TABLE 2.
Rooibos preparation methods providing the highest total polyphenol content and total antioxidant capacity.
| Rooibos preparation method | Biochemical content† | Comment | ||
|---|---|---|---|---|
| Total polyphenols‡ (mg/L) | FRAP§ (µmol/L) | TEAC¶ (µmol/L) | ||
| Rooibos type†† | ||||
| Green, unfermented (1) | 457.7 ± 40.9‡‡ | 3219 ± 82§§ | - | Limited consumer availability |
| Traditional, fermented (2) | - | - | 1140 ± 143‡‡ | - |
| Rooibos form¶¶ | ||||
| Powdered extract (traditional/fermented) (3) | 604.6 ± 39.0‡‡ | 4004 ± 395‡‡ | - | Limited consumer availability |
| Iced tea (with rooibos extract – traditional/fermented) (4) | - | - | 1701 ± 565‡‡ | More costly to the consumer, although convenient |
| Rooibos preparation (brewing time)* | ||||
| 30 min (5) | 543.2 ± 125.7§§ | 3107 ± 731§§ | 1212 ± 270§§ | - |
| Household flavouring types and amounts** | ||||
| Honey (6) | 413.0 ± 72.7§§ (large amount addition as 15 g) |
2489 ± 437‡‡ (small amount addition as 5 g) |
1868 ± 172§§ (small amount addition as 5 g) |
Health implications of use of a large amount of honey (fructose) questionable |
| Whole milk | 519.1 ± 82.7‡‡ (large amount addition as 30 mL) |
2100 ± 453‡‡ (large amount addition as 30 mL) |
- | High polyphenol content probably because of interference with the absorbance of the assay by some of the milk constituents |
| Skim milk | - | - | 3025 ± 325‡‡ (large amount addition as 30 mL) |
- |
| 30 mL whole milk and 15 g honey | 545.1 ± 65.7‡‡ (large amount additions as 30 mL and 15 g, respectively) |
- | - | High polyphenol content probably because of interference with the absorbance of the assay by some of the milk constituents |
| 30 mL whole milk and 10 g brown sugar | - | 2310 ± 609‡‡ (large amount additions as 30 mL and 10 g, respectively) |
- | High polyphenol content probably because of interference with the absorbance of the assay by some of the milk constituents |
| 30 mL skim milk and 5 g honey | - | - | 3773 ± 146§§ (large and small amount additions as 30 mL and 5 g, respectively) |
- |
| Significant difference | (6)-(3)(5)*** | (3)-(1)*** | (2)-(4)(6)**** | - |
| (6)-(1)(3)(5)*** | (5)-(4)(6)**** | |||
, biochemical content values: Mean ± standard deviation.
, total polyphenol content presented as milligram (mg) per litre (L).
, FRAP: Ferric-reducing antioxidant power assay presented as micromole (µmol) per L.
, TEAC: Trolox equivalent antioxidant capacity assay presented as µmol per L.
, rooibos types included traditional (fermented), green (unfermented), organic traditional (fermented).
, highest in preparation method grouping.
, significantly highest in preparation method grouping.
, rooibos forms included traditional fermented rooibos leaves, green unfermented rooibos leaves, organic rooibos tea leaves, rooibos powder, ready-to-drink unflavoured iced teas with traditional fermented rooibos.
, steeping times include a quick steeping time (1 min), an average (5 min) and a long (10 min) steeping time (Campanella et al. 2003). Steeping times of 20 and 30 min were also tested to determine the effect of prolonged steeping.
, the rooibos samples representing the type of milk added and the combined household flavourings were not included in the statistics analysis carried out because of the interference with the polyphenol content analysis of the former (F. Rautenbach, pers. Commun., 10 March 2016).
, overall significant (p < 0.05) difference in the Levene’s test for equality of variances of the samples with the significant (p < 0.05) differences transpiring in the pairwise multiple comparisons of the Student–Newman–Keuls test indicated as a rooibos sample providing a high total polyphenol and total antioxidant capacity (number presented in brackets [e.g. green, unfermented as 1] significantly different (-) to another rooibos sample providing a high total polyphenol content and total antioxidant capacity (TAC) with each sample presented as a number in brackets [e.g. traditional, fermented as 2]).
, overall significant (p < 0.05) difference in the Kruskal–Wallis Test one-way analysis of variance by ranks of the samples with the significant (p < 0.05) contrasts transpiring on the post hoc pairwise multiple comparisons indicated as a rooibos sample providing a high total polyphenol content and total antioxidant capacity (number presented in brackets [e.g. green, unfermented as 1] significantly different (-) to another rooibos sample providing a high total polyphenol content and TAC with each sample presented as a number in brackets [e.g. traditional, fermented as 2]).