Water Activity and Temperature Effects on Fungal Growth and Ochratoxin A Production by Ochratoxigenic Aspergillus carbonarius Isolated from Tunisian Grapes

Abstract

This study investigated the effects of temperature (15 to 37 degrees C) and water activity (0.90 to 0.99) on the growth and production of ochratoxin A (OTA) by Aspergillus carbonarius cultured on synthetic nutrient medium (SNM) after 5 and 10 d of incubation. Total of 8 ochratoxigenic A. carbonarius, isolated from vineyards located in different regions of Tunisia, were used. Growth data were modeled by the flexible model of Baranyi and growth rates at each set of conditions were obtained. For both growth and OTA production, optimal water activity was 0.99; however, optimal temperature varied. The optimal temperature for growth was 30 degrees C. At 37 degrees C, the growth rate decreased significantly (P < 0.05). Maximum toxin production occurred at temperatures in the range of 15 to 25 degrees C with the optimum one depending on the isolate tested. Significant amounts of OTA were produced after only 5 d of incubation. Our results showed that A. carbonarius isolated from Tunisian grapes behave as those from European and Australian grapes, as reported in the literature, although some differences in trends for growth and OTA production were observed.

Modelling the influence of temperature, water activity and sodium metabisulphite on the growth and OTA production of Aspergillus carbonarius isolated from Greek wine grapes

“…Moreover, our findings are in line with Lasram et al (2010) who reported a significant decrease of A. carbonarius growth when temperature increased over 37 C. Pateraki et al (2007) after assessing the germination of five A. carbonarius strains under different a w levels and NaMBS Fig. 1.…”

“…Moreover, Astoreca et al (2007) reported that the highest OTA amounts were measured at 30 C/0.99 a w when assessing two A. carbonarius strains isolated from dried grapes. The highest levels of OTA were found at 0.98 a w and decreased when a w decreased as reported by other researchers as well (Mitchell et al, 2004;Bellí et al, 2005;Medina et al, 2007;Lasram et al, 2010;Patharajan et al, 2011). After treatment with NaMBS, results showed that OTA content was enhanced even in the cases where fungal growth was delayed by the presence of the antifungal agent.…”

“…Maximum rates for OTA production were mainly detected at 20 C/ 0.98 a w followed by 38 C/0.98 a w , regardless of NaMBS concentration. The statistical analysis showed that all single factors and the interaction of NaMBS with temperature had significant effects on OTA accumulation (p < 0.05) ( Table 2) also reported conditions of 30 C and 0.98 a w as optimum for OTA production, followed by 25 C and 35 C, but not within the range of 15e20 C that is usually reported by other researchers (Mitchell et al, 2004;Bellí et al, 2005;Leong et al, 2006;Lasram et al, 2010). Esteban et al (2006) also reported high OTA amounts at temperatures of 30 C and 0.98 a w, although the optimum was detected at lower temperature (15 C) for the same a w level.…”

Ochratoxin A and ochratoxigenic black Aspergillus species in Tunisian grapes cultivated in different geographic areas

“…On the contrary, A. carbonarius was unable to grow in such climatic conditions. In a previous study (Lasram et al, 2010) the rare A. carbonarius strains isolated from Regueb region showed that under dry and hot conditions, they grew significantly faster than A. carbonarius strains those coming from northern regions. These isolates could have developed a tolerance towards arid climate.…”

Effect of Water Activity, Temperature, and Mixed Fungal Spore Interactions on Ochratoxin A Production by Aspergillus carbonarius

“…Fungi were allowed to grow on a synthetic grape juice medium (SGM) at diverse mixed spore ratios (0:100, 25:75, 50:50, 75:25, and 100:0) in different temperatures (15, 20, and 25°C), water activity (aw) levels (0.95 and 0.98), and incubation time (7,14,21, and 28 days). The results obtained from this work could be useful in elucidating the role of atoxigenic fungal species and their ability to control toxigenic isolates/strains and reduce OTA production.…”