| Deoxynivalenol (DON) is a kind of type B trichothecene. It is the secondary metabolites mainly produced by fusarium graminearum and fusarium culmorum. It widely exists in nature and could cause serious pollution to grains and feeds, and thus results in huge economic losses throughtout the world. A certain amount of DON intake could be a serious threat to the health of humans and animals. So the research on DON prevention is imminent.At present, the degradation methods for DON mainly include physical methods, chemical methods and biological methods. The degrading effect of physical treatments on DON is not obvious due to its high chemical stability and non-polar structures. Although the degrading effect of chemical treatments on DON is better than physical treatments, it could cause varying degrees of reduction of the nutritive value and thus results in new harmful pollution to grains and feeds. While, the microbiological and enzymatic treatment seem to be the best method for DON degradation as the detoxification process is under mild conditions without using harmful chemicals and without nutrients losses.Based on the above presentation, this article aimed to use the microbiological and enzymatic treatment for DON degradation, which was considered the best method for reducing the DON damage on foods. Briefly, the As-W6 strain capable of degrading DON was screened by using the phenyl epoxy ethane as only carbon source, and the As-W6 strain was identified as Aspergillus oryzae. The degradative enzyme was purified and characterized, and the degrading effect of the strain on DON degradation were estimated and compared with the degradative enzyme.The main work summarized as follows:The As-W6 strain capable of degrading DON was screened. Hypha of the As-W6 strain was white at the beginning of the growth, then turned to yellow-green, and hypha developed with diaphragm, conidium string, a globose or ellipsoid, the top capsule gose out radially was measured by the morphological observation, staining microscopy, electron microscope scanning and molecular biology identification. The strain’s DNA was extracted and through out PCR propagating, the target gene length was 531 bp by using sequence analysis. The gene sequence was compared with Genbank database (NCBI) Blast sequence, the result showed that the homology of strain As-W6 with several Aaspergillus oryzaes was above 99%, therefore, We confirmed the strain As-W6 was a strain of Aspergillus oryzae.The purified degradative enzyme was obtained from strain As-W6 through the procedure of ammonium sulfate fractionation, dialysis, DEAE-52 cellulose chromatography, Sephadex G-75 gel filtration, and a given 86.7-fold purification was achieved with a yield of 23.2%. The 1D-LC-MS liquid mass spectrometry identified the degradation enzyme contained 383 amino acids, the molecular weight was 40810.3 Da and the isoelectric point was 5.80. The alignment score of 158 matched with 6 peptides, the results showed the degradative enzyme was a kind of lipase. The result showed that the optimum temperature and pH of the enzyme were 40℃ and 7, respectively. The enzyme was stable under 40℃ with pH ranging from 6 to 8. The lipase activity could be enhanced by Ca2+、Mg2+ and Acetone, while inhibited by Cu2+、Fe2+、Mn2+ and SDS. It achieved maximum values when soybean oil was used as the substrate, which indicated that the lipase showed a significant specificity toward soybean oil.The concentration of DON was quantitatively determined by high performance liquid chromatography (HPLC), the results showed that the DON was degraded by the lipase, and the degradation rate reached over 60%. After the extraction of degradation products, liquid chromatography-mass spectrometry (LC-MS) was used for the qualitative analysis of the biodegradation products, and it was found that the molecular weight of DON decreased from 296.1 to 282.2, it indicating that DON was biodegraded and converted into another substance. |
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