Alginate und Carrageenane ? Eigenschaften, Gewinnung und Anwendungen in Schule und Hochschule

Alginates and carrageenans are derivatives of polysaccharides. Whereas alginates occur as structural components in the cell walls of brown seaweed, carrageenans can be found in certain species of red algae. Although the two algal polysaccharides have been applied commercially for several decades, fairly little is known about their properties and applications. Hence we are usually not aware of the fact that we almost daily use products containing these seaweed extracts. In this thesis, alginates and carrageenans are discussed extensively: After a description of their chemical composition and structure the most important functional properties of the two algal polysaccharides are dealt with in detail. These include their ability to form viscous aqueous solutions and gels as well as their stabilising effect on emulsions and suspensions. The solubility and gelation of alginates and carrageenans are also made use of in the manufacture of these polysaccharides from brown and red algae. In this thesis, laboratory methods for the extraction of alginates from Laminaria species and Fucus vesiculosus were developed and optimised. With a minimum of apparatus and time, these experimental procedures mimic major steps of the industrial production process. This is also true for the method which was devised for isolating carrageenan from Chondrus crispus, Gigartina radula and Eucheuma cottonii. The main emphasis of this thesis is set on the applications of alginates and carrageenans. Examples of everyday and promising future uses are examined closely in terms of their chemical background and illustrated with simple, but convincing experiments for teaching purposes. Alginates and their organic derivatives are employed as thickening agents and stabilisers in various food products. In addition, they are utilised in the manufacture of structured food, such as pimiento fillings for olives. In biotechnology, alginates are of importance as immobilisation matrices for micro-organisms and enzymes. For example, yeast cells entrapped in calcium alginate gel beads can be used for the production of ethanol from carbohydrates as well as for the preparation of sparkling wine. Besides, alginates have a variety of pharmaceutical and medical applications: Wounds can be treated with dressings composed of calcium alginate fibres, which have a beneficial effect on the healing process. Furthermore, alginates are contained in dental impression materials as well as in remedies for oesophageal reflux. Finally, the administration of calcium alginate is an effective preventive and therapeutic measure against radiostrontium poisoning. Carrageenans have their main applications in the food industry. This thesis presents experiments which illustrate the use of these red seaweed polysaccharides as thickening and gelling agents in water- and milk-based food systems. Furthermore, a simple analytical method for the detection of carrageenans in salad dressings, glazes and jellies was devised. In addition to demonstrating existing application areas of alginates and carrageenans, the present dissertation had the aim of investigating new potential chemical uses of these algal polysaccharides. This resulted in the development of an experimental procedure for the quantitative determination of calcium, strontium and barium ions, using chromatography columns filled with alginic acid beads as ion exchangers. The relevance of alginates and carrageenans for chemistry lessons at schools is discussed in the final chapter of this dissertation. Dealing with these algal polysaccharides is not only new and fascinating for both teachers and pupils but also gives learners the opportunity of deepening their knowledge of important scientific, interdisciplinary and application-orientated topics of the chemistry curriculum. The experiments designed to illustrate the production process, functional properties and applications of alginates and carrageenans explain interesting phenomena of everyday life. Many experiments can be carried out by pupils since they do not involve the use of hazardous chemicals or complex apparatus. Some of the experiments devised in this thesis are also of relevance for chemistry teaching at university level.