Classification and effectiveness of different thickeners(1)

Thickeners can be divided into natural and synthetic ones, the latter being mainly chemically derived gums. The natural ones can be divided into plant seed gums, plant secretory gums, seaweed gums, microbial gums, etc. according to their origin.

Natural thickeners are mostly extracted from white seaweed and plants containing polysaccharide mucilage, as well as protein-containing plants and micro-organisms.

They mainly include gum arabic, pectin, agar, guar gum, gelatine, xanthan gum, etc.

1.1. Gelatine

Gelatin is a polymer of high molecular polypeptides obtained by partial hydrolysis of animal skin, bone, cartilage, ligaments, muscle membranes and other tissues containing collagen. It has a relative molecular mass of 10,000 to 70,000 and is produced by both alkaline and enzymatic methods. Gelatine is a white or yellowish, translucent, slightly lustrous flake or powder, with a special odour, similar to gravy; it is easily decomposed by bacteria after deliquescence.

Gelatine is insoluble in cold water, but when water is added it slowly absorbs water and swells and softens, absorbing 5-10 times the mass of water. It dissolves in hot water and condenses into a gelatinous mass when the solution is cooled. Gelatine is insoluble in ethanol, ether, chloroform and other organic solvents, but soluble in acetic acid and glycerol. Compared to agar, gelatine has a weaker coagulation force, below 5% it cannot be coagulated into jelly, generally it needs about 15%. The dissolution temperature is not very different from the solidification temperature, below 30°C it is a gel and above 40°C it is a sol. The larger the relative molecular mass, the longer the molecules, the less impurities, the higher the gel strength and the higher the viscosity of the sol.

1.2. agar

Agar, also known as agar, is one of the components of the cell wall of red algae such as Caulifloweraceae and Erythrinaceae, and its basic chemical composition is a polysaccharide with galactose as the backbone, the main components are agarose and agar gel. Agar is a colourless, transparent or yellowish translucent flake or yellow powder, odourless, with a light taste. It is not soluble in cold water, but can be dispersed in boiling water and swollen by absorbing 20 times of water, and can be heated to 100°C with stirring to form a 5% solution. The gel temperature is 32-39°C and the melting temperature is 80-97°C. It does not degrade or hydrolyse in the gel state and is resistant to high temperatures.