Microflora of heat-damaged rapeseed

Abstract

Microfloral components present on two sound lots (1 and 2) and three sample grade, heat-damaged lots (3 to 5) of stored Canadian rapeseed (Brassica campestris L. and B. napus L.) were determined with and without surface disinfection. Lots 1 and 2 were from a granary and a warehouse, respectively, and lots 3 to 5 were from primary elevators. Seed in lots 4, 5, and 3 showed progressively increased effects of heat damage as shown by the crush test. Sound lots 1 and 2 had mainly Alternaria and Cladosporium spp. with traces of Eurotium amstelodami, E. repens, and Penicillium spp. Lot 4 seed had low–medium levels of Alternaria alternata, Absidia ramosa, E. amstelodami, and Mucor pusillus. Lot 5 had high levels of E. amstelodami and low levels of Talaromyces thermophilus but A. alternata and M. pusillus were largely absent. Lot 3 had deeper-seated E. amstelodami, T. thermophilus, and Penicillium spp. than lots 4 and 5. Eurotium amstelodami was the predominant storage fungus in the heat-damaged lots. During the early stages of heating, E. amstelodami was often accompanied by the primary sugar fungi M. pusillus and A. ramosa, and after severe heating, by T. thermophilus. The thermal death point was between 50 and 60 °C for moist seed and between 80 and 90 °C for dry seed after 30-min exposure. With the exception of E. amstelodami, heat resistance of the fungal flora did not exceed that of the seed.