Effects Of Different Treatments On Polyphenols And Pesticide Residues In Litchi Pericarp

The litchi processing produces a large number of seeds and pericarp by-products,in which the pericarp is rich in polyphenols and has excellent biological activities.The research and application of extracting polyphenols as a high value-added product with litchi pericarp as raw material has been carried out.However,most of the litchi is planted in South China.During the growth period,high temperature and high humidity are prone to pests and diseases.Chemical pesticides are generally needed to control pests and diseases,which may cause pesticide residues in litchi pericarp polyphenol extracts to exceed the standard.Therefore,it is necessary to take measures in the process of pretreatment and extraction of polyphenols to reduce pesticide residues and retain polyphenol content.In this subject,litchi pericarp was used as raw material,four common pesticides such as carbendazim,azoxystrobin,pyraclostrobin and difenoconazole were used as experimental pesticides to investigate the polyphenols and pesticide residues in litchi pericarp treated by different treatment,which including degradation treatment,drying treatment,extraction.The results provide a basis for the safety and practical application of litchi processing.The main results were as follows:(1)Effects of different degradation methods on polyphenols and pesticide residues in litchi pericarpThe optimal processes for the six degradation treatments were:(1)ultrasonic/H?O? treatment:50?70 min,200 W,60?70°C,pH 7?9;5?10 mol/L H₂O₂;(2)ultrasonic/pH 9 treatment::50?70 min,200 W,60?70?,pH 7?9;(3)UV/H?O? treatment:60 min,208?W/cm²,5?10 mol/L H₂O₂;(4)UV/TiO? treatment:60 min,208?W/cm²,0.20 g/L TiO₂;(5)ozone fumigation:60 min;(6)ozone water treatment:40°C,30 min.The effects of six degradation methods on the removal of pesticide residues in litchi pericarp were as follows:ultrasonic/H?O? treatment>ozone water treatment>UV/H?O? treatment>UV/TiO? treatment>ultrasonic/pH 9 treatment>ozone fumigation treatment.Based on principal component analysis,the ultrasonic/H?O? treatment effect was the better,and removal rate of the four pesticides in ultrasonic treatment was 50.37%?80.99%,and the polyphenol yield was 57.41%,and next was ozone water treatment.And ozone fumigation treatment was worse,for the pesticides removal rate ranged from 36.05% to 50.61%.(2)Effects of different drying methods on polyphenols and pesticide residues in litchi pericarpThe removal effects of pesticide residues in litchi pericarp by five drying methods were as follows:hot air drying>sun drying>freeze drying>microwave drying.Using processing factors to better evaluated changes in pesticide residues after different drying treatments,the processing factors of four pesticides in microwave drying ranged from 0.83 to 0.95,when the processing factors of azoxystrobin and difenoconazole in freeze drying were 0.85 and 0.88,respectively,and the pesticide residues were almost unchanged.The pesticide processing factors in other drying treatments were all less than 0.80,which would reduce the level of pesticide residues in litchi pericarp.On the side,different drying methods had different effects on litchi pericarp polyphenols yield.Hot air drying and sun drying destroied some litchi pericarp polyphenols,while sun drying and hot air drying may destroied some litchi pericarp polyphenols,while microwave drying and freeze-drying polyphenols had higher retention rates.In the end,based on principal component analysis,the effect of hot air drying was better.The pesticides removal rate was 40.31%?51.67%,and the polyphenol yield was 71.31%.(3)Effects of different extration methods on polyphenols and pesticide residues in litchi pericarpUsing water to extracted litchi pericarp polyphenols,the most ideal process conditions for hot water extraction,ultrasonic extraction and microwave extraction were respectively:(1)hot water extraction:1:40(w/v),100 min,90°C;(2)ultrasonic extraction:1:50(w/v),40min,90°C,0.44 W/cm²;(3)microwave extraction:1:60(w/v),3 min,23.40 W/g.The highest polyphenols content was 13.93 mg/g DW of microwave extraction,secondly was ultrasonic extraction,which content was 12.75 mg/g DW,and the lowest content was only9.20 mg/g DW for hot water extraction.At the same time,the three extraction methods averaged removed 73.48%,57.06% and 33.81% of the pesticide residues in the litchi pericarp.The comprehensive analysis results showed the effects of ultrasonic extraction and hot water extraction were better.The polyphenol content was 9.20?13.93 mg/g DW,and the average pesticide removal rate was 57.06%?73.48%.(4)Combined experimentThe litchi pericarp was treated in turn by the methods:ultrasonic/H₂O₂ treatment(70min,200 W,60?,5 mol/L H₂O₂),hot air drying(60°C,4 h),hot water extraction(1:40,90°C,100 min),and the pesticide removal rate was 95.88% to 100%,when polyphenol content was 6.22 mg/g DW.