Identification of Umami Substances in Foods

Some people who are following our portal may be wondering: “How can we know if the food we are eating contains umami?” This is a question that involves numerous aspects and also the exact, biological and human sciences.

Disciplines such as Analytical Chemistry can identify these molecules through different methods, such as those involving enzymatic reactions, liquid chromatography coupled to UV-VIS spectroscopy detectors, fluorescence and mass spectrometry, and also sensors, which are called e-tongues, that is, ‘electronic tongue’.

In a very summarized way, we can explain these methods, but it is worth noting that there are many complexities involved:
Enzymatic reactions with detection through an electrode
The analysis is based on the principle of oxygen consumption from the enzymatic reaction between the glutamate present in the sample, the enzyme glutamate oxidase and the coenzyme FMN (flavin mononucleotide). This reaction consumes oxygen and removes two hydrogens from the amino acid, which in turn forms an α-keto acid and hydrogen peroxide. The oxygen consumption for hydrogen peroxide formation is measured using an electrode, which corresponds to the amount of glutamate contained in the sample.

Liquid Chromatography
Liquid chromatography is an analytical technique used to separate ions or molecules that are dissolved in a solvent. If the sample in solution comes into contact with a stationary phase (column – where different types of silica or other products are usually used), the different solutes will interact with this phase to varying degrees, mainly due to the adsorption, ion exchange, partitioning, or size of the molecules. These differences allow the mixture of components to separate from each other by using different transit times (retention time) in the passage of the solute through the column. After passage, the ions or molecules are detected by other methodologies, which include mass spectrometry, UV, or fluorescence at different times, according to the column exit.

Mass Spectrometry
Mass spectrometry is an analytical detection technique that differentiates the components of a sample through their atomic mass. The sample is vaporized until a gas is formed and ionized (formation of ions). The ions are then accelerated through a potential difference. The compounds are separated through their mass-to-charge ratio and identified. This technique can be used after passing through a chromatograph or also by direct analysis. It all depends on the objectives being proposed for the analyses.

UV-VIS Spectroscopy (ultraviolet/visible)
The UV-VIS spectrometer can also be one of the detectors chosen after a sample has passed through the chromatograph. UV-VIS detectors measure the UV-VIS light absorption capacity of a chromophore (molecule or part of it responsible for its color). This can be done between one or more wavelengths in the range of 190-400nm. For this to occur, the compounds of interest must possess chromophores or react with other substances that can introduce color into this molecule so that it can be detected.

Fluorescence Spectroscopy
Similar to UV-VIS spectroscopy, different ions or molecules can react with substances, which can form different types of compounds, which in this case are fluorescent compounds. The atoms or molecules are excited to high energy levels by absorbing electromagnetic radiation and are then detected.

Electronic Sensors (e-tongue)
The electronic tongue is an instrument that can measure and compare different tastes. The chemical compounds responsible for the sensations of the five tastes are detected by electronic instruments called sensors. After some reactions, electrical signals with different potentiometric variations are generated, which are detected by the sensors.

The methods used in Sensory Analysis may involve discussions that refer to the human sciences, mainly with regard to the physical, environmental and psychological conditions involved in the perception of a human panel. These analyses are generally carried out by groups of individuals with a keen sense of taste, who initially indicate possible descriptors (a term used to describe a sensation), before conducting research on the population that will likely consume the food.

All the methods mentioned use statistics, an exact science, to make their predictions; however, there are always inherent errors and confidence intervals, at least when we talk about sensations, since it is unlikely that any method will truly identify what we feel. This is a mystery that science is still trying to unravel, and therefore, we need the human sciences to discuss the art of being on Earth as a human being.