Abstract
Rhodococcus erythropolis was found to effectively degrade aflatoxin Bl produced by Aspergillus flavus and Aspergillus parasiticus . However, one problem of concern was the slow growth of this strain. In this study, Plackett–Burman design was used to select the most important variables, namely, temperature, pH, inoculum size, liquid volume, agitation speed and culture time that affected the growth of R. erythropolis. Central composite experimental design and response surface analysis were adopted to derive a statistical model for optimizing the culture conditions. From the obtained results, it can be concluded that the optimum parameters were: temperature, 15.3°C; pH, 5.56; inoculum size, 4%; liquid volume, 70 ml in 250 ml flask; agitation speed, 180 rpm; and culture time, 58.2 h. At this optimum point, the populations of the viable organisms could reach 10 8 colony forming units (CFU)/ml, which was 100 times higher than that incubated under the initial conditions. After 58.2 h incubation in this optimum cultivating conditions, 53.9 ± 2.1% of aflatoxin B 1 was degraded, while only 20.6±1.4% of aflatoxin B 1 was degraded in the initial conditions. Key words: Rhodococcus erythropolis, culture condition, optimization, Plackett–Burman design, central composite design, response surface methodology.
Highlights
Aflatoxins (AFs) are a family of toxic secondary metabolites produced by certain strains of the common molds Aspergillus flavus and Aspergillus parasiticus (Bennett and Christensen, 1983)
Plackett–Burman design was used to select the most important variables, namely, temperature, pH, inoculum size, liquid volume, agitation speed and culture time that affected the growth of R. erythropolis
We found the more viable R. erythropolis in the culture, and the less aflatoxin B1 remained
Summary
Aflatoxins (AFs) are a family of toxic secondary metabolites produced by certain strains of the common molds Aspergillus flavus and Aspergillus parasiticus (Bennett and Christensen, 1983). Studies performed on hazelnuts and pistachios suggested that optimum temperature and relative humidity for aflatoxin production is 25 to 30°C and 97 to 99%, respectively (Arrus et al, 2005). The aflatoxins are freely soluble in moderately polar solvents (example chloroform and methanol), especially in dimethylsulphoxide, and have some water solubility. These compounds are very stable at high temperature, with little or no destruction occurring under ordinary cooking conditions or during pasteurization. AFB1, AFG1, and AFM1 have higher carcinogenic activity than AFB2, AFG2 and AFM2, respectively (Hwang and Lee, 2006)
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