Detection And Evaluation Of Nitrate In Lettuce Leaves Based On Chlorophyll Fluorescence Spectrometry

Nitrate is one of the important pollutants in the evaluation of pollution-free vegetables,and is a direct expression of the excessive application of nitrogen fertilizer in the body of vegetables,which is seriously harmful to the human body.Commonly used detection methods of nitrate content are mostly chemical method,limited to laboratory determination,and destructive,low efficiency,which is not conducive to a wide range of promotion and application.Therefore,achieving rapid,real-time non-destructive testing of nitrate content of vegetables and making a reasonable evaluation of nitrate quality not only guide the rational fertilization of vegetables,but also regulate the healthy vegetable consumption market.In this paper,lettuce was used as the research object.Adopting controllable soilless cultivation mode,lettuce samples with different nitrate contents were fostered by adjusting the nitrogen level in the nutrient of Hogan gluten.The rapid non-destructive testing model of nitrate content in lettuce leaves was established by using chlorophyll fluorescence spectroscopy and chemical stoichiometry.And on this basis,the evaluation model of lettuce nitrate hygiene quality was established and nitrate evaluation standard of lettuce was simplified,which realizes the reasonable evaluation of the quality of lettuce nitrate.The main research contents and conclusions are as follows,(1)Screening out the best spectral pretreatment method.The pretreatment of chlorophyll fluorescence spectroscopy was carried out by using a variety of pretreatment methods.After analyzing and comparing the pre-model performance and effect of PLS,the effect of spectral pretreatment method SG-FD was the best.(2)Extracting the optimal characteristic wavelength.The characteristic wavelengths of chlorophyll fluorescence spectra were extracted by spectral feature information comparison and successive projections algorithm.After analysis and comparison,five optimal characteristic wavelengths were established,which were F509,F518,F673,F686 and F739,respectively.(3)Establishing detection model of nitrate content in lettuce leaves.The detection models of nitrate contents in three kinds of lettuce leaves of OCW-PLS,OCW-MLR and OCW-SVM were established respectively based on the optimal characteristic wavelengths.The performance and effectiveness of OCW-SVM were determined after comparison analysis,the set coefficient R2 cis 0.8583 and the RMSE was 0.2136.(4)Achieving a reasonable evaluation of the quality of lettuce nitrate.The evaluation criteria of the hygienic quality of lettuce was extracted and simplified from the evaluation criteria of vegetables.Then the AM evaluation model was established to realize the reasonable evaluation of the nitrate quality of lettuce.The overall evaluation accuracy was 93.33%,and the highest discrimination rate was up to98.44%.In this paper,the combining method of chlorophyll fluorescence spectrum analysis and chemical metrology was used to measure and evaluate the nitrate content in lettuce leaves,the research content of other vegetables nitrate content detection and evaluation of nitrate quality has some reference value.