Non-targeted high-resolution mass spectrometry study for evaluation of milk freshness-Supplementary Material

Supplementary material to the article "Non-targeted high-resolution mass spectrometry study for evaluation of milk freshness-Supplementary Material"

Abstract:
Milk freshness is an important parameter for both consumers’ health and quality of milk-based products.
Up to now there have been neither analytical methods nor specific parameters to uniquely define milk freshness from a complete and univocal chemical perspective. In this study, 8 molecules were selected and identified as responsible for milk aging, using a liquid chromatography–high-resolution mass spectrometry approach followed by chemometric data elaboration.
For model setup and marker selection, 30 high-quality pasteurized fresh milk samples were collected directly from the production site and analyzed immediately and after storage at 2 to 8°C for 7 d. The markers were then validated by challenging the model with a set of 10 milk samples, not previously analyzed. Our results demonstrated that the markers identified within this study can be successfully used for the correct classification of non-fresh milk samples, complementing and successfully enhancing parallel evaluations obtainable through sensory measures.

Description of Supplementary Material:

SECTION 1 – MULTIVARIATE DATA ELABORATION
The final PCA (negative mode) and the OPLS-DA (negative mode) scores plot of the results obtained are presented in figures S1-S2.
The variance of the x and y variables explained by the model (R^2 X (cum) and R^2 Y (cum)), and the cumulative predicted variation in the Y matrix (Q^2 (cum)) are reported below each figure.

Figure S1. ESI - PCA scores plot of milk samples. Blue dots: Fresh Samples; green dots: “7 days” samples
Figure S2. ESI - OPLS‐DA scores plot of the fresh samples against the “7 day” samples

SECTION 2 – COMPOUNDS IDENTIFICATION
Figure S3. Trends of the identified molecules through all the time points: Mean area values (+/- Standard Error) of the target compounds through the time points. Time points: blue bar, “t zero”; yellow bar, “1 day”; orange bar, “2 days”; green bar, “3 days”; violet bar, “4 days”; red bar, “7 days”

SECTION 3 – SENSORIAL EVALUATIONS
Table S1: List of the tasted sample
Table S2: Resume of the panelist’s evaluations