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Food science unites the physical, chemical, and biochemical sciences to study the nature of foods, what makes them deteriorate, the principles underlying how we grow crops and create dishes, and means of improving food for public consumption. It shouldn’t be confused with food technology, which focuses on the production processes used to make foods and covers procedures like canning and pasteurization.
Researchers are presented with many challenges when it comes to analyzing particles and fibers, studying food preservation, microbiology or pathogens. Most foods are of biological origin, but processing techniques change their appearance almost to the point of being unrecognizable – think bread versus grain, cheese versus milk. These are changes at the minute level, which can be observed using various microscopy techniques. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) are popular choices to determine chemical compositions.
Scanning Electron Microscopy and its Use in Food Science
SEM and food science have been strongly intertwined for years; it has been used to study herbs, fruits, engineered and natural foods.
Electron microscopy offers a good resolution – the details the image holds - and depth of field, the distance between the nearest and the farthest objects that are in acceptably sharp focus in an image. SEM creates images by scanning the surface of a sample with a focused beam of electrons; these electrons interact with atoms in the sample and produce signals containing information about the surface topography and make-up of the sample.
However, it requires a vacuum for the electrons to flow, and this doesn’t mix well with oil or water which is sucked out of a sample over time. This can be overcome with cryogenic preservation or chemical fixation, but this can also cause more problems than it solves.
Specimens are often prepared as thin sections or fractured to reveal a cross-section. They may be cleaned, fixed, dehydrated, mounted on stubs, coated, examined, freeze-dried or etched, or subjected to other techniques.
Case Study: Pacific Oyster
Scientists have analyzed the effect of different drying methods on the Pacific oyster, China’s cultivated shellfish, to see how each process affects surface topography and structure.
They focused on the oyster’s polysaccharides; SEM showed that spray drying created smaller and more uniform polysaccharide particles, while freeze-drying and rotary evaporation drying led to oval shapes and smooth surface topography. The latter could indicate a higher bioactive and antioxidant activity.
The scientists concluded that spray drying was the recommended method for producing polysaccharides.
Case Study: Starch from Banana
Starch is a polymer of glucose, the main energy reserve of higher plants like the banana. SEM has been employed to analyze starch samples and revealed elongated, spheroid and oval grains.
The results confirmed previous observations, and provided information about the physiochemistry and functional properties of starches, enhancing their application in the food industry as a substitute for commercially-available starches.
Case Study: Essential Oils
Oregano is a well-known aromatic plant that grows close to the Mediterranean Sea. Although it has been used for centuries, it is only recently that essential oils have become a popular research interest.
Oregano has antimicrobial, antioxidant and anti-inflammatory properties, thought to stem from its phenolic content, mainly Carvacrol. SEM was used to observe dried oregano essential oil inclusion complexes; researchers revealed that the complexes didn’t exhibit special morphologies, only prisms, and parallel, smooth sides.
Other Imaging Methods
Advances in microscopy and imaging techniques have mostly been made outside of food sciences; processing conditions that transform biological raw materials into food cause textural and structural changes, which alter the food’s innate properties and behavior. This means techniques must be adapted to be relevant in the field.
Techniques include confocal laser scanning microscopy, atomic force spectroscopy, and magnetic resonance imaging. Another technique is mass spectrometry (MS) which can be used to determine the molecules and their location in biomolecules; for example, its be utilized to uncover the functional constituents and nutrients in herbal medicine products, such as ginsenosides and capsaicin.
References and Further Reading
Microscopy and other imaging techniques in food structure analysis
Mass spectrometry imaging: applications to food science
The Future of Food Science?
Scanning Electron Microscopy in Food Science and Technology
Food science research: how scanning electron microscopy is used