, store water and food . Chia and flaxseeds mucilage is used in vegan baked goods. Chia seed mucilage

24. Physical Properties Appearance – Mostly white, yellowish, or brownish powders or granules. Odour - Neutral or slightly sweet odour. Taste - Neutral or slightly sweet taste. Texture - Powder or granular texture. Viscosity - High viscosity Melting Point - No distinct melting point, but degrades at high temperatures. Flowability - Varies, but most gums are free-flowing powders. Hygroscopicity - Affect their texture and flowability.

25. Chemical Properties Solubility - Varies, but most are water-soluble, forming viscous solutions. Hydrophilic – High affinity for water Polarity - Able to form hydrogen bonds. Hydrogen bonds enhance viscosity. pH Stability - Generally stable over a wide pH range (2.5-7.5). Temperature Stability – Usually stable up to 180°F (82°C), degrades at higher temperatures. Moisture Retention - Gums retain moisture

26. Applications Thickening agent in salad dressing and gravies, replacing starch. Stabilization of food products like mayonnaise and yoghurt. Maintain smooth texture of food products like ice creams and other frozen desserts. Used in reduced fat products as they increase viscosity Helps to replace texture and mouthfeel provided by fat . Coating agent on fried foods and confectioneries.

27. C ONCLUSION Pectic substances, pectins and food gums Valuable ingredients with diverse applications. Essential components in various industries. Used in various food products because of their gelling ability. Ability to produce food products of various texture. Increased the choice and quantity of various food products.

28. REFERENCES Vickie A. Vaclavik , Elizabeth W. Christian (2008) Essentials of Food Science. Springer Verlag, New York. John M. deMan, John W. Finley, Chang Yong Lee (2018) Principles of Food Chemistry. Springer . Lee, F. (2012). Basic Food Chemistry . Springer Science & Business Media Mishra A. K., Mishra K. K., Singh C. S., Sharma M., Sharma D. C. Diversity and Industrial Applications of Fungal Pectinases. Doesberg J.J. Pectic substances in fresh and preserved fruits and vegetables. Joslyn M. A ., The Chemistry of Protopectin: A Critical Review of Historical Data and Recent Developments Mukherjee K. Pulok. (2019) Quality Control and Evaluation of Herbal Drugs.

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