Aluminium contamination of several types of tea

Abstract

Introduction: Camellia sinensis, a widely used plant, optimally grows in a low pH soil that in most cases contains high amounts of aluminum. Objectives: The aluminum content of the tea obtained from Camellia sinensis and other plants was compared. The influence of pH on the aluminum content of the tea was also measured. Materials and methods: The aluminum content of 48 samples was measured using a colorimetric method. The method is based on the ability of aluminum to form a stable complex with xylenol orange at low pH; this complex has an absorption maximum of 555 nm. Results: The method was validated for tea obtained with water and for tea obtained with water containing citric acid. The method proved linear over the rage of 0.7 – 7 ug/ml, coefficient of variation ranged between 2.6 – 7.68% (was dependent on the pH of the solution used to obtain the tea), accuracy was suitable for quantitative measurement (92.39-102.92%) and the complex proved to be stable for at least 1 hour. The following concentrations were measured: green tea (1.59 - 7.70 µg/ml), black tea (1.39 - 5.60 µg/ml), fruit tea (1.01 - 5.63 µg/ml) and herbal tea (1.03 - 5.24 µg/ml). Conclusion: The method proved useful and easily applicable for screening aluminum content of plants used for tea brewing. Camellia sinensis both green and black types had significantly higher aluminum contents than other type of teas. Adding citric acid, as would result from use of lemon juice, significantly increased the aluminum extraction from the plants used for tea brewing.