FOODS AND BEVERAGES

Chitin, chitosan and their derivatives have a range of potential uses as food additives, packaging agents and aids to beverage processing. As in the case of health care, introduction to the market will require the time and expense of obtaining regulatory approval.

The ability of the chitosan molecule to scavenge fat and cholesterol in the digestive system, plucking it from the stomach and excreting it in the duodenum (see Health Care, above) has significant implications for its use as a beneficial food additive. Foods containing chitosan, or chitosan complexed with a fatty acid, could be designed to reduce obesity, cholesterol levels and the incidence of colon cancer. When broken down into small polymers, known as microcrystalline chitin, chitin has possible uses as an additive to enhance the flavor and taste of foods. Unlike conventional chitin, this form of the biopolymer distributes itself evenly throughout aqueous solutions, as tiny particles. Heated to normal cooking temperatures, microcrystalline chitin forms pyrazines, which are responsible for the roasted taste and aroma of several foods.

Chitosan, meanwhile, has potential uses in recovering flavor components from seafood processing streams. Amino acids present in the streams, such as arginine, alanine, glutamic acid, serine and glycerin, contribute significantly to the taste of seafood. They can be removed from the streams using ligand-exchange chromatography; the amino acids form complexes with copper metal, which is fixed on a chitosan support.

Both chitin and chitosan can provide fiber in diets. The addition appears entirely safe. In laboratory studies, animals have grown normally while consuming up to 10% of their diet in the form of chitin. Chitin imposes stability on food emulsions. For example, whipped dessert topping containing chitin can be frozen and thawed without breaking up.

Films made from chitosan have two characteristics highly desirable to the food industry: they are biodegradable and they have low permeability to oxygen. At present, those beneficial characteristics of chitosan films come at the expense of other desirable properties such as tensile strength. However, the application of genetic engineering techniques, can potentially change the distribution of molecular weights in chitosan, particularly that derived from fungi. That would permit scientists to change such characteristics of films as tensile strength, flexibility, gas permeability and rate of degradation in the environment.

Cross-linking chitosan films with epichlorohydnn in alkaline conditions improves the film's tensile strength by factors up to 100, bringing it close to that of synthetics such as polyethylene and polypropylene that are used to package film. m addition, cross-linked films have better wet strength than noncross-linked films. Studies indicate that films of higher molecular weight forms of chitosan are more brittle, even when plasticizer is added to them. An alternative application in food packaging involves sprinkling chitosan powder on synthetic packaging film or spraying a chitosan solution on the film. If agents that increase viscosity are added, the material can be deposited on the film by letterpress. In these eases, the chitosan is used as an antibiotic or anti- mold treatment.

Chitosan also has potential as a coating to preserve fruit. N.O-earboxymethyl chitosan, a derivative made when chitosan reacts with monochloracetic acid, forms a strong film that is selectively permeable to such gases as oxygen and carbon dioxide. The film is made by spraying an aqueous solution of N.O-carboxymethyl chitosan on the fruit, or by dipping the fruit into the solution. Apples coated with the material and left in cold storage retain their freshness for more than six months, and keep their titratable acids about 250 days. The film can be removed by washing with water before consumption of the fruits.