Application of Chromatographic Technology to Determine Aromatic Substances in Tobacco during Natural Fermentation: A Review

Revealing alcoholization-related volatile compounds and determining alcoholization indices in tobacco using GC-IMS coupled with chemometrics

Alcoholization is an integral part of tobacco processing and volatile compounds are key to assessing tobacco alcoholization. In this study, a total of 154 volatiles from nine categories were determined by gas chromatography-ion mobility spectrometry (GC-IMS) from four grades of tobacco, of which 114 were better identified. And then, the dynamic trends of volatile compounds with significant changes in tobacco alcoholization were analyzed. The relevant volatiles with the alcoholization indices (AIs) (R > 0.8) were screened as indicators of tobacco alcoholization. Cinnamyl isobutyrate, linolenic acid alcohol, propanoic acid-M and propanoic acid-D in all tobacco samples were highly correlated with the AIs and tended to increase during the alcoholization process. In addition, linear discriminant analysis (LDA), back-propagation neural network (BPNN) and random forest (RF) classifiers were constructed for discrimination of tobacco AIs. Three classifiers trained with a combination of 20 volatiles achieved satisfactory results with area under the curve (AUC) of 0.95 (LDA), 0.94 (BPNN) and 0.97 (RF), respectively. The RF classifier gained optimal accuracy of 100 % and 96.1 % for the training and test sets, respectively. The study confirmed that GC-IMS can be used to characterize the changes of volatile compounds in tobacco during alcoholization and combined with machine learning to achieve the determination of AIs. The results of the study may provide a new means for the tobacco industry to monitor the alcoholization process and determine the degree of alcoholization.

Based on metabolomics, the optimum wind speed process parameters of flue-cured tobacco in heat pump bulk curing barn were explored

To explore the influence of wind speed on the quality of tobacco in this study, we employed a heat pump-powered intensive curing barn and a three-stage curing process. By evaluating the influence of fan parameters on the quality of tobacco leaves at different curing stages, the optimal wind speed was determined. After adopting the optimized wind speed process, the degradation of macromolecular substances was faster, the accumulation of aroma substances was delayed to 55 °C, and the accumulation was more complete. Among them, the contents of reducing sugar and total sugar in flue-cured tobacco leaves were 22.25% and 29.2%, respectively, which were lower than those in the control group. The sugar was converted into more aroma substances, and the total amount of neutral aroma substances was 48.82% higher than that of the control group. The content of related aroma substances increased significantly. The content of petroleum ether extract related to aroma substances increased by 0.93% compared with the control group. The macromolecular substances were degraded more fully than the control group, such as the starch content decreased to 1.56%. The results of metabolomics showed that the contents of aldehydes, heterocyclic compounds, alcohols, ketones and esters increased significantly in different degrees after this process. These results show that the optimization of wind speed parameters can significantly improve the baking quality of tobacco leaves. This study provides a reference for the optimization of the flue-cured tobacco baking process.