Analysis of characteristic flavor compounds in coffee peels subjected to different thermal processing treatments based on GC–IMS and HS-SPME–GC–MS combined with chemical pattern recognition

This study investigated the effects of microwave thermal processing treatment (MD) and hot-air thermal processing treatment (HAD) on the volatile flavor compounds of coffee peel, using sun-dried (SG) samples as the control. GC-IMS and HS-SPME-GC-MS were combined with multivariate analyses (PCA and PLS-DA) and ROAV evaluation. A total of 62 and 56 volatile organic compounds (VOCs) were tentatively identified by GC-IMS and GC-MS, respectively, with ketones, aldehydes, alcohols, and esters representing the predominant classes. The two analytical methods exhibited complementary detection capabilities. PCA and PLS-DA clearly differentiated the three thermal drying treatments. Aroma-related compounds (VIP > 1 and ROAV ≥ 1) included 2-furanmethanethiol, 3-methylbutanal, (E)-2-decenal, ethyl heptanoate, hexanal, benzyl alcohol, linalool and β-ionone. Based on the nine core coffee flavor categories, SG exhibited a complex aroma profile characterized by herbal/vegetable, fruity, and nutty/cocoa notes; HAD was distinguished by highly pronounced floral notes; whereas MD presented both floral and roasted characteristics. The integrated analytical strategy effectively discriminated among different thermal processing treatments and identified putative aroma markers, which require further validation through olfactometry or sensory evaluation. This study provides a scientific basis for elucidating the flavor profile of coffee peel and supports the further development of coffee cascara tea products.