Aroma characteristics and odor source analysis of roasted Xinjiang thin-shell walnuts (Juglans regia L.) by using multivariate statistical analysis

Since the correlation between the overall aroma of in-shell walnuts and the volatile compounds existing in both their kernels and shells remained unclear, the odor profiles of roasted in-shell Xinjiang thin-shell walnuts including kernel and shell have been well investigated by sensory analysis, electronic nose, and HS-SPME/GC-MS, while volatile compounds were analyzed by multivariate statistical analysis of PLS-DA, variable impor-tance projection (VIP) values and relative odor activity value (ROAV). Color and sensory evaluations confirmed the walnut shell did not change significantly after roasting, and it may have an odor-shielding effect on the kernel. Electronic nose could effectively distinguish the aroma difference of raw and roasted walnuts by signal intensities. A total of 94 volatile compounds were identified by GC-MS, and 31 odor-active compounds were recognized by further ROAV analysis. Although 2-methyl-furan with a spicy smoky aroma was increased in the roasted shell, benzaldehyde was raised in the roasted kernel with a bitter almond note, which played an important role in the roasted whole in-shell walnut odor. Overall, this study firstly explored the shell contri-bution to the whole odor of walnuts and illuminated the aromatic characteristics of in-shell roasting walnuts, which will provide a better understanding for the walnut processing and will be beneficial to the quality control for the roasted walnuts.