Introduction
• Hay Milk and EU TSG: Hay milk is an Alpine dairy product, recognized with a Traditional Speciality Guaranteed (TSG) label.
• Silage-Free Feeding: While hay milk should be produced only from cows fed with a silage-free diet, currently no official control exists.
• CPFAs as Authenticity Markers: To protect hay milk from frauds, the use of cyclopropane fatty acids (CPFAs) as biomarkers is promising, because they are present only in milk coming from a silage-based diet
• ¹H-NMR Method: This work aimed to screen 245 milk samples from South Tyrol (Italy) and build a classification model for assuring hay milk authenticity using the ¹H-NMR signal of CPFAs.
Materials and Methods
– Targeted ¹H-NMR approach in milk
245 raw milk samples of three distinct groups, namely hay milk, milk from grass silage and milk from maize silage feeding, were lyophilized. The milk fat, dissolved in CDCl₃ solvent, was analyzed using high-resolution liquid- state (600 MHz) ¹H-NMR spectroscopy.
– Targeted ¹H-NMR approach in yoghurt
7 yoghurt samples from two distinct groups, produced from hay milk and conventional milk respectively, were collected from supermarket. The fat contents of yoghurt samples were extracted using centrifugation followed by extraction with organic solvent, and the purified fat fraction was analyzed by ¹HNMR.
Results
The presence of CPFAs were detected in 97% and 77% of milk from maize and grass silage feeding, respectively (Table 1), using the ¹H signal of the cis-Hydrogen of the cyclopropane ring at −0.30 and −0.35 ppm (Figure 1). Furthermore, all 49 authentic hay milk samples no CPFAs were found. All results for milk analysis were validated with GC-MS as a complementary method.
Figure 1. Representative ¹H NMR spectrum of a lyophilized milk sample from maize silage feeding in the region of CPFAs (600 MHz, CDCl3).
Table 1. Presence of CPFAs in 245 milk samples analyzed by ¹H-NMR and GC-MS.
The three yoghurt samples labelled as hay milk product showed no presence of CPFAs while all analyzed conventional yoghurt samples contain CPFAs (Figure 2, Table 2).
Figure 2. Superimposed ¹H NMR spectra of fat fraction of yoghurt samples in the region of CPFAs (600 MHz, CDCl3)
Table 2. Quantification of CPFAs in commercial yoghurt samples.
Conclusions, Future Perspectives and Achievements
The presence of CPFAs in both conventional milk and yoghurt samples was confirmed using ¹H NMR (600 MHz) spectroscopy.
Targeted ¹H NMR method can be considered as a valuable analytical tool for verifying hay milk authenticity, as it allows for precise detection of CPFAs within the specific chemical shift range between −0.30 and −0.35 ppm.
¹H NMR-based metabolomics in hay milk is a promising tool to characterizing and establishing a methodology to verify the authenticity of hay milk.
Eltemur et al., Applications of Solution NMR Spectroscopy in Quality Assessment and Authentication of Bovine Milk (Review), Foods, 2023, 12(7), 3240