Microbial biomass protein from the fungus Chaetomium cellulolyticum. II. Effect of method of drying and response to amino acid supplementation

Abstract

A Chaetomium cellulolyticum microbial biomass protein (MBP) culture produced on glucose substrate in a batch process was divided in half before drying. One half was dried in a forced-draft oven at 60°C (oven-dried, OD), the other half was frozen at −25°C and freeze-dried (FD) to a dry matter content of 90%. The crude protein contents of the OD and FD samples were 48.9 and 48.0%, respectively. Purified diets calculated to contain 10% crude protein were fed to weanling male Sprague-Dawley rats for two weeks. A control diet contained casein as the only protein source, another included isolated soyabean protein (ISP) as the sole source of protein. In two other diets, one half of the crude protein was provided by ISP and the other half by MBP-OD or MBP-FD. The diet containing the OD sample yielded poorer growth, feed consumption and feed utilization efficiency than the diets containing ISP plus the FD sample. All three of these diets showed significant responses to supplementation with 0.4% dl-methionine and a slight but non-significant improvement with the further addition of 0.15% l-lysine. The double-supplemented MBP diets, however, showed a weight gain that was significantly greater than that of the similarly supplemented ISP diet and similar to that of the casein control diet. The rats receiving the MBP basal diets showed the lowest feed consumption, whereas with amino acid supplementation they showed the highest consumption. The relatively poor feed gain ratio of the rats fed the MBP-OD diet alone or fully supplemented indicated a lower feed and dietary protein utilization efficiency than the control or the fully-supplemented MBP-FD group. Dry matter and crude protein digestibility values, however, were similar for the unsupplemented MBP diets. Therefore, observed differences in body weight gain and feed gain ratios must have been due to differences in nutrient utilization resulting from differences in the drying methods, freeze-drying being the preferred method. However, the tremendous improvement in response to amino acid supplementation of this fungal MBP product overcomes the difference between the two methods. It also provides good grounds for optimism for the future use of this non-conventional protein source in animal production.