Again, there are strong links with the material in the core syllabus (page 20) which deals with genetically engineered bacteria. Students should be aware that there is potential for applying the techniques used for pharmaceutical products, such as insulin and antibiotics, to the enhancement of food production. Some students will be able to offer sensible suggestions, in general terms, as to possibilities. These might include yeasts with high alcohol tolerance; microbes with enhanced ability to digest such plant material as waste straw, or peat (even materials like coal and oil) or simply microorganisms whose existing capacity to produce valuable substances such as enzymes, flavourings or colouring is greatly improved.
Background
The major areas currently attracting attention are:
Lactic acid bacteria
A commercially important area is the production of new strains of lactic acid bacteria which carry out faster, more efficient fermentation. For example, using plasmid technology, new strains of Lactobacillus sp have been produced to provide much improved starter cultures for cheese production. The potential for the more rapid production and maturation of cheeses, and a whole range of other fermented products, is being exploited. Another important achievement is the introduction into lactic acid bacteria of genes resistant to destructive bacteriophages. Additionally, lactic acid bacteria are excellent producers of peptidases, which are already widely used in food technology. This characteristic is thought to have enormous potential, not least because these bacteria, being associated with the production of traditional foods, are largely recognised as being 'safe'.
Enzymes
Enzymes are very important in food processing. Apart from enhancing nutritional value, they can be used to influence flavour, aroma, texture, appearance and speed of production. Microorganisms are the most important sources of these enzymes; there is no reason why the ability to synthesise enzymes normally associated only with plants and animals should not be engineered into microorganisms for culture in fermenters. This was achieved some time ago in the case of the enzyme chymosin (rennin), used in cheese manufacture. Traditionally, the enzyme was obtained from the 'stomach' of calves but this source became scarce and expensive. Additionally, some vegetarians find this source unacceptable. It became possible to insert the DNA coding for bovine chymosin into lactic acid bacteria and, more recently, into yeast. The chymosin produced by these modified organisms is identical with the bovine product.
Yeasts
Much attention is currently being focused on the possible uses of yeasts as a vehicle in which to express transferred genes. Chymosin from transgenic yeast (see above) was the first enzyme from a genetically modified organism to gain regulatory approval for food use. In 1994, the Brewing Research Foundation International gained approval for the use of a genetically modified yeast to make low-carbohydrate beer. The yeast Saccharomyces cerevisiae var diastaticus, whilst not itself suitable for use in brewing, produces an amylase capable of hydrolysing starch residues which normally remain in the brew. The high-calorie starch residues are thus converted into fermentable sugar. A gene coding for the enzyme is transferred, via a plasmid, to normal brewing strains of yeast. The transgenic yeast can be used to produce a high alcohol premium product or, alternatively, a greater volume of low calorie 'lite' beer.
When evaluating the potential for using genetically modified microorganisms for food production, students should be made aware that the processes are not as simple as they may appear and that the technical and other problems are formidable.
Background
For example, whilst plasmids are generally able to transfer only a single gene, it may be necessary to introduce:
Further, very stringent safety requirements have to be met.