Abstract
In this work, the concentration process of three different tea extracts (medicinal Rosil No. 6, Black, and Forest Fruit teas) using the osmotic evaporation (OE) process, was studied. The effect of the OE process on the content of phenolic compounds and antioxidant activity was evaluated. The concentration process was carried out in a hollow-fibre membrane contactor with an effective surface area of 0.54 m2. The tea extract was circulated through the shell side of the contactor, while a concentrated osmotic solution (CaCl2 5 M) was circulated inside the fibres. The flux, the driving force, and the mass transfer coefficient were evaluated. A decrease of the water flux over time was observed and was attributed only to the decrease of the driving force, caused by the dilution of the osmotic solution. Using a surface area/feed volume ratio of 774 m2·m−3, it is possible to reach a tea concentration of 40% (w/w) in 5 h, with a constant water flux and without losing the phenolic content and antioxidant potential in most teas.
Highlights
Tea consumption dates from the 27th century B.C., and today remains in the diet of millions of people, being one of the oldest beverages produced by biotechnological methods [1]
In the study of the hydrodynamic conditions in the fibres, the overall mass transfer coefficient was calculated using Equation (5) and P*wt and P*ws using the average temperatures of the bulk
The value of this plateau is very similar to the estimated value of the membrane mass transfer coefficient using Equation (6)
Summary
Tea consumption dates from the 27th century B.C., and today remains in the diet of millions of people, being one of the oldest beverages produced by biotechnological methods [1]. Tea is globally one of the most consumed beverages and its consumption occurs mainly in the form of infusion. The interest in tea comes mainly from its aroma, as well as the beneficial effect that the beverage can have on the health of consumers. Half of the dry matter of tea is insoluble in water and some of its constituents are polyphenols, amino acids, caffeine, sugars and fatty acids. The polyphenols represent about 25% of dry matter and belong mostly to the group of flavonoids or catechins depending on the type of tea. The important antioxidant potential present in most teas results from their content in phenolic compounds, chemical structures critical in the absorption and neutralisation of free radicals
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