Abstract
Several countries have enacted regulations on tolerance limits for common
mycotoxins because of the hazardous nature and widespread occurrence of these
fungal secondary metabolites in agricultural commodities. Screening of agricultural
commodities destined for animal consumption for the presence of mycotoxins is now
becoming a prerequisite in several countries as a means of minimizing ingestion of
these toxins.
Silage samples were analyzed for pH, % dry matter (DM) content, and the presence of
total fungi, yeasts and the types of lactic acid bacteria present. The samples were also
analyzed for mycotoxins that have been reported to commonly occur in silage. The
pH of the samples was found to be acidic ranging from pH 3.4 to 4.7, with few
samples having pH values above 6. There was a significant difference in the % DM
content amongst the sampling regions. There was no significant difference in the
extent of fungal contamination amongst the different regions. Aspergillus fumigatus
was the predominant species from all the samples. Most of the yeast species were
isolated from the Bergville region. The yeast species isolated from all samples were
Trichosporon, Cryptococcus and Candida species, which are all regarded as nonlactate
fermenters. Lactobacillus plantarum and Lactobacillus buchneri were the only
two lactic acid producers isolated from the samples.
Aflatoxins, citrinin and patulin were the most predominant toxins in the samples.
Ochratoxin A and deoxynivalenol was not detected in all samples using thin layer
chromatography, while the latter two toxins were only detected in two samples using
VICAM fluorometry. The level of fumonisins that was found in the forage crops used
for silage production was fairly low with the highest level being 9.36 ppb. Most of the
mycotoxin extracts were found to reduce the % cell viability of human lymphocytes
after 18 hours of incubation as determined by the MTT assay.
Professor Mike Dutton
Mr. F. E. Van Zyl