These compounds are drawn out from tea leaves throughout developing and can be affected by numerous aspects, such as water temperature level, brewing time, and the materials used in tea preparation vessels.
The tea leaves were separated, and the supernatant (liquid lying above solid residue) was blended with glaze powders coated on ceramic tiles. The tea services mixed with Oribe, Namako, and Irabo glazes revealed substantially lower concentrations of epicatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate, while the Toumei glaze selectively deteriorated epigallocatechin gallate. “And it is very intriguing that thearubigins and theaflavins are the main elements of fermented tea like black tea. In other words, green tea brewed by specific ceramic tea sets can be turned into black tea.”
Researchers from the Nagoya Institute of Technology have actually found that the glazing on ceramic tea sets considerably influences the preservation of catechin flavonoids in tea.
Glazes on tea sets significantly decrease the quantity of catechins, changing the health, aroma, and flavor advantages of tea.
Introduced as a medicinal beverage around 2700 B.C., tea has grown to be the one of the most popular beverages worldwide. One of the essential factors for its popularity is its rich content of flavonoids and polyphenols, which contribute to the antioxidant residential or commercial property, flavor, and aroma of tea, offering numerous prospective health benefits. These compounds are drawn out from tea leaves throughout developing and can be influenced by a number of aspects, such as water temperature, developing time, and the materials used in tea preparation vessels.
Current Research Findings
Just recently, scientists from Nagoya Institute of Technology (NITech) in Japan have actually exposed, for the first time, that the option of glazing on ceramic tea sets utilized to prepare tea plays a key role in the retention of catechin flavonoids. In their research study released just recently in the journal Scientific Reports, Associate Professor Takashi Shirai, in addition to Dr. Yunzi Xin, Mr. Sota Shido, and Dr. Kunihiko Kato from the Advanced Ceramics Research Center at NITech, analyzed the impact of four different common Japanese industrial glazes– Oribe, Namako, Irabo, and Toumei– on the content of catechins, the most plentiful flavonoid discovered in green tea.
Glazes on tea sets substantially decrease the amount of catechins in tea by oxidizing them, altering the fragrance, taste, and health benefits of tea. Credit: Dr. Takashi Shirai from NITech, Japan
Properties and Composition of Glazes
While glaze coatings mostly include feldspar minerals, such as silicon, aluminum, calcium, and salt oxides, they likewise include unique metal oxide types that impart a distinct appearance and texture to the ceramic vessel. Oribe glaze mainly contains copper (Cu) oxides and imparts a lively green color, while Namako glaze includes cobalt (Co) oxides for a dark blue appearance. Irabo glaze includes iron (Fe) oxides that impart orange tones, while Toumei glaze has a high titanium (Ti) content, providing a transparent finish.
Method and Observations
To analyze the impact of the glaze on tea catechins, the researchers brewed a green tea service utilizing ion-exchanged water at 80 ° C( 176 ° F) for 3 minutes. The tea leaves were separated, and the supernatant (liquid lying above strong residue) was mixed with glaze powders covered on ceramic tiles. The glaze-tea mix was then allowed to react for six hours, followed by the elimination of the glaze powder through centrifugation and purification.
The researchers observed that the beautiful tea service had a clear intense yellow color, however after 6 hours of deterioration, it turned into a yellowish-brown color. On the other hand, the tea options degraded by different glazes showed darker brown or black colors. To put it simply, the level of color change depended considerably on the kind of glaze.
Test pieces of glaze-coated tile (b) tea solutions before and after combining with glazes (top) and deteriorated tea options with and without existence of glazes (bottom). Credit: Takashi Shirai from NITech, Japan
A selective decrease in the quantity of altered catechins in tea was likewise observed by the scientists. The tea solutions combined with Oribe, Namako, and Irabo glazes showed significantly lower concentrations of epicatechin, epicatechin epigallocatechin, epigallocatechin, and gallate gallate, while the Toumei glaze selectively broken down epigallocatechin gallate. The reduction in catechin concentration and the resulting color change can be credited to the oxidation procedure of catechins, which forms brownish thearubigins and reddish-orange theaflavin and its oxide pigments.
Scientific Explanation and Implications
“And it is very fascinating that thearubigins and theaflavins are the primary parts of fermented tea like black tea. In other words, green tea brewed by specific ceramic tea sets can be turned into black tea.”
In summary, this research study highlights that the choice of glaze products used in ceramic tea sets can substantially affect the concentration of advantageous substances such as catechins in tea. “The specific function of glazes on the deterioration of catechins not only provides primary details for the design and advancement of practical products but can likewise impact daily tea drinking and long-term human health-related concerns,” concludes Dr. Shirai.
Reference: “Glazes induced destruction of tea catechins” by Yunzi Xin, Sota Shido, Kunihiko Kato and Takashi Shirai, 28 June 2023, Scientific Reports.DOI: 10.1038/ s41598-023-37480-8.
The authors acknowledge Mizuno Kagaku Kogyo Co., Ltd for supplying the glaze items.
