Study On Cultivation Of Rhodococcus Erythropolis And Its Degradation Of Aflatoxin B₁

Aflatoxins are secondary metabolites produced by a variety of fungi, suchas,Aspergillus flavus、Aspergillus parasiticus、Aspergillus nonius and Aspergillustamari, and aflatoxin B₁（AFB₁） has the most toxic and the stable chemical character.Aflatoxins are liver toxins, can cause damage to liver and other organs. These toxinsare mutagenic, teratogenic and carcinogenic, and do great harm to human andanimal’s health, cause tremendous economic loss.Using physical and chemical methods can remove or degrade aflatoxins, but thereaction conditions are severe, and these methods can cause secondary pollution,reduce the qualities of product. Many studies focus on biological means because thesemethods have mild reaction conditions and do not destroy the product’s quality. TheAFB₁degradation of Rhodococcus erythropolis was investigated in this study. Thisresearch mainly includes:（1） The culture conditions of Rhodococcus erythropolis were optimized toimprove the bacterial concentration, the best culture conditions were as follows:temperature30℃, pH5.56, liquid volume70mL in250mL flask, inoculum size4%,agitation speed180rpm, culture time58.2h;（2） To study the effect of differentculture mediums on AFB₁degradation. The glucose was the best carbon source, theyeast extract was the best nitrogen source, compared with other metal ions, and thefermentation broth with copper chloride had the best degradation ability. Usingorthogonal experimental design and regression analysis, the optimum medium wasobtained as follows: glucose1.0g/L, yeast extract1.4g/L, copper chloride0.07mol/L.Using response surface analysis to obtain the best conditions: temperature23.2℃, pH7.17, inoculum size4%, liquid volume24.6mL in100mL flask, agitation speed180rpm, culture time81.9h;（3） The compounds with AFB₁degradation activity was fromthe extracellular extracts. Using ammonium sulfate to obtain the multienzyme, the60%deposition was the best. The multienzyme’s optimum time was84h and the ratio was74.5%,the optimum temperature was15℃, the optimum pH was5.0. The enzymeactivity was enhanced in the presence of Na+;（4）The ferment culture can inhibit thebiosynthesis of AFB₁on peanut. Using orthogonal experimental design to investigatethe factors, the results showed that, temperature had the most influence, followed bybacterial concentration, glucose, hydrogen peroxide, sodium nitrate, peptone, and thebest conditions were: bacteria concentration106CFU/mL, temperature25℃,hydrogen peroxide6%, sodium nitrate10g/L, peptone5g/L, glucose0, under thiscondition, the inhibition was25.8%.This study extracted active compounds from ferment culture of Rhodococcuserythropolis, investigated some properties of crude protein extracts. Using fermentculture to inhibite the biosynthesis of AFB₁on peanut, this would be an idealcandidate to control peanut contamination by AFB₁during cereal storage.