Mineral infusion and in-vitro bioaccessibility in Camellia sinensis and herbal tea: influence of matrix and brewing format

Abstract

This study provides a comprehensive evaluation of mineral composition, time-dependent mineral infusion (5, 10, and 15 min), and in-vitro bioaccessibility across six widely consumed teas, including four Camellia sinensis varieties (black, green, white, and Ceylon) and two herbal teas (rosehip and fennel). Elemental concentrations were quantified using inductively coupled plasma optical emission spectrometry (ICP-OES). An in-vitro gastrointestinal digestion model was employed to determine mineral bioaccessibility, while FT-IR spectral characterization was used to interpret the matrix-related chemical structures influencing solubility and mineral stability. The results indicated that potassium was the most efficiently released element (>50%), followed by magnesium and sodium, whereas calcium and iron exhibited limited dialyzability (<30%), reflecting differences in complexation behavior. Rosehip tea exhibited notably higher bioaccessibility of iron (~36%) and zinc (~81%), likely due to its acidic pH and high organic acid content, while Camellia teas displayed lower values, possibly resulting from polyphenol–mineral interactions and the presence of complexing tannins. In contrast, Mg bioaccessibility peaked in green tea (~62%), highlighting element - specific matrix effects. Fennel infusion showed intermediate levels of mineral bioaccessibility, suggesting matrix-dependent variability among herbal teas rather than compositional uniformity. Statistical evaluation demonstrated that both brewing time and tea format significantly affected mineral release, with loose-leaf teas consistently yielding higher extractable levels of Cu, Fe, Mg, and Zn than bagged forms. Increasing the infusion duration enhanced solubilization for most elements, although excessive steeping sometimes reduced apparent bioaccessibility, suggesting secondary precipitation or complex formation. A single serving of tea provides measurable bioaccessible amounts of minerals; moreover, the observed differences among tea types and formats indicate that physicochemical characteristics, infusion conditions, and matrix-related factors influence mineral release and post-digestion bioaccessibility under the standardized brewing conditions applied in this study. These findings provide mechanistic insight into how tea matrices act as natural nutrient-stabilizing environments and highlight the importance of processing and preparation variables in modulating mineral bioaccessibility.