Influence of Water Activity and Temperature on the Growth and Accumulation of Ochratoxin A Produced by Aspergillus carbonarius Isolated from Garri

This study determined the influence of water activity, temperature and their interactions on growth, asexual sporulation and ochratoxin A accumulation in Aspergillus carbonarius using standard microbiological techniques. Results obtained shows that at 35°C, OTA was more produced than at other temperatures while both sporulation and mycelial growth were more enhanced at 25°C. A water activity of 0.99 produced the greatest interactions for all except for asexual sporulation that was best at 0.96a . No growth was w seen at water activity range of 0.90 to 0.94 for plates incubated at 40°C. The peak time for ochratoxin A was at 56 day with rapid production within the first 28days while the rate of production between 28 and 56 days th th were relatively slower. When the two factors ( water activity and temperature) were treated as combined variables for regression analysis, it was disclosed that both have a statistical significant relationship with ochratoxin A production and their regression equation were given as Y = 31.029 -29.14a -0.052t, 1 w Y = -16.881+ 12.12a -0.073t and Y = -17.217 +22.02aw-0.082t for concentration of OTA in spores, biomass 2 w 3 and medium respectively. Regression determinant confirmed that both water activity and temperature accounted for 60%, 52.6% and 42.6% of the total ochratoxin A content present respectively. This observation was also ascertained by the distribution of the bell shaped regression standardized residual histogram around zero. In conclusion, the results of this study reject the null hypothesis which states that the ability to complete wild type asexual sporulation could be a prerequisite for toxin biosynthesis. Rather, such attribute could be linked to certain extrinsic factors that includes temperature and water potential.