Study On Detection Of Wheat Infected With Toxigenic Aspergillus Flavus Based On Complex Nano-colorimetric Sensing Technology

In China,wheat production accounts for about 1/5 of grain production.However,wheat is prone to mold during transportation and storage,and even produces toxins,especially aflatoxins.It is urgent to establish a mature early detection method for mildew of wheat infected with Toxigenic Aspergillus flavus.In this study,the main source of toxigenic Aspergillus flavus and the atoxigenic Aspergillus flavus infected wheat were the research objects.The composite nano-colorimetric sensor technology was used to establish a method for early detection of the mildew degree of wheat infected with Aspergillus flavus.The specific research content is as follows:(1)Analysis of the production law of AF from Aspergillus flavus.In the experiment,the national standard method isotope dilution liquid chromatography-tandem mass spectrometry was used to detect the contents of four aflatoxins in fresh wheat and moldy wheat infected with toxigenic Aspergillus flavus for 1?10 days.Through statistical analysis of the detection data of aflatoxin content in the process of mildew.Through the two infections of Toxigenic Aspergillus flavus moldy wheat in the AF content detection experiment in this chapter,the results showed that at the critical point of the 7th day of mildew of wheat(AFB₁=14.05?g/kg),the content of AFB₁exceeded the national standard limit of 5?g/kg(GB 2761-2017),and after the 7th day,the content of aflatoxin was exponentially Type growth.Therefore,the 7th day was regarded as the critical point for infection with Toxigenic Aspergillus flavus wheat mildew,which provided data support.(2)Analysis of VOCs from Toxigenic Aspergillus flavus.The experiment uses headspace solid-phase microextraction technology combined with gas chromatography-mass spectrometry(HS-SPME-GC-MS)to detect fresh wheat,different molds infected with Toxigenic Aspergillus flavus and Atoxigenic Aspergillus flavus.Wheat samples with varying degrees(mildew cycle is 0,1,4,7,10 days).Through the statistical analysis and correlation analysis of the volatile gas composition,type and quality changes of each wheat sample before and after the critical point of mildew.During the mildew of wheat infected with Aspergillus flavus,the percentage of 2-methylbutyraldehyde increases with the increase of AFB₁,and at the 7th day of the critical point of mildew in wheat,there is a significant increase,but when infected with Atoxigenic Aspergillus flavus,there is no 2-methylbutyraldehyde.Therefore,2-methylbutyraldehyde was selected as a volatile marker for AFB₁ exceeding the standard of moldy wheat infected with Toxigenic Aspergillus flavus.At the same time,3-methylbutyraldehyde,hexyl octyl ether,hexanal and 1-pentanol were included in the interfering VOCs when optimizing the selectivity of the composite nano-colorimetric sensor in the later stage.(3)Construction of composite nano-colorimetric sensor array.First,for the volatile marker 2-methylbutyraldehyde that is infected with Toxigenic Aspergillus flavus moldy wheat,6 composite nano-colorimetric materials to 5ppm 2-methylbutanal were screened out of 30 composite nano-colorimetric materials.Sensitive materials were NO₂Br BDP@MOF?NO₂BDP@MOF?NO₂Br₂BDP?HBDP@PSN?(CH₃BDP)₂Ni(II)@PSA and COOCH₃-Diol@PSA.Then,the above 6 kinds of composite nano-colorimetric materials are exposed to the interfering VOCs 3-methylbutanal,hexyl octyl ether,hexanal and 1-pentanol,and the response value is low,that is,only for volatile Marker 2-methylbutanal sensitive material.Through experiments and result analysis,three composite nano-colorimetric materials were screened out:NO₂BDP@MOF?HBDP@PSN and COOCH₃-Diol@PSA,which were combined to construct the final product Composite nano-colorimetric sensor array.(4)Wheat mildew detection based on composite nano-colorimetric sensing technology.The experiment selected NO₂BDP@MOF?HBDP@PSN and COOCH₃-Diol@PSA,which are sensitive and selective to the infection with Toxigenic Aspergillus flavus wheat mold marker 2-methylbutanal,to construct composite nanometers.Nano-colorimetric sensor arrays are used to detect wheat infected with different Aspergillus flavus and different degrees of mildew.Combined with PCA,LDA and KNN recognition models were established respectively.The results were showed that:(1)Moldy wheat infected with toxigenic and atoxigenic Aspergillus flavus at 4,7,and 10 days of mildew has a good degree of discrimination.The cumulative contribution rate of the first three PCs of PCA are 98.10%?99.32%and 98.33%respectively.(2)It is possible to accurately predict the different mold days of wheat infected with Aspergillus flavus toxigenic bacteria(the cumulative contribution rate of the first three PCs of PCA reaches 98.97%;when LDA is PC=6,the recognition rate of the training set and prediction set of the model reache 100%and 93.33%respectively;when KNN is PC=2 and K=7,the recognition rate of the KNN model reaches 100%).This study analyzes the VOCs produced by the mildew of wheat infected with toxigenic and atoxigenic Aspergillus flavus and explores the relationship between AFB₁and VOCs in the process of wheat mildew.Using composite nano-colorimetric materials,the colorrimetric sensor made has the selectivity and sensitivity to the volatile markers of mildew of wheat infected with Aspergillus flavus in the mixed gas.Utilizing composite nano-colorimetric sensor technology,when wheat is infected with Aspergillus flavus,the detection of toxigenic Aspergillus flavus in wheat is realized,which provides a basis for the early diagnosis of toxigenic Aspergillus flavus in cereals.