Micobiota do arroz armazenado numa fábrica de processamento

Abstract

In Portugal, rice crops are very important in the Portuguese agriculture with rice market valued at 200000 tons. In our country the average consumption per capita is the highest in Europe around 17 Kg per year. Rice is one of the most staple food of over half world-wide population, so the destruction and losses that could take place during storage can affect the food reserves. Most food processed in the industry are susceptible to a variety of enemies that will be able to cause damages in the product before and after the processing. In storage, the presence of fungi is a problem of difficult resolution. In particular Aspergillus, Fusarium and Penicillium species are the most responsible for qualitative and quantitative losses in cereals. Under specific conditions they can produce mycotoxins that can be responsible for economical injuries and public health risks. Mycotoxins study has got some importance because of the direct and indirect economical injuries that cause in the industry. The aim of this work was to contribute for the knowledge of the stored rice mycobiota which is processed in Portugal. Under this work six national rice samples from 2006 campaign (paddy rice, brown rice and polished rice), and three samples of imported rice (brown rice and polished rice) with 3 to 13 months of storage were studied. The samples came from a Portuguese processing industry, and all national rice samples studied belong to Ariete (two samples), Gládio (two samples), Fani (one sample) and Albatros (one sample) varieties. The evaluation of the mycobiota, of a national rice samples and an imported rice samples, shows a greater diversity of species in national rice than in the imported rice. In national rice samples were identified 55 taxa while 20 taxa were found in the imported rice samples in a total of 57 identified taxa, from field fungi and storage fungi. Species like Alternaria alternata, Aspergillus candidus, A. flavus, A. fumigatus, A. niger, A. terreus, Bipolaris oryzae, Chaetomium trilaterale, Fusarium semitectum, Nigrospora oryzae, Penicillium islandicum, Syncephalastrum racemosum, Trichoderma harzianum, Trichoconiella padwickii, Trichotecium roseum and a Geotrichum specie are the same in national rice samples and in imported rice samples. In paddy rice and brown rice samples, the most common taxon were Aspergillus, Eurotium and Alternaria species, while in polished rice was only Aspergillus and Eurotium. It was observed that fungi diversity decreases along the process (paddy rice, brown rice and polished rice), where the polishment is particularly effective in the fungi reduction. However for the elimination of storage fungi, the polish was not so efficient as it was with field fungi, because the isolations carried out in the polish rice corresponded in some cases to 60 % or more of the isolations effectuated in the brown rice. For the polished rice samples, the Aspergillus and Eurotium species appeared with bigger frequency than Penicillium and Fusarium ones. Relatively to the type of storage, in silo or in bin it was observed that the samples with bigger diversity of storage fungi were originating from silos, and field fungi appeared more in the samples originating from bin. From the studied samples a total of 170 taxa were identified namely Absidia, Alternaria, Aspergillus, Bipolaris, Chaetomium, Curvularia, Epicoccum, Eurotium, Fusarium, Nigrospora, Mucor, Penicillium, Rhizopus, Sordaria, Stemphylium, Syncephalastrum, Trichoderma, Trichoconiella, Trichotecium, Ulocladium species. The identification took place on basis in cultural, morphological and biometrics characteristics.