Weekly+Lecture+Summary


 * Maria 's weekly summary**

week 1 -5

__What is Hydrocolloid?__


 * === The term ‘hydrocolloids’ - to a range of polysaccharides and proteins (also known as ‘water soluble gums’ or just ‘gums’.) ===
 * === Primary functions- Thickening agents, Gelling or texturizing agents ===
 * === Secondary functions- Stabilization of emulsions, suspension of particulates, control of crystallisation, encapsulation, formation of film ===

__ Main classes of hydrocolloids __

 * **derivatives from exudation or sap of trees (e.g. cellulose, gum arabic, gum karaya, gum ghatti, gum tragacanth)**
 * **extract from seed (e.g. guar gum, LBG, tara gum, tamarind gum)**
 * **extract from seaweeds (e.g. agar, carrageenan)**
 * **microbial gums (e.g. xanthan, dextrun,curdlan)**
 * **extract from tubers (e.g. konjac)**
 * **extract from plant parts (e.g. starch, pectin, cellulose)**



__Factors affect gum properties__

 * molecular weight
 * monosaccharide composition
 * type of chains
 * number of side chains
 * distribution of side chains

Main Hydrocolloids - Thickeners

 * 1) xanthan gum
 * 2) carboxymethylcellulose
 * 3) methylcellulose and hydroxypropyl cellulose
 * 4) galactomannas (guar and LBG)



__Thermoreversible gelling agents__

 * 1) **gelatin**
 * 2) **agar**
 * 3) **kappa carrageenan**
 * 4) **iota carrageena**
 * 5) **low methoxy (LM) pectin**
 * 6) **gellan gum**

__Thermally irreversible gelling agents__

 * 1) **alginate**
 * 2) **high methoxyl (HM) pectin**
 * 3) **konjac mannan**
 * 4) **locust bean gum**

Pectin
- **High methoxyl pectin (HMP)**
 * d erived from peel of citrus fruits, apple pomace, sugar beet, sunflower heads.
 * types of pectin---High methoxyl pectin (HMP), DE> 50%
 * ** DE---58% to 75% **
 * ** to form gel, soluble solid content 55-85%, pH 2.8-3.8. (e.g. jam and jellies) **
 * ** ultrarapid/rapid set (DE as high as 77)---used in jam with whole fruits, to ensure uniform distribution of fruits particles. **
 * ** slow set (DE~58) ---used in very acid fruits such as blackcurrant to avoid premature gelation. **

**Low methoxyl pectin (LMP)**
 * - DE < 50% — two sub-groups: Conventional low methoxyl pectin (LMP) and Amidated low methoxyl pectin (ALMP) **
 * - Form gels in the presence of Ca2+, with a low solids content & wide pH range (1-7) [but soluble solids can be up to 85%] **
 * - LMP – less Ca2+ reactive than ALMP ⇒ used as a thickening agent in yoghurt fruit **
 * - ALMP – very Ca2+ reactive ⇒ assist gelation in low sugar fruit preparations, e.g. low-sugar jams & jellies **



**Carrageenan **
**- Carrageenan is a highly refined extract of seaweed from the rhodophyta family.** **- Chemically its composition is a long chain of galactose residues linked, resulting in a long chain of high molecular weight.** **a) Iota Carrageenan - It is extracted from //Eucheuma Spinosum// seaweed.** **b) Lambda Carrageenan - It is extracted from //Gigartina//, //Iriadeae// and //Chondrus crispus// seaweed.** **c) kappa Carrageenan - It is a extracted from //Eucheuma cottonii// and from //Chondrus crispus// seaweed. **



**Alginate**
- **Derived brown seaweed (Laminaria hyperborea)**

**- Made up of blocks of Dmannuronic acid (M-blocks) & Lguluronic acid (G-block)** **- Alginate gels are heat- and freeze/thaw-stable, and can be prepared at very low solids and low temperatures with moderate shear. ** **- Alginates work well as stabilizers in a wide variety of food applications, and are particularly useful in the formulation of restructured fruits and vegetables. **



**Guar Gum**
**- Derived from guar ( Cyamopsis tetragonolobus ) seeds, this long, rigid, linear molecule of beta-1,4-D-galactomannans with alpha-1,6-linked D-galactose.** **- This galactomannan is soluble in cold water, hydrating quickly to produce viscous pseudoplastic solutions that, although shear-thinning, generally have greater low-shear viscosity than other hydrocolloids.** **- It is stable over a wide pH range, but will degrade at pH extremes at high temperature. The molecules’ interfacial binding allows guar to act as an emulsifier.** **- Guar gum binds water and retards ice-crystal growth.**

** Gum Arabic **
**- It is very water-soluble (except at a pH lower than 3), compatible with high solids and provides low viscosity with Newtonian flow at concentrations below 40%.** **- Its applications include encapsulating flavors, emulsifying beverages, clarifying wine, coating candy shells and controlling water.** **- Gum acacia seyal comes from the Acacia seyal tree and is used for coatings and encapsulation.**
 * - An exudate from the  Acacia senegal tree, gum arabic is comprised of arabinogalactan and a lesser amount of polysaccharide/ protein complexes. **

** Locust Bean Gum **
**- LBG finds use mainly in dairy products, particularly ice cream, where it protects against heat shock and imparts a desirable mouthfeel.** **- It can also act as a binder in meats and stabilize sauces, gravies and dressings.**
 * - Also called carob gum, as it’s derived from carob (Ceratonia siliqua) seeds, locust bean gum (LBG) has an irregularly shaped molecule with branched beta-1,4-D-galactomannan units. - This neutral polymer is only slightly soluble in cold water; it requires heat to achieve full hydration and maximum viscosity. **

**Xanthan Gum**
**- Xanthan has excellent solubility in hot or cold mediums, exhibits stability to heat and pH and in the presence of high salt concentrations, and resists many enzymes.** **- This gum is often used to thicken and stabilize emulsions, foams and suspensions in applications including sauces and dressings.**
 * - A fermentation product of  Xanthomonas campestris bacteria, xanthan gum develops a weak gel for high-viscosity solutions at low concentration that show little effect in the temperature range from 0° to 100°C. It is pseudoplastic (shear-reversible) over broad shear rate and concentration ranges, but imparts a stringy texture. **