| Aflatoxins are secondary metabolite mainly produced by Aspergillus parasiticus and Aspergillus flavus. Aflatoxins is highly toxic, mutagenic and carcinogenic to both human and livestock. Aflatoxin B1 is most toxic of all aflatoxins. In this paper, statistical method was used to optimize the fermentation process of aflatoxin B1 degradation strain HSK8 which preserved in laboratory. Furthermore, the biotransformation mechanism of HSK8 was researched. The results are listed as follows:(1) High Performance Liquid Chromatography(HPLC) was used for selection of strain for next experiment by determining the AFB1 degradation rate. HSK8 strain was selected from three aflatoxin B1 degradation strain preserved in lab, the degradation ratio of AFB1 was 39.06%. HSK8 was identified as Cladosporium uredinicola by China Center for Type Culture Collection(CCTCC).(2) The fermentation condition was determined as follows by statistics method: fermentation temperature 28 oC, loading volume 75 mL/250 mL, inoculation amount 15%(v/v), fermentation time 36 h, initial p H 8.0. The optimum fermentation medium was obtained as follows(per litre): corncob powder 35 g, NaNO3 15 g, MgSO4 0.5 g, MnSO4·H2O 1.41 g, K2HPO4·3H2O 1.0 g, KCl 0.5 g. AFB1 biotransformation rate reached 96.00±3.48% under optimum conditions which was 140% times higher than that of unoptimized conditions.(3) During the optimization of fermentation time, AFB1 incubated with fermentation supernatant for 24 h, and extracted by CH2Cl2. To organic phase, both High Performance Liquid Chromatography(HPLC) and Thin layer chromatography(TLC) detected a AFB1 biotransformation product perspectively which was confirmed to be the same compound. The results of LCMS indicated that the molecular mass of AFB1 biotransformation product was 342 which was 30 higher than AFB1.(4) The results of cytotoxicity on HeLa cells indicated that the culture supernatant-treated AFB1 is much less toxic compared to AFB1. |
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