Optimization of microwave acid assisted hydrolysis 1 by multivariate calibration applied to the determination of seleno-amino acids bound to proteins in milk samples

ROMINA LOPEZ; LUIS ESCUDERO; ROBERTO D´AMATO; BUSINELLI DANIELA; MASSIMO TRABALZA MARINUCCI; SOLEDAD CERUTTI; PABLO PACHECO

FOOD CHEMISTRY

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2019 vol. 79 p. 128 - 133

0308-8146

Selenium (Se) is an essential element present in milk as seleno-amino acids and seleno-proteins. To perform anaccurate seleno-amino acid analysis, a complete hydrolysis of proteins is necessary. Microwave-assisted acidhydrolysis (MAAH) can be used; however, some variables must be optimised to avoid incomplete hydrolysis andoxidation. Multivariate calibration showed that the volume of the reducing agent, the concentration of the acidused, and the microwave power were statistically significant (95% confidence), and since these are the variablescontrolling the system, a final optimisation was performed to increase the method efficiency. This was performedusing a 2(4−1) central composite design. A robustness study was performed employing the Taguchi design, whichdemonstrated that the optimised MAAH technique was not dependent on the protein concentration of the milksamples. Following MAAH optimisation, a 30-fold recovery improvement was obtained for seleno-amino acids,reaching a limit of detection of 0.053 μg 100g−1 for selenocysteine. Selenocysteine, selenomethionine, and seleno-methyl-selenocysteine were determined at concentration ranges of 5.06 ± 0.20?22.5 ± 0.90,0.75 ± 0.03?19.7 ± 1.2 and 1.25 ± 0.05?16.3 ± 0.85 respectively, in commercial powder milk samples andinfant formula, lyophilized selenium-enriched ewe milk, lyophilized human milk and reference material ERMBD150skimmed milk powder.