| Walnut oil is known as one of the main woody oil in China,but the chemical composition of walnut oil in China is not clear due to the rich Juglans species,wide walnut varieties,the different growing environment,and various processing methods.Walnut oil is a kind of nutritious oil,but it is difficult to elaborate the characteristics of nutrition in an objective way.Therefore,we collected thirty-five walnut oil samples,incorporating 24 varieties of Juglans species from 11 provinces in China which are the three major producing areas for walnut oil,and then analyzed the walnut oil for the fatty acid,triacylglycerol composition,tocopherol,phytosterol,and polyphenol content.Through the biological evaluation of antioxidant and cholesterol-lowering,the effects of species,producing areas and processing methods of walnut oil were systematically evaluated by chemometrics.And a new walnut oil processing model was preliminarily established.Firstly,this study has systematically analyzed the lipid composition and minor component content of the thirty-five representative walnut oil samples from the northwestern area,the southwestern area,and the eastern area of China.The results showed that C18:2 content of the north-western area(average value:64.26%)was 2.35%and 2.73%higher than the southwestern area and the eastern area.The LLLn content of the eastern area(average value:12.82%)was 2.90%higher than other areas,the tocopherol content(average value:814.41 mg/kg)and the polyphenol content(average value:20.83 mg/kg)were higher than the southwestern area and the northwestern area.The phytosterol content of the southwestern area(average value:736.30 mg/kg)was 41.61%and 50.28%lower than the northwestern area and the eastern area.The PUFA content of Shandong Luguang walnut oil was the highest(78.51%).Xiangling is the walnut variety with the highest content of minor components(tocopherol:1042.13,phytosterol:46.77,phytosterol:1608.23 mg/kg,respectively)in walnut oil.The contents of C16:0(5.53-6.43%)in common walnut oil were significantly higher than those in iron walnut oil(4.97-5.25%).C22:1(0.23-0.44%)was the special fatty acid of iron walnut oil.The contents of tocopherols(441.03-490.32 mg/kg),polyphenols(44.78-64.61 mg/kg),squalene(4.41-5.21 mg/kg)and phytosterols(1014.49-1211.40 mg/kg)in common walnut oil were significantly higher than those in iron walnut oil.Cluster analysis showed that processing methods were also important factors affecting the chemical composition of walnut oil.Then,a comparison study has been performed on processing methods(cold pressing,roasting pressing,n-hexane extraction,subcritical butane extraction and supercritical carbon dioxide extraction)of walnut oils in China.The outcome implied that subcritical butane extraction was a good approach in terms of walnut lipid extraction,and different processing methods actually do not affect the lipid composition of walnut oil.Moreover,the tocopherol content of supercritical carbon dioxide extraction iron walnut oil(474.19 mg/kg),the phytosterols content of cold pressing iron walnut oil(1249.61 mg/kg),the polyphenol content of roasting pressing iron walnut oil(84.49 mg/kg),and the squalene content of subcritical butane extraction iron walnut oil(13.03 mg/kg)were higher than other samples.The tocopherol(41 1.09 mg/kg)and polyphenol(42.61 mg/kg)content of roasting pressing common walnut oil,the phytosterols content of subcritical butane extraction common walnut oil(1065.12 mg/kg)and the squalene content of n-hexane extraction common walnut oil(9.48 mg/kg)were higher than other tested oils.Further,this study focused on the oxidative stability and free radical scavenging capacity(DPPH assay,FRAP assay,ABTS assay,and ORAC assay)of walnut oils from different Juglans species and using distinct processing methods.In addition,MLR was employed in order to evaluate the contributions of chemical components to antioxidant capacity of walnut oils.The experimental results demonstrated that antioxidant capacity of walnut oil was significantly correlated with polyphenol and a-tocopherol,these phenols played an antioxidant role by capturing hydroxyl radicals(HO·),alkoxyl radicals(RO·)and peroxide radicals(ROO·).The antioxidant capacity of walnut oil is negatively correlated with 8-tocopherols,which participated in the tocopherol-mediated peroxidation.The evaluation model of antioxidant capacity of walnut oil can be established:Y=0.25(polyphenols)＋0.24(α-tocopherol)-0.21(δ-tocopherol)+0.12(stigmasterol)-0.10(β-sitosterol)-0.08(A5-avenasterol).Walnut oil polyphenols contained glansreginin A,glansreginin B,Di-HHDP glucose and HHDP digalloyl glucose.Based on the evaluation model of antioxidant capacity,common walnut was the suitable Juglans species,and roasting method had significantly increased the fat-soluble phenolics content of walnut oil,which was the best processing method of walnut oil.Finally,the effects of walnut oil obtained from different Juglans species and processing methods on cholesterol lowering in HepG2 cells were investigated.MLR was employed to predict a model for the cholesterol lowering effect of walnut oil.This study showed that walnut oil treatment had significantly decreased cholesterol synthesis through increasing the expression of HMGCR,CYP51,and SREBP-2,and increased cholesterol efflux through increasing the expression of ABCG1,the contents of TC and TG decreased significantly(p<0.05).Tocopherols,polyphenols,squalene and phytosterols in walnut oil effected cholesterol lowering,and the optimal concentration of a-tocopherol was 5 μg/mL,γ-tocopherol was 10 μg/mL,δ-tocopherol was 2.5 μg/mL,walnut oil polyphenols was 12.5 μg/L,squalene was 40μg/mL and phytosterol was 10μg/mL.The evaluation model of cholesterol lowering of walnut oil was established:Y＝0.43(stigmasterol)-0.26(C16:0)-0.18(POL)+0.07(campesterol)+0.06(polyphenol).Stigmasterol was the key substance affecting the cholesterol lowering of walnut oil.Based on the evaluation model of cholesterol lowering,subcritical butane extraction was an appropriate processing mothed of common walnut oil,and cold pressing was an appropriate processing mothed of iron walnut oil.In conclusion,through Juglans species and walnut varieties selection,process optimization and efficacy evaluation,the suitable processing scheme of walnut oil in China was proposed,and a new processing mode of walnut oil based on biological evaluation was preliminarily established,providing guidance for high quality and nutritive value production of walnut oil. |
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