Antioxidant Content and Activity of Untreated and Processed Guayusa Tea
Guayusa (Ilex guayusa, Aquifoliaceae) is an evergreen tree native to South America with a long history of use by the indigenous tribes of the Amazon. Traditionally, the twigs and leaves are infused in hot water to create a beverage. A distant relative of yerba maté (I. paraguariensis), this plant is a source of caffeine and is used as a pain reliever. The increasing commercial use of guayusa has led to more interest in its health benefits. The aim of this study was to characterize the phenolic and carotenoid content, as well as the antioxidant activity, of both untreated (green) and processed (blanched or fermented) guayusa.
Guayusa leaves were collected in Pastaza, Ecuador. Both green untreated and processed leaves were provided by the RUNA Foundation (the nonprofit arm of RUNA LLC, a beverage company that processes and sells guayusa; Archidona, Napo, Ecuador). The untreated and processed leaves were freeze-dried and made into separate powders. Blanching and fermentation of guayusa leaves were conducted at the manufacturing plant of the RUNA Foundation, following the standard protocols of the company. The leaf powders were extracted with alcohol-based solvents and assessed for total phenolic content (TPC), phenolic composition, carotenoid composition, and antioxidant capacity by chromatographic or biochemical assay techniques.
A total of 14 phenolic compounds were identified from all sources, nine of which were hydroxycinnamic acids or derivatives (neochlorogenic acid, chlorogenic acid, isochlorogenic acid, five other caffeoyl derivatives, and feruloylquinic acid), and five of which were flavonoids (four quercetin derivatives and one kaempferol derivative). Out of the hydroxycinnamic compounds, chlorogenic acid was the most abundant compound (24.10 mg/g DW [dry weight]). This concentration was similar or higher in comparison to maté and other Ilexspp., but lower than green coffee (Coffea spp., Rubiaceae). In terms of the flavonoids, the flavonol glycoside quercetin-3-O-hexose was the most abundant compound. The flavonol concentration of guayusa (11 mg/g DW) was around two, 20, and 28 times higher than described for yerba maté, other Ilex spp., and tea (Camellia sinensis, Theaceae), respectively.
Industrial processing (blanching or fermentation) did not alter the phenolic profile but did alter phenolic concentrations. As with the unprocessed green leaves, chlorogenic acid was the major phenolic compound found in the blanched samples, while isochlorogenic acid was the most abundant compound in the fermented samples. The TPC of the leaves without industrial processing was 54.86 mg gallic acid equivalents (GAE)/g DW. This is reportedly higher than yerba maté, but lower than green and black tea TPC. Blanching the guayusa leaves resulted in a significant increase in TPC (48.5%, 106.62 ± 4.41; P < 0.05), a concentration that is higher than what has been reported in maté and green and black tea. Fermentation resulted in no significant change in TPC compared to the unprocessed guayusa leaves.
A total of five carotenoid compounds were detected in the green and processed guayusa samples (α- and β-carotene, lutein, and violaxanthin + neoxanthin). In the unprocessed leaves, the concentrations of α-carotene and violaxanthin were higher compared to other teas, but β-carotene and lutein were about the same. There were no significant differences between the total carotenoids of unprocessed and processed leaves, but significantly more total carotenoids were found in the blanched guayusa vs. the fermented guayusa (P < 0.05). Higher contents of β-carotene and lutein were found in the blanched leaves compared to the green untreated leaves (305.39% and 141.52% more, respectively), but there were lower concentrations of α-carotene and violaxanthin + neoxanthin (55.27% and 22.38% less, respectively) (P < 0.05). Fermenting guayusa leaves had no significant effects on the concentrations of β-carotene and lutein. Overall, the results indicated that violaxanthin + neoxanthin was the most easily degraded carotenoid by industrial processing, with 77.6% and 92.5% lost after blanching and fermentation, respectively. Similar effects were seen for other teas.
Guayusa green leaves and blanched leaves had the highest antioxidant activity. The antioxidant activity of the green leaves (2,2-diphenyl-1-picrylhydrazyl [DPPH] assay: 32.98 mM Trolox/100 g DW; oxygen radical absorbance capacity [ORAC] assay: 154.03 mM Trolox/100 g DW) was similar to other studies on this plant species, yerba maté, and tea. The polyphenol and carotenoid content indicated there was a positive and direct correlation with antioxidant capacity, especially with the ORAC assay.
The authors conclude that guayusa has similar antioxidants and activity as yerba maté and tea and that blanching produces the highest concentration of polyphenols, as well as specific carotenoids. It would be interesting if this study also assessed hot water extracts of the tea rather than alcohol extracts since guayusa is often consumed as a hot water infusion. As the authors suggest, more studies are warranted that investigate the content and bioavailability of the bioactive compounds of guayusa to better understand the health benefits of this plant species.
García-Ruiz A, Baenas N, Benítez-González AM, et al. Guayusa (Ilex guayusa L.) new tea: phenolic and carotenoid composition and antioxidant capacity. J Sci Food Agric. September 2017;97(12):3929-3936.