| Walnut has a long history of cultivation and rich resources in China.Its planting area and yield rank first in the world.However,in the harvest season,a large number of discarded walnut green husks not only cause waste of resources,but also have a great impact on the environment.Gallic acid is one of the main active components in walnut green husk.It has many biological activities such as anti-oxidation,anti-tumor,antibacterial and antiviral,and is widely used in food,medicine,health care and other fields.This study is based on the large amount of walnut green husk produced during the processing of walnuts.The gallic acid in walnut green husk was extracted by ultrasound-assisted extraction,and purified by macroporous resin to study the antioxidant and antibacterial properties of gallic acid in walnut green husk.The gallic acid antibacterial gel of walnut green husk was prepared with gallic acid as the active component,and its preparation process and antibacterial activity were studied.The main tasks are as follows:(1)Study on extraction,purification and antioxidant activity of gallic acid from walnut green huskA high performance liquid chromatographic(HPLC)method was used for the determination of gallic acid,and Inertsil C8-3(4.6 mm×150 mm,5μm)was used as chromatographic column,the detection wavelength was 270.0 nm,methanol and 0.2%phosphoric acid aqueous solution(20%:80%)as mobile phase,the flow rate was 0.8 m L/min,the column temperature was 25°C,and the injection volume was 5μL,and under these conditions,the linear relationship between the mass concentration of gallic acid and the peak area was good.Under the conditions of ultrasonic power of 600 W,ethanol volume fraction of70%,solid-liquid ratio of 1:30 g/m L,extraction temperature of 50°C and extraction time of50 min,the extraction amount of gallic acid in walnut green husk was 15.385 mg/g.The gallic acid in walnut green husk extract was purified by ADS-17 macroporous resin under the conditions of 2 BV/h adsorption rate,2 BV/h desorption rate and 2 BV desorption volume,and the adsorption capacity was 0.89 mg/g and the desorption rate was 75%,The calculated purity was 83.07%.The results of antioxidant experiment showed that with the increase of concentration,the scavenging rates of DPPH·free radical and ABTS~+free radical of walnut green husk crude extract,walnut green husk gallic acid purified extract and gallic acid standard solution increased gradually.At the same concentration,the extract purified by macroporous resin adsorption had the best scavenging effect on DPPH·and ABTS~+free radicals.The scavenging effect from large to small is:walnut green husk gallic acid purified extract>gallic acid standard solution>vitamin C reference solution>walnut green husk crude extract.(2)Study on bacteriostasis of gallic acid and gallic acid bacteriostatic gel in walnut green huskGallic acid from walnut green husk had strong bacteriostatic effect on Staphylococcus aureus,Escherichia coli and Candida albicans,and the bacteriostatic effect was not much different from that of gallic acid standard solution at the same concentration,and it was showed that gallic acid was the main bacteriostatic active ingredient in the extract purified by macroporous resin adsorption.The minimum inhibitory concentration(MIC)of gallic acid from walnut green husk against Staphylococcus aureus,Escherichia coli and Candida albicans were 3.125,6.250 and 3.125 mg/m L,respectively.When the concentration of gallic acid purified extract from walnut green husk was 1.0 MIC of each bacteria,the bacteria were cultured for 24 h,and the inhibition rates of Staphylococcus aureus and Escherichia coli were71.68%and 66.81%,respectively.At 3.0 MIC,the inhibition rates of Staphylococcus aureus and Escherichia coli were 96.55%and 94.23%,respectively.Under the conditions of carbomer 940 dosage of 1.5%,glycerol dosage of 10%and triethanolamine dosage of 0.5%,the maximum content of gallic acid in the prepared antibacterial gel was 10.737 mg/g,and it had good antibacterial effect.(3)Study on the preparation,structure characterization and antibacterial activity of gallic acid derivativesGallic acid benzophenone derivatives were prepared by hydroxyl protection,carboxyl acylation and Friedel-Crafts acylation reaction using gallic acid as raw material.The structure of the product was characterized by NMR,FTIR and UV-Vis,and the antibacterial activity was studied.The structures of the two derivatives were determined by structural characterization.The product 1 was 3,4,5,4,-tetramethoxybenzophenone with white crystal appearance and the yield was 74%.The product 2 was 3,4,5,4,-tetramethoxy-2-chloro-benzophenone,with a yellow oily liquid appearance and a yield of 1.8%.The two derivatives have poor antibacterial properties,indicating that the antibacterial properties of gallic acid and gallic acid benzophenone derivatives are related to phenolic hydroxyl groups.The poor bacterial inhibition of the two derivatives indicated that the inhibition of gallic acid and benzophenone gallate derivatives was related to the phenolic hydroxyl group.The two Gallic acid benzophenone derivatives also had good absorption of ultraviolet light at 280～345 nm,which coincidences the absorption requirements of benzophenone ultraviolet absorbers and can provide reference for the application of ultraviolet absorbers. |
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