Effects of spice oil treatment of rice on moulding and mycotoxin contamination

Abstract

Moulding and mycotoxin production have been studied during storage of rice at 85 and 90% relative humidity (r.h.) following treatment with cinnamon and clove oils. The clove oil-treated rice was artificially inoculated with Aspergillus flavus. Aflatoxin B 1 and ochratoxin A were determined by monoclonal antibody-based enzyme-linked immunosorbent assay. Both moulding and mycotoxin were inhibited by 9 μl cinnamon oil g −1 but, with smaller doses, fungi could be isolated during the early part of storage, but not subsequently. Thus, following treatment with 3 or 6 μl cinnamon oil g −1, fungi were isolated from direct plated grains after 30 days but not after 45 days. Fungi were also isolated from washings of grain up to 30 days after treatment with 3 or 6 μl g −1, although fewer than from untreated grain. Propagules could also be detected up to 15 days after treatment with 9 μl g −1. Clove oil was much less effective than cinnamon oil in preventing moulding. After treatment with 8 μl g −1, the proportion of seeds infected with fungi and numbers of propagules in washings decreased only after 60 days' storage and with 4 μ g −1 after 90 days at both relative humidities. However, aflatoxin contamination could not be detected 90, 60 and 60 days after treatment with, respectively, 2, 4 and 8 μl g −1 at 85% r.h., although ochratoxin A was present in all treatments. At 90% r.h. aflatoxin was absent only after 90 days from treatment with 4 and 8 μl g −1. No T2 toxin was detected.