Abstract
Complex formation is among the mechanisms affecting metal bioaccessibility. Hence, the quantification of organic metal complexation in food items is of interest. Organic ligands in solutions of environmental and/or food origin function as buffering agents against small changes in dissolved metal concentrations, being able to maintain free metal ion concentrations below the toxicity threshold. Organic matter in vinegars consists of bioactive compounds, such as polyphenols, Maillard reaction endproducts, etc., capable of complexing metal ions. Furthermore, transition metal ions are considered as micronutrients essential for living organisms exerting a crucial role in metabolic processes. In this study, differential pulse anodic stripping voltammetry (DPASV), a sensitive electrochemical technique considered to be a powerful tool for the study of metal speciation, was applied for the first time in vinegar samples. The concentrations of Cu complexing ligands (LT) in 43 vinegars retailed in Greece varied between 0.05 and 52 μM, with the highest median concentration determined in balsamic vinegars (14 μM), compared to that of common vinegars (0.86 μM). In 21% of the vinegar samples examined, LT values were exceeded by the corresponding total Cu concentrations, indicating the presence of free Cu ion and/or bound within labile inorganic/organic complexes. Red grape balsamic vinegars exhibited the highest density of Cu ligands per mass unit of organic matter compared to other foodstuffs such as herbal infusions, coffee brews, and beers. Among the 16 metals determined in vinegars, Pb is of particular importance from a toxicological point of view, whereas further investigation is required regarding potential Rb biomagnification.
Highlights
Vinegars are one of the few acidic condiments used as a flavoring agent, preservative and, in some countries, a healthy drink [1,2]
The fraction of metals which can be retained by the human body through vinegar consumption is related to the levels of metals in the harvest as well as metal impurities due to manufacturing processes [6] in addition to the bioavailability of metal species present in vinegar [7]
It is noteworthy that none of the common vinegars analyzed had an Organic carbon (OC) that exceeded 50 mg L−1, whereas in the balsamic vinegars, the lowest measured concentration was equal to 90 mg L−1 (Table 1)
Summary
Vinegars are one of the few acidic condiments used as a flavoring agent, preservative and, in some countries, a healthy drink [1,2]. The acidity of wine vinegar (acetification obtained exclusively from wine) must be at least 6% w/v [5]. Due to hydrogen atom transfer and single-electron transfer, phenolic antioxidants protect against free radical formation by binding and/or inactivating metal ions [8,9,10]. Such a mechanism of antioxidant action is quite significant, despite the fact that the contribution of free radical scavenging or metal chelation to the overall antioxidant activity is still not fully specified [11]
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