Ecophisiology of Aspergillus awamori isolated from coffee beans.

ASTORECA A.,; BARBERIS C.,; MAGNOLI C.,; COMBINA M.,; DALCERO A.

Estambul, Turquía

Congreso; XII International IUPAC Symposium on Mycotoxins and Phycotoxins; 2007

Ochratoxin A (OTA) is a fungal secondary metabolite, which has been described as a potent nephrotoxin, carcinogen and teratogen, with immunotoxic properties in rats and possibly in humans (group 2B) (IARC 1993). OTA has been extensively documented as a global contaminant of a wide variety of commodoties. It has also been detected in coffee beans (Taniwaki et al., 2003). OTA has been shown to be produced by several species in the Aspergillus genera. Some authors have shown the presence of OTA-producing strains in coffee samples (Urbano et al., 2001; Taniwaki et al., 2003). The presence of OTA in coffee beans is normally a result of badly controlled harvesting procedures, insufficient drying of the beans, and inadequate storage conditions, allowing for the proliferation of toxigenic fungi (Urbano et al., 2001). The temperature and water activity range where there is the greatest risk for mould proliferation and OTA formation must be defined, to optimize drying and processing of coffee. Preventing germination and growth of these strains will necessarily prevent the production of OTA by these species. Objectives: The aim of this study was to determine the effect of water activity (aW), temperature, and their interactions on in vitro mycelial growth rate and ochratoxin production after 7, 14 and 21 days of incubation of two strains of Aspergillus section Nigri isolated from coffee beans. Materials and methods: One strain of Aspergillus niger (RC4) and one strain of A. awamori (RC20) isolated from coffee beans were used in this study, which produced levels of 14 ng mL-1. The basic medium used in this experiment was a 3% coffee meal extract agar. The water activity of basal medium was modified by the addition of known amounts of glycerol 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 25 and 30 °C during 21 days. The Petri plates were daily examined and two diameters at right angles were measured of each colony. The increase in radial growth was determined and used to calculate the growth rate (mm day-1) by linear regression, under each set of treatment conditions for each isolate. OTA production was analyzed after 7, 14 and 21 days of incubation at each temperature assayed using HPLC screening method. 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. Results: The results showed that the maximum growth rates for the strains assayed were obtained at 0.97 aW and 30 ºC. Temperature influenced the effect of aW on growth. The strain was unable to growth in a range of aW between 0.85 and 0.95 at the minimum temperature assayed (Figures 1 y 2). Anyone of the strains isolated from coffee beans was able to produce OTA on the medium assayed. The caffeine or some other component of the coffee could be kidnapping the toxin or inhibiting the in vitro production which serious to be expected since OTA was not found in any of the coffee samples.