What is the difference in processing steps between supercritical CO2 extraction of tea polyphenols and decaffeination in green tea?

 - **Tea polyphenol extraction**: green tea usually needs to be dried and crushed in order to increase the air permeability of the tea leaves so that SC-CO2 can better contact with the tea leaves.
- **Decaffeination**: In the decaffeination process, tea leaves may need to be infiltrated with an ethanol solution not exceeding 70% for 1-4 hours as a pre-treatment step, in addition to drying and crushing.

- **Tea polyphenol extraction**: process conditions such as pressure, temperature, time, and type and amount of entrainer are optimised by one-way and orthogonal tests. For example, the optimal conditions may be pressure 35 MPa, kettle temperature 50°C, static extraction time 1 hour, and dynamic extraction time 1 hour.
- **Caffeine removal**: Optimal process conditions may include an extraction temperature of 60°C, an extraction pressure of 28 MPa, an extraction time of 3.5 hours, and a water addition of 20%.

- **Tea polyphenol extraction**: the extracted tea polyphenols may require simple vacuum freeze-drying to obtain tea polyphenol products with a high content of meso-catechins.
- **Caffeine removal**: CO2 with caffeine is sent to a wash tank to transfer the caffeine to the aqueous phase, then the caffeine is recovered by distillation and the CO2 is recycled.

- **Tea polyphenol extraction**: the goal is to extract tea polyphenols, so the optimisation of the process parameters mainly revolves around increasing the extraction rate of tea polyphenols.
- **Caffeine removal**: the goal is to remove caffeine, so the process parameter optimisation mainly revolves around improving the caffeine removal rate.