ARS | Publication request: TEA VARIETY AND BREWING TECHNIQUES INFLUENCE FLAVONOID CONTENT OF BLACK TEA

Submitted to: Journal of Food Composition and Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 13, 2004
Publication Date: May 26, 2004
Citation: Peterson, J., Dwyer, J., Jacques, P., Rand, W., Prior, R., Chiu, K. 2004. Tea variety and brewing techniques influence flavonoid content of black tea. Journal of Food Composition and Analysis. 17(3-4):397-405.

Interpretive Summary: Teas vary by country or region (Assam, China, Darjeeling), type (black, green, oolong, Pu'er), variety (blended, unblended) and further details such as processing (conventional, CTC - cut, tear, curl). Unblended teas are named by their country or region. Blended teas are named generically (Earl Gray, Irish Breakfast) rather than by the unblended teas they include. Black tea is processed in two different ways, "conventional" processing and "CTC" or "unconventional" processing. The main difference between the two methods is the rolling phase of the fermentation process. The older, conventional method involves rolling of the tealeaves. CTC uses a machine that actually tears the leaf, causing more fermentation throughout the leaf in a shorter period of time. Teas are divided roughly into two main categories ' plain and flavory teas. Plain teas, which include breakfast teas, are most commonly produced from Indian hybrids, by CTC processing. Flavory teas are produced mostly from China hybrids, by conventional processing. Brewing techniques vary considerably from country to country. Differences in brewing times among individuals also exist. In addition to its popularity as a refreshing beverage, tea is now receiving scientific attention because it and the flavonoids it contains appear to have beneficial health effects. This study examined the influence of variety and brewing technique on the characteristic flavanols of tea by collating and by evaluating high quality data published in the analytical literature. Tea variety, weight of tea or teabag, and brewing techniques all affect estimates of flavonoid intake. More research is needed on the effects of brewing techniques so accurate formulas can be developed to determine flavonoid intake.

Technical Abstract: We examined the influence of variety and brewing technique on the catechins, theaflavins, and thearubigins in black tea using published data. Differences due to tea variety were examined by comparing values for the characteristic flavanols that are responsible in part for the distinct flavors of the various teas. These included catechins, theaflavins, and thearubigins in varieties of blended teas (from several regions) and unblended teas (from only one region) in the published literature. Total catechins, theaflavins, and thearubigins were calculated per 180 ml serving of tea for teabags of different weights. For brewing techniques, infusion strength of 1.25% (typical US 2.25 g teabag per 180 ml water) and an illustrative extraction efficiency were compared to analytical results at 2 minutes brewing time. The unblended teas (e.g. Assam, Kenya, Ceylon, China, or Darjeeling) varied greatly in the amount and pattern of their flavonoid content. Compared to unblended teas, the blended teas were lower in total catechins and mid-range in theaflavins. Brewing techniques, particularly tea weight and variety, also influenced flavonoid content. However, differences in tea variety and weight accounted for most of the flavonoid content per tea serving. Tea variety, weight of tea or teabag, and brewing techniques all affect estimates of flavonoid intake. For research purposes it would be helpful to list tea type (black, green, oolong, Pu'er), unblended or blended, and if data suffice for unblended by region (Assam, China, Darjeeling) and for blended by name (Earl Gray, English Breakfast). More research is needed on the effects of brewing techniques so accurate formulas can be developed to determine flavonoid intake.