Fermentations

Larry L. McKay, professor of food microbiology, and Kathleen A. Baldwin, assistant scientist, Department of Food Science and Nutrition, University of Minnesota, St. Paul.

The food fermentation industry has tremendous potential for growth and diversification as a result of the impact of biotechnology on the production of fermented foods. Biotechnological applications are endless, but these industries will have to integrate this new technology into their longterm goals. The impact of biotechnology on the industry will depend, in part, on advances in genetically manipulating the micro-organisms involved in producing fermented foods.

Fermentations

The use of micro-organisms in food fermentations is a significant phase of food production. (In fermentation, an enzyme is used to change an organic compound into other substances such as carbon dioxide and alcohol.) Microorganisms are directly involved in the successful outcome of numerous food production processes such as brewing, baking, sausage manufacture, fermentation of vegetable material for sauerkraut and pickles, the manufacture of fermented dairy products, and numerous other fermented foods.

In recent years, plasmid biology has become an exciting area of research with respect to those bacteria in dairy, meat, and vegetable fermentation processes as well as those used for silage and for health benefits.

Plasmids can be defined as small, circular pieces of DNA which exist in the bacteria cell and maintain themselves separate from the chromosome.

Certain metabolic properties vital for successful dairy fermentations are determined by genes carried on these plasmids. Examples would be the ability to use milk sugar (lactose), to degrade milk protein (casein), to produce butter aroma, to produce antagonistic substances against disease-causing and spoilage bacteria, as well as to resist attack by bacterial viruses.

An ultraviolet system detects plasmid DNA molecules that control characteristics such as butter aroma or acid production in dairy product fermentation.

Genetic Technology

Recent advances in genetic research have received considerable publicity, and companies based on this new technology are springing up worldwide. Prospects are good for major advances in food fermentation technology through the cloning of desirable genes in food fermenting bacteria, yeasts, and molds. The techniques used are highly sophisticated and include a process of enzyme surgery (wherein the genes to be cloned are inserted) into vector DNA, usually a plasmid, which, in turn, is introduced into a host micro-organism to propagate new genes. To apply this concept to food fermentation organisms, we need an indepth understanding of the molecular biology, metabolism, and plasmid biology of these bacteria.

Acquiring New Strains

The potential of a given micro-organism is determined by the nature of :he genetic material contained in the individual cells. Access to the large number of possible variations in the expression of the genetic material can be made by several approaches. The first is the isolation and selection of strains from sources in nature the primary method for selecting strains or food fermentations since the turn of the century. The second is the artificial mutation of the genetic material of existing strains followed by selection of desired mutants.

The most exciting possibility for obtaining new strains for food fermentation processes is the use of recombinant DNA technology to construct an organism for a specific process.

Accelerated Cheese Ripening

The application of genetic engineering techniques, including recombinant DNA technology, to micro-organisms used in food fermentations could improve fermentation efficiency, flavor, texture, nutritive value, or appearance of the final product. Such applications could enhance consumer acceptance or provide economic savings to the manufacturer.

One example would be the ripening of Cheddar cheese in which a storage period of 6 to 12 months is required. Reducing this ripening period, which constitutes a major proportion of the total processing cost of cheese, has long been a goal of the cheese industry. Since milk protein degradation may be involved in cheese ripening and since some of the enzymes used are linked to plasmid DNA, the genes for different enzymes could be exchanged between strains, and the level of their activity controlled through genetic engineering techniques. The manipulation of existing bacterial enzymes or the introduction of new ones from nondairy sources could lead to strains capable of accelerating the ripening of cheese.

Antagonistic Properties

The ability of many food-fermenting micro-organisms to produce antagonistic compounds other than organic acids is well documented. The linkage of the ability to produce some of these antagonistic compounds to plan mid DNA may lead to the construction of "super"-antagonistic-compound-producing derivatives through the manipulation of existing genes. Such strains may have considerable commercial value. In addition, the ability to transfer the genetic factors controlling inhibitory substance production to other desirable bacteria may ultimately lead to construction o strains with enhanced antagonistic properties against food spoilage organisms and food-borne pathogens. Such strains could extend the shelf life of fermented dairy products as well as other food items.