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Various techniques for handling enzymes in vitro have been developed which make it possible to apply enzymes to industrial processes in a controlled way. Enzyme immobilization on inert matrices enables the catalysts to be reused in continuous bioreactors and facilitates product recovery (Kennedy et al, 1990). Examples of this which are relevant to the food industry include immobilized (3-galactosidase for the hydrolysis of lactose in milk products (Gekas & Lopez-Leiva, 1985) and glucose isomerase for the production of high-fructose corn syrup from corn starch hydrolysate (Carasik & Carroll, 1983). Encapsulation may be used to protect enzymes or to direct their activity. Kirby et al (1987) demonstrated the use of liposome-encapsulated proteases to improve the efficiency of enzymatic accelerated cheese ripening. Encapsulation reduced enzyme losses, ensured even distribution and prevented premature action. Enzymes protected by encapsulation in reverse micelles have been used suspended in non-aqueous solvents (Martinek, 1989). Zaks & Klibanov (1985) demonstrated that enzymes need not only be used in aqueous solution but can be active as direct suspensions in organic solvents. Indeed, certain hydrolytic enzymes such as lipases and proteases can carry out synthetic condensation reactions under these conditions. This principle has been applied to the enzymatic synthesis of food ingredients such as emulsifiers, oligosaccharides and flavours, and to the biotransformation of fats and oils (Vulfson, 1993). Enzymes often have enhanced stability in these systems and they can be used with substrates that have low water solubility. Supercritical fluids have also been used as solvents for enzyme reactions in which substrates or products are sparingly soluble in water (Randolf et al, 1991).

Developments such as these have resulted in a new generation of biotechnological processes which are quite distinct from traditional food fermentations. These operate under highly controlled conditions, carry out highly specific functions and use well characterised enzyme catalysts. Emerging enzyme and genetic technologies have the potential to help meet many of the demands which are made of food manufacturers for products with good storage properties, that are more healthy and nutritious and are more attractive. They also have a role to play in food production and agriculture in the developing world to enhance productivity, reduce crop disease and to control pests. A list of current or impending commercial applications of genetic technology to food production is given by Beck & Ulrich (1993). For further reviews of food biotechnology, the reader is referred to Wasserman et al (1988), Bell & White (1989), Pilnik & Voragen (1990), Whitaker (1990), OECD (1992), among many others.

The latest developments in biotechnology have had their biggest impact in medicine, pharmaceuticals and fine chemicals. It is perhaps surprising, considering the close relationship between the food industry and biotechnology, that their influence has not been greater in food processing. There are several factors which contribute to this. The food industry is by nature very conservative compared to most modern biotechnology industries in which commercial survival is dependent on innovative research and development. There is little history of fundamental research being carried out by the food industry itself. It was noted by de Vogel (1991) that most "high-tech" industries spend 10-20% of their annual turnover on research and development while such expenditure hardly reached 1% in the food industry. This figure is in agreement with a survey of UK food companies which found that the average expenditure on "innovation" was 0.55% of turnover (CEST, 1993).

Consumers are also conservative with regard to new food ingredients and processes. People are suspicious of new technologies and demand, quite rightly, assurance of the absolute safety of food products. Studies carried out to assess public attitudes to biotechnology have shown that its application to food production is less acceptable than to medicine and health (Frewer, 1992). As profit margins are low in the food industry, manufacturers have to be sure that their investment in new technologies will result in a product which is acceptable to the consumer and to the regulatory authorities. To some extent, the effects of biotechnology on food processing are often not apparent to the consumer. They rarely result in obviously new food products, but most often are used to enhance the properties of products which are already widely accepted (Beck & Ulrich, 1993). In addition, the production of food additives by means of biological agents may be seen as more "natural" than chemical synthesis (Armstrong & Yamazaki, 1986). However, the application of biotechnology in the food sector presents new issues of regulation, particularly for additives which have previously been regarded as safe when encountered in traditional foods, or which have already had approval when produced by conventional chemical synthesis. It is not likely that enzymes currently used in food processing, or well characterised enzymes which are already known to have no toxic effects, will require further safety testing when applied to novel processes. Regulatory authorities such as the Food and Drug Administration in the USA will probably require safety testing of enzymes which are not normally encountered in food products (Kessler et al, 1993).

Another important limitation to the adoption of emerging biotechnologies by the food industry is process economics. The product of a new process must be better and cheaper than that produced by conventional means if a change in production method is to be justified. The costs of research and development, new plant and obtaining regulatory approval must all be met from increased profits. These difficulties are often greater for the food industry where profit margins are small and prices must be kept low. There is little doubt that a great deal of innovative research on novel enzyme technologies for the food industry is being carried out in the laboratory. However, a bottleneck exists in the development of the means to transfer this technology to an industrial scale, particularly for low-cost/high-volume products. The importance of research into the biochemical engineering aspects of bioprocessing to match advances in genetics and enzyme technology has been highlighted in a number of reports (OECD, 1982; Michaels, 1984; OTA, 1984; Lilly, 1992).

Many emerging enzyme technologies require the production of large amounts of enzyme in a higher state of purity than is currently usual in food applications. Process scale enzyme purification is already carried out by the pharmaceutical and fine biochemical industries, but in this sector higher processing costs are offset by high product values. As was demonstrated in an analysis by Nystrom (reported in Dwyer, 1984), there is a strong correlation between the concentration of a product in the starting material and its selling price (Figure 1). The degree of required purification therefore has a significant influence on product cost. For recombinant DNA products, downstream processing can account for 8090% of total product cost (Dwyer, 1984). It is unlikely that this would be acceptable for a food-related product. The reduction of downstream processing costs will thus be essential if many of the products of modern enzyme technology are to be applied to the food sector. The field of separations is therefore one which can have a significant impact on the economic feasibility of biotechnological processes in the food industry.

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