Nowadays, milk and milk products are highlighted because of their nutritional value and protein amount, and among these dairy products, cheeses are taking up space in the Brazilian market. Therefore, the production, commercialization, and internationalization of Artisanal Minas Cheese grow more and more. However, there are still few studies dedicated to this type of food. Thus, the present study aimed to use a method of preparing the cheese sample using dissolution in alkaline medium in order to determine Cu, Mn, Fe, Zn, Mg, and Ca, as well as evaluating the matrix effect in the analyzes by Flame Atomic Absorption Spectrometry (F AAS).
The method of preparing the cheese samples was the solubilization in alkaline medium using tetramethylammonium hydroxide (TMAH), which was previously optimized using a 2^4 experimental design. The fresh cheese samples were weighed (~ 1 g) directly into a 50 mL centrifuge tube. Then, 9.5 mL of triton x-100 solution in deionized water (~ 5% v/v) and 0.5 mL of TMAH 25% (w/v) were added. Subsequently, the tubes were taken to an ultrasound bath for 30 min at 50 ºC, aiming at the solubilization of the matrix and extraction of the metallic elements. Finally, the samples were diluted and taken for analysis in flame atomic absorption spectrometry.
For the analysis, the external calibration (dilution of the standards in water) and matrix-matched calibration curves were evaluated. The solutions obtained in the sample preparation were mixed to obtain a pool, which was used to prepare the matrix-matched curves at the appropriate dilutions for each element, 2x (Cu, Mn), 4x (Fe, and Zn), 20x (Mg), and 100x (Ca). The dilutions were chosen according to the concentration of the analytes in the samples and in the certified reference material (NIST 1846). To evaluate the possible matrix effect, the slopes of the external and matrix-matched curves were compared. The results showed that for Cu, Fe, and Zn there is a significant matrix effect because the slopes are more than 10% different among the curves. However, it is possible to determine these elements if the matrix-matched calibration curve is used. Finally, for the other elements (Mn, Mg, and Ca), the variation was lower than 10%, then it is possible to use an external calibration curve to analyze the cheese samples.