Electron microscopy is an effective method to evaluate the chemical nature of ingredients and provides complementary information for chemical analysis. The purpose of this type of study applied to food science and technology is to provide data on the quality of the nutrients present; to detect irregularities in their physical structure; to detect the level of processing of the components in the food; to detect contaminants and microbiological growth; to determine fat content; among others.
What is an electron microscope and how does it work?
Electron microscopes are very useful instruments in food science. With this type of instrument it is possible to visualize images at higher levels than with optical microscopes. In industry, they are often used for quality control and process failure analysis. In food technology, it is used for a wide range of applications, including the analysis of textures, geological structures, and biological mechanisms in food; and contaminants present in products such as fibers, pathogens, etc.
The principle of their operation is based on using electrons instead of visible light. Because the wavelength of electrons is much shorter than that of photons, they are used to investigate ultrastructures of a variety of specimens. The electrons are accelerated to high speeds, and impact the specimen in a manner equivalent to how light might illuminate it, with the result that some electrons are reflected by the specimen and others pass through it. The images are called micrographs, and are captured by specialized digital cameras and frame grabbers that detect the electrons and build the image.
Types of electron microscopes
There are two types of electron microscopes, of which the following details stand out:
- Transmission Electron Microscope (TEM): in this type of microscope a fine beam of electrons is accelerated at high speed and conducted towards the sample by means of electromagnetic lenses, so that upon impacting the sample they are able to pass through and produce a dispersion in different trajectories. The electrons captured by the detector give rise to the high-resolution image, which is magnified and projected onto a fluorescent screen for viewing. This technique is useful for determining details of internal structure in the sample.
- Scanning Electron Microscope (SEM): the principle of operation of these microscopes consists of scanning the surface of the sample to be analyzed with a beam of electrons accelerated in its electric field by means of a potential difference. Then, using an electromagnet detector, a scan is made across the different points of the surface. In this irradiation process, part of the initial energy of the electrons is transformed into heat or X-ray emissions, and secondary electron emission also occurs. This type of microscope produces high-resolution images with a large depth of field of the sample surface.
Parts of an electron microscope
Electron microscopes are mainly composed of:
- Electron source: also called electron gun, it would be the equivalent of the light source of an optical microscope. It is a tungsten filament used to generate and direct a beam of electrons towards the sample. The filament is heated until the energy level of the electrons in its atoms is such that they can be released and then directed.
- Electromagnetic lenses: in the case of electron microscopes, these lenses produce electric and magnetic fields that allow the electron trajectory to diverge or converge. In such a way that their function is to deflect the trajectory inside the vacuum chamber.
- Vacuum chamber: its function is to prevent the electrons from interacting with the air molecules, otherwise it is impossible to determine the trajectory of the electrons.
- Fluorescent detector or screen: depends on the type of microscope. If it is a scanning electron microscope, the detector is a sensor whose function is to collect and measure the information from the electrons bouncing off the sample. If it is a transmission electron microscope, the fluorescent screen is responsible for collecting the information from the electrons passing through the sample.
- Sample digitization system: is the integrated system of data acquisition, recording, software and hardware, which is responsible for the operation and control of the microscope, as well as for processing the information, analysis and recording of the captured images.
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