Microbial biomass protein from the fungus Chaetomium cellulolyticum. I. Composition and nutritive evaluation

Abstract

Microbial biomass protein (MBP) products of the cellulolytic fungus Chaetomium cellulolyticum were produced in batch culture with glucose substrate (MBP-1W) or molasses substrate (MBP-2W) as the main carbon source. Their chemical composition and nutritive values were compared with other MBP feedstuffs, Torula yeast, brewers' yeast and dried mushrooms. C. cellulolyticum MBP products contained about 45% crude protein on a dry matter basis and their amino acid profiles after acid hydrolysis compared well with that of dried skim milk, but the total amino acids analyzed accounted for only 75.6 and 62.5% of the crude protein of the MBP-1W and MBP-2W, respectively, compared to 81.8% for dried skim milk. In a 4-week growth trial, weanling male rats were fed on purified diets with the test material providing the only source of protein at a level of 10%. Product MBP-1W gave a 4-week weight less than that on brewers' yeast but greater than that on the Torula yeast diet. The MBP-2W and dried mushrooms gave the lowest body weights and feed consumption apparently because of their poor acceptability to the test animals. Brewers' yeast protein showed the highest PER value of the MBP diets but was significantly lower than the casein control diet. Its value was significantly greater than that of the MBP-1W with similar protein intake. Torula yeast showed a significantly higher PER value than MBP-1W, although protein intake was lower. Product MBP-2W and dried mushrooms, under very low dietary intakes gave similar low PER values. The NPR values, being greatly influenced by intake levels, proved to be a much less useful measure of protein quality. Dry matter digestibility ranged from 86% for the mushroom diet to 96% for the control casein diet. The MBP-1W and MBP-2W diets were inferior to the Torula yeast and brewers' yeast diets. Digestibility of crude protein was also highest for the casein diet, averaging close to 93% for the second and fourth week measurements, followed by Torula yeast with an average of 82%. The MBP-1W average digestibility of 78.7% was similar to that of brewers' yeast (77.3%) and superior to that of the MBP-2W and the dried mushroom diets. However, the latter diets had low intakes which result in underestimation of digestibility. Overall, the fungal MBP products tested showed reasonable potential as a new source of protein. The fungal protein grown on glucose was superior in nutritive value to that grown on molasses mainly because of its greater acceptability.