Fermentation is the enzyme-catalyzed, metabolic process by which food-borne microbes break down and convert molecules such as glucose into metabolites, compounds that determine the quality and preservability of fermented foods.
Across the globe, food manufacturers harness this microbial activity to produce a wide range of fermented foods and drinks including vegetables, dairy products, meats, fish, bread and cereals.
Lactic acid bacteria
One group of microbes widely used for this purpose is lactic acid bacteria (LAB). It is the metabolites that result from the activities of LAB that determine the nutritional, functional and sensory qualities of fermented foods. Researchers have therefore become increasingly interested in using advanced analytical techniques to establish exactly which metabolites are responsible for these qualities.
The LAB strains used to ferment foods are wide-ranging, with the bacteria exhibiting diverse fermentation characteristics. Scientists are keen to identify strains with desirable metabolic activities, but the chemical analysis required to detect them is often laborious and time consuming.
The newly emerging field of metabolomics is the large-scale characterization of the thousands of metabolites present within biological systems such as organisms, tissues and cells. These metabolites, along with their interaction with such systems is collectively referred to as the metabolome.
Metabolomics enables researchers to observe the metabolic status, biochemical events and physiology associated with a biological system, as well as serving as a powerful method for discovering new or unexpected metabolites and providing detailed measurement of metabolite activity.
Recently, metabolomics has been used to discriminate the metabolite profiles of foods that have been fermented with different strains of LAB. Despite metabolomics showing potential for evaluating the fermentation characteristics of different LAB strains, the technology has not yet been fully explored as a means of characterizing a wide range of these strains.
In Tsukuba, Japan, Satoru Tomita and colleagues from the Food Research Institute, National Agriculture and Food Research Organization (NARO) have recently used Bruker BioSpin’s NMR technology to investigate the applicability of NMR-based metabolomics in discriminating the species- and strain-dependent fermentation characteristics of LAB.
To assess this discrimination capability, the team analyzed six type strains of Lactobacillus species and six L. brevis strains present in fermented vegetable juices.
Vegetable juice as a fermented food model
The environment inside fermented foods is significantly different to that of the growth media used in laboratories due to various factors including limited nutrients, a low initial pH and the presence of inhibitory compounds and undigested proteins and fibers.
These conditions are reflected in fermented vegetable juice, potentially making it a useful model of plant-based fermented food. Furthermore, many species of LAB species require rich and complex growth media due to their inability to synthesize the nucleic acids, amino acids, vitamins, and nucleic acids required for growth. For example, the ability of LAB to absorb and digest carbohydrates has been shown to exhibit strain-dependent characteristics.
It can therefore be expected that the metabolite profile of fermented vegetable juices would show strain-dependent patterns that could enable the discrimination of fermentation characteristics at the strain level.
Discriminating fermentation characteristics of LAB strains
Overall, Tomita and team identified a total of 53 metabolites. Based on the differences in the metabolite profiles of the juices, NMR-based metabolomics was able to discriminate the fermentation characteristics of the different strains and species.
It also provided information on the metabolites responsible for those characteristics, which can affect the functional and nutritional properties of the foods, as well their taste and aroma.
The authors propose that discrimination by NMR-based metabolomics can serve as a rapid, high-throughput technique for screening individual LAB strains from a large sample set and for indicating the potential impact a certain strain of LAB and its metabolites could have on the quality of fermented foods.
Advantages of NMR
The use of Bruker’s NMR instruments provided several benefits including simple sample preparation, rapid measurement of spectra, wide dynamic range and reproducibility. Bruker is also aware that metabolomic analysis needs to be highly accurate in determining even the smallest changes in metabolite profiles related to environmental variation in fermented foods, as well as those related to outcomes in other areas such as genetic modification, disease progression, and therapeutic intervention.
By providing advanced and integrated technology capable of providing a complete picture of the metabolome, Bruker remains a world leader in metabolomics solutions.
To record NMR spectra in the current study, Tomita and team used Bruker’s Avance-500 spectrometer, equipped with a carbon/proton CPDUL CryoProbe and a SampleJet automatic sample changer, as well as Bruker’s automated software IconNMR. For metabolomic analysis, 1H NMR spectra were acquired using the Bruker pulse program zgpr.
- Tomita, S et al. Rapid discrimination of strain-dependent fermentation characteristics among Lactobacillus strains by NMR-based metabolomics of fermented vegetable juice. PLoS One 2017: https://doi.org/10.1371/journal.pone.0182229
- Khalid. K. An overview of lactic acid bacteria. International Journal of Biosciences 2011;1:1-13
- Mozzi, F. Lactic Acid Bacteria. Encyclopedia of Food and Health 2015:501-508: https://doi.org/10.1016/B978-0-12-384947-2.00414-1
- Metabolomics Society. Available at: http://metabolomicssociety.org/
- Encyclopaedia Britannica. Fermentation – chemical reaction. Available at: https://www.britannica.com/science/fermentation
- New World Encyclopedia. Fermentation. Available at: http://www.newworldencyclopedia.org/entry/Fermentation
- Bruker. Metabolomics. Available at: https://www.bruker.com/applications/life-sciences/metabolomics.html
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