Evaluation of the mineral content in milk and yogurt types using chemometric tools

Abstract

In this work, the concentration of Ca, K, Mg, Na, and Zn in milk samples (powder and liquid), milk compound and yogurt were determined, employing inductively coupled plasma optical emission spectrometry (ICP OES). Sample treatment was carried out in a microwave-assisted digester using the proportion of dilute HNO3 and H2O2 established through a two-level factorial design. Accuracy and precision of the method were confirmed through analysis of certified reference materials of Non-fat milk powder (NIST 1549) and Whole egg powder (NIST 8415). The agreement between found and certified values varied between 85 ± 10% for K and 116 ± 3% for Ca. Precision was expressed as relative standard deviation (%RSD), being below than 5.0%, for all elements. Samples of bovine skimmed milk powder contained higher levels of Ca (12,575 mg kg−1) and Na (4670 mg kg−1), while whole goat milk powder presented highest concentrations of K (13,550 mg kg−1) and Mg (1245 mg kg−1), and milk compounds higher content of Zn (31.0 mg kg−1). Plain yogurt samples, when compared with flavored yogurts, presented greater levels of all elements: Ca (1438 mg kg−1), K (1,345 mg kg−1), Mg (133 mg kg−1), Na (988 mg kg−1) and Zn (6.00 mg kg−1). Principal component analysis (PCA) and hierarchical cluster analysis (HCA) allowed the discrimination of milk powder samples from liquid milk and yogurt samples, through the concentrations of Ca, K, Mg, Na, and Zn, and liquid milk and yogurt samples presented lower concentrations of these elements. The yogurt samples were differentiated from the liquid milk samples due to the Zn contents. Concentrations of Zn, found in all samples, were in agreement with Brazilian current legislation (<50 mg kg−1).