Gas chromatography-mass spectrometry and Fourier-transform infrared spectroscopy coupled to chemometrics for metabolome analysis of different milk types in the light of green analytical chemistry.

Background: Milk is an important dietary source for a healthy and balanced diet, owing to its rich content of proteins, fats, sugars, vitamins, and minerals. Due to the importance of milk macronutrient content for consumers' preferences, a multiplex metabolomics-based approach using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) fingerprinting platforms was employed for the characterization of metabolites in different types of buffalo (BM), cow (CM), goat (GM), and camel (LM) milk. Methods: GC-MS and FTIR coupled to chemometric tools (multivariate data analysis) were employed for the discriminative qualitative and quantitative analysis of BM, LM, CM, and GM milk, targeting their primary metabolites. A side-by-side comparative assessment of the performance of both the FTIR and GC-MS methods was implemented in the light of green analytical chemistry principle (GAC) and white analytical chemistry principles (WAC) using the 12 green analytical chemistry principles (12 GAC), analytical greenness metric approach (AGREE), national environmental methods index (NEMI), eco-scale assessment (ESA) and complementary green analytical procedure index (ComplexGAPI), and the red green blue (RGB) 12 algorithms. Results: The milk types were qualitatively identified by visual inspection of their characteristic FTIR spectra as a fingerprint for each milk type. Quantitatively, GC-MS revealed the presence of 87 peaks belonging to alcohols, amino acids/nitrogenous compounds, fatty acids, organic acids, sterols, sugars, and vitamins. Sugars, mainly lactose, appeared as the major component in all milk types. The highest lactose content was detected in CM 1.07-fold higher than LM making LM a potential alternative for lactose intolerance. Both BM and CM were found to contain the highest organic acid content 5.2-fold higher than that in LM, accounting for their acidity (sourness), while the lowest level was found in LM. On the other hand, LM had the highest vitamins content compared to other milks. Lastly, FTIR outperformed GC-MS in terms of greenness and whiteness, suggesting its utilization as an alternative to traditional chromatographic techniques such as GC-MS.