Identification of changes in the volatile compounds of robusta coffee beans during drying based on HS-SPME/GC-MS and E-nose analyses with the aid of chemometrics

In this study, headspace solid-phase microextraction/gas chromatography-mass spectrometry (HS-SPME/GC-MS) and electronic-nose (E-nose) analyses were performed to examine the comprehensive flavor profiles of robusta coffee during heat air drying. A total of 62 volatile compounds were identified by HS-SPME/GC-MS, the level of acids, aldehydes, alcohols and esters decreased during drying process, however, the relative content of hydrocarbons and acids increased. Principal component analysis of the E-nose results clearly differentiated the samples related to drying time, and it was found that samples of initial stages (0 h, 3 h, and 6 h) had strong positive with different sensors. Partial least squares-discriminant analysis (PLS-DA) indicated that alcohols, ketones, and esters were the main contributing compounds to the flavour of coffee beans. The VIP score of PLS-DA larger than one illustrated that T30/1, T70/2, PA/2, and P30/2 were positive with ketones, sulfur compounds, and esters. These results could provide theoretical evidence about the change rule in volatile compounds of coffee beans during drying process, and could be applied to other thermally sensitive tropical agricultural products.