Biotechnology: Its Application in the Microbial World

Using Biotechnology in Food Processing Today

Daryl B. Lund, chairman, Department of Food Science, University of Wisconsin-Madison.

Biotechnology has been described as the last great technical innovation of the 20th century, but it has been used to produce food and food ingredients through fermentation for thousands of years.

Biotechnology was largely a practiced art in food processing and not scientifically understood. Now, through recent research in genetic engineering, the understanding of biotechnology's scientific basis has increased. Innovations have followed in process engineering, improvements in products, and cost reduction.

Biotechnology is defined here as the integrated use of biochemistry, molecular genetics, microbiology, and process engineering to commercially produce products of reactions of micro-organisms, cell cultures, or parts of micro-organisms or cells. As research is focused on these and other potential products, biotechnology's role in producing food and food ingredients will increase.

The following sections identify fermentation, separation, and purification operations as major areas of research needed to enhance the use of biotechnology for producing consumer products, including food.

Increasing Efficiency of Fermentation Systems

Fermentation is used to produce alcoholic beverages, bread, and cheese. It is a reaction or series of reactions in which a biocatalyst, usually a microbial cell or isolated enzymes, is used to convert a substrate or chemical constituent into a desirable product. Applications in the food industry include the production of alcoholic beverages, bread and cheeses. In most cases, the transformations of substrates to products are extremely complex and require control of other nutrients, oxygen transfer, and maintenance of the biocatalyst.

In designing a fermentor or bioreactor, the following technical areas must be considered: biological kinetics, piping and equipment design to maintain sterility, fluid hydraulics, mass transfer of substrate materials into the micro-organism, mass transfer of atmospheric oxygen through the bulk liquid and into the microorganism, mass transfer of product material out of the micro-organism into the bulk liquid, heat transfer for removal of metabolic heat, the control system desired, and scale-up. Intensive research is probing these areas to make such operations more efficient and affordable.

Bioreactors. Bioreactors are classified as batch reactors or continuous reactors. Batch reactors produce a variety of products, such as beer, bread and pickles. They are especially important in facilities producing a wide variety of high-value, low-volume fermentation products. They also are relatively easy to maintain in disease-free condition because the run time is relatively short, 1 to 2 days, compared to run times of several months for continuous reactors. Their main disadvantages are extra operating costs and low productivity.

Research will increase the role of biotechnology in production of food products from animal and plant sources.

Continuous reactors fall into three main groups: 1) chemostats; 2) tower fermentors, and 3) immobilized cell bioreactors. The chemostat is like a batch reactor except it has a continuous feed stream and a continuous product draw-off stream. The volume is maintained constant by matching the feed stream rate to the product stream rate. The main disadvantage is the loss of unconverted feed and nutrient components in the product draw-off stream.

The tower fermentor generally operates by injecting air at the bottom of a tower and relies on the upflow of the gas to provide continuous agitation. The organism is carried around in the fermentor and, as a result, encounters a variety of changing conditions. Placement of feed points, including air inlets, must be designed to minimize these extremes. The product is continuously withdrawn, and the design requires location of the draw-off point to minimize loss of nutrients and carbon source substrate.

The immobilized cell bioreactor, the newest type, traps whole cells in an inert carrier or matrix that allows nutrients and oxygen to enter and products to leave without releasing the whole cell. Individual enzymes also have been immobilized on materials such as ceramic beads of ion-exchange resins and gels with significant success. The most notable commercial application is the production of high-fructose corn syrup.

Several problems must be overcome for a significant expansion of immobilized whole cell reactors, including prevention of clogging of the matrix and maintenance of the cells for extended periods. Immobilized cell or enzyme reactors provide one of the most promising areas for fermentor development.

Scale-up Research. Scale-up is Perhaps the most critical issue when a new process is to be commercialized.

This topic is as old as the first entrepreneur who wanted to increase plant production by increasing the size of equipment. The approach to scale-up often used in the past relied on geometric similarity, trial and error techniques, and a "make do" philosophy. With the potential for biotechnology, these techniques are no longer adequate, and scale-up has been a research topic of great interest. Biotechnology encourages a closer examination of all the rate-limiting steps, rather than simply adding physical capacity.