Swells rapidly in cold or hot water to form highly viscous dispersions, up to 4000 mPas at 1% solids ( 2009)įorms highly viscous dispersions which are not influenced by addition of salts forms thermally irreversible gels with alkali Wielinga and Maehall ( 2000), Turabi et al. Very high low-shear viscosity highly shear thinning independent of electrolytes but degrade and lose viscosity at high and low pHs and at high temperaturesĭairy products including ice cream, ketchup, fruit juices, pudding powder, cake batter Galactomannans (Guar gum, Locust bean gum and tara gum) Ravi and Bhattacharya ( 2004), Sopade et al ( 2008), Mothe and Rao ( 1999) Low viscosity gum shear thinning at low shear rates (<10/sec) near Newtonian behaviour above 100/sec of shear rate Salad dressings, cake batters, beverages, whipped toppings Viscosity increases with temperature but independent of pH and electrolytes
Methyl cellulose (MC) and hydroxypropylmethyl cellulose (HPMC) Salad dressings, gravies, fruit pie fillings, ketchup High viscosity but is reduced by adding electrolytes and at low pH Urlacher and Dalbe ( 1992), Sahin and Ozdemir ( 2004) Soups and gravies, ketcups, instant beverages, desserts, toppings and fillings Highly shear thinning maintains viscosity in the presence of electrolytes, high temperature and wide pH ranges The gelling type hydrocolloids are alginate, pectin, carrageenan, gelatin, gellan and agar. Hydrocolloids that are commonly used as thickening are starch, xanthan, guar gum, locust bean gum, gum karaya, gum tragacanth, gum Arabic and cellulose derivatives. The other sensory properties such as opacity, mouth feel and taste also depend on the hydrocolloid employed. The textural properties (e.g., elastic or brittle, long or spreadable, chewy or creamy) of a gel vary widely with the type of hydrocolloid used. In other words, it becomes viscoelastic exhibiting both characteristics of a liquid and a solid. Gel formation is the phenomenon involving the association or cross-linking of the polymer chains to form a three dimensional network that traps or immobilises the water within it to form a rigid structure that is resistant to flow.
While all hydrocolloids thicken and impart stickiness to aqueous dispersions, a few biopolymers also have another major property of being able to form gels. The extent of thickening varies with the type and nature of hydrocolloids, with a few giving low viscosities at a fairly high concentration but most of them giving high viscosities at concentration, below 1% (Glicksman 1982). This water-thickening property is common to all hydrocolloids and is the prime reason for their overall use. Hydrocolloids disperse in water to give a thickening or viscosity producing effect. These include thickening, gelling, emulsifying, stabilisation, and controlling the crystal growth of ice and sugar though the basic properties for which hydrocolloids find extensive use are thickening and gelling. Hydrocolloids have a wide array of functional properties in foods. Considering their role in the adjustment of viscosity and texture of food formulations, several studies have been conducted in various food systems employing different hydrocolloids either singly or in combination. They are also used in many food products like ice-cremes, jams, jellies, gelled desserts, cakes and candies, to create the desired texture. Various food formulations like soups, gravies, salad dressings, sauces and toppings use hydrocolloids as additives to attain the desired viscosity and mouth feel. It is obvious that several hydrocolloids belong to the category of permitted food additive in many countries throughout the world. The modification of texture and/or viscosity of food system helps to modify its sensory properties, and hence, hydrocolloids are used as important food additives to perform specific purposes. This includes two basic properties of food system namely, flow behaviour (viscosity) and mechanical solid property (texture). The foremost reason behind the ample use of hydrocolloids in foods is their ability to modify the rheology of food system. Considering these two properties, they are aptly termed as ‘hydrophilic colloids’ or ‘hydrocolloids’. Further, they produce a dispersion, which is intermediate between a true solution and a suspension, and exhibits the properties of a colloid. Presence of a large number of hydroxyl (-OH) groups markedly increases their affinity for binding water molecules rendering them hydrophilic compounds. Hydrocolloids are a heterogeneous group of long chain polymers (polysaccharides and proteins) characterised by their property of forming viscous dispersions and/or gels when dispersed in water.
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