| Zearalenone(ZEN)is a non steroidal mycotoxin,also known as F-2 toxin.ZEN is mainly produced by Fusarium graminearum and widely exists in cereal crops and their by-products,such as corn,peanut and commercial feed,which affects the yield and quality of feed.ZEN has stable heat resistance and will not degrade after feed processing.It enters the human body through the food chain and seriously endangers the health of human and animals.At present,the degradation methods of ZEN are mainly divided into physical method,chemical method and biodegradation method.Although physical treatment will achieve high degradation rate,it will destroy the nutrients of food and feed after treatment,and chemical treatment will often cause secondary pollution.Therefore,biodegradation has become a research hotspot.In this study,moldy feed,feces and soil samples were collected,and ZEN was used as the only carbon source to screen degradation strains;The biological characteristics and degradation characteristics of the degrading strains were studied;The degradation conditions of the strain were optimized and used for detoxification of contaminated feed.The specific research results are as follows:1.By collecting moldy feed,soil,feces and other samples,diluting the samples,inoculating the supernatant into the culture medium with ZEN as the only carbon source,picking out the single colony that can grow,rescreening with the degradation rate as the standard,and screening the strains with strong degradation ability of ZEN by ELISA.The strains were identified by morphological and molecular biological methods to determine their genera and species.The results showed that two strains L-9and G-6 with strong ZEN degradation ability were selected from 96 isolated strains,and the degradation rates were 91.14%and 81.19%respectively.Bacterial morphology and 16S r RNA identified that L-9 strain was Bacillus velezensis G-6 strain was Bacillus amyloliquefaciens.2.Some biological characteristics and degradation characteristics of L-9 and G-6strains were studied.L-9 and G-6 strains reached the maximum number of viable bacteria at 12 h,and the number of viable bacteria was respectively 8.91×10~7CFU/ml and 8.15×10~8cfu/m L;The survival rates of L-9 and G-6 strains were 77.38%,60.37%,36.81%,16.74%,33.04%,18.08%,11.27%,and 2.05%in 50℃,60℃,70℃,and 80℃,respectively;The survival rates of strains L-9 and G-6 were 17.83%and8.06%respectively when the medium salt concentration was 7%;The viable numbers of L-9 and G-6 strains were determined by 0.1%,0.2%and 0.3%bovine bile salt.The survival rates were 73.45%,69.56%,38.21%and 67.89%,53.25%and 24.35%respectively;The degradation effects of L-9 and G-6 strains in AFB1,don and OTA were studied.The degradation rates were 91.16%,94.41%,21.46 and 20.41%,24.26%and 14.47%respectively.The results of degradation characteristics showed that the degradation mechanisms of ZEN by L-9 and G-6 strains mainly included cell wall adsorption and enzyme degradation,and enzyme degradation was the main degradation pathway.Cell wall can adsorb both living and inactivated cells.Extracellular enzymes are the main degradation pathway for the degradation of different active components of ZEN.3.The degradation conditions of L-9 and G-6 strains and the degradation of ZEN in feed raw materials and polluted Yellow storage were optimized.The results showed that the optimum degradation conditions of strain L-9 were as follows:temperature37℃,medium p H 7.0,inoculation amount 3%,culture time 48 h;The optimum degradation conditions of strain G-6 were as follows:temperature 37℃,medium p H5.0,inoculation amount 3%and culture time 72 h.The optimized conditions were applied to different feed raw materials and polluted Yellow storage.The results showed that strains L-9 and G-6 could degrade Zen in soluble starch,corn flour and soybean meal 100%;In the polluted Yellow storage,the degradation rate of L-9 strain was 76.25%,and that of G-6 strain was 83.59%. |
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