The chemical estimation of chitin has been successfully applied to the quantitative estimation of fungus in a solid substrate fermentation. The fermentation examined was the protein enrichment of cassava starch by Rhizopus oryzae to form a product known as Cassava Cheese. After acid hydrolysis and ion-exchange chromatography, the fungal chitin was estimated colorimetrically as glucosamine. The assay conditions were examined to ensure reliable and reproducable estimates of glucosamine. The relationship between the glucosamine content of the fungus and its dry weight was found to vary with growth conditions and age of the culture. Values for the glucosamine content of the Rhizopus oryzae growing in the solid substrate were determined by examination of the glucosamine content of the fungus grown in liquid media and membrane cultures. Attempts were made to measure the amount of fungus present in mouldy cereals by means of the chitin method but it was found to be impossible because of the presence of a variety of fungi with differing chitin contents. Examining the amino-sugar composition of the fungi isolated from maize and wheat by means of the gas-liquid chromatograph, galactosamine was found to be present in Aspergillus candidus, Aspergillus ftavus, Aspergillus niger and Aspergillus versicolor. To circumvent problems encountered when trying to use chitin as a measure of fungal growth in mixed fungal populations, a method was developed based on the quantitative polyacrylamide gel electrophoresis of proteins extracted from Aspergillus chevalieri and Aspergillus flavus. Specific proteins were found in these fungi which could be related to fungal dry weight, thus enabling the amount of fungus present in artificially contamined wheat samples to be determined. It is suggested that a rigorous examination be made of the relationship between the specific fungal proteins and such factors as age, culture conditions and morphology to check the validity of the method. However, the method does appear to offer potential for quantitatively measuring the amount of an individual fungus present in a mixed fungal population.
|Date of Award||1974|