In modern nutrition research, mass spectrometry has developed into a tool to assess health, sensory as well as quality and safety aspects of food. Two strategies are followed for nutrient and metabolite analysis either in foodstuffs or in biological fluids sampled from the food consumer:
The “traditional” targeted conception, which measures only selected compounds with pre-determined properties such as a given mass or structure as described later.The more recent non-targeted conception, which includes fingerprinting of samples and evaluating the unidentified signals with statistical methods (e.g., principal component analysis, linear discriminant analysis, discriminant function analysis etc.).
For nutrients and metabolite identification purposes, in addition to NMR, two major techniques are currently applied, namely tandem mass spectrometry and accurate mass measurements. Tandem mass spectrometry enables elucidation and confirmation of metabolite structures, while accurate mass measurements in combination with isotope pattern analysis provide elemental composition of the metabolite. Furthermore, hydrogen/deuterium exchange experiments are combined with mass spectrometry 1 to distinguish between isomeric structures of analytes. On the other hand, quantification of nutrients and metabolites is mostly achieved using the selected-reaction monitoring technique on quadrupole-based platforms. Quadrupole analyzers provide the best linear and dynamic range for biological samples, but application of high-resolution with time-of-flight or Orbitrap analyzers can also separate the signal of interest from interferences thereby enhancing detection limits.
In this chapter, we will focus on a brief description of each mass spectrometric technique applied to nutrition research, with a short emphasis on the working principle of each ionization, mass separation and ion detection method. We will also describe some specific technologies like those enabling detection of stable-isotope labelled macro- and micro-nutrients.