The biotransformation of canola meal
Gropp, Gordon M.
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Canola meal was obtained from each of two oil seed crushing plants in the Prairies. One type of meal was derived predominantly from the seeds of Brassica napus, whereas the other was derived predominantly from the seeds of Brassica rapa. Proximate, amino acid, and protein electrophoresis analyses were conducted on each type of canola meal. It was found that the two types of canola meal resembled one another with respect to the components analyzed. The composition of the two canola meals was studied further by examining the indigenous microflora of the meals. The microbiological load of the meals was found to be relatively low and comparable to vegetable products which are processed. Twenty one species of filamentous fungi were isolated from the meal samples and identified at least to the genus level. Four species were found in both types of meal and were from the genera Aspergillus, Eurotian, Moniliella and Mucor. Strains unique to the Brassica napus meal occurred among the genera Aspergillus, Cladosporium, Hadrotrichum, Mucor and Penicillium. Strains unique to the Brassica rapa meal occurred among the genera Cladosporium, Monoascus, Paecilomyces, Penicillium, Phoma, Polyscytalum, Rhizopus, and Rhizomucor. Several of the fungal strains isolated from the meal are known to be toxigenic and/or pathogenic to humans or livestock. The indigenous filamentous fungi of the meals were examined for their capacity to produce extracellular enzymes. A number of these species produced the enzymes necessary for the biotransformation of canola meal. In particular, Cladosporium sp., Mucor sp. M1, Penicillium fellutanum, and Rhizopus stolonifer showed the capacity to degrade lignin or cellulose. The growth of the indigenous microflora in the meals resulted in a reduced nutritional quality of the meal. Canola meal biotransformed by its indigenous microorganisms had an elevated content of ash, total dietary fibre, and non-protein nitrogen. It was found that the dominant species resulting from the growth of the microbial population could be influenced by the use of differing levels of moisture in the meal. Furthermore, the enzymatic activity residing in the biotransformed meal samples was found to be correlated with the dominant species which resulted from the growth of the microflora. Two species of filamentous fungi know to have the capacity to degrade plant cell walls, Chaetomium cellulolyticum and Ganoderma colossus, were grown on the meal in a solid substrate fermentation process. It was found that C. cellulolyticum grew rapidly on the meal. The meal end product possessed less total dietary fibre and protein, and more ash and non-protein nitrogen than the untreated meal. Further examination revealed that C. cellulolyticum has a high capacity for rapid proteolysis of canola meal protein. The white-rot fungus G. colossus was also found to grow on canola meal and degrade meal fibre, but had less capacity to degrade meal protein than C. cellulolyticum. In relation to its control, incubation of G. colossus at 37°C resulted in an increase in the essential amino acids lysine and valine, whereas incubation at 45°C resulted in less proteolysis of meal proteins and encouraged ligninase activity.