Biotechnology

Nutritional Additives

Food Additives

are any of various chemical substances added to foods to produce specific desirable effects. Additives such as salt, spices, and sulfites have been used since ancient times to preserve foods and make them more palatable. With the increased processing of foods in the 20th century, there came a need for both the greater use of and new types of food additives. Many modern products, such as low-calorie, snack, and ready-to-eat convenience foods, would not be possible without food additives.

Food additives and their metabolites are subjected to rigorous toxicological analysis prior to their approval for use in the industry. Feeding studies are carried out using animal species (e.g., rats, mice, dogs) in order to determine the possible acute, short-term and long-term toxic effects of these chemicals. These studies monitor the effects of the compounds on the behaviour, growth, mortality, blood chemistry, organs, reproduction, offspring, and tumour development in the test animals over a 90-day to two-year period.

The lowest level of additive producing no toxicological effects is termed the no-effect level (NOEL). The NOEL is generally divided by 100 to determine a maximum acceptable daily intake (ADI).There are four general categories of food additives: nutritional additives, processing agents, preservatives, and sensory agents. These are not strict classifications, as many additives fall into more than one category.

are utilized for the purpose of restoring nutrients lost or degraded during production, fortifying or enriching certain foods in order to correct dietary deficiencies, or adding nutrients to food substitutes. The fortification of foods began in 1924 when iodine was added to table salt for the prevention of goitre. Vitamins are commonly added to many foods in order to enrich their nutritional value. For example, vitamins A and D are added to dairy and cereal products, several of the B vitamins are added to flour, cereals, baked goods, and pasta, and vitamin C is added to fruit beverages, cereals, dairy products, and confectioneries. Other nutritional additives include the essential fatty acid linoleic acid, minerals such as calcium and iron, and dietary fibre.

9. Read the text about biotechnology and be ready to explain the terms in italics.

The growth of the field of biotechnology is closely linked to the development in the 1970s of genetic engineering (the directed alteration of genetic material). Substances that have been produced in this manner include human interferon (a natural virus-fighting substance), human insulin, and human growth hormone. The techniques of genetic engineering--splicing, transplantation, and chemical replantation of repressed, nonfunctional genes--also offer the possibility that a number of heredity disorders may be "corrected" by manipulation. Recombinant-DNA techniques in conjunction with the development of a technique for producing monoclonal antibodies (antibodies produced by single clones of antibody-producing cells) have made an evident impact on medical diagnosis and oncology. Another important use of genetic engineering is the production of bacteria used to biodegrade oil spills and toxic wastes.

Biotechnology had its origins in a 1980 decision by the U.S. Supreme Court that "a live human-made microorganism is patentable matter." This ruling resulted in the establishment of a number of commercial firms--among them Genentech, Biogen, New England BioLabs, Cetus, and Genex--that manufacture quantities of gene-engineered substances for a variety of mostly medical and ecological uses.

Genetic engineering: recombinant DNA

Since the 1970s, biologists have made major advances in understanding the molecular nature of genes and their functioning through the use of the powerful experimental techniques of recombinant DNA. The term recombinant DNA literally means the joining or recombining of two pieces of DNA from two different species. Recombinant DNA techniques allow an investigator to biologically purify (clone) a gene from one species by inserting it into the DNA of another species, where it is replicated along with the host DNA. Actually, the term includes a variety of molecular manoeuvres, including cleaving DNA by microbial enzymes called endonucleases, splicing or recombining fragments of DNA, inserting eucaryotic DNA into bacteria so that large quantities of the foreign genetic material can be produced, determining the nucleotide sequence of a segment of DNA, and even chemically synthesizing DNA.

Дата добавления: 2014-11-16