Extraction of green tea and drying with a high pressure spray process
Green tea is a beverage widely consumed throughout the world and is produced from non-fermented leaves of Camellia Sinensis. Traditionally, green tea leaves are extracted with water. To form solid products, these aqueous products have to be dried. The main focus of the investigation is how to avoid antioxidant degradation during solvent removal. The work was separated in two major sections, firstly investigation of the extraction process secondly, optimizing of the drying process. In the first experiments extractions with different solvents (H2O, EtOH and MeOH), at different temperatures (20, 40, 60 and 80 °C) and extraction times (15, 30, 60, 90 and 120 min) were preformed to obtain optimum conditions for further processing. For further work extracts obtained with water extraction at 80°C for 15 min were used. In the PGSS (Particles from Gas Saturated Solutions) drying process, extracts with up to 98 wt % water are mixed with preheated carbon dioxide in a static mixer in order to obtain a homogenous mixture. The mixture is led via a single path nozzle into a spray tower. Driven by the expansion of the gas, fine droplets are formed and the heated gas evaporates the solvent, which is exhausted together with CO by a blower. Fine powder is formed and collected in the spray tower. The amount of solvent which is to be removed and the residual humidity obtained in the product depend strongly on flow rate and temperature of the gas. From obtained results it can be seen, that high pre-expansion temperatures Tp (145 °C) cause degradation of polyphenols (1.05 wt %). Maintaining Tp at approximately 130 °C and lower gave satisfying results; total amount of polyphenols in the obtained powders was between 4.97 and 8.77 wt %. Temperature in spray tower ranging from 33 to 65 °C has no significant effect on the amount of total polyphenols, but higher temperature results in lower water residue in the sample.