Effect of Ethanol on the Extraction Efficiency of the Characteristic Aroma Compounds of Tolu Balsam Analyzed by Pervaporation Combined with Solid-Phase Supported Liquid-Liquid Extraction Coupled with Gas Chromatography-Mass Spectrometry

In order to analyze the aroma characteristics and composition of tolu balsam, tolu balsam extracts prepared with five different concentrations of ethanol were separated by pervaporation. The retentate and permeate were evaluated by sensory evaluation and their volatile and semi volatile components were analyzed by solid-phase supported liquid-liquid extraction coupled with gas chromatography-mass spectrometry (SLE-GC-MS). Chemometrics was adopted to explore the difference in target components and the correlation between sensory properties and components. The results showed that the major aroma characteristics of both retentate and permeate were ointment-like and sweet, followed by resin-like, fruity, fresh, and spicy aromas as well as weak creamy, floral, bean-like, and woody aroma notes. A total of 92 components were identified by GC-MS, with esters and alcohols being the predominant ones, accounting for more than 55% of the total, followed by acids, aldehydes, phenols, others and olefins, together with relatively low levels of ketones. Principal component analysis (PCA) and cluster heatmap analysis indicated that tolu balsam extracts obtained with low and medium ethanol concentrations were distinguished from that obtained with high ethanol concentration, and the contents of the identified compounds were overall higher in the former than in the latter. By orthogonal partial least squares discriminant analysis (OPLS-DA), 43 differential compounds were selected. Partial least square regression (PLSR) showed that the characteristic aroma substances of tolu balsam extracts had significant positive correlation with ointment-like, resin-like, fresh and spicy aromas, but had no significant correlation with sweet, fruity, creamy, floral, bean-like or woody aroma. The results of this study may provide a theoretical basis for research on the sensory quality and fine processing of tolu balsam.