Aluminium in tea: SEC-ICP-MS speciation studies of infusions and simulated gastrointestinal digests

Abstract

The speciation of aluminium in tea infusions and in vitro gastrointestinal digests of tea infusions has been investigated using size exclusion chromatography coupled to inductively coupled plasma mass spectrometry (SEC-ICP-MS). At pH 2.5, following simulated gastric treatment, AI from tea eluted at a similar retention volume to that obtained for an aqueous AI standard. At pH 5.5, an aqueous AI standard was eluted from an SEC column in Tris buffer (AI recovery "" 1 00%) only in the presence of a complexing agent (NaF), and at a retention volume corresponding to a molecular mass greater than that expected for an ionic species. Aluminium associated with a tea infusion eluted in two fractions: a higher molecular weight fraction corresponding to AI strongly bound to ligands in the tea, and a lower molecular weight fraction probably comprised of labile AI eluting as AI-F complexes. Simulated gastrointestinal digestion produced three Al-bearing fractions, of which the two at higher molecular mass represented ligand-bound AI. The molarity of the Tris buffer strongly influenced the retention volume of the AI fractions, particularly for the ligand-bound AI. After simulated gastrointestinal digestion, the soluble labile fraction (15% of the AI from the tea infusion) was considered to be potentially available for absorption. The actual proportion of the fraction that might be absorbed would depend upon a number of physiological and nutritional factors.

Bioavailability of Al in alum‐treated drinking water

“…If zero bioavailability of Al from tea is assumed, then the bioavailability of Al from food alone is 0.64 percent. However, Al in tea has been shown to be largely bound in high relative molecular mass complexes 28 . In this research only 15 percent of Al in tea was chemically labile, so if it is assumed that only 15 percent of Al in tea is potentially available for uptake, then Al bioavailability from food is 0.53 percent.…”

“…Ruoff 29 found that the bioavailabilities of manganese, nickel, and cadmium in water were similar to their bioavailabilities in food. Furthermore, the bioavailabilities of manganese, zinc, copper, or Fe from food were the same whether the metals were naturally present in the food or were added separately as a tracer 28 …”

Selective Determination of Aluminum Bound with Tannin in Tea Infusion

“…Other speciation methods are based on kinetic discrimination of the species, using fluorometric or spectrometric reagents. [8][9][10] A few studies have been carried out for the speciation of Al in tea infusions. [10][11][12] Al species in tea infusion could be categorized into three groups: large organic compounds, small stable organic compounds and free ionic form of Al.…”

“…6 Studies on Al species under stomach conditions before and after gastrointestinal digestion were published. 10 Ultrafiltration studies showed that as much as 86% of the 0.45 µm filterable Al in tea infusions was retained by a 20000 Da molecular-mass cut-off filter and 96% was retained by 10000 and 500 Da molecular-mass cut-off filters. 22 This indicates that the large part of Al in tea infusions exists as large organic complexes.…”

“…Most studies on polyphenol-Al complexes were carried out using such model solutions. 1,3 Owen et al 10 used size exclusion chromatography coupled with ICP-MS to study the behaviors of Al in tea infusion before and after simulated gastrointestinal digestion and indicated that about 14% of the Al existed as stable species.…”