Influence of Steep Time on Polyphenol Content and Antioxidant Capacity of Black, Green, Rooibos, and Herbal Teas

Abstract

Potential health benefits of tea consumption are often attributed to the antioxidant activity of polyphenols. Whether steep time, often variable in a real-life situation, makes a biological difference in terms of polyphenol content and antioxidant activity is uncertain. The study objective was to characterize eight popular and commercially available teas for total polyphenol content (TPC) and antioxidant capacity in relation to steep time. Dragonwell (DW), Sencha (S), English Breakfast (EB), Golden Monkey (GM), Green Rooibos (GR), Red Rooibos (RR), Chamomile (C), and Peppermint (P) loose leaf teas were individually steeped in water for 1-10 min at 1 min intervals. TPC increased with longer durations of steep time; however, the majority of polyphenols observed after 10 minutes were extracted in the first 5 min regardless of tea type. After 5 min of steeping, differences (p < 0.05) in TPC were observed across teas (JS~EB~P > DW > GM~GR~RR > C). Different teas also varied in their ability to inhibit the free radical 2, 2-diphenyl-1-picrylhydrazyl (DPPH) when normalized for polyphenol concentration (1 µg/mL) and there was no effect due to steep time. Predicted antioxidant capacity of teas also demonstrated significant differences among teas after 5 and 10 min. In conclusion, steep time modulates TPC but not the antioxidative capacity of tea polyphenols.

Total Polyphenol Content and Antioxidant Capacity of Tea Bags: Comparison of Black, Green, Red Rooibos, Chamomile and Peppermint over Different Steep Times

“…Steep time was studied from 1 to 10 min at 1-min intervals, thus mimicking steep times often used by consumers. This study showed that over 50% of polyphenols were released in the initial 5 min of steep time and that TPC increased in a nonlinear relationship for all tea types tested [13]. Interestingly, longer steep time was not associated with greater antioxidant capacity (measured as the percent inhibition of the free radical DPPH) when the polyphenol content was standardized, but tea types did differ in their antioxidant capacity.…”

“…The methods used in the current experiments have been described in detail previously [13], and only minor changes have been made to the apparatus to allow the steeping of tea prepared from tea bags, which requires a larger vessel than that required for loose-leaf products. Tea samples consisted of Orange Pekoe (OP) or Green (G) teas, or Red Rooibos (RR), Peppermint (P), or Chamomile (C): all products were purchased from a local supplier and prepared according to the manufacturers recommendations (see Tables 1 and A3 for tea product details).…”

“…Samples (100 µL) were extracted at 1-min intervals for 10 min, after which they were microfiltered (0.2 µm) and immediately analyzed for polyphenol content. The boiling vessel used in the present study was larger than that used for our previous work with loose leaf teas [13], and therefore rather than independent tea batches steeped to each time point, we utilized a repeated-measures design where small aliquots were removed from the 500 mL vessel for each of the time points to reduce inter-batch variability in the study design. which they were microfiltered (0.2 µm) and immediately analyzed for polyphenol content.…”

“…Polyphenols were extracted using a modified Folin-Ciocalteu's method with a Gallic acid standard, as previously described [13,17] and in accordance with the International Organization of Standardization (ISO 14502-1). Using distilled water, tea samples were prepared using dilutions of 1:100.…”

“…Two considerations include the steep time as well as whether loose tea or a commercial tea bag is used. The effect of steep time on polyphenol content and antioxidant activity in eight commercially available and popular loose teas has been previously reported by our group [13]. Steep time was studied from 1 to 10 min at 1-min intervals, thus mimicking steep times often used by consumers.…”