2023-09-13 12:22:00
Rich in catechins (flavonoids), green tea offers many health benefits. Some studies have shown that its consumption can reduce the risk of cardiovascular diseases or promote cognitive functions. However, the way you consume your green tea might influence the benefits of the catechins present in it.
“These compounds are extracted from tea leaves during brewing and can be influenced by several factors, such as water temperature, brewing time and materials used in tea preparation containers”, explain researchers from the Nagoya Institute of Technology (Japan). According to them, the different ceramic glazes of the tea sets (glazing which covers the cup and gives it its appearance as well as its color) might play a role in the conservation of catechins. The results were published in the journal Scientific Reports and shared in a press release on the University website on September 6.
Ceramic cups: not all contain the same materials
For their study, the researchers examined the impact of four typical Japanese commercial ceramic glazes on the catechin content. This difference color and texture is due to different metal oxides. “Although glaze coatings mainly consist of feldspathic mineralssuch as silicon, aluminum, sodium and calcium oxides, they also contain distinct metal oxide species which give a unique appearance and texture to the ceramic container”, explain the researchers.
here are the four types of coatings used in the study:
- Orib : it mainly contains leather oxides (Cu), which give it its color bright green.
- My friend : it contains cobalt oxides (Co) which gives it its color dark blue.
- I will go : it contains iron oxides (Fe), responsible for its tons orange.
- Toumei : it contains a high content of titanium (Ti), which offers it a transparent finish.
To study the effect of coating ceramic cups on the tea catechinsthe researchers prepared a green tea solution using ion exchange water at 80°C for three minutes. “The tea leaves were separated and the supernatant (liquid above the solid residue) was mixed to icing powders applied to ceramic tiles. The icing-tea mixture was then left as is for six hours, then the icing powder was extracted by centrifugation and filtration“, explain the authors in the press release.
Green tea: ceramic glazes might reduce the number of catechins
The researchers observed that the virgin tea solution, without any colored enamel, had a clear bright yellow color. Six hours later, it changed to one color yellowish brown. In contrast, the tea solutions degraded by the different coatings showed darker black or brown colors. So the extent of color change depends on the type of enamel. This color change can be attributed, according to experts, to to the catechin oxidation process. Enamel colors are therefore associated with a reduction in the number of catechins. “Tea solutions mixed with glazes Oribe, Namako and Irabo had significantly lower concentrations of epicatechin, epicatechin gallate, epigallocatechin and epigallocatechin gallatewhile the Toumei glaze selectively degraded epigallocatechin gallate,” details the press release.
So, by modifying the compounds present in tea, specific tea sets might transform it into black tea, thereby reducing its health benefits. “The specific function of enamels on catechin degradation not only provides primary information for the design and development of functional materials, but also may have an impact on daily tea consumption and long-term human health problems“, concludes Dr Shirai, lead author of the research.
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