Fluorescence is the phenomenon where a molecule absorbs light within its absorption band and then emits this light at longer wavelengths within its emission band.

Fluorescence Spectroscopy

This phenomenon can be used to identify, quantify, and observe chemical activity, and it is a popular method due to its high levels of sensitivity, simplicity, and specificity. In fluorescence spectroscopy, a light of a specific wavelength band is passed through a solution, which emits the light towards a filter and into a detector for measurement. The amount of light that is absorbed by the sample (excitation spectrum) and the amount of light that is emitted by the sample (emission spectrum) can be quantified.
The concentration levels of the analyte compound within the solution can be determined as these levels are directly proportional to the emission spectrum. For a given fluorophore, the emission and excitation wavelengths are mirror images of each other. The spectral intensity and / or peak wavelength of fluorophores depend on variables such as concentration, interactions with other molecules, pH and temperature.
Many organic molecules fluoresce under light and can thus be identified by spectroscopic methods. This includes amino acids, fluorescent proteins (FP) and chlorophylls. There are two types of fluorescence spectrometry instruments: filter fluorimeters (which use filters to isolate incident light) and spectrofluorometers (which use diffraction grating monochromators.) Incident light sources used include LEDs , lamps and lasers. The lamps particularly used in the technique are xenon arcs and mercury vapor lamps. Fluorescence spectroscopy is used as an analytical tool in many different industries in addition to the food industry, including the chemical and pharmaceutical industries, wastewater treatment and the mining industry. It is eminently more sensitive than absorption techniques.

Fluorescence spectroscopy for food quality analysis

There has been a growth in spectroscopic applications for food quality analysis in recent decades due to its non-destructive, rapid and sensitive nature. This is due to the widespread application of chemometric tools and the improvements made to the technical and optical aspects of spectroscopic equipment. Food quality is one of the most important aspects of the food industry. The nutritional, physical and chemical aspects of the food sample must be measured and understood to provide a quality product that helps consumers make an informed choice. The quality of perishable foodstuffs (meat, eggs, dairy products, fish, etc.) is particularly important for the food industry. These foods are considered part of a healthy diet, providing important vitamins, minerals and essential oils that help the body and the brain to function healthily. Fresh food has a limited shelf life and is affected by time-limited supply chains and storage processes, which means that careful analysis of their components improves freshness, safety and benefits. Microbial growth can also spoil food, which can lead to outbreaks of harmful diseases such as listeria and salmonella. Additives and preservation techniques for non-perishable and long shelf life foods (eg canned, pickled and dry food products) can also be studied for quality using spectroscopic techniques. The use of spectroscopic fluorescence methods in food quality studies has helped the food industry to improve the overall quality of the food we eat. Recent studies have also helped improve food preservation techniques and reduce harmful chemical and microbial adulteration.

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