Launched as a medicinal drink round 2700 B.C., tea has grown to be the some of the well-liked drinks worldwide. One of many key causes for its recognition is its wealthy content material of flavonoids and polyphenols, which contribute to the antioxidant property, taste, and aroma of tea, providing numerous potential well being advantages. These compounds are extracted from tea leaves throughout brewing and will be influenced by a number of elements, reminiscent of water temperature, brewing time, and the supplies utilized in tea preparation vessels.

Lately, researchers from Nagoya Institute of Know-how (NITech) in Japan have revealed, for the primary time, that the selection of glazing on ceramic tea units used to organize tea performs a key position within the retention of catechin flavonoids. Of their examine revealed on-line within the journal Scientific Studies on June 28, 2023, Affiliate Professor Takashi Shirai, together with Dr. Yunzi Xin, Mr. Sota Shido, and Dr. Kunihiko Kato from the Superior Ceramics Analysis Middle at NITech, examined the influence of 4 completely different typical Japanese industrial glazes — Oribe, Namako, Irabo, and Toumei — on the content material of catechins, essentially the most plentiful flavonoid present in inexperienced tea.

Whereas glaze coatings primarily include feldspar minerals, reminiscent of silicon, aluminum, sodium, and calcium oxides, in addition they include distinct metallic oxide species that impart a novel look and texture to the ceramic vessel. Oribe glaze predominantly comprises copper (Cu) oxides and imparts a vibrant inexperienced shade, whereas Namako glaze comprises cobalt (Co) oxides for a darkish blue look. Irabo glaze comprises iron (Fe) oxides that impart orange tones, whereas Toumei glaze has a excessive titanium (Ti) content material, offering a clear end.

To look at the impact of the glaze on tea catechins, the researchers brewed a inexperienced tea resolution utilizing ion-exchanged water at 80°C for 3 minutes. The tea leaves have been separated, and the supernatant (liquid mendacity above strong residue) was blended with glaze powders coated on ceramic tiles. The glaze-tea combination was then allowed to react for six hours, adopted by the elimination of the glaze powder by means of centrifugation and filtration.

The researchers noticed that the pristine tea resolution had a transparent vivid yellow shade, however after six hours of degradation, it became a yellowish-brown shade. In distinction, the tea options degraded by completely different glazes exhibited darker black or brown colours. In different phrases, the extent of shade change depended considerably on the kind of glaze.

Moreover, the researchers additionally noticed a selective discount within the quantity of altered catechins in tea. The tea options blended with Oribe, Namako, and Irabo glazes confirmed considerably decrease concentrations of epicatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate, whereas the Toumei glaze selectively degraded epigallocatechin gallate. The discount in catechin focus and the ensuing shade change will be attributed to the oxidation means of catechins, which types brownish thearubigins and reddish-orange theaflavin and its oxide pigments.

“Throughout the degradation course of, Cu-, Co-, Fe-, and Ti-oxides in glaze powders can act as a Lewis acid catalyst and promote the oxidation of catechin molecules to ortho-quinones, adopted by additional response to kind thearubigins and/or theaflavin and its oxides. One other oxidation route is thru the polymerization of intermediate free radical catechins,” explains Dr. Shirai. “And it is extremely attention-grabbing that thearubigins and theaflavins are the primary parts of fermented tea like black tea. In different phrases, inexperienced tea brewed by particular ceramic tea units will be became black tea.”

In abstract, this examine highlights that the selection of glaze supplies utilized in ceramic tea units can considerably have an effect on the focus of useful compounds reminiscent of catechins in tea. “The particular perform of glazes on the degradation of catechins not solely offers principal data for the design and growth of useful supplies however also can influence every day tea ingesting and long-term human health-related points,” concludes Dr. Shirai.