Bioaccessibility of Copper in Turkish Hazelnuts (Corylus avellana L.) by Chemical Fractionation and In Vitro Methods

Copper is known as either an essential or toxic trace element in foods to living organisms at sufficient or excess intake levels, respectively. In this study, in vitro simulated gastric and intestinal digestion methods combined with n-octanol extraction and activated carbon adsorption were applied to Turkish hazelnuts (Corylus avellana L.) to evaluate the bioaccessibility of copper. Additionally, analytical fractionation procedures based on water, diethyl ether, n-hexane, and methanol extractions were applied to identify copper-related matrix structures. The macrochemical compositions of the samples were determined to be associated with the fractionation results. The total contents of copper in the samples, digests, and fractions were determined by inductively coupled plasma mass spectrometry after microwave-assisted digestion, and additional validation was performed using atomic absorption spectroscopy. The limits of detection and quantification were 0.016 and 0.053 mg kg(-1), respectively. The bioaccessibility of copper was found to be in the range from 16 to 31 % for hazelnut samples. The recommended dietary allowance of copper for adults is 0.9 mg daily, and considering this value, 100 g of hazelnuts supplies 33-44 % of daily copper intake.