Study On The Change And Degradation Measures Of Polycylic Aromatic Hydrocarbons Content In Postharvest Vegetables

With the increase of human activities,the pollution of Polycyclic Aromatic Hydrocarbons?PAHs?in the environment is increasing,which leads to the inevitable contamination of PAHs by vegetables during the growth process.PAHs pollution poses a great threat to the quality and safety of agricultural products and human health.At present,the research on reducing PAHs in vegetables is mainly based on prevention and control.According to the effect of PAHs stress on vegetable growth and the distribution characteristics of PAHs in vegetables,improve the growth environment of vegetables and reduce the pollution of PAHs.However,there are few reports on reducing the PAHs in postharvest vegetables through different treatments.Based on the optimization of pre-treatment technology of PAHs in vegetables,the changes of PAHs content in vegetables were analyzed from two aspects of storage and degradation.According to the common preservation measures,the changes of PAHs in vegetables and their storage time and storage time were studied.After the vegetables were treated by physical and chemical methods,the PAHs content was used as the evaluation index to select high-efficient PAHs cleaning agent.The main results are as follows:?1?In this study,the Lactuca sativa homogenate was used as a test material to optimization the pre-treatment process of polycyclic aromatic hydrocarbons in vegetables by orthogonal test.The results showed that the optimum pre-treatment conditions were 48 m L of extract volume,13 g of sample mass,ultrasonic extraction for 30 min,13 m L of sulfuric acid volume,35%of sulfuric acid,eluent type of 6 m L n-hexane and 6 m L dichloromethane/n-hexane?V₁:V₂=3:7?.Under these conditions,the extraction ratio of polycyclic aromatic hydrocarbons was up to 961.541?g/kg;The recovery rate of the process is80.54%?142.04%,and the RSDs are 1.35%?8.96%,which has good accuracy and precision.The pretreatment process established by the orthogonal method has many advantages,mainly including simple sample preparation,powerful ability to detect a large number of samples at the same time,and a good repeatability.These fine qualities prove that the pretreatment process can be applied to the extraction of polycyclic aromatic hydrocarbons in vegetables.?2?By comparing the PAHs content of the Lactuca sativa under eight different storage treatments,the following conclusions were drawn.The results showed that the PAHs content of untreated Lactuca sativa decreased significantly with the increase of storage time and temperature under the conditions of normal temperature storage,15?cold storage and 4?cold storage,among which the PAHs content decreased most under the condition of15?.After being stored at normal temperature,15?and 4?respectively,the PAHs content of the packaged Lactuca sativa increased in the early stage of storage,and the growth rate was negatively related to the temperature,and the PAHs content was mainly changed by LPAHs.Under 15?cold storage,the decrease rate of PAHs content in Lactuca sativa was in the order of H₂O₂treatment>no treatment>oxalic acid treatment>fresh bag treatment.Under different storage conditions,the PAHs content of 2-ring and 3-ring changed most significantly,followed by 4-ring,and 5-ring and 6-ring changed least.The Ba Peq of the Lactuca sativa decreased with the storage time,and was significantly correlated with the content of.This study is of great significance for the systematic analysis of PAHs residues in vegetables during storage and the improvement of safety and health evaluation of vegetables.?3?In this experiment,tomato,pepper,eggplant,cucumber,radish,beans,Lactuca sativa were selected as experimental samples and soaked in 500?g/kg PAHs solution for 2 h and 4 h respectively.PAHs concentration characteristics of different vegetables were analyzed by detecting PAHs content in the exposed part of the peel and the pulp of vegetables.By comparing the coefficient of variation of PAHs average content in different vegetables,the uniform experimental materials were screened,and then the appropriate conditions of soaking were determined through further experiments.After soaking treatment,most of the vegetables showed that the PAHs enrichment ability of the peel was stronger than that of the pulp,and the PAHs migration ability decreased with the increase of PAHs ring number.By comparing the variation coefficient of PAHs content,it is found that the content of all vegetables except the Lactuca sativa and vegetable is not the same,and the average content of fruit pulp fluctuates greatly.Further experiments were conducted with Lactuca sativa as the experimental material,and the results showed that the appropriate immersion condition was 500 living g/kg of PAHs solution and 60 min of immersion time.?4?In this study,NAP,PHE,FLA,Bb F and Ba P were used as the research objects.Eight kinds of cleaning agents were used to treat the Lactuca sativa polluted by PAHs,and the degradation effect of PAHs was used as the evaluation standard to select the best cleaning agent.The degradation rate of lightweight PAHs was higher than that of heavy PAHs in Lactuca sativa treated with five cleaning agents.By comparing the degradation rate of PAHs by different cleaning agents,and the results showed that fruit and vegetable detergents and ozone water had the worst degradation ability,and ultrasonic cleaning only had good degradation effect on light PAHs,with the degradation rate up to 72.72%.There are seven groups of the optimal cleaning agent treatment,all of which are oxidant treatment.The degradation rate of each treatment group was compared,it was found that the best degradation effect was achieved when the concentration of Fenton?n H₂O₂:n Fe SO₄=8:1?reagent was800 mg/L,with an average degradation rate of 79.29%for light and 59.07%for heavy PAHs in Lactuca sativa.By exploring the enrichment characteristics of vegetables for PAHs and comparing the degradation effects of different cleaning treatments on PAHs,this experiment provided theoretical guidance for the development of corresponding pollution control measures and consumers'selection of reasonable and efficient cleaning agents.