Acid hydrolysis of shrimp-shell wastes and the production of single cell protein from the hydrolysate

Abstract

The acid hydrolysis of waste shrimp shell to obtain glucosamine was investigated. The waste had a high protein (39.6%), chitin (22.6%) and ash (28.1%) content. It seemed possible, therefore, that the waste could be converted into two sources of protein; one directly, through the production of protein, and the other indirectly through a bioconversion process of the chitin to produce single cell protein. The optimum conditions for the extraction of protein preparations from the shell waste were determined in the pretreatment stage and were a pH of 12 for 2 h at 30°C with constant stirring and a solid/solvent ratio of 1:20. The acid hydrolysis process, using concentrated HCl, gave a glucosamine yield of 80%. The use of this hydrolysate for the production of single cell protein using the yeast Saccharomyces cerevisiae K1V-1116 was investigated using both batch and continuous growth studies. The batch growth was done in Erlenmeyer flasks (0.5 l) and used different substrate concentrations and a controlled aeration and stirring rate. The continuous process used a C-30 Bioflo fermenter with a working volume of 0.45 m 3. It was operated with different dilution rates (0.1–0.3/h) and had temperature, aeration and stirring rate controls. The continuous cultivation of Saccharomyces cerevisiae showed that the maximum specific growth rate was 0.389/h and that the cell yield coefficient was 0.447 kg dry cells/kg glucosamine used. The highest cell production rate, 0.423 kg dry cells/m 3h, was achieved at a dilution rate of 0.25/h. With batch growth conditions, the yield coefficient was 0.58 kg/kg and the highest specific growth rate was 0.23/h.