Study On Extraction,isolation And Activity Of Antioxidant Components From Walnut Kernel Pellicle

Walnut（Juglans regia L.）is an important economic tree species in my country.It is widely distributed.The annual output of nuts is about 4 million tons.However,the utilization rate of by-products such as kernel pellicle,septum,green husk and pollen is low.Previous studies have shown that walnut kernel pellicle contains a large amount of antioxidant active substances such as polyphenols and flavonoids,which has the potential to develop into natural antioxidants.In this study,by-products such as kernel pellicle were used as test materials,the in vitro antioxidant activity,chemical composition of the extracts and the lipid-lowering and hypoglycemic activity of the compound ellagic acid were studied.The main results are as follows:（1）In the 7 tissue parts of walnut（leaf,pollen,green husk,septum,kernel pellicle,kernel,peeling kernel）tested,kernel pellicle had the highest the content of total phenolic and flavonoid.The contents of total phenolic and flavonoid in the kernel pellicle were 536.80 mg GAE/g AE and 282.18 mg RE/g AE,respectively.The DPPH,ABTS free radical scavenging ability and FRAP reducing ability of kernel pellicle were also the strongest.Among the extracts of different polar parts of kernel pellicle,ethyl acetate extract（EAE）had the highest total phenolic content,which was 565.47 mg GAE/g EAE,and had the strongest DPPH,ABTS free radical scavenging ability and FRAP reducing ability.Its DPPH radical scavenging ability(IC₅₀=1.361μg/m L)was 3.46 times that of the positive control V_C(IC₅₀=4.704μg/m L).（2）The results of oil oxidation stability showed that ethyl acetate extract（EAE）had a stronger inhibitory effect on oil oxidation than other polar extracts,and the addition of 0.02%EAE could extend the shelf life of walnut oil from 68.8 d to 84.8 d,which extended the shelf life of lard from 270.4 d to 352.0 d.（3）Using HPLC-ESI-MS-MS technology,46 kinds of antioxidant active compounds were identified in EAE,including 20 kinds of flavonoids and 26 kinds of polyphenols.The flavonoid and polyphenol with the highest content are naringenin and ellagic acid,respectively.The content of free ellagic acid was 68.29 mg/g EAE.The acid hydrolysis conditions were optimized,and the best process was obtained as follows:the concentration of trifluoroacetic acid was 3.5 mol/L,the hydrolysis temperature was 95℃,and the hydrolysis time was 3.5 h.The total ellagic acid content under this process condition was 573.01 mg/g EAE.（4）The purity of the kernel pellicle ellagic acid was increased from 44.91%to 93.58%after alkali-dissolving acid precipitation treatment.The in vitro lipid-lowering activity of purified ellagic acid was carried out.The results showed that when concentration tested was 5 mg/m L,the ability of purified ellagic acid to bind cholate was lipid-lowering drug simvastatin of 81.19%,ability to adsorb cholesterol under p H 7 was 85.41%of simvastatin.The results of the in vitro hypoglycemic study on the test samples showed that the ability of purified ellagic acid to inhibit the activity ofα-glucosidase(IC₅₀=5.954μg/m L)was the most common hypoglycemic agent acarbose(IC₅₀=1.933μg/m L)32.47%,the ability to inhibitα-amylase activity(IC₅₀=88.688μg/m L)was 10.32%of acarbose(IC₅₀=9.151μg/m L).In summary,the ethyl acetate extracts of walnut kernel pellicle have stronger free radical scavenging activity and anti-oil oxidation activity.Its main phenolic compound,ellagic acid,has strong lipid-lowering and hypoglycemic activities.The development of kernel pellicle as a new type of plant-derived antioxidant and walnut kernel with skin as a health food to assist in lowering lipids and blood sugar have laid a solid theoretical foundation.