Effect and Mechanism of High-Pressure Processing: A Case Study of Flue-Cured Tobacco

After a high-pressure processing (HPP) treatment sensory evaluation of flue-cured tobacco showed modifications. There was no significant difference (P > 0.05) between the routine chemical components (total sugar, reducing sugar, nicotine, and total nitrogen) of flue-cured tobacco after high-pressure processing treatment (HPP sample) and that of an untreated control group (CG). An overall judgement, which can be made from the observations of scanning electron microscopy (SEM), X-ray computed microtomography (micro-CT) and transmission electron microscopy (TEM), is that HPP could compress the inner tunnel and tissue gap in a flue-cured tobacco leaf. However, the ultrastructure, such as the cellular cytoskeleton, would not be changed. Compared with CG, the apparent density of the HPP sample rose by 19.3%, while the true density only rose by 1.4%. This also explained that the main effect of high-pressure processing on flue-cured tobacco was microstructure compression rather than compression on the ultrastructure level. The differences between the lamina (leaf-shaped) sample, which were caused by high-pressure processing, were reflected in terahertz time-domain spectroscopy (THz-TDS), simultaneous thermal analysis (STA), and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). When the same tests were carried out using a sample that was milled to a powder, however, these differences were nearly removed. The milling process destroyed most of the microstructure of the flue-cured tobacco lamina; therefore, the results of THz-TDS, STA, and Py-GC/MS confirmed the hypothesis: That 400 MPa high-pressure processing treatment minimally changes the ultrastructure of flue-cured tobacco and only changes its relatively larger microstructure.