Mycobiota and mycotoxins in freshly harvested and stored maize

Abstract

The incidence of mycobiota and mycotoxin levels were investigated in the freshly harvested maize kernel samples from October 2014 and in the samples of stored maize kernels from February 2015. Toxigenic fungal species (moulds) were isolated, cultivated and identified on agar plates according to standard mycological methods, while mycotoxins were detected by enzymelinked immuno-sorbent assay (ELISA). Mycological analyses of kernels showed the presence of toxigenic species from genera Aspergillus, Fusarium and Penicillium. Among the Aspergillus species, Aspergillus flavus was identified with higher incidence in the stored kernels (10.25%), than in freshly harvested kernels (3.67%) whereas A. parasiticus was the predominant species in the freshly harvested kernels (4.17%) compared to the stored kernels (0%). From the genus Fusarium three species were identified: F. graminearum, F. subglutinans and F. verticillioides, with the incidence of 1.08%, 8% and 25.75%, respectively in freshly harvested kernels and the incidence of 2.50%, 7.10% and 29.75%, respectively in the stored kernels. Species from genus Penicillium had higher incidence in freshly harvested kernels (14.25%) than in the stored kernels (9%). In addition, tested samples of harvested and stored maize kernels were 100% positive with aflatoxin B1 (AFB1), deoxynivalenol (DON) and total fumonisins B1, B2 and B3 (FBs). The mean levels of AFB1, DON and FBs were 2.77 μg kg-1, 117.83 μg kg-1, and 3700.84 μg kg-1, respectively in the freshly harvested kernels and a mean levels of 2.16 μg kg-1, 2034.40 μg kg-1, and 5976.50 μg kg-1, respectively in the stored maize kernels. In the freshly harvested maize kernel samples, statistically significant (P ≤ 0.05) positive correlations of kernel moisture content with the incidence of Penicillium spp. (r = 0.47), and levels of AFB1 (r = 0.46) and FBs (r = 0.47), and between the incidence of Penicillium spp. and level of AFB1 (r = 0.53) were established. In the stored maize kernel samples, statistically significant (P ≤ 0.05) positive correlations were found between the incidence of F. subglutinans and level of FBs (r = 0.50) and between levels AFB1 and FBs (r = 0.52). A highly significant (P ≤ 0.01) positive correlation was established between the incidence of F. verticillioides and level of FBs (r = 0.64) in freshly harvested maize kernel samples. These results indicate that the incidence of toxigenic fungi and levels of mycotoxins, in particular DON and FBs, were higher in the stored maize kernel samples than in freshly harvested maize kernels. Therefore, to prevent the development of toxigenic fungi and mycotoxins accumulation in post-harvest period it is necessary to thoroughly dry maize and keep it in hygienic food storages.

U radu je proučavana učestalost mikobiota i sadržaj mikotoksina u uzorcima zrna kukuruza sakupljenih tokom berbe u oktobru 2014. godine i u uzorcima uskladištenog zrna sakupljenih u februaru 2015. godine. Toksigene vrste gljiva (plesni) su izolovane, odgajene i identifikovane na hranljivoj podlozi prema standardnim mikološkim metodama, dok je sadržaj mikotoksina detektovan primenom imunoadsorpcione enzimske metode (ELISA). Mikološkim analizama zrna kukuruza ustanovljeno je prisustvo toksigenih vrsta iz rodova Aspergillus, Fusarium and Penicillium. Među Aspergillus vrstama, Aspergillus flavus je identifikovana u većem procentu u uzorcima uskladištenog zrna (10,25%) nego u uzorcima sveže požnjevenog zrna (3,67%), a A. parasiticus bila je predominantna vrsta (4,17%) u uzorcima sveže požnjevenog u odnosu na uskladišteno zrno kukuruza (0%). Tri vrste roda Fusarium su identifikovane sa učestalošću od 1,08% (F. graminearum), 8% (F. subglutinans) i 25,75% (F. verticillioides) u požnjevenom zrnu, i sa učestalošću od 2,50% (F. graminearum), 7,10% (F. subglutinans) i 29,75% (F. verticillioides) u uskladištenom zrnu kukuruza. Vrste iz roda Penicillium imale su veću učestalost u uzorcima požnjevenog (14,25%) nego u uzorcima uskladištenog zrna (9%). Ispitivani uzorci sveže požnjevenog i uskladištenog zrna bili su 100% pozitivni sa aflatoksinom B1 (AFB1), deoksinivalenolom (DON) i ukupnim fumonizinima FB1, FB2 i FB3 (FBs). Prosečne koncentracije ovih toksina su iznosile 2,77 μg kg-1 (AFB1), 117,83 μg kg-1 (DON) i 3700,84 μg kg-1 (FBs) u uzorcima sveže požnjevenog zrna i 2,16 μg kg-1 (AFB1), 2034,40 μg kg-1 (DON), i 5976,50 μg kg-1(FBs) u uzorcima uskladištenog zrna. Statistički značajne (P ≤ 0.05) pozitivne korelacije ustanovljene su između sadržaja vlage zrna sa učestalošću Penicillium spp. (r = 0,47) i koncentracijama AFB1 (r = 0,46) i FBs (r = 0,47), kao i između učestalosti Penicillium spp. i koncentracije AFB1 (r = 0,53). U uzorcima uskladištenog zrna, statistički značajne (P ≤ 0.05) pozitivne korelacije ustanovljene su između učestalosti F. subglutinans i koncentracije FBs (r = 0,50) i između koncentracija AFB1 i FBs (r = 0,52). Statistički veoma značajna (P ≤ 0.01) pozitivna korelacija ustanovljena je između učestalosti F. verticillioides i koncentracije FBs (r = 0,64) u uzorcima sveže požnjevenog zrna kukruza. Rezultati ovih istraživanja ukazuju da su učestalosti toksigenih vrsta gljiva i koncentracije mikotoksina, posebno DON i FBs, bile više u uzorcima uskladištenog zrna nego u uzorcima sveže požnjevenog zrna. Zbog toga, da bi se sprečio razvoj toksigenih gljiva i akumulacija mikotoksina u postžetvenom periodu neophodno je kukuruz dobro osušiti i čuvati u higijensko ispravnim skladištima.