USE OF API-ZYM STRIPS AND 4-NITROPHENYL SUBSTRATES TO DETECT AND QUANTIFY HYDROLYTIC ENZYMES IN MEDIA AND GRAIN COLONIZED WITH ASPERGILLUS, EUROTIUM AND PENICILLIUM SPECIES

Hydrolytic enzymes produced by fungi that cause deterioration of cereal grains were identified from culture media and grain using API Zym strips and with 4-nitrophenyl substrates, using a newly developed microtitre plate method. A wider range of extracellular enzymes was produced by spores of common grain-contaminating fungi than by their mycelium growing in shake culture. In barley grain containing 20% water, Eurotium amstelodami greatly increased N-acetyl-beta-D-glucosaminidase activity over that in uninoculated grain and while it usually gave the largest increase in alpha-galactosidase activity other fungi also produced this enzyme. Aspergillus nidulans, A. versicolor and Penicillium viridicatum markedly increased beta-D-xylopyranosidase activity. Acid sulphatase activity was found only in uninoculated barley grains. The activities of 21 hydrolytic enzymes in inoculated grains containing 15, 20 or 25% water during 30 days incubation at 25-degrees-C was also compared with those in uninoculated wheat grain at the same water contents and in dry grain containing 13.5% water. Increased N-acetyl-beta-D-glucosaminidase activity was indicative of fungal invasion while alpha-D-galactosidase activity indicated E. amstelodami invasion. Further tests are required to confirm whether these enzymes could be used to detect the early stages of fungal colonization.