Lipolytic activity and degradation of rapeseed oil and rapeseed by spoilage fungi.

ABSTRACT

Aspergillus, Eurotium and Penicillium spp. from rapeseed were able to grow and produce lipases over a range of water activities (aw) at both 15 and 25 degrees C on tributyrin agar. The ability to produce lipases was not directly related to growth rate. The clearing zone growth rate ratios gave lipase indices which varied markedly between test fungi and with aw. The fungi with the highest indices were Aspergillus candidus and Aspergillus versicolor and Penicillium expansum and Penicillium hordei. The Aspergillus spp. generally grew faster on a 1% crude rapeseed oil at 25 degrees C and 0.995 and 0.95 aw than on the tributyrin agar. P. hordei degraded the rapeseed oil more rapidly than Eurotium amstelodami or Penicillium aurantiogriseum, with optimum activity at 0.98 aw. E. amstelodami was the least effective at degrading the rapeseed oil under all aw conditions. The lipase indices were compared with the ability of the test fungi to degrade irradiated rapeseed. Dry matter loss over 4-week periods were greater at 25 than 15 degrees C, regardless of aw. At 15 degrees C, Penicillium spp. caused significantly greater dry matter losses than Aspergillus spp. A. niger degraded rapeseed faster than other Aspergillus spp. tested at 0.98 aw, but at 0.95 and 0.90 aw there was little difference between species.