Initial Study On Near Infrared Detection In The Pesticide-residues Of Vegetables Based On The Ultra-high Pressure Pretreatment

Issues of food safety are worldwide highlights. Pesticide residues in vegetables are among the most sensitive problems in daily life, which not only results in the loss of finance,credibility, even the lives, but also causes the economic barriers to the international trade and serious environmental pollution. Only by enhangcing the monitoring efforts, exploring more convenient, faster, cost-effective detection method, can the harmful effects of the pesticide residues be kept within limits effectively.The current analysis methods of the pesticide residues have some drawbacks. For example, the complication of the operation process, time-noneffective and poor stability of the prepared samples which often makes the accuracy of the analysis below acceptable standard. So, a novel method, near infrared detection of the pesticide residues in vegetables based on ultra-high pressure pretreatment, is put forward.Near infrared detection is fast, efficient, simple and no sample pretreatment required. Ultra-high pressure provides high rate of extraction, low impurities, short time of extraction, less use of solvents and pollution-free. The active ingredients are more stable at room temperature conditions.In this paper, near infrared detection technologies of the pesticide residues in vegetables based on ultra-high pressure pretreatment are studied. The organophosphorus pesticide residue-rogor in Chinese cabbage is taken as representative study object. Research programs are identified according to theoretical analysis. Pretreatment process parameters are selected for fitting near infrared detection. The technical parameters of near infrared detection instrument are determined. The impacts of ultra-high pressure pretreatment on near infrared detection are analyzed by visual observation of near infrared spectrum and analysis of partial least squares model of near infrared spectrum. It is aimed at finding a new way to improve the speed and stability of the analysis of pesticide residues in vegetables. The main research contents of this thesis are as follows:1,The theories of near infrared detection, factors and parameters in near infrared detection, impacts of ultra-high pressure pretreatment on near infrared detection and near infrared spectrum characteristics of rogor and vegetables are analyzed. It is found that the changes of some chemical bonds, some composition, particle size and amount of suspended solids affect the material characteristic peak of near infrared spectrum, optical path and absorbance of near infrared spectrum, in turn affect the wave. So near infrared detection of the pesticide-residue in vegetables based on ultra-high pressure pretreatment is raised through theoretical analysis.2,According to the gas chromatography tests and the analysis of particle size and amount of suspended solids, pretreatment process parameters are selected for fitting near infrared detection of rogor residue in Chinese cabbage, immersion time is 3 minutes, volume of reagent is 50mL, quality of vegetables is 25mg, pressure is 300MPa. The nominal resolution is 4cm-1 selected through the numbers of data points that the near infrared spectra transforms into, the accumulating scans is 32 chosen according to the effect of reducing the noise after averaging the spectrum, the optical path of near infrared detection annex is 1mm selected by absorbance and energy situation of the spectrum. T est is operated in about 20℃; the concentration of rogor is from 10-3 to 10-6. The total number of samples is 28, which is divided into validation set , 24 ,and prediction set , 4.During choosing the ultra-high pressure pretreatment parameters, it is found that vegetable juice treated by different pressures (no pressure, 100MPa, 200MPa, 300MPa, 400MPa) deposits form the high pressure distinguished from 300MPa after standing in a short time. Over time, all samples deposit, the juice is clearer in turns along with increasing pressures. The less suspended solids are contained in samples, the less seriously the scattering is impacted, which is good for improving spectral quantity. The phenomena indicates that affecting scattering made by suspended solids in samples become less with increasing pressure.3,The impacts of ultra-high pressure pretreatment on near infrared detection are studed initially. The near infrared spectrum are observed from intuition. The absorbance, position of peak and smooth of the spectra are not affected by the ultra-high pressure. There are no remarkable differences in spectrum treated by different pressures.4,the PLS models are used to analyze impact of ultra-high pressure pretreatment on near infrared detection. In the process of data preprocessing and modeling, data of samples treated by pressure are more stable than that of samples without ultra-high pressure. There are less outliers. By comparing results obtained by different spectral pretreatments, the appropriate wave-length range and methods of preprocessing of samples with pressure and without are got. Spectrum of samples without ultra-high pressure are dealt with in the range between 4500 and 10000 cm-1, treated by VN, smooth (25 points), after optimized, the wave-length are reduced in the 6101.9-5448.1 cm-1 and 4601.5-4499.3 cm-1, the PLS model is established by FD+MSC. Spectrum of samples with ultra-high pressure are dealt with in the range between 4100 and 11000 cm-1, treated by smooth (21 points), after optimized, the wave-length are reduced in the 6800-6099.9 cm-1 and 4601.5-4248.5cm-1, the PLS model is built by VN.The model's quantity of samples with ultra-high pressure is better than that of samples without ultra-high pressure. Analyzing the PLS model and the results of prediction processed by OPUS, the related coefficient of models of samples with pressure and without are 75.93% and 56.8% respectively, the RMSECV are 0.139 and 0.192, the errors of the tow group samples'prediction are 1.557%, 8.17%, -86.88% and 26.57%, -49.39% -93.06%.The limit of near infrared detection of model of samples with ultra-high pressure is improved, 2 times higher than no pressed samples model. Model of samples with ultra-high pressure can detect the 10-5 (quality-volum concentration), Model of samples without ultra-high pressure does not finish detecting at 10-4(quality-volum concentration). The limit of detection of the two models can't meet the prescription of rogor pesticide residue ruled by the ministry of agriculture, 10-6.5,Calculating in terms of the full-time work, the detection speed of near infrared detection of the pesticide residue in vegetables based on ultra-high pressure pretreatment, is 20 times higher than that obtained by NY/T761-2004 detection of organic phosphorus. Full operation of near infrared detecting pesticide residues based on ultra-high pressure pretreatment, a FT-NIR instrument can detect 30 samples in 1 hour; while a gas chromatogragh instrument can detect 30 samples in 24 hours.Limited by the test time and personal experience,the near infrared detection of rogor residue in Chinese cabbage based on ultra-high pressure pretreatment is investigated in this pater. In terms of the results of the preliminary study, the crafts of pretreatment and the methods of data pretreatments and modeling need to be consummated further. The near infrared detection of pesticide residues in various vegetables should be researched deeply.