Z Lebensm Unters Forsch A (1997) 205: 170—173 ( Springer-Verlag 1997

ORIGINAL PAPER

Mario Muller · Manfred Anke ·Heike Illing-Gunther

Availability of aluminium from tea and coffee

Received: 9 January 1997

Abstract The amount of aluminium in different kinds oftea and ground coffee was analysed, the transfer of alumi-nium into the infusion was determined and aluminiumintake via tea and coffee was calculated within the frame-work of our investigations. Aluminium concentrationsamounted to (in lg/g dry matter): black tea, 899; flavouredblack tea, 763; peppermint tea, 477; mountain herbal tea,419; fruit tea, 292; ground coffee, 19. About 30% of thealuminium stored in black tea’s dry matter was transfer-red into the infusion, which contained 4.2 mg Al/l. Incontrast, the availability of aluminium from peppermintand fruit tea as well as from ground coffee was very low(about 5%). The calculated aluminium intake via tea andcoffee was 0.2 to 0.3 mg/day and contributed about 5% tothe total aluminium intake. Only black tea infusions area significant source of aluminium intake via beverages.

Key words Aluminium · Tea · Coffee · Aluminium intake

Introduction

Aluminium is the most abundant metal of the earth’scrust. Occurring only in compounds (bauxite, complexaluminosilicates, etc.) its concentration amounts toabout 80 g/kg earth’s crust. Toxic effects of aluminiumhave been known to occur in dialysis patients as well asin those on total parenteral nutrition for many years.Pathogenesis and symptoms have been described indetail elsewhere [1—6].

Recently, there has been increasing concern that alu-minium is a contaminant of the food chain, playinga role in the aetiology of neurodegenerative diseases

M. Muller · M. Anke ( ) · H. Illing-GuntherFriedrich Schiller University, Biological-Pharmaceutical Faculty,Institute of Nutrition and Environment, Unit of Foodstuffand Environment Toxicology, Dornburger Strasse 24,D-07743 Jena, Germany

such as morbus Alzheimer and amyotrophic lateralsclerosis [7—15].

Along with several spices, black tea leaves have oneof the highest concentrations of aluminium, when itscontent is related to that of dry matter (DM). Mat-sumoto et al. [16] measured a concentration of about20,000 lg Al/g DM in older tea leaves; thus, tea infu-sions may contribute significantly to aluminium intakeby humans. As a result, the amount of aluminium inblack tea leaves and also the transfer rate of aluminiuminto black tea infusions have been investigated inten-sively over the last few years [17—24]. However, thesedata are highly variable.

Our investigations aimed at determining the alumi-nium content in different kinds of tea and ground coffeeas well as the transfer rate of aluminium from the rawmaterial into the infusion. Additionally, the contribu-tion that tea and coffee make to the total aluminiumintake of adults in Germany was calculated.

Materials and methods

The aluminium content in the dry matter of different kinds andblends of tea and ground coffee was determined (Table 1).

Samples of raw tea and ground coffee were dried to a constantweight at 105 °C, dry-ashed in a muffle furnace at 450 °C anddissolved in diluted hydrochloric acid. Infusions of fruit tea (n"6),peppermint tea (n"6) and black tea (n"12) were prepared: freshlyboiled water (100 ml) was poured into a tea cup containing one teabag and infused for 5 min. Coffee was prepared with a coffee-makerusing about 7 g coffee/100 ml infusion. Aliquots of tea and coffeeinfusions were directly analysed without special preparation.

Aluminium determination was carried out by graphite furnaceatomic absorption spectroscopy with the device combination AAS3030, HGA 400, AS 40 (Perkin Elmer) and a magnesium nitratematrix modifier (Merck). Reference material IAEA H-9 (mixed hu-man diet) was used for checking the method. There was goodagreement between reference results (16.56 lg Al/g) and our ownanalysis (17.37 lg Al/g). The relative and the absolute detectionlimits of the method are 1.3 lg/l and 26pg (pipette volume 20ll),respectively. The analytical procedure has been described in detailelsewhere [25].

Table 1 Analysis materialKind of tea/coffee Blend n

Fruit tea Cupule of rose-ship and mallow bloom mixedwith different flavouring agents

27

Mountain herbal tea Different mixtures of indigenous mountain herbs 15Peppermint tea 15Flavoured black tea Black tea of unknown provenance mixed with

different flavours (strawberry, cinnamon, rose-ship,apple, vanilla, plum, almond, etc.)

30

Black tea Provenance Ceylon, India, Kenya; various suppliers 36Ground coffee Mixture of different provenances 48

Table 3 Transfer of aluminiumfrom the raw material of tea orcoffee into the infusion

Tea/coffee Al concentration Al concentration Transfer (%)(lg Al/tea-bag)! (lg Al/100 ml)"

Peppermint tea 506 14 1.3Fruit tea 603 42 6.2Black tea 1543 419 27Coffee 105 7.7 2.8

! 7 g coffee/100 ml infusion" 4.8 lg Al/100 ml water

Combining the data of the quantity of aluminium in tea and coffeeinfusions with the intake data obtained with the framework of thesecond MONICA survey 1988 [26] and the Nutritional Survey1991/92 (C. Thiel, personal communication), the aluminium intakevia these beverages was calculated.

Results

The average aluminium content (on a DM basis) indifferent kinds of tea was within the range of 292 lg/g(fruit tea) to 899 lg/g (black tea leaves) (Table 2). Thedifferent blends of mountain herbal tea and pepperminttea contained about 450 lg Al/g DM. The aluminiumconcentration in flavoured black tea amounted to763 lg/g DM.

In contrast, the aluminium content in ground coffeewas low, with a mean value of 19 lg/g DM. Transferrates of aluminium from the raw material into theinfusion were very low in the cases of peppermint tea,fruit tea and ground coffee, i.e. 1.3%, 6.2% and 2.8%respectively (Table 3). When preparing infusions from

Table 2 Aluminium content in tea and coffee (lg Al/g DM)

Tea/coffee Al concentration

Fruit tea 292$157Mountain herbal tea 419$159Peppermint tea 477$52Flavoured black tea 763$195Black tea 899$292Ground coffee 19$10

black tea leaves, nearly 30% of its aluminium content istransferred into the infusion.

The calculated aluminium intake of the average con-sumer via tea and coffee infusions is shown in Table 4.The relative contribution of these beverages to the totalaluminium intake amounts to about 5%.

Discussion

According to literature data, the aluminium contentin black tea leaves amounts to 300—1800 lg/g DM[18, 23, 24, 27]. The 1000 lg/g level seems to be a typi-cal value and is similar to our result of about 900 lgAl/g DM. The amount of 20,000 lg Al/g DM, as meas-ured from older leaves of black tea by Matsumoto et al.[16], may represent an extreme value. The aluminiumconcentration in flavoured black tea was a little lowerbecause of the slight diluting effect of flavouring agents.Comparing with other foods, the dry matter of fruit,mountain herbal and peppermint teas contained highaluminium levels, too. At 19 lg Al/g DM, the alumi-nium concentration in ground coffee was astonishinglylow.

Despite the high aluminium content in all the kindsof tea investigated a marked increase of oral aluminiumintake via these kinds of beverages is only possiblein the case of black tea infusions. Literature data (re-lated to infusion basis) showed aluminium contentsof 0.6—4.5 mg Al/l [17—19, 22, 27—29], the majorityof these data being within the upper range. Compar-ing these facts with the results of Table 2 it can beconcluded that black tea infusions have a typical

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Table 4 Aluminium intake via tea and coffee infusions

Year Men Women

mg/day % ! mg/day % !

1988 0.25 3 0.18 31991 0.22 4 0.29 6

! Total intake"100%, intake via tea and coffee infusions"x%

aluminium concentration of 3.0—4.0 mg/l. Only Rao[21] reported lower aluminium concentrations in blacktea infusions (range 0.02—0.08 mg/l), which differed sig-nificantly from those mentioned above and from thevalues obtained in this study.

The aluminium content in coffee infusions was deter-mined to be about 0.08 mg/l, a value which differs fromthose described in the literature. Schenk et al. [22] aswell as Varo et al. [27] described an average aluminiumlevel in coffee infusions of about 0.50 mg/l.

Until now, literature data on the transfer rates ofaluminium from raw tea into the infusion have onlybeen available for black tea. However, these transferrates cover a range of 4% to 61% [18, 20, 23, 24]. Inour experiment nearly 30% of the aluminium storedin black tea leaves was transferred into the bever-age. Similar transfer rates of about one-third were ob-tained by Fairweather-Tait et al. [18] and Owuor et al.[20]. Thus, it seems that the average availability ofaluminium from black tea leaves is about 30%. Trans-fer rates of aluminium from fruit and peppermint teasas well as from ground coffee into the infusion werefound to be about 5%; thus, availability of aluminiumfrom these kinds of tea and coffee is considered to benegligible.

The normal aluminium content of other beveragesis usually (0.5 mg/l. Thus, black tea infusions rep-resent an important aluminium source in human nu-trition and extensive tea consumption will consider-ably increase the aluminium intake via beverages.The normal aluminium intake of adults in MiddleEurope amounts to about 5 mg/day [30]. Accordingto our investigations the daily consumption of 1 l ofblack tea would deliver an additional 4 mg Al/day.Therefore, individual habits of black tea consumptionhave a marked influence on the total aluminium in-take by adults. In contrast, the aluminium content inthe other kinds of tea and coffee infusions investigatedis comparable with those of beverages. These findingsare important and interesting from a clinical nutritionperspective.

Nevertheless, bioavailability of aluminium fromblack tea infusions is defined as low in the literature[31—33]. Drewitt et al. [31] concluded from investiga-tions with 12 healthy volunteers that, in the short-term,drinking tea does not contribute significantly to thetotal burden of aluminium. Studies on the bioavailabil-ity and metabolism of aluminium from foods must be

one important area of research in the future in order todiscover more about the pathways and distribution oforally ingested aluminium.

The average aluminium intake of German adults viatea and coffee infusions was about 0.18 to 0.29 mg/day.The relative contribution to the total intake amountedto 3—6%. The average aluminium consumption viathese beverages is higher in China (0.2—1.1 mg/day[23]), Finland (about 0.50 mg/day [27]) as well as inthe USA (0.4—0.7 mg/day [34]).

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