1Concentrations (mg/kg) of minerals in the dry tea leaves of eight traditional and herbal teas from different geographical regions. http://sajs.co.za/index.php/SAJS/article/downloadSuppFile/623/3080
2Concentrations (mg/kg) of minerals in residues of infusions of eight traditional and herbal teas from different geographical regions. http://sajs.co.za/index.php/SAJS/article/downloadSuppFile/623/3081
3Mean mineral content (mg/250 mL) of the residue of infusions of eight traditional and herbal teas from different geographical regions. selected minerals. http://sajs.co.za/index.php/SAJS/article/downloadSuppFile/623/3082
4Dietary reference intakes of men and women (1950 years old) for selected minerals. http://sajs.co.za/index.php/SAJS/article/downloadSuppFile/623/3083
Results and discussion Mineral composition Perusal of the mineral composition data presented in Tables 1 and 2 reveals that each tea contained the full set of eleven minerals. However, the amount of a specific mineral differed from one tea to another, displaying a unique mineral profile for each tea. It is also clear that the dry tea leaves and corresponding infusions exhibited different mineral profiles. According to our results presented in Table 1, five of the six major minerals (K, Ca, Mg, P and S) are the most abundantly occurring minerals in the dry tea leaves. The infusions exhibited the same general pattern except that relatively less Ca than Mg, P and S was present (Table 2). Three of the trace minerals – Zn, Cu and Fe – were the elements present in the lowest concentrations in both leaves and infusions. Comparison of the mineral profiles (Table 1) of the eight dry tea leaf samples reveals that Athrixia, black and coca teas had the highest total mineral content. Maté and coca teas had the largest variety of minerals in appreciable amounts, followed by black and green teas. The herbal teas, rooibos and especially honeybush, had significantly lower amounts of all minerals (except sodium in rooibos). The Camellia sinensis teas were the richest sources of K, Cu, S and Al, whilst maté tea leaves were exceptionally rich in Mg, Mn, Fe and Zn. The highest concentrations of Ca were in Athrixia and coca leaves. Coca tea leaves were also rich in P and Fe. These results are largely consistent with those obtained by Malik et al.19 for Ca, Mg, Fe, Mn and Zn. However, Malik et al. found considerably lower amounts of Al in black and green teas than were found in the present study. It should be noted that the results for Al obtained in this study agree with those of Jansen et al. 41who indicated that Camelia sinensis are Al accumulators and concentrations exceeding 1000 mg/kg have been found in their leaves. The variation in mineral profiles between the tea leaves may be as a result of a number of factors, the most likely being differences in the soil type, climate, 42altitude, cultivation procedures such as fertiliser application, and genetic differences between the different plant species. It is notable that rooibos and honeybush, both indigenous to the Cape and which grow in sandy soils, had similar mineral profiles. Rooibos, which grows only on the West Coast, was exceptionally rich in Na. Conversely, Athrixia, which grows in dolomitic areas, contained relatively large amounts of Ca and Mg. Comparison of the profiles of minerals in the infusions of all eight teas (Table 2) reveals that black teas provided the richest sources of all minerals; in terms of high concentrations of individual minerals, maté and coca teas were superior to all the other teas. Excluding Al, black tea from Sri Lanka (Ceylon) surpassed tea made from a blend of African teas as a source of minerals, and Athrixia was a richer source of minerals than the other South African herbal teas. These mineral profiles of the infusions are generally in agreement with previous research 19,43 indicating that the concentrations of a number of minerals in traditional black and green teas far exceeded those in South African herbal teas. A comparison of results with those by Malik et al. 19showed that our values were lower across the board, except for Al. These lower values could be expected because Malik et al. infused their tea leaves for 15 min, whilst our steeping time was only 6 min. Dietary value From a nutritional perspective, tea is regarded as fluid intake that generally does not contribute to mineral requirements. Tea, especially black and rooibos, is regularly consumed by South Africans as a beverage. 44In order to determine to what extent tea consumption might supply dietary minerals, the amount of available minerals for each cup of tea was calculated. These amounts were derived from Table 2 using a conversion factor of 1 mg/kg = 0.0025 mg/cup, assuming that 1 g tea leaves are used per 100 mL boiling water at household level, and that 1 cup holds 250 mL liquid (Table 3). The nutritional attributes of tea consumption can be assessed by comparing the values in Table 3 with the dietary reference intakes (DRIs) given in Table 4. It is evident that teas contain minute amounts of minerals, and therefore they do not make a significant contribution to meeting mineral requirements. The exception is maté tea which provides about 1.95 mg Mn per 250 mL (Table 3). This concentration is the required daily Mn intake for adult women (Table 4). Men would have to consume at least one and a half cups of maté tea per day to meet their DRI for Mn. The positive contribution that maté tea could make as a dietary source of Mn has also been noted by others. 19,45 Although green and black teas from Africa also contain considerable amounts of Mn, consumption of three to four cups would be required to meet the daily Mn requirement. Even though the K levels are higher than any of the other minerals in all of the teas, one cup of tea still provides less than 1% of the DRI for adults. In this study, none of the other infusions could be considered as rich sources of the major and trace minerals. The low concentrations of potentially harmful minerals in teas can be considered to be advantageous. Sodium is present in very low concentrations in all eight teas. Even rooibos, with the highest Na content, could not be considered to constitute a health risk. Concerns have also been expressed about the intake of Al in food, 46as well as in traditional teas. 45,46,47 The World Health Organization (WHO) 48limits the Al content in drinking water to 200 μg/L (i.e. 0.2 mg/L or 0.05 mg/cup 49) and, in 2007, the WHO 48established a provisional tolerable weekly intake for food of 1 mg Al/kg body mass. The Al concentrations of 1.25 mg/cup of black tea and 0.9 mg/cup of green tea should be taken note of by people with low body mass who consume numerous cups of tea per day. The excessive consumption of black and green tea by young children should be discouraged. ConclusionWe have reported on the mineral content of three traditional black and green teas and five herbal teas from different geographical regions. Traditional teas all derive from the plant Camellia sinensis, whilst the herbal teas included maté and coca teas from South America, and rooibos, honeybush and Athrixia tea from South Africa. All eight teas are consumed in relatively high quantities and are believed to have health-promoting properties. Chemical analyses were conducted to determine the concentration of eleven minerals: Ca, Mg, K, Na, P, S, Mn, Zn, Fe, Cu and Al, in dry tea leaves as well as in tea infusions, using ICP-OES. Although the recommended infusion times vary between 30 s to 10 min or more for different infusions and, traditionally, some of these teas are boiled, a standard infusion time of 6 min was used in this study for two reasons. Firstly, to ensure standardisation of results and, secondly, to determine mineral intake levels of the common consumer who rarely has time to boil the infusions or infuse ‘teas’ for more than a few minutes before consumption. It should, however, be noted that differences in infusion time may well affect the bioavailability of minerals. We found that all teas contained the full complement of eleven minerals, but in minute quantities when compared to the daily mineral requirement. The exception was the concentration of Mn in maté tea – one to one-and-a-half cups of maté tea per day could supply the recommended intake of Mn. Our study thus confirms previous findings 21indicating that, in general, teas cannot be considered as a major source of dietary nutrients. Nevertheless, even the small amounts of minerals present in teas would supplement those nutrients consumed in food. Paradoxically, the low concentrations of some minerals may be advantageous. Al is present in very low concentrations in the speciality teas but its higher content in black and green teas should be noted. A comparison of the mineral content of the eight teas revealed that maté and coca teas were superior to the others. Although Camellia sinensis teas have higher values of K, Cu and S than the other teas, their relatively high Al content detracts from their postulated health effects. Rooibos and honeybush have considerably lower concentrations of most minerals when compared to the other teas. Of the three South African indigenous herbal teas, Athrixia is the most mineral rich. In terms of their mineral profiles, the consumption of herbal teas such as maté, coca, rooibos, honeybush and Athrixia teas are a good choice for health-conscious consumers. Acknowledgements We thank the University of South Africa and the National Research Foundation of South Africa for financial support (GUN: 2048685); Lynne Meyer and Leslie Adriaanse for editorial assistance; Jackie Viljoen and Unisa Language Services for editing the manuscript and Christel Troskie-de Bruin for critical reading. 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