The potential of vibrational spectroscopy techniques to determine minor milk fatty acids

Milk fatty acids (MFA) have the potential to serve as biomarkers for monitoring nutrients produced during digestive processes and diagnose metabolic disorders such as acidosis and ketosis. MFA of particular importance in this respect are odd and branched (iso and anteiso) chain and trans C18:1 and cis/trans C18:2 isomers. Timely implementation of appropriate nutritional and management decisions on dairy farms requires that these interesting MFA are analyzed on a routine basis. Conventional chromatography MFA analytical methods require sample derivatization and expert knowledge and thus are considerably slow, tedious and restrict determination to a limited number of samples per day. On the other hand vibrational spectroscopy techniques are fast (matter of seconds to few minutes) and cost effective. The focus of this PhD thesis was to assess the potential of infrared spectroscopy (IR), including mid-infrared spectroscopy (MIR) and near-infrared spectroscopy (NIR), and Raman spectroscopy techniques for determination of minor MFA. This was achieved by selecting a subset of milk samples from a large multi-experiment dataset containing a wide variation of the MFA of interest and constructing chemometrical prediction models for the quantification of individual and grouped MFA. The calibration models were based on accurate gas chromatography reference data and MIR spectra of raw milk or MIR, NIR and Raman spectra of milk fat. The milk fat was extracted using a newly designed routine milk fat extraction method based on dichloromethane. The study illustrates the potential of spectra acquired at different temperature conditions for improving MFA determinations and illustrates the challenges in the routine analysis of minor MFA. Finally, a new Combinatorial Spectroscopy approach based on combining the milk fat spectra from MIR and Raman spectroscopy techniques would allow for addition of new MFA specific information and could prove useful for a diverse range of applications, other than the currently demonstrated determination of MFA