Polysaccharides 11

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 & apple pomace) in acid Not a very well defined material Pectins from different sources may differ in chemical and functional details ~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 DE  hard texture Old ripened plants/fruits have lower DE  softer texture Food use A. Thickener - some use, but less common than gums B. Pectin gels - 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

Pectin Pectin and quality problems Example: Cloud in citrus juices Normal juice - colloidal pectin - cloud Pectin esterase - demethoxylates pectin get loss of cloud - precipitation - due to H-bonding of COOH and Ca2+ bridging Must heat juice to inactivate enzyme - causes dramatic flavor changes

Cellulose Most abundant organic compound on the planet Plant cell wall component Gives tensile strength to cell wall Very high molecular weight insoluble polymer of glucose -1-4 glycosidic bonds These bonds give cellulose a very rigid straight parallel chain that has extensive H-bonds v.s.

Cellulose Hydrogen Bond

Cellulose Properties Crystalline regions have very tight H-bonding Insoluble in water No effect on viscosity (why?) Little access to hydrolytic reagents and enzymes Very tough texture Not digestible by humans -1-4 glycosidic bonds Pass through digestive system Contributes no calories Dietary fiber Possibly lower cholesterol Improve bowel movements

Cellulose Uses in foods Can improve function slightly by heating Unmodified cellulose is made from wood pulp or cotton (dry powder)  very cheap Minimal effect on viscosity Added as "fiber" (breads and cereals) Non-caloric bulk (no flavor, color etc) Very little effect in foods Can improve function slightly by heating Small number of H-bonds break Slight swelling, softening Only slightly soluble in water No change in digestibility

Cellulose Cellulose can be modified to dramatically improve its function and use: Microcrystalline cellulose (MCC) Prepared by partial acid hydrolysis Non-crystalline regions are penetrated by acid and cleaved to release the crystalline regions Crystalline regions combine to form microcrystals Still insoluble (all crystalline) Limited food uses: Stabilizes emulsions Absorbs oils & syrups Dry mixes - keeping them free-flowing

Cellulose Two main products of MCC Powdered MCC Spray dried MCC Forms aggregated porous/sponge-like microcrystals Uses: Flavor carrier Anticaking agent in powders and cheese

Cellulose Colloidal MCC Mechanical energy applied after hydrolysis to rip microcrystals apart to form small micro-aggregates Water dispersible – similar function as food gums Food uses: Foam and emulsion stabilizer Pectin and starch stabilizer Fat and oil replacement

Cellulose B) Methyl cellulose Cellulose treated with alkali to swell fibers and then methyl chloride is introduced: Get methyl ether group O CH 2 OH OCH 3 1] NaOH 2] CH Cl

Cellulose Unique results: “Soluble” in cold water Methyl ether group breaks H-bonding Solubility  as temperature  Heating dehydrates the cellulose and hydrophobic methyl ether groups start to interact Viscosity increases and methyl cellulose forms a gel Becomes soluble again on cooling

Cellulose Food uses: Thermogelation properties Fat replacer Fat/oil barrier in batters for deep fried food applications The cellulose gels on heating and prevents fat uptake Holds moisture in food during thermal processing Acts as binder during thermal processing Fat replacer Methyl ether groups gives it fat-like properties Emulsion and foam stabilizer Due to increased viscosity (thickening effect) Film forming ability (e.g. water soluble bags)

Cellulose C) Carboxymethyl cellulose (CMC) Cellulose treated with alkali to swell fibers and then chloroacetic acid is introduced: Get carboxymethyl ether group O CH 2 OH 1] NaOH 2] ClCH COOH CO - pH DEPENDENT

Cellulose Food use: Major use: non-digestible fiber in dietetic foods Hot and cold water soluble Weak acid  properties affected by pH due to carboxyl group COOH  COO- Negative charge leads to repulsion between CMC making it a good thickening and stabilizing agent repulsion = viscosity

Cellulose Food uses (cont.) Common stabilizer in ice cream Retards ice crystal formation Foam stabilizer E.g. commercial meringues Tends to interact with proteins due to charge, increasing their viscosity & solubility Used to stabilize milk proteins in milk Can form gels and films between pH 5-11

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: 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 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 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: 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

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

Gums B) Non-ionic gums Guar gum and Locust bean gum No effect of pH and ions (salts) since they are uncharged Guar gum has galactose side-groups on every other mannose unit (2:1) while locust bean gum does not have uniform distribution (4:1)

Gums B) Non-ionic gums Guar gum and Locust bean gum Guar gum produces: soluble in hot/cold water; very viscous solutions at 1% and gels and films at 2-3%; thixotropic Ground meats, salad dressings and sauces…… Locust bean gum: Soluble at 80/90oC; very viscous solutions; Synergist with xanthan gum or carrageenan Binder in luncheon meat products and used in frozen desserts

Guar gum uses Ice creams: Smooth creamy texture Bakery products: Texture, moisture retention Noodles: Moisture retention, machine runnability Beverages: Body, mouth feel Meat: Binder, absorb water Dressings: Thickener, emulsion stabilizer

Gums Gum arabic One of the oldest known gums, from the bark of Acacia trees in the Middle-East and N- Africa Very large complex polymer Up to 3.500.000 Dalton (varies greatly with source) Glucuronic acid and galactose main building blocks Rhamnose and arabinose in minor amounts Very expensive compared to other gums but has unique properties

Gums Properties of gum arabic Readily dissolves in water Colorless and tasteless solutions of relatively low viscosity Can go up to 50% w/w Newtonian behavior <40% Pseudoplastic behavior >40% Can manipulate solution viscosity of gum arabic by changing pH Low or high pH = low viscosity pH 6-8 = higher viscosity

Gums Applications of gum arabic Gum candy (traditional hard “wine gums”) and pastilles Retards sugar crystallization Coating agent and binder Ice cream and sherbets induces and maintains small ice crystals Beverages foam and emulsion stabilizer used in beverage powders (e.g. citrus drink mixes) to maintain and stabilize flavor (encapsulates flavors) Bakery and snack products Lubricant and binder

Gums C) Branched ionic gums Xanthan Produced by Xanthomonas a microbe that lives on leaves of cabbage plants Cellulose backbone with charged trisaccharide branches Branching prevents gelation Very viscous due to charged branches Expensive ingredient

Gums Xanthan is widely used due to unique function Soluble in hot and cold water Very high viscosity at low concentrations Has pseudoplastic properties viscosity decreases when it is poured or agitated (shear-thinning) Viscosity is independent of temperature (10-95°C) and pH (2- 13) High freeze-thaw stability Compatible with most food grade salts

Gums Xanthan is widely used due to unique function Ideal for emulsions excellent in fat-free dressings due to viscosity, pseudoplasticity and smooth mouth feel Excellent food stabilizer Good for thermally processed foods Expensive!