| Applications of biotechnology to traditional fermented foods |
Leslie Fook-Min Yong
The preparation of fermented foods predates the recorded history of Man. Early humans used observation of the apparent effects of microbial alteration of food characteristics to develop processes for food fermentation. The resultant fermented products normally have a different texture and flavor compared to the unfermented starting materials, thus making them more palatable and digestible and prolonging their shelf life. Technical progress was initially slow, as reflected in the long fermentation periods required; it was incremental to the technical know-how and basic scientific information then available. It is probably fair to say that in the very early days brew-masters were more artisans than technologists. With the rapid advancement in understanding of the basic sciences of microbiology and biochemistry, coupled with the introduction of new equipment, the developed nations have forged ahead in improving the safety and efficiency of the bioprocesses used to manufacture traditional fermented foods, such as cheese fermentation.
"OLD" AND "NEW" BIOTECHNOLOGY
With the rapid progress in the biological sciences, both basic and applied aspects, it has been possible to gain a better understanding of the mystery that has surrounded fermentation processes. The types of microorganisms involved has been isolated and identified, and the physiology and metabolism of these organisms have been studied. Hence, traditional fermented foods can now be made better, faster, and more economically. The application of available knowledge to improve traditional food fermentations in developed countries has far outpaced that in developing countries.
In this paper I draw on my experience working with soy sauce fermentation and then proceed to discuss the production of flavor and fragrance materials by microbial fermentation. Experience gained from this traditional fermented condiment has enabled me to develop novel bioprocesses for the production of aroma chemicals.
The terms "old biotechnology" and "new biotechnology" have been used - "old" to mean the undirected manipulation of microorganisms and plants, such as by mutagenesis and selection of the better strains. In this old biotechnology I would like, for convenience, to include directed control of the physical and chemical environments of the fermentation process, which could result in better performance of the useful microbes.
Though mutation increases the ability to select better strains, there can, of course, be little directed alteration of genetic material. The new biotechnology, such as recombinant DNA techniques, overcomes this problem. The new biotechnology can, of course, be of tremendous help in producing superstrains of microbes that could enable acceleration of fermentation processes, provide more efficient utilization of raw materials, and produce better-quality products. How best can developing nations apply these biotechnologies to traditional fermented foods? Should it be application of the "old" before the "new," "new" without the "old," or "old" and "new" simultaneously?
In their enthusiasm to promote the new biotechnology for traditional fermented food applications, scientists from developed countries should not forget the different environments that exist in developed and developing countries. In developed countries the old biotechnology is already well understood and practiced efficiently in fermented food industries. Developing countries may need to acquire a better understanding of the old biotechnology before efficiently absorbing and implementing the new biotechnology to its fullest.
APPLICATION OF BIOTECHNOLOGY
Preparation of traditional fermented foods is more complex and time consuming than that involved in the production of single chemical substances. For example, in soy sauce fermentation more than one type of microorganism is involved, whereas in citric acid fermentation only one species of fungus is normally used. How can developing countries apply new knowledge in the old and new biotechnologies to their own complex traditional food fermentations?
Take soy sauce fermentation as an example of a traditional fermentation process conducted in a developed country, such as Japan compared with that in a country like Malaysia. The technology in use in Japan is sophisticated, very advanced, and highly productive and mechanized. The microbes used have been selected over the years for their performance in producing a better-quality product. The cottage industry soy sauce fermentation in Malaysia is highly labor intensive and usually relies on "natural" inoculation of raw materials using unwashed trays for previous fermentations rather than using a separately prepared inoculum of Aspergillus oryzae.
The equipment used in Japan to conduct the fermentation is state of-the-art machinery with microprocessor or computer control to provide the optimum conditions for microbial growth and activity. The microorganisms used have been manipulated by mutagenesis to give better performance, such as better enzymatic activity to give better hydrolysis of proteinaceous matter in defatted soybean meal as well as better flavor production. In comparison the average process used in Malaysia could be considered primitive.
This disparity is attributable to a better understanding of the theoretical and practical bases of soy sauce fermentation by scientists and technicians in Japan's soy sauce factories. The old biotechnology involved in this type of traditional fermentation is well understood in Japan, and the Japanese are now able to make better use of the new biotechnology - such as the directed alteration of genetic material of the mold (Aspergillus oryzue), yeast (Saccharomyces rouxii), and bacteria (Pediococci) used in soy sauce fermentation so as to improve their fermentative qualities.
For developing countries to make full use of the available biotechnologies in their traditional food fermentations, an understanding and acquisition of expertise in the following areas are essential.
Art of fermentation
A clear understanding by the master brewer of every step used in the fermentation is needed. This is the art of fermentation. Although the master brewers might not have scientific backgrounds, they could normally ensure a proper fermentation as a result of years of experience. Without a knowledge of the art of traditional food fermentation, a scientist cannot provide a scientific explanation for the process and proceed to provide assistance in improvement of the process.
It is essential to know which microorganisms involved in food fermentations are useful and how the physiology and metabolism of these microbes are affected by the physical and chemical environments of fermentations, as well as how their microbial activities in turn affect the fermentation processes. Microorganisms normally break down carbohydrates, proteins, and lipids present in the raw materials to be fermented by releasing enzymes into the medium. As the raw materials are hydrolyzed, the environment is changed, as sometimes reflected by a drop in pH value. Moreover, the breakdown products such as peptides and amino acids can be further converted into smaller volatile molecules that are odoriferous and hence improve the flavor characteristics of the fermented foods.
Upstream and downstream processing
Normally raw materials are pretreated before fermentation. It is important to comprehend how such pretreatment could affect the fermentation process. In soy sauce fermentation, whole soybeans are steamed to make the soy protein more easily hydrolyzable by the proteases of Aspergillus oryzae. In so doing, too much moisture is introduced and wheat flour must be added to lower the moisture content to a level that does not favor early bacterial growth and hence prevents spoilage of the fermentation.
Downstream processing does not affect the bioprocess involved. However, it could alter the normal organoleptic properties of the product, especially when downstream processing involves heating, such as in the pasteurization of soy sauce. Heating causes a change in the flavor of soy sauce due to nonenzymic browning reactions, which could result in the production of pyrazine compounds.
An understanding of the biochemical activities of the microbes actively participating in the fermentation could help to explain the change in the texture of the raw material as well as the origin of flavoring substances often present in fermented foods. Flavor and texture are important properties of fermented foods. Elucidation of flavor production in such fermentations could result in the development of processes for producing of flavoring materials by fermentation, as in the production of cheese flavors by Penicillium roquefortii.
Fermentation equipment and techniques
Practical experience in the use of both solid-state and submerged culture fermentation equipment is very useful. Normal training includes submerged culture bioreactors but not solid-state fermenters. It is useful to know both types of fermentations because traditional food fermentations often involve solid state fermentation. In soy sauce fermentation an initial solid-state fermentation is followed by a submerged fermentation step. Systems that measure and control pH, dissolved oxygen, temperature, and moisture help to make these bioprocesses more efficient and reduce the time required for production of a quality product.
For developing countries, future directions in applying biotechnology to traditional fermented foods should be: (1) training of a pool of technicians in the art and science of traditional food fermentations and (2) investigations by local scientists into the scientific basis of indigenous food fermentations.
Theoretical basic science education, such as the microbiology and biochemistry of food fermentations, could be taught in schools; so could the use of modern bioreactor systems. However, the application of such biotechnological knowledge to actual commercial fermentations can come about only after a practical experience in a fermented food factory for a period of time. The approach to be taken in applying biotechnology to traditional food fermentations should be that of finding solutions to existing bioprocessing problems and not trying to find problems with newly acquired biotechniques.
Only after the old biotechniques of fermentation have been successfully used can industries in developing countries look forward to using the new biotechniques of recombinant DNA to improve the genetic constitution of the microorganisms involved.