To investigate the connection between ingredients, processing and texture, the main types of instrument used are scanning electron microscopes (cryo-EM and element analysis). They supply high-resolution 3D images. Food analysts can obtain quantitative information from microscope images. In-situ microscopy makes dynamic studies possible.
Microbiology: Bacteria, Moulds, and Viruses
Moulds, bacteria, and viruses are all types of microorganism. Certain microorganisms are essential for production of, amongst other things, cheese, yoghurt, or alcoholic drinks such as beer. Conversely, microorganisms can result in food perishing, meaning that such foods need to be conserved, or they can trigger illnesses that are transmitted via foods. Common examples of this are species of salmonella and moulds. Microorganisms that are relevant in food accordingly range from pathogenic or toxinogenic microorganisms to spoilage microorganisms to organisms used by food technologists in fermentation and maturation.
Fluorescence microscopy using dyes is available to demonstrate the presence of microorganisms such as bacteria. Gram staining is typically used to investigate and observe bacteria such as Staphylococcus aureus, E. coli, Salmonella, Campylobacter, and Shigella. Blue staining of starch using iodine, and Fast Green FCF or Acid fuchsin are valuable methods, particularly for localization of proteins.
An Example of a Practical Application: The Brewing Process
As part of the brewing process, for example, light microscopes are important monitoring tools. The aim behind microscopic examination in the brewery is optimal and comprehensive evidence of the raw materials, of the yeast growth during the process, and of potential foreign bodies. This examination is also fast and efficient, and it is used to accompany production. The darkfield process has proven effective thanks to its high contrast and high sensitivity. Contaminants are spotted visually (see Fig. 2), while high throughputs are achievable.
When checking the wide range of samples from the entire brewing process, the origin of the samples is critically important. This makes it possible to look for discrepancies in the microscopic image in a targeted fashion. If discrepancies are found, further analyses can be carried out for identification. These might include, for example, evidence of live/dead condition, by staining microorganisms using fluorescent dyes.
* K. Unger, A. Koenen: Carl Zeiss Microscopy GmbH, 07745 Jena, Germany