Quality Analysis of Juglans sigillata Kernel from Different Producing Areas in Yunnan Province by UHPLC-QE-MS Metabolomics

Non-targeted metabolomics method was used to investigate the differences of metabolites of Juglans sigillata kernel from different regions in Yunnan. The metabolomic profiles of Juglans sigillata kernel were investigated by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-QE-MS) with principal component analysis, orthogonal partial least squares discriminant analysis, cluster analysis and metabolite and metabolic pathway difference analysis. The results showed that a total of 305 metabolites were detected, with the highest proportion of fatty acids, shikimates, phenylpropanoids, amino acids and peptides, which were mainly involved in the metabolic pathways of phenylalanine metabolism, flavone and flavonol biosynthesis, valine, leucine and isoleucine biosynthesis. A total of 185 differential metabolites were screened in the Juglans sigillata kernel from 8 producing areas (VIP>1 and P<0.05). Indolelactic acid, xanthohumol and ketoleucine were identified as signature compounds of walnut kernel in Yongping county of Dali prefecture. Syringic acid, dIDP and capric acid were found to be signature compounds of walnut kernel in Gucheng town of Lijiang city. Coniferaldehyde was the signature compound of walnut kernel in Shangri-La city of Diqing prefecture. Isoalantolactone, kaempferol, biliverdin were found to be signature compounds of walnut kernel in Yangbi county of Dali prefecture. Vanillin was identified to be signature compound of walnut kernel in Jingdong county of Pu’er city. Kaempferide, leucine and isoleucine were identified as signature compounds of walnut kernel in Dayao county of Chuxiong prefecture. N-acetylphenylalanine, malonic acid and asparagine were the signature compounds of walnut kernel in Changning county of Baoshan city. Dopaxanthin, 4-methylumbelliferyl acetate and undecanoic acid were found to be signature compounds of walnut kernel in Fengqing county of Lincang city. These differences might have certain effects on the antioxidant activity of walnut kernels. Similarity analysis from fingerprints showed effective distinction among Juglans sigillata kernel from different producing areas. This study has provided information about the metabolites of Juglans sigillata kernel from different producing areas in Yunnan province, and demonstrated that UHPLC-QE-MS technology is feasible for the identification of Juglans sigillata kernel.