JOURNAL HIGHLIGHTS BY Raquel Enciso-Serradilla
Tea is rich in bioactive compounds but the levels of them in a drink are dependent on the origin of the tea, how it is processed and on the brewing method. Now, a new study published in the Journal of the Science of Food and Agriculture has investigated the use of a continuous stepwise extraction process, which can improve the flavanol content of tea beverages.
Tea is the second most popular beverage worldwide, typically prepared by brewing leaves in hot or boiling water. The researchers focused on the use of a novel continuous stepwise temperature extraction process, which has shown significant improvements in the antioxidant capacity, total phenolic content and flavanol concentration of various tea beverages.
The continuous stepwise temperature extraction process uses six different temperature points and involves gradually lowering the temperature during extraction, which helps to maximise the extraction of beneficial compounds while preserving the tea’s sensory qualities.
This method contrasts with traditional high-temperature extractions used in industry that often led to the degradation of sensitive polyphenols and the loss of flavour. By enhancing the flavanol content, this method could lead to the production of tea drinks with greater health benefits, including improved antioxidant properties. The researchers believe this method can be scaled up for large-scale beverage production, offering a practical solution for the tea industry to produce high-quality, health-promoting products.
‘Our findings revealed a beneficial impact of continuous step-wise temperature extraction on the antioxidant capacity, phenolic content, and flavanol profile in different types of tea,’ the authors note. ‘This method may be significant in improving the value of tea leaves that had inherently lower flavanol content,’ the researchers, from the University of Hong Kong, add.
Results showed an increased antioxidant capacity of all tested tea types. Yuhua tea exhibited the highest absolute antioxidant capacity. The method also led to substantial increases in the concentration of major tea flavanols such as epigallocatechin gallate (EGCG), catechin, epicatechin (EC), and epicatechin gallate (ECG).
Lapsang Souchong tea, despite its low baseline flavanol content, showed increases in catechin and epigallocatechin-3-gallate levels by over 500% and 300%, respectively. Moonlight White tea demonstrated the greatest percentage change in total phenolic content, highlighting the method’s effectiveness across different tea varieties. Additionally, the study reports significant increases in other bioactive compounds such as EC and EGC. The researchers say their continuous stepwise temperature extraction showed a moderate increase in caffeine concentration in all the tea samples.
The researchers are actively addressing the limitations of their study by measuring other tea polyphenols such as theaflavins, flavonoids and tannins. ‘The next step is to measure these classes of polyphenols to understand the effect of this stepwise temperature extraction method. We would also like to supplement these results with analyses of flavour and aroma compounds and sensory evaluations,’ they explain. ‘Altogether, this will further refine the step-wise temperature extraction method in order to maximise the polyphenol content without compromising on its sensory values,’ they add.
The team envisions scaling up the continuous stepwise temperature extraction method for large-scale beverage production by the first or second quarter of 2025.
The researchers acknowledge that the concentration of bioactive compounds in tea is dependent on both the origin of the tea leaves and the brewing method used. Each type of tea is unique, based on its processing method, which may slightly modify the optimum extraction conditions. ‘Further testing is required on different types of tea to fully confirm the extrapolation and the specific extraction condition,’ they say.
‘The continuous stepwise extraction reported in this investigation retained valuable antioxidant capacity and flavanols, in particular Yuhua tea. Furthermore, the extraction is applicable to large-scale tea beverage production,’ the researchers say.
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