Assessment of aflatoxin B1 and ochratoxin A in interacting mixed cultures of Aspergillus flavus and Aspergillus niger aggregate on peanut grains.

BARBERIS C.L.; CARRANZA M.C.; DALCERO A.M; MAGNOLI C.E,

Mendoza

Congreso; Mycored- Argentina. Strategies to rteduce the impact of mycotoxins in Latin America in a global contex.,; 2011

Universidad Nacional de Río Cuarto

Aspergillus species are important contaminant of several oilseeds as peanut in pre, post harvest and stored stage. Furthermore A. flavus is the main specie isolated from peanuts in Argentina followed by A. niger aggregate strains. The objective of this work was to evaluate the colony forming units, aflatoxin B1 (AFB1) and ochratoxin A (OTA) production at different inoculums levels during the interaction between A. flavus and A. niger aggregate strains at water activity (aW) and temperature controlled on peanut grains. A. flavus (RCP 40) and A. niger aggregate (RCP 42) isolated from peanut were used in these experiments. Individual spore suspension of A. flavus and A. niger aggregate was adjusted to 107 spores/ml and serial decimal dilutions were done to obtain the different inoculums sizes (102, 103 and 104 spores/ml). Irradiated peanuts were re-hydrated to 0.970 aW by adding sterile distilled water. One hundred grams of peanut grains were inoculated with different inoculums sizes (102, 103 and 104) of both strains in singles and pairing cultures. Cultures were incubated at 28ºC for 21 days. The colonization of the grains was assessed after 7, 14 and 21 days of incubation. Serial decimal dilutions until 10-14 were spread on the surface of MEA. Plates were incubated at 28ºC for 7 days. The results were expressed as colony forming units per gram of peanut grains (CFU/g). The AFB1 and OTA levels were determined at intervals of 7, 14 and 21 days. All the experiments were done by triplicate and repeated three times. Peanuts grains from each single and interacting mixed culture were removed and extracted for AFB1 and OTA, and quantified by TLC following the methodology proposed by Official Method of Analysis (AOAC, 1995) and Pittet y col (2002), respectively with some modifications. In general fungal counts of A. niger aggregate strain were significantly higher than those observed in A. flavus strain at the end of incubation period (21 days). This behavior was also observed in the interacting mixed cultures when the initial inoculums of A. flavus were higher than those A. niger aggregate strain. In single cultures of A. flavus strain with the lowest initial inoculums (102 spores/ml), the highest levels of AFB1 were detected at 7, 14 and 21 days of incubation. In all mixed cultures assays the AFB1 production was significantly reduced in comparison with the accumulation in single cultures of A. flavus. The highest percentage (95%) of mycotoxin production inhibition was observed at 7 and 14 days when the initial inoculums sizes of both strains were 104 spores/ml. An increased in OTA production was observed with the lowest concentrations of A. niger spores (102 and 103 spores/ml) when increased the initial inoculums of A. flavus strain. The highest levels of OTA accumulation were observed at 14 days for all interactive cultures. The maximum level of this mycotoxin was reach with 104 spores/ml of A. flavus and 103 spores/ml of A. niger (1240 ng/g).