The so-called 'metabolome' describes the entirety of all low molecular weight compounds in a given biological system – for example, a single cell, a tissue, a biofluid or a food. The metabolome comprises endogenous primary or secondary metabolites like sugars, amino acids, amines, organic acids, alcohols, steroids, fatty acids, nucleosides etc. as well as compound of exogenous origin and their metabolites. The term 'metabolomics' designates all analytical approaches or methods aiming to cover a given metabolome as comprehensively as possible.
Metabolomics – a key approach in modern life sciences
In recent years, metabolomics has developed into a key approach in modern life sciences. At the Max Rubner-Institute, the decision to establish metabolomics platforms in several departments (lead by the Department of Safety and Quality of Fruit and Vegetables) was made in 2010. The aim of this initiative is to enable cutting-edge research in the fields of food safety and food quality as well as health-oriented nutrition research in the mid-term.
Metabolomics is an innovative analytical approach as it enables the detection of hundreds to thousands of known and unknown metabolites in one run. Here, in contrast to traditional targeted analytical methods, typically signal intensities instead of absolute concentrations are determined. On this basis, a so-called relative quantification is performed which means that relative concentration ratios between different groups (‘control’ vs. ‘treated’ or ‘healthy’ vs. ‘diseased’) are calculated. As an example, the level of a given organic acid may be 50% lower in stored apples than in freshly harvested apples. The major advantage of this strategy is the possibility to identify known or even previously unknown compounds as relevant markers and to elucidate their structure afterwards if necessary. In a nutshell, metabolomics means the simultaneous quantification of a broad range of low molecular weight compounds in biological samples with the intention to enable an unbiased, open-ended analysis.
The food metabolome
Due to their comprehensive nature, metabolome analyses are an increasingly popular tool for the evaluation of food safety and food quality. Numerous applications of metabolomics in the food field are possible: For example, metabolomics can be used to gain a better understanding of how different cultivation systems or storage conditions influence food quality, enabling an optimization of such systems or conditions. With the help of an untargeted metabolome analysis, it is further possible to identify previously unknown and maybe early-emerging spoilage markers. Metabolomics may also contribute to the safety evaluation of novel food processing techniques. In plant breeding, metabolomics is an increasingly important tool for the characterisation of cultivars with a higher resistance against pathogens. Since 2014, especially the Department of Safety and Quality of Fruit and Vegetables focuses on food-related research questions using metabolomics methods in collaboration with various agronomic partners. For this, the expertises from the different workgroups (mycology, microbiology, post-harvest physiology, instrumental analysis and bioinformatics/ statistics) are combined in order to work on the different research topics in an interdisciplinary manner.
The human metabolome
The metabolome of a biological system is determined by many factors such as age, sex, genotype, health status, nutritional status or physical activity. As the end product of highly complex metabolic networks, the metabolome is extremely variable.
Until now, it is not entirely clear which lifestyle factors have a determining influence on the human metabolome. Likewise, it is not known if certain metabolite patterns are associated with health, higher quality of life, higher performance and a lower disease risk. For this reason, current nutritional research uses metabolomics as a tool for a comprehensive characterization of the human metabolome, focusing especially on the identification of markers for dietary patterns and other life-style factors. With the establishment of the ‘Karlsruhe Metabolomics and Nutrition‘ (KarMeN) cohort comprising more than 300 healthy participants, the Max Rubner-Institut contributes to answering the open questions around the influence of nutrition and other factors on the human metabolome. If these efforts are successful, this may be an important step towards the prevention of nutrition-related diseases.
The metabolomics platforms at MRI
The Max Rubner-Institut focuses primarily on the development and application of mass spectrometry-based metabolomics methods. In addition, NMR-based metabolomics studies are also performed in collaboration with the Karlsruhe Institut of Technology (KIT).
So far, especially an untargeted metabolomics platform based on comprehensive two-dimensional gas chromatography/mass spectrometry (GC×GC-MS) has been established and used for several food and human metabolomics studies. With this platform, typically between 200 and 400 metabolites can be reproducibly semi-quantified, depending on the biological material. Beyond that, several targeted GC-MS and LC-MS methods covering compound classes like sugars, phenolic acids or bile acids are available. An untargeted LC-MS-based metabolomics platform is under development.