A Biochemical Study of Fungal Cell Extracts

Abstract

The production of microbial protein has been suggested as one of the means of alleviating the world protein deficiency. This work attempts to contribute to our knowledge of the production and processing of fungal proteins. It is shown that fungal biomass can be produced easily in aerobic tower fermenters. Several fungi were grown and the Fungi Imperfect found to be the most suitable. The protein content of the biomass produced ranged from 34% to 58%. A significant portion of the mycelial protein could be solubilised by an enzymatic extraction. This involved drying and grinding the mycelium and subsequently extracting the mycelium in an aqueous suspension with pepsin under acidic conditions and moderate temperatures. Neutralised extracts on evaporation to a semi-solid consistency gave tasty meaty-flavoured products. Several fungal extracts were prepared and found to have a range of flavours. Amino acid analyses of the various fungal extracts showed them to be rich in the essential amino acids. In particular the extracts are rich in lysine which would make them ideal protein supplements to the diets of people in underdeveloped countries. Feeding trials were carried out on mice fed on a diet supplemented with 10% Aspergillus niger extract. The supplementation had a beneficial effect and the mice showed weight gains greater than those of mice feed on the unsupplemented diet. Serological and histological studies showed no adverse effects. Mice fed on the extract bred normally. The mice survived a 15-day period of 50% supplementation with no serious adverse effects. It is also shown that fungal extracts are good fermentation adjuncts suggesting a means of recycling much of the nitrogenous constituents of fermentation media and minimising on effluent problems. An economic evaluation shows that fungal extracts can be produced at a competitive price compared to other protein hydrolysates.