SINGLE CELL PROTEIN

The following topics are covered in this paper: the European feedstuff business, size, shape and source; the protein and amino acid requirements of the principal target species; the place of single cell protein (s.c.p.); the raw material options and the technical challenge of large scale s.c.p. manufacture; fermentation of s.c.p., its stoichiometry, mass and heat transfer requirements; static and dynamic optimization and control; the pressure cycle fermenter; the principle of sterility and the engineering design constraints; the nutritional performance of I.C.I.’s ‘Pruteen’ and the future for s.c.p. Single cell protein (s.c.p.) technology has had a most extraordinary history during the last 20 years. As a new venture, it has been expensively embraced by many industrial and academic suitors, and yet, as the sceptics remind me from time to time, none of these suitors has gained any satisfaction. This new business venture has had its detractors, who indulge in polemic reminiscent of the arrival of the steam railway, the iron ship and the motor car. The objectors raise issues of practicability, morality, economics, safety and even international politics. However, a number of major industrial organizations not noted for whimsical investment have substantial commitments in this new horizon of industrial microbiology. Perhaps the most satisfying aspect of the development has been the seemingly endless variety of microbiological and engineering approaches which will help in the solution of problems in other areas of what is becoming known as biotechnology. In this paper I shall describe the progress made by I.C.I. in this field, but the views and opinions expressed are my own. I shall concentrate first on a description of the market in which s.c.ps must compete. The competition makes important demands upon the technology. Many of the answers to these demands have wider application to other developments in large scale industrial microbiology and I shall dwell on two areas in detail: aerobic fermentation and engineering for sterile operation. S.c.ps have been in use for many years, for both human and animal nutrition. The ruminants rely heavily on the production of bacterial protein, which is absorbed in the hindgut and derived from a well controlled continuous anaerobic chemostat. The organisms in the rumen consume cellulose as the major carbon and energy source, and use plant proteins, or urea as substitute, for nitrogen. These animals have been around for thousands of years, but it has taken man until the middle of the twentieth century successfully to design, construct and operate similar installations for the production of an animal feedstuff. The reasons for the delay are not difficult to find. To enter the s.c.p. business, the complete technological armoury of the large scale chemical industry is essential. To the skills index that includes chemical, mechanical, civil and electrical engineering, chemistry, mathematics and computer science, physics and material .