Measurement of Epigallocatechin Gallate (EGCG) and Caffeine Content of 32 Green Tea Dietary Supplements for the Dietary Supplement Ingredient Database (DSID)
Authors: Andrews Karen W , Dang P T , Savarala S , Gusev P A , Han F , Pehrsson P R , Harnly J M , Chen P , Zhao Y , Dwyer J T , Betz J M , Saldanha L G , Costello R B 
Published: November 2023

According to the 2007–10 NHANES, 7.5% of the US population reports botanical dietary supplement (DS) use. The DSID provides analytically‐derived estimates of the ingredient contents of DS. Commonly consumed and frequently studied, green tea (GT) DS were chosen as the first botanical DS for the DSID botanical initiative. The most abundant GT constituents are the catechins, especially EGCG, and caffeine. Our goal was to evaluate methods of analysis for individual catechins, caffeine and other GT constituents of interest, decipher patterns in constituent content labeling, and examine relationships between label claims and measured phytochemical constituent content.

Current labeling regulations require information on the amount of each botanical or botanical extract present in a DS. Claims about the concentration of naturally occurring phytochemical constituents of the botanicals or botanical extracts in the products are not mandatory. For researchers to more accurately estimate phytochemical intake from DS, the content of these constituents should be measured.

DS that contained GT as the only or primary botanical were selected for analysis in order to minimize interferences from sources of the same phytochemicals in non‐GT ingredients. Two lots of 32 DS purchased in various market channels and in a variety of forms (27 capsules, 2 liquids, 1 tablet, 1 softgel, 1 powder) were sent for analysis to 3 laboratories. Quality control results from all three laboratories showed good agreement with certified values for GT Standard Reference Materials®, indicating that methods employed by the laboratories can produce reliable and consistent data.

As required, all 32 DS listed the weight of GT leaf/extract on the label, but a wide range (0.5–309.5 mg/serving) of EGCG content was found for the most common GT content claim (500 mg per serving, n=9). Eighteen of 32 DS voluntarily listed EGCG content on the label. Twelve products had only 1 listed source of EGCG, and amounts of EGCG in 9 of 12 were within ± 20% of label claim. The remaining 6 DS claimed an additional botanical source of EGCG but lacked information for its EGCG content. ANOVA indicated that the measured EGCG amount (mg/serving) in DS without EGCG label claims was significantly different from EGCG measured in DS with an EGCG claim on the label (for both single and two GT EGCG sources; 60 ± 53, 216 ± 146 and 141 ± 41, mean ± SD, respectively; p<0.05). The measured amount of EGCG in the latter two DS groups was not significantly different (p>0.05).

The caffeine content (mg/serving) measured in DS without caffeine label claims (n=25) was lower than in DS with such claims (n=7) (means: 30 and 14, medians: 36 and 5, respectively; Kolmogorov‐Smirnov test, p = 0.02).

Thus, different label formats for GT DS may differ in their predictive strength for analytical constituent content. Labels that provide only the amount of GT leaf or extract may not permit accurate estimates of GT phytochemical constituents and are thus less informative for phytochemical intake estimates from DS.

Support or Funding Information

Funding: ARS/USDA & ODS/NIH Y1CN501006