Abstract
Development of fungal mycelia and citrinin or aflatoxin production in each steamed rice inoculated and cultured with Penicillium citrinum or Aspergillus flavus, after cross sectioning the kernels (30 μm thick) by using a cryotome, were observed by an optical microscopic method (fluorescence and ordinal, respectively). In the P. citrinum-inoculated rice, fluorescence due to citrinin production was observed only in the surface layer of the kernel even after 14 days' culture at 28°C. It was not found in the central part of the kernel. In the same section, the fungus digested the cell walls, as well as starch, in the surface layer only. In the A. flavus-inoculated rice, fluorescence due to the aflatoxin production was found in the entire part of the section of the kernel after 7 to 8 days' culture at 28°C. The same section was shown that most of the walls of starchy cells disappeared by fungal digestion. These results showed that mycelial invasion and mycotoxin production, viz. citrinin or aflatoxins, are almost concurrent in the inoculated rice kernels. The modes of the invasion and the digestion were somewhat different between those of P. citrinum and A. flavus.
