Serra da Estrela cheese’s free amino acids profiles by UPLC-DAD-MS/MS and their application for cheese origin assessment

Abstract

Serra da Estrela cheese is a high-value Portuguese Protected Designation of Origin cheese, produced with raw ewe milk. Thus, information regarding its composition is of utmost relevance for both consumers and certified producers. In this work, the chromatographic profiles of free amino acids in cheeses (45 days of maturation, 6 producers located in 5 municipalities and produced from November 2017 to March 2018) were established by UPLC-DAD-MS/MS. The proposed method allowed detecting 19 free amino acids and cystine with overall limits of detection and quantification lower than 44 μmol/L (1.4 mg/100 g cheese, wet matter) and than 134 μmol/L (4.2 mg/100 g cheese, wet matter), respectively. In all cheeses, 17 free amino acids were quantified including 8 essential amino acids (histidine, leucine-isoleucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine) and 9 non-essential amino acids (arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, proline, serine and tyrosine). The amounts of the free amino acids, essential free amino acids, branched chain free amino acids (leucine, isoleucine and valine) plus the free amino acids ratios (mg/g protein) were further used to identify the producer of Serra da Estrela cheeses. Linear discriminant analysis coupled with the simulated annealing variable selection algorithm was used allowing the correct classification of 96% and 90 ± 8% of the samples, for leave-one-out and repeated K-fold cross-validation procedures, respectively. The satisfactory predictive performance pointed out the possibility of using cheeses' amino acids profiles as origin biomarkers for authenticity control, warranting the correctness identification of the cheese producer/brand, which is quite relevant for ensuring the consumer confidence and satisfaction when purchasing this high-value dairy food.

Dataset on free amino acids contents of Serra da Estrela PDO cheeses determined by UPLC-DAD-MS/MS

“…Data concerning the free amino acids (FAA) contents of the Serra da Estrela PDO cheeses were obtained by UPLC-DAD-MS/MS [4]. A chromatographic system (Dionex Ultimate 3000 UPLC instrument from Thermo Scientific, USA) equipped with a diode-array detector (DAD) and coupled to Linear Ion Trap LTQ XL mass spectrometer (ThermoFinnigan, San Jose, CA, USA) with an ESI source was used.…”

“…The system was operated with a spray voltage of 5.5 kV, a source temperature of 400 °C and a capillary voltage of 18 V. The tube lens offset was kept at a voltage of 25 V. Mass spectra were acquired by full range acquisition covering 100–1500 m / z . For each amino acid the mass spectrometry parameters, confirmation and quantification mass transition ( m / z ), and their collision energies were determined [4]. Data acquisition was carried out with Xcalibur®data system (ThermoFinnigan, San Jose, CA, USA).…”

“…The internal standard (IS) method was used for calibration purposes using N-Acetyl- l -Tyrosine as the internal standard since it was not detected in the protein fraction of the cheese samples. The limits of detection and quantification ( data not shown , but can be calculated using the raw data provided as supplementary material in file Table_S2_DIB-D-19-02387.xlsx) of the established UPLC-DAD-MS/MS method were previously reported [4] and ranged, respectively, from 0.20 μmol/L, for aspartic acid, to 44.2 μmol/L, for alanine, and 0.62 μmol/L to 134 μmol/L, for the same amino acids. The intra-day repeatability intervals (expressed as the coefficient of variation in percentage, CV%) are given in Table 3, for each amino acid, corresponding to the minimum-maximum values calculated based on 3 injections of each standard solution concentration used to establish the calibration curves, and varied from 0.02 to 10.3%, corresponding, in general, the highest values to the lowest concentrations and/or responses (raw data of the peak areas ratios as well as the mean values, standard deviations and respective coefficient of variation can be found in the provided supplementary material, namely in the Excel file: Table_S2_DIB-D-19-02387.xlsx).…”

Organoleptic Chemical Markers of Serpa PDO Cheese Specificity

“…The results may indicate that this group of FAAs is more prevalent in Serpa cheese with 30 days of ripening and probably may have an essential role in their specificity. Additionally, Serra da Estrela cheese, a traditional Portuguese PDO cheese produced with raw ewe's milk and coagulated with C. cardunculus L., showed higher concentrations in some of these FAAs, namely, Leu, Phe, Ala and Val [26,57]. Concerning Terrincho cheese, a raw ewe's milk coagulated with animal rennet, the most incident FAAs identified were Leu, Val, Asp, Glu and Pro [56].…”

Amino Acid Profiling with Chemometric Analysis as a Feasible Tool for the Discrimination of Marine-Derived Peptide Powders

“…Vegetable oils and honey samples could be correctly classified according to their botanical origins or geographic regions based on amino acid profiles with chemometric approaches [20][21][22][23][24]. Amino acid profiles have also been proven to be potential markers for the origin assessment of Serra da Estrela cheese and authenticity identification of plastron-derived functional foods [25,26]. Here, the objective of this study is to determine characteristic amino acids profiles for four categories of marine-derived peptide powders, namely, sea cucumber peptides, oyster peptides, Antarctic krill peptides, and fish skin peptides, and investigate the feasibility of employing amino acid profiles alongside chemometric analysis for the detection of adulteration.…”