“The analyses illuminated the differences among various metabolites involved in key metabolic pathways of LAB occurring in fermented food production”
Food manufacturers across the globe commonly use lactic acid bacteria (LAB) to produce fermented foods including vegetables, dairy products, meats, fish and bread. These food-borne microbes convert molecules such as glucose into compounds called metabolites, which influence the food’s functional and nutritional quality, as well as its taste and aroma.
A wide range of LAB strains are currently used in food fermentation, with the bacteria possessing diverse fermentation characteristics. Scientists are increasingly interested in establishing which strains exhibit desirable metabolic activities. However, the chemical analysis this requires can be labour intensive and time consuming.
At the Food Research Institute, National Agriculture and Food Research Organization (NARO) in Tsukuba, Japan, researchers Satoru Tomita and team 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.
Metabolomics refers to the comprehensive qualitative and quantitative analysis of the thousands of metabolites present in biological systems such as organisms, cells and tissues.
To assess the capability of the method in discriminating these characteristics, Tomita and colleagues analyzed fermented vegetable juices that had been inoculated with six type strains of Lactobacillus species and six L. brevis strains.
Bruker’s Avance-500 spectrometer, equipped with a carbon/proton CPDUL CryoProbe, a SampleJet automatic sample changer and the automated software IconNMR were used to obtain NMR spectra and Bruker’s pulse program zgpr was used to obtain the 1H NMR spectra for metabolomic analysis.
With the Bruker technology, provided and equipped to detect and measure metabolites across the entire metabolomics chemical space, Tomita and team identified 53 metabolites. The metabolite profiles obtained from the fermented vegetable juices revealed differences among various metabolites involved in key metabolic pathways that take place during the production of fermented food.
The analysis clearly separated the samples into those inoculated with homolactic fermentative species (those that only produce lactic acid) and heterolactic fermentative species (those that produce lactic acid in addition to other acids and alcohols). This separation was mainly explained by differences in the amounts of dominant metabolites, namely lactic acid, ethanol, mannitol and acetic acid.
For homolactic fermentation, the analysis showed the contribution of six low-abundance metabolites, namely, acetoin, p-hydroxyphenyllactic acid, phenyllactic acid, glycerophosphocholine, and succinic acid. For heterolactic fermentation, the contributors were ornithine, tyramine, and γ-aminobutyric acid (GABA).
Further analysis of L. brevis showed strain-dependent differences in fermentation characteristics that mainly depended on the bacteria’s ability to use sucrose and citric acid to convert glutamic acid into gamma-aminobutyric acid (GABA) and tyrosine into tyramine.
The authors say the success they had in discriminating the strain-dependent fermentation characteristics of LAB strains, as well as the information that was found about the metabolites responsible for those characteristics suggests that NMR-based metabolomics could serve as a high-throughput method for screening LAB strains.
The team also suggests that real-time NMR metabolomics could be used to gain further insight into dynamic metabolic changes in certain strains and aid the application of their fermentation characteristics in the production of fermented foods.