Abstract
The primary aim of this research was to determine whether herbal infusions, yerba mate (Ilex paraguariensis A. St.-Hilaire) and rooibos (Aspalathus linearis (Burm. F.) R. Dahlgren), could make a significant contribution to the dietary intake of polyphenols. A secondary aim was to determine whether the trace elemental content of these herbal infusions were of dietary significance. The total polyphenol (using the Folin-Ciocalteu assay), the individual polyphenol compounds (by ultra-high performance liquid chromatography) and the trace element content (by inductively coupled plasma mass spectrometry) was determined in the leaf and infusions of 47 yerba mate and 54 rooibos commercial products (tea bags and loose leaf). This research, for the first time, developed an extraction procedure and two ultra-high performance liquid chromatography methods that enabled the determination of 38 polyphenol compounds in yerba mate and 22 in rooibos samples. Fourteen trace elements were determined in leaf and infusion samples, enabling the extraction efficiency of trace elements to be calculated for the first time for these herbs. The total polyphenol content of green yerba mate (79.9 – 303.1 mg gallic acid equivalents (GAE)/ 200 ml) and fermented rooibos infusions (40.1 – 101.9 mg GAE/ 235 ml) was within the range of that of other beverages (tea, coffee, fruit juices) as reported in the literature. It was noted that yerba mate in tea bags contained significantly higher levels of polyphenols than loose leaf products (ANOVA and Tukey’s test, probability, p < 0.05) due to the absence of stems. The total chlorogenic acid content of green tea bag yerba mate (90.1 – 395.4 mg/200 ml) and the total flavonoid content of fermented rooibos infusions (6.65 – 20.03 mg/235 ml) was higher than that reported for coffee and fruit juices, respectively. It was concluded that regular consumption of 1 -2 cups/day of yerba mate or rooibos would make a significant contribution to the dietary intake of polyphenols. The manganese content of a yerba mate infusion (360 – 2985 µg/200 ml) would provide 39.7 – 60.8% for men and 57.1 – 86.2% for women of the World Health Organisation (WHO) adequate daily intake of manganese. Therefore, 1 – 2 cups per day could provide the entire daily nutritional requirement of manganese. In addition, consumption of yerba mate in the traditional South American manner could provide nutritionally significant levels of chromium, copper and zinc. The trace element content of rooibos was not nutritionally significant.