Variation in Phenolic Content and Antioxidant Activity of Fermented Rooibos Herbal Tea Infusions: Role of Production Season and Quality Grade

Abstract

Data are required to calculate the dietary exposure to rooibos herbal tea flavonoids and phenolic acids. Representative content values for the principal phenolic compounds and total antioxidant capacity of fermented rooibos infusion, taking into account variation caused by production seasons (2009, 2010, and 2011) and quality grades (A, B, C, and D), were determined for samples (n = 114) from different geographical areas and producers. The major phenolic constituents were isoorientin and orientin (>10 mg/L), with quercetin-3-O-robinobioside, phenylpyruvic acid glucoside, and aspalathin present at >5 mg/L. Isovitexin, vitexin, and hyperoside were present at <3 mg/L. Rutin, ferulic acid, and isoquercitrin were present at <2 mg/L. Nothofagin was present at <1 mg/L. Only traces of luteolin-7-O-glucoside and the aglycones quercetin, luteolin, and chrysoeriol were present. Substantial variation was observed in the individual content values of the phenolic compounds and total antioxidant capacity within production seasons and quality grades.

Anti-Peroxyl Radical Quality and Antibacterial Properties of Rooibos Infusions and Their Pure Glycosylated Polyphenolic Constituents

“…Artificial rooibos infusions were prepared using the most abundant and available polyphenols naturally present in this beverage based on HPLC analysis of the infusions according to the method described by [24,33]. Stock solutions (2.0 mM in pure methanol, stored at −20 °C) of the polyphenols were prepared prior to their combination in the artificial infusions, representing green and fermented rooibos.…”

“…The effectiveness of these glycosylated polyphenols against reactive radical species that are directly involved in causing oxidative stress within living organisms remains unknown [32]. Recently, Joubert et al [24,33] have reported the oxygen radical scavenging capacities of rooibos infusions and extracts, using fluorescence detection (ORAC-FL). However, the antioxidant quality and the contribution of the glycosylated polyphenols to that anti-peroxyl radical scavenger ability of natural rooibos infusions are still unknown.…”

Tea and bone health: Findings from human studies, potential mechanisms, and identification of knowledge gaps

“…As the benefits may be mediated through flavonoid interactions, it is important to note that higher grades are associated with higher flavonoid concentrations (Joubert, et al, 2012). When assessing different grades of rooibos for flavonoid content, higher levels of the following flavonoids: aspalathin, isoquercetin, rutin, hyperoside, quercetin-3-O-robinobioside, were observed with higher quality rooibos (Joubert, et al, 2012).…”

“…When assessing different grades of rooibos for flavonoid content, higher levels of the following flavonoids: aspalathin, isoquercetin, rutin, hyperoside, quercetin-3-O-robinobioside, were observed with higher quality rooibos (Joubert, et al, 2012). Flavonoid content can also be altered through fermentation.…”

Hyperglycemia-induced oxidative stress and heart disease-cardioprotective effects of rooibos flavonoids and phenylpyruvic acid-2-O-β-D-glucoside

“…Food processing may also change their content. The orientin and isoorientin content of a ready-to-drink rooibos beverage showed a slight change as a result of pasteurization and storage, postulated to be due to the conversion of aspalathin to these compounds [110, 127]. Except for luteolin, there is very limited data on the characteristic metabolism and transportation of these flavone glucosides.…”