Ochratoxin A production by Aspergillus niger aggregate at different environmental conditions

ASTORECA, ANDREA; BARBERIS, CARLA; MAGNOLI, CARINA; COMBINA, MARIANA; DALCERO, ANA MARÍA

Florianopolis, Brasil

Congreso; V Congreso Latinoamericano de Micotoxicología; 2006

Sociedad Latinoamericana de Micotoxicología y Micotoxinas (SLAM)

Mycotoxin contamination of food and feed represents a high risk for human and animal health. Ochratoxin A (OTA) is a nephrotoxin naturally found in a wide range of food commodities throughout many countries around the word. The objective of this study was to evaluate the in vitro ochratoxin A production by two strains belonging to the A. niger aggregate at differents aW and temperatures after 7, 14 and 21 days of incubation. The OTA-producing strains used in this study were two species of A. niger aggregate (ANM 42 and ANM 176) isolated from stored peanut seeds which produced levels of 14.6 and 17.9 ngmL-1, respectively. The basic medium used in this experiment was a 3% peanut meal extract agar (PMEA) with a final pH of 6.5-7. The water activity of basal medium was modified by the addition of known amounts of glycerol (Dallyn and Fox, 1980) to 0.85, 0.89, 0.91, 0.94, 0.95, 0.97 and 0.995. Petri plates were inoculated centrally with a 4 mm diameter agar plug from the margin of 7-day-old colonies on malt extract agar (MEA). Inoculated plates of the same aW were sealed in polyethylene bags. Triplicate sets of each treatment were incubated at 15, 25 and 30 °C for 21 days. The experiment was repeated twice. Each strain was only inoculated on the media, based on the substrate where its originally was isolated. OTA production was analyzed after 7, 14 and 21 days of incubation at each temperature assayed using high- pressure liquid chromatography (HPLC) screening method. On each sampling occasion, three agar plugs were removed from different points of the colony and extracted with 1 mL of methanol. The extracts were filtered and injected into the HPLC. Both isolates produced the highest level of OTA at 25ºC. The maximum levels of OTA were detected at 0.97 aW while the minimum levels were detected at 0.85 aW at seven days of incubation at the optimum temperature. The amounts of OTA detected decreased when increasing incubation time at 25 and 30ºC. Some authors suggested that strains could remove and assimilate phenylalanine moiety from the OTA molecule, as other nitrogen sources of the culture medium become exhausted (Téren et al., 1996) In another hand, at 15ºC, the highest level of OTA was detected after 14 days of incubation. These results suggest that the minimum temperature assayed influenced the metabolic activity decreasing the fungal growth. This fact induced the latter OTA production. It is necessary to test different environmental conditions to find out the optimal conditions for OTA production which may clarify this fact.