Utilization of collagenous by-products from the meat packing industry: production of single-cell protein by the continuous cultivation of Bacillus megaterium.

The conditions for continuous cultivation of Bacillus megaterium on a collagen-derived substrate (SP-100) were determined. The optimum conditions of temperature, pH, and dilution rate were 34 C, pH 7.0, and 0.25/hr, respectively. Increasing the substrate concentration in plain tap water resulted in proportional increases in the productivity of cell mass from 0.6 g per liter per hr at 1% substrate to 1.8 g per liter per hr at 10% substrate; however, the protein content of the biomass decreased from 60 to 36%, and the protein yield decreased from 91 to 50% at substrate concentrations of 1 and 10%, respectively. These effects (decreases) were reversed up to 7.5% substrate by mineral supplementation of the medium. The productivity of biomass increased from 0.6 to 1.9 per liter per hr; the protein content of the biomass, from 43 to 54%; and the protein yield, from 60 to 93%, respectively, as the substrate concentration (with mineral supplementation of the medium) was increased from 1 to 7.5%. Spent medium could be refortified and recycled as often as five times. The amino acids in the substrate protein appeared to be utilized for growth and metabolism more or less uniformly. Analysis of the B. megaterium biomass indicated considerable enrichment of the essential amino acids and reduction of proline, glycine, and hydroxyproline as compared to the collagen-derived substrate. The Protein Efficiency Ratios obtained on the collagen-derived substrate (SP-100) and on the B. megaterium biomass, expressed as percentages of the casein reference protein, were 14 and 74%, respectively. Thus, considerable improvement in nutritional value was effected by bacterial conversion of the collagen-derived substrate into single-cell protein.