The definition and properties of subcritical water
Subcritical water, also referred to as super-heated water, high-pressure hot water or hot liquid water, is water that is heated to a high temperature above 100°C but below the critical temperature of 374°C under a certain pressure, and the water remains in a liquid state. In the subcritical state, the microstructure of water undergoes changes, including alterations in hydrogen bonding, ionic hydration, ionic conjugation, and cluster structure. Consequently, the physical and chemical properties of subcritical water differ significantly from those of water at room temperature and pressure. As the temperature rises, the hydrogen bonds of subcritical water are opened or weakened, and the polarity decreases, thus enabling the extraction of non-polar compounds. Conversely, under conditions of lower temperature and pressure, the polarity of water increases, and polar compounds can be extracted.
The merits of subcritical water extraction in the context of black tea production
Green and environmental protection: subcritical water extraction technology employs pure water as the extractant, eschewing the use of organic solvents. This approach eliminates the potential for environmental contamination, a principle that aligns with the tenets of green chemistry.
The technology is also highly efficient in its extraction process. Through the precise regulation of temperature and pressure during extraction, it is possible to achieve continuous extraction as well as selective extraction of different polar components in black tea. This, in turn, results in an enhancement of the extraction efficiency.
The preservation of active ingredients is also noteworthy, as the subcritical water extraction process does not require excessive heating, which avoids the destruction and oxidation of heat-sensitive ingredients and preserves the active ingredients in black tea.
The economic benefits of subcritical water extraction technology are twofold: firstly, it reduces the consumption of solvents and consequently decreases production costs when compared with traditional extraction methods; secondly, given the low working pressure and the safety of the equipment used, it also reduces equipment investment and maintenance costs.
Finally, the separation of the active ingredients in black tea and the solvent (water) during subcritical water extraction is a straightforward process, which in turn simplifies the post-treatment process.
Application Prospects
The application of subcritical water extraction technology in the processing of black tea is a promising avenue for research. The increasing demand for high-quality black tea among consumers, coupled with heightened environmental awareness, has led to a growing focus on efficient and sustainable extraction methods. Subcritical water extraction technology boasts several unique advantages, which suggests its potential for widespread adoption in the black tea industry.
Conclusion
In summary, subcritical water extraction technology has significant advantages in black tea extraction, including green, efficient extraction, protection of active ingredients, cost reduction and easy separation. These advantages make subcritical water extraction technology a potential green extraction technology in black tea processing.With the continuous development and improvement of the technology, subcritical water extraction technology is expected to play a greater role in the black tea industry and promote the sustainable development of the industry.
