Rooibos types and forms and how prepared and flavoured influence the total polyphenol content and total antioxidant capacity (TAC).
To denote an optimal rooibos cup as having the highest total polyphenol content and TAC, considering the different types, forms, preparation methods and flavourings and amounts (Phase 1), and determine the demographic, lifestyle and rooibos consumption characteristics of adult rooibos consumers, and the association of these characteristics with drinking the optimal cup (Phase 2).
Assays: Oxidative Stress Research Centre, Cape Peninsula University of Technology; Consumer survey: George area, South Africa.
Phase 1 entailed determining the total polyphenol content (Folin–Ciocalteau method) and TAC (Trolox equivalent antioxidant capacity and ferric-reducing antioxidant power assay) of the prepared rooibos samples. For Phase 2, a developed, pilot tested questionnaire was used to profile adult rooibos consumers.
Phase 1: the following samples delivered higher total polyphenol content and TAC: green (type), green leaves and powdered extract (forms), and sample steeped for 10 min or longer (preparation method). The identified optimal cup was sample steeped for 10 min or longer. Phase 2: a total of 308 respondents completed the questionnaire. Few consumed more than one rooibos cup per day (25.3%;
The optimal cup was identified as sample steeped for 10 min or longer. The rooibos consumers did not consume it sufficiently, nor steeped it long enough.
Limited research has been conducted on the preparation of rooibos (
The fact that rooibos herbal tea is free of caffeine and has a low tannin level in relation to
As limited information could be established regarding the above, the effects of these preparation aspects on tea are in the main presented. Bramati, Aquilano and Pietta (
The form of the tea, along with its weight, are important factors that determine the flavonoid content of steeped tea (Peterson et al.
Peterson et al. (
Consumers usually add a sweetener like sugar or honey and/or milk to traditional fermented rooibos herbal tea. Studies performed by Leenen et al. (
De Godoy et al. (
Geleijnse et al. (
The different types and forms in which rooibos herbal tea are available and the ways in which rooibos herbal tea is prepared and flavoured for consumption will influence the total polyphenol content and the TAC of this beverage. Preparation methods of rooibos herbal tea are done according to the specific taste of the consumer. The optimal cup of rooibos herbal tea delivering the highest total polyphenol content and TAC might not necessarily be the most common way consumers drink this beverage.
The goal of this study was to denote an optimal cup of rooibos herbal tea as having the highest total polyphenol content and TAC, taking into consideration the different rooibos types, forms, preparation methods and the type and amounts of different added household flavourings.
This study further aimed to determine the demographic, lifestyle and rooibos consumption and preparation characteristics of adult rooibos herbal tea consumers in the George area in the Western Cape, SA, and the association of these consumer characteristics with drinking the optimal cup of rooibos.
The methodology consisted of two phases: Phase 1 dealt with the selection and preparation of rooibos herbal tea samples. These samples included different rooibos herbal tea types, forms, steeping times and household flavourings and their added amounts for the analysis of the total polyphenol content and the TAC. This provided the composition information for a database to screen the rooibos herbal tea samples for identification of those with the highest polyphenol content and TAC. This was carried out to denote the ‘optimal’ cup of rooibos.
Phase 2 obtained information on how consumers drink their rooibos herbal tea (bearing in mind the identified rooibos beverage with the highest total polyphenol content and TAC in Phase 1), as well as identifying the demographic and lifestyle information of rooibos herbal tea consumers, and in particular those who consume rooibos as a prepared beverage providing the highest total polyphenol content and TAC.
A total of 640 samples were prepared from the different sample brands (two to three brands per rooibos type and form) bought from two different large retail chain supermarkets that offered a wide product range, providing for duplicate samples and prepared to represent each of the various factors investigated. A retail chain supermarket located in the central and in the northern regional sectors of the city of Cape Town was used for this purpose.
A batch for each brand of traditional (fermented) rooibos from each supermarket was made up. Seven teabags from each brand were steeped in 1.26 L of boiling water (to represent one teabag per 180 mL, as the tea volume in a cup) (Langenhoven et al.
For all the samples, except for the analysis of the form and type of rooibos herbal tea, traditional fermented rooibos herbal teabags were used, as this form is the most widely available in supermarkets and thus represents the most commonly available rooibos herbal tea form to the rooibos herbal tea consumer. Prepared samples were stored in a test tube at 4°C for analysis and coded for identification purposes.
The different brands of traditional (fermented) (
Samples were also prepared from traditional fermented (
Only one brand of rooibos herbal tea powder could be prepared (done in triplicate) as this form of tea is not yet readily available on supermarket shelves. A small amount of powder (50 mg) was dissolved in 25 mL of boiling water according to the manufacturer’s preparation instructions. The sample was stirred for 30 s and left for 3 min before the sampling took place.
Tea samples (
The different amounts of household flavourings added were predetermined and are presented in
Types and amounts and their amount representations of the household flavouring additions.
Household flavouring |
Amount addition | Reference | ||
---|---|---|---|---|
Small | Medium | Large | ||
Langenhoven et al. |
||||
Skim | 10 mL | 20 mL | 30 mL | |
Low fat | 10 mL | 20 mL | 30 mL | |
Whole | 10 mL | 20 mL | 30 mL | |
Langenhoven et al. |
||||
White | 4 g | 6 g | 10 g | |
Brown | 4 g | 6 g | 10 g | |
5 g | 9 g | 15 g | Langenhoven et al. |
, the different household flavourings in the different amounts were added to 180 mL (a cup) of rooibos herbal tea.
, for logistical reasons, long life milk cartons were purchased. One batch of milk, sugar and honey were used to eliminate any interference through nuisance variables.
Each 100 microlitre (µL) sample was diluted with 900 µL of distilled water before the assays were performed. Each assay was done in triplicate for precision. All the sample values for a specific factor across the different brand and supermarket purchases were used to calculate an average for that factor. The Trolox equivalent antioxidant capacity (TEAC) (Re et al.
The SPSS (IBM, Armonk, NY) 22 Statistics Data Editor program was used. One-way analysis of variance (ANOVA) was performed to test for differences between the rooibos herbal tea samples. The dependent variables were the total polyphenol content and the TAC, while the different rooibos types, forms and preparation methods and the added household flavouring types and amounts were the independent variables. Levene’s test for equality of variances and the Student–Newman–Keuls test were applied. Levene’s test for equality of variances as inferential statistic was used to assess the equality of variances for a variable calculated for two or more groups, and the Student–Newman–Keuls Test was conducted as a post hoc test if a positive ANOVA result (
Section A of the questionnaire included multiple-choice questions related to the respondents’ beverage, tea and herbal tea consumption. To determine whether a respondent consumed an optimal cup of rooibos herbal tea, the time of infusion was considered. If the respondent chose a steeping time of 10 min or longer it was considered to be an optimal cup of rooibos herbal tea. This was based on the findings of Phase 1.
Section B of the questionnaire consisted of questions related to respondents’ demographics, lifestyle and health, also presented in multiple-choice format. The age category listing started at 25 years of age because of the finding that tea consumers are mostly older persons (Song & Chun
The compiled questionnaire was prescreened for content-related evidence of validity by food and food science (
A convenient and purposive sample of adult respondents aged 25 years and older who consume rooibos herbal tea and reside in the George area, Western Cape, SA, was recruited through the use of 12 trained recruiters. The distribution of the population by age for the George Municipality from the
A minimum sample size of 267 individuals was calculated, but considering the possibility of non-response bias across the age stratus representing the quota sample, the age strata was multiplied by 1.5 to make sure that the required sample size within each stratus was obtained, but having the same ratio representation as the age strata of the population. A total of 344 respondents who met the inclusion criteria were invited to participate, of whom 36 declined, resulting in a response rate of 89.5%. The sample consequently comprised 308 respondents.
Frequencies of the questionnaire responses and associations (Pearson’s chi-squared statistic) between the respondents’ consumption of the optimal cup of rooibos herbal tea or not and the respondent profile responses at a significance level of 5% (
Ethical approval for Phase 2 of the study was granted by the Cape Peninsula University of Technology (Ref. 12/2013). All the respondents who participated voluntarily in the study were required to sign the consent form. A participant code was allocated to each respondent to facilitate anonymous participation.
The rooibos preparation method across the biochemical parameter analysis providing the highest total polyphenol content and TAC is presented in
Rooibos preparation methods providing the highest total polyphenol content and total antioxidant capacity.
Rooibos preparation method | Biochemical content |
Comment | ||
---|---|---|---|---|
Total polyphenols |
FRAP |
TEAC |
||
Green, unfermented (1) | 457.7 ± 40.9 |
3219 ± 82 |
- | Limited consumer availability |
Traditional, fermented (2) | - | - | 1140 ± 143 |
- |
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 |
30 min (5) | 543.2 ± 125.7 |
3107 ± 731 |
1212 ± 270 |
- |
Honey (6) | 413.0 ± 72.7 |
2489 ± 437 |
1868 ± 172 |
Health implications of use of a large amount of honey (fructose) questionable |
Whole milk | 519.1 ± 82.7 |
2100 ± 453 |
- | High polyphenol content probably because of interference with the absorbance of the assay by some of the milk constituents |
Skim milk | - | - | 3025 ± 325 |
- |
30 mL whole milk and 15 g honey | 545.1 ± 65.7 |
- | - | 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 |
- | 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 |
- |
(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.
, 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 (
, overall significant (
Because of limited availability and cost implications to the consumer, the rooibos type, as green unfermented rooibos, and the rooibos form, as powdered rooibos extract (traditional fermented) and iced tea (with rooibos extract – traditional fermented), were not considered to conclude an optimal cup. The sample with the addition of honey in a large amount was also not considered because of the possible health implications of the addition of the large amount of fructose contained in honey. Though there is reason to believe that moderate fructose ingestion could be beneficial for health, an excess intake would be a risk (Livesey
Permitting for the household preparation of rooibos and taking cognisance of the consumer availability and cost implications of the rooibos type and form, the traditional fermented rooibos in bag form steeped for 30 min was considered as the preparation method that provided for the highest total polyphenol content and TAC. Sharpe et al. (
The sample had a high representation of female (68.2%) and white (70.1%) respondents. The sample furthermore had a near equal representation of respondents aged 25 to 39 years (young adults) (47.4%) and those aged 40 years and older (52.6%) (see
Respondent profile and rooibos herbal tea drinking behaviour.
Variable | Characteristics | Total respondent sample ( |
Respondents consuming optimal cup of rooibos herbal tea |
Significance ( |
||||
---|---|---|---|---|---|---|---|---|
Frequency ( |
Percentage (%) | Yes ( |
No ( |
|||||
Frequency ( |
Percentage (%) | Frequency ( |
Percentage (%) | |||||
Gender | Males | 98 | 31.8 | 17 | 34.7 | 81 | 31.3 | 0.620 |
Females | 210 | 68.2 | 32 | 65.3 | 178 | 68.7 | ||
Age group |
Young adults | 146 | 47.4 | 24 | 49.0 | 122 | 47.1 | 0.735 |
Middle aged adults | 126 | 40.9 | 18 | 36.7 | 108 | 41.7 | ||
Older adults | 36 | 11.7 | 7 | 14.3 | 29 | 11.2 | ||
Population group | Black/Indian or Coloured |
92 | 29.9 | 15 | 30.6 | 77 | 29.7 | 0.901 |
White | 216 | 70.1 | 34 | 69.4 | 182 | 70.3 | ||
Perceived food and beverage intake | Consumed foods/beverages popular with and consumed by most adults of same age | 192 | 62.3 | 34 | 69.4 | 158 | 61.0 | 0.334§ |
Consumed foods/beverages considered healthier choices | 116 | 37.7 | 15 | 30.6 | 101 | 39.0 | ||
Physically active | Yes |
158 | 51.3 | 23 | 46.9 | 135 | 52.1 | 0.535§ |
No | 150 | 48.7 | 26 | 53.1 | 124 | 47.9 | ||
Dietary supplement |
Never | 108 | 35.1 | 19 | 38.8 | 89 | 34.3 | 0.388 |
Seldom | 108 | 35.1 | 13 | 26.5 | 95 | 36.7 | ||
Irregular (when remembered, fairly regularly), regularly |
92 | 29.9 | 17 | 34.7 | 75 | 29.0 | ||
Smoking status |
Non-smoker | 226 | 73.4 | 35 | 71.4 | 191 | 73.7 | 0.727§ |
Current smoker/former smoker |
82 | 26.6 | 14 | 28.6 | 68 | 26.3 | ||
Perceived body weight status | Underweight/optimal/normal body weight |
185 | 60.1 | 28 | 57.1 | 157 | 60.6 | 0.649 |
Slightly overweight/overweight/obese |
123 | 39.9 | 21 | 42.9 | 102 | 39.4 | ||
Consumption frequency | Seldom (almost never, 1–3 cups per month) |
96 | 31.2 | 16 | 32.7 | 80 | 30.9 | 0.968 |
Weekly (1–6 cups per week) |
97 | 31.5 | 16 | 32.7 | 81 | 31.3 | ||
One cup per day | 37 | 12.0 | 6 | 12.2 | 31 | 12.0 | ||
More than one cup per day |
78 | 25.3 | 11 | 22.4 | 67 | 25.9 | ||
Form usually | Tea bags | 286 | 92.9 | 45 | 91.8 | 241 | 93.0 | 0.762 |
consumed | Loose tea leaves/iced tea (ready-to-drink, powder form) |
22 | 7.1 | 4 | 8.2 | 18 | 6.9 | |
Usual preparation method |
Tea bag steeped in cup or mug | 271 | 88.0 | 35 | 74.5 | 236 | 91.1 | 0.001 |
Tea bags steeped in teapot | 35 | 11.4 | 12 | 25.5 | 23 | 8.9 | ||
Temperature at which usually consumed | Hot/near boiling | 107 | 34.7 | 19 | 38.8 | 88 | 34.0 | 0.485 |
Warm/still heated | 184 | 59.7 | 26 | 53.1 | 158 | 61.0 | ||
Cooled/near cold | 17 | 5.5 | 4 | 8.2 | 13 | 5.0 | ||
Flavouring usually added | Do not add flavouring(s) / lemon juice only |
52 | 16.9 | 13 | 26.5 | 39 | 15.1 | 0.228 |
Sweetening agent only | 59 | 19.2 | 9 | 18.4 | 50 | 19.3 | ||
Milk only | 13 | 4.2 | 1 | 2.0 | 12 | 4.6 | ||
Sweetening agent and milk | 184 | 59.7 | 26 | 53.1 | 158 | 61.0 |
, usually consumed rooibos strength (represented by steeping time) used as criteria to group the respondents into those consuming an optimal cup of rooibos (
, Pearson’s chi-square.
, Fisher’s exact test (done for 2 × 2 tables).
, young adults as the age group 25 to 39 years; middle aged adults as the age group 40 to 64 years; and older adults as the age group 65 years and older (Hamarat et al.
, response options grouped together because of low cell counts.
, regular moderate exercise (e.g. walking or cycling) or strenuous exercise (jogging, football and vigorous swimming) for 4 h or more per week (Yusuf et al.
, a vitamin, mineral, herbal, plant extract, amino acid, metabolite, constitute or extract or a combination of any of these substances (Marriot,
, non-smoker have never smoked; current smoker smoked in the last 12 months or quit in the past year and former smoker quit smoking more than a year ago (Yusuf et al.
, tea leaves as response option omitted because of low respondent usage (
Most (62.3%) of the respondents indicated that they consumed food and beverages popular with and consumed by most adults of the same age and not food and beverages considered healthier choices, were non-smokers (73.4%), had a perceived optimal or normal body weight or considered themselves underweight (60.1% as 56.8% and 3.2%, respectively) and did not use or seldom used dietary supplements (35.1%, respectively), while slightly more respondents indicated they were physically active (51.3%) rather than not (see
Slightly less than a third of the respondents indicated that they consumed rooibos seldom or weekly (31.2% and 31.5%, respectively), while only a quarter (25.3%) of the respondents indicated a consumption frequency of more than one cup per day (see
Furthermore, two to three cups of tea or herbal tea per day were indicated by almost a third (32.1%) of the respondent sample as their daily consumption frequency of tea and herbal tea, while a very small number of the respondents indicated a consumption frequency of four to six cups and more than six cups per day (17% and 6%, respectively). This was a further disappointing finding. Popkin et al. (
The majority of the respondents usually used rooibos in the form of teabags (92.9%). Although the majority (88%) of the respondents indicated that they steeped their teabag in a cup or mug, and only 11.4% of the respondents indicated that they usually prepared their teabags steeped in a teapot; this delivered a significant (
More than half (59.7%) of the respondents indicated that they consumed rooibos warm or still heated, while about a third (34.7%) indicated that they consumed it hot or near boiling. A sweetening agent together with milk was indicated by more than half (59.7%) of the respondents as their additions to rooibos, while only a fifth (19.2%) of the respondents indicated that they only added a sweetening agent and only 13 respondents (4.2%) that they only added milk (see
The interference of the non-phenolic components present in milk in the assays resulted in a false total polyphenol content, hence not providing an accurate value for the samples with milk added as flavouring. The market unavailability of some of the types and forms of rooibos does not make the biochemical parameter findings related to these samples of pertinent value to the consumer. As the respondent selection for the quota sample was non-random, sample bias is an almost certain limitation of Phase 2 of the study. The sample would also have been more representative if more individuals from the non-white population groups completed the questionnaire. The few research studies completed that have a likeness to that of Phase 1 (Catterall et al.
By addressing the daily amount of rooibos consumed and applying a longer steeping time, the consumption of rooibos herbal tea can make a valuable contribution to the daily dietary TAC. Van Graan et al. (
The different rooibos types, forms and preparation methods in particular had an influence on the total polyphenol content and TAC of rooibos consumed as a beverage. The rooibos sample steeped for 10 min or longer was identified as the optimal cup of rooibos. A mere 15.9% of respondents consumed an optimal cup of rooibos. There was no significant difference between the respondents consuming an optimal cup of rooibos and those who did not, where their demographic and lifestyle characteristics were concerned. The only significant difference found was related to the preparation method of rooibos. Although the respondents generally steeped their teabag in a cup or mug, more of those respondents who steeped it in a teapot consumed the optimal cup considering the steeping time of 10 min and longer. This finding should be considered in relation to the finding that these respondents as rooibos consumers also did not consume it in an amount (as a minimum of 4 to 6 cups per day) that would fully provide for obtaining its health benefits, while a very small number of the respondents indicated a consumption frequency of four to six cups and more than six cups of tea or herbal tea per day. Rooibos herbal tea was hence not consumed enough by the respondents, as only a few indicated that they consumed four or more cups per day. Concerning the demographic and lifestyle characteristics of these rooibos herbal tea consumers, it can be concluded that they can generally be assumed to be healthy and practising healthy lifestyle behaviours.
The authors hereby thank the University Research Funding (RH67) from the Cape Peninsula University of Technology for the financial input for Phase 1 of the study. They also thank the respondents and recruiters for partaking in the study. Prof. Dirk van Schalkwyk and Dr Corrie Uys (Cape Peninsula University of Technology) are acknowledged for the statistical analysis undertaken for Phase 2 of the study.
The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this manuscript.
This article is based on research conducted by H.P. under the supervision of I.V. and co-supervision of J.L.M., while F.R. assisted with the laboratory analysis and statistical analysis of Phase 1.