Comparative analysis of physicochemical properties, flavor compounds, and metabolites among three major cultivated walnut (Juglans sigillata Dode) varieties in China Yunnan

This study investigated the physicochemical properties, flavor substances, and metabolites of three major cultivated walnut kinds Xixiang walnut kernels (XXWK), Santai walnut kernels (STWK), and Yangbipao walnut kernels (YBWK) in China Yunnan. The lowest oil content and the highest protein content were found in the YBWK. The total content of 17 amino acids, including threonine, valine, and lysine, in YBWK was significantly higher than those of XXWK and STWK. The unsaturated fatty acid contents of XXWK, STWK, and YBWK were 85.92%, 86.78%, and 87.58%, respectively. The flavor compounds with the highest OAV values were hexanal, trans-2-nonenal, and trans-2-nonenal in XXWK, STWK, and YBWK, respectively. A total of 156 metabolites with significant differences were identified, the highest content of lipids and lipid-like molecules. Vitamin B6 metabolism, alpha-linolenic acid metabolism, and purine metabolism were the important metabolic pathways in walnut kernels. Hexanol and methyl hexanoate showed a highly significant positive correlation with icariside E5, and 1-nonanal, decyl aldehyde showed a highly significant positive correlation with 8 amino acids, including leucine, isoleucine, and phenylalanine. This study provided a theoretical basis for understanding the characteristics of main cultivated walnuts and developing walnut products in Yunnan. • YBWK possessed the highest amino acid and unsaturated fatty acid content • The key flavor substance of XXWK were hexanal, and STWK and YBWK was trans-2-nonenal • Purine metabolism plays an important role in the formation of fresh walnut flavor