Comparative analysis of aroma profiles in walnut, pecan and hickory nuts during the roasting process using E-nose, HS-SPME-GC-MS, and HS-GC-IMS

Walnut, pecan, and hickory nuts are well known for their nutritional value and health benefits, with consumption having increased significantly in recent years. Outstanding aroma is an important indicator for nut quality evaluation. However, the impacts of thermal processing on their aroma formation are not well understood. To address this gap, a comprehensive analysis of the aroma profiles were conducted during the roasting process using both sensory evaluation and advanced analytical equipment, including an electronic nose (E-nose), headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS), and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). The results indicated that thermal processing had a substantial effect on the sensorial characteristics of the nuts, with hickory nuts exhibiting a distinct nutty aroma compared to walnuts. HS-SPME-GC-MS analysis further identified 118 volatile organic compounds (VOCs), encompassing 33 heterocyclic compounds, 18 aldehydes, 11 aromatics, 18 ketones, and other compounds, while HS-GC-IMS analysis detected 63 volatile compounds. Notably, the roasting process led to the reduction in alcohols and acids, while simultaneously caused the increase of esters, ketones, pyrazines, and phenols, all of which are crucial for the development of nut aroma. Especially, some components like 1-Octanol, 2-Pentyl-furan, Hexanal, Acetylpyrazine, Benzophenone, and Octyl ester may contribute to unique odors of pecan and hickory nuts. These findings provide valuable insights into the flavor formation of the three nuts and the optimization of roasting process.