Pantsi et al. (2011:1225) quantified the major polyphenols in unfermented and fermented rooibos. Unfermented rooibos provided higher levels of aspalathin, orientin, iso-orientin, vitexin, isovitexin and rutin compared to fermented rooibos. The flavonol content of both the unfermented and fermented rooibos were higher in comparison to the flavonol content of green tea. Green tea though had a higher flavanol content than both unfermented and fermented rooibos (Pantsi et al., 2011:1225).
Bramati et al. (2003:7472) also quantified the major flavonoids in unfermented rooibos herbal tea. The main compounds determined were also aspalathin, iso-orientin, orientin and rutin. The total flavonoid content detected in the unfermented rooibos herbal tea was 59.08 ± 0.59 mg/g compared to that of the fermented type which was 5.521 ± 0.055 mg/g. The level of aspalathin in unfermented rooibos was found to be 50 times higher than that of the fermented rooibos (49.92
± 0.8 mg/g and 1.234 ± 0.01 mg/g respectively) and the TAC of the unfermented infusion double that of the fermented infusion (Bramati et al., 2003:7473).
The flavonoid and total polyphenol content in rooibos and honeybush herbal tea (fermented and unfermented) were recorded by Marnewick et al. (2000:160). On fermentation the flavonoid and total polyphenol content of both these herbal teas decreased significantly (p < 0.001). The total flavonoid values for unfermented rooibos (28.06 ± 0.25 g/100 g) and unfermented honeybush (27.1 ± 0.2 g/100 g) were almost the same, while the difference for the total polyphenols was higher (41.15 ± 0.25 g/100 g and 35.52 ± 0.03 g/100 g respectively). The flavonoid values for fermented honeybush were almost half (9.86 ± 0.18 g/100 g) that of fermented rooibos (18.8 ± 0.35 g/100 g). The fermented rooibos also had a higher total polyphenol content (29.74 ± 0.36 g/100 g) in comparison to the fermented honeybush (19.8 ± 0.26 g/100 g) (Marnewick et al., 2000:160).
Joubert (1996:403) confirmed that processing of rooibos decreased the aspalathin and nothofagin content with the decrease depending on the extent of the oxidation of the tea material. Most of the aspalathin and nothofagin is oxidised in the period prior to the fermentation process. The method of drying, as controlled drying vs sun-drying, had no effect on the rooibos apalathin, nothofagin or total polyphenol content (Joubert, 1996:411).
Von Gadow et al. (1997b:75) assessed rooibos herbal tea’s antioxidant activity against that of black, green and oolong tea. Semi-fermented and fermented rooibos had a lower percentage of respectively total polyphenols and flavonoids than unfermented rooibos, expressed as percentage of the total water-soluble solids. This is a further indication that fermented rooibos herbal tea has a lower antioxidant activity. Green tea had the highest flavonoid content and fermented rooibos herbal tea the lowest (Von Gadow et al., 1997b:75).
Villano et al. (2010:679) investigated the influence of the rooibos herbal tea on the plasma TAC of healthy human volunteers. This study indicated that both fermented and unfermented rooibos herbal teas increased the plasma TAC. The unfermented rooibos herbal tea produced a 28%
higher in vitro antioxidant capacity than fermented rooibos herbal tea, measured as the chain breaking antioxidant activity (TRAP) (Villano et al., 2010:680). Both the unfermented and fermented form of rooibos herbal tea produced a lower plasma TAC than black tea or green tea in this study (Villano et al., 2010:681). The lower antioxidant capacity is linked to the fermentation process where a decline in the polyphenol content of rooibos occurs (Villano et al., 2010:682). Joubert and Schulz (2006:142), in describing rooibos herbal tea’s quality aspects, confirmed that unfermented rooibos herbal tea contains more aspalathin than fermented rooibos herbal tea.
In an investigative study, unfermented and fermented honeybush and rooibos herbal teas were tested for their antimutagenic properties. The Salmonella typhimurium mutagenicity assay was used. The study concluded that the unfermented form of the rooibos extract displayed greater antimutagenic properties compared to the fermented form of rooibos with these protective effects not observed with honeybush herbal tea (Marnewick et al., 2000:162). The fermentation process seems to decrease the protective effects of the herbal teas studied (Marnewick et al., 2009:220).
The ability of unfermented and fermented honeybush and rooibos herbal teas to regulate methylbenzylnitrosamine (MBN)-induced oesophageal cancer in experimental rats was evaluated by Sissing et al. (2011:601). It was reported that aspalathin was the major flavonoid in unfermented rooibos, whereas in the fermented form, orientin was the major flavonoid (Sissing et al., 2011:603). The aspalathin content of fermented rooibos herbal tea (0.48% of soluble solids) was much lower than that of the unfermented type (14.73% of soluble solids). In the unfermented form of honeybush the mangiferin content was 4.59% of the soluble solids, whereas in the fermented form it was 0.42% of the soluble solids (Sissing et al., 2011:605). The researchers concluded that fermentation of herbal teas does indeed decrease the protective effects on papilloma progression which is associated with the reduced polyphenolic constituent content (Sissing et al., 2011:608).
Literature has also indicated that after the fermentation process of green tea to black tea, the percentage of catechins present decreases to less than 10% (Dreosti, 2000:692). These changes that take place during tea processing can be ascribed to oxidative changes (Peterson et al., 2004:397). This possibly explains why there is a qualified health claim for green and not for black tea as the catechins are a group of very active flavonoids having biological properties that may be responsible for the health promoting effects (Hodgson & Croft, 2010:497). The flavanol content of blended and unblended teas also differ to some extent (Peterson et al., 2004:397) as blended teas are lower in catechins than unblended teas (Peterson et al., 2004:400).