With the growing improvements in food standards, analytical tools are required to enable the monitoring of foods to ensure that these high standards are met. Fluorescence spectroscopy is a well-established analytical technique that is increasingly been utilized to monitor food standards.
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This includes investigating different qualities of food such as tenderness of meats and authenticity of the food product, as well as looking for microbial contamination of the food.
Why use fluorescence spectroscopy to analyze food quality?
Fluorescence spectroscopy is an attractive option for use in food quality analysis, as it can be performed quickly, required little sample preparation as well as being non-destructive to the sample. Also, it is possible to establish a correlation between specific fluorescence spectra and microbial values, which means that fluorescence spectroscopy can be used to monitor food samples for microbial contamination.
How can fluorescence spectroscopy be used to analyze food quality?
Fluorescence spectroscopy can easily be applied to the analysis of dairy products, as they contain naturally occurring fluorophores or molecules which cause fluorescence. For example, the amino acids tryptophan, tyrosine, and phenylalanine occurring in milk proteins, and vitamins A and B2.
A study in 1997 by Dufor and Riaublanc compared the fluorescence spectra using tryptophan and vitamin A as the fluorophores obtained from raw milk, heated milk, homogenized, and homogenized and heated milk by using a principal component analysis. This showed that the different treatments applied to milk yielded different fluorescence spectra, and this was further confirmed by more recent studies. Therefore, fluorescence spectroscopy could potentially be used to assess the success of various treatments applied to milk.
Another study has utilized fluorescence spectroscopy to differentiate between a variety of cheeses; here, it was found that the fluorescence spectra generated by using vitamin A as the fluorophore was the most effective at differentiating between 8 soft cheeses. Therefore, fluorescence spectroscopy could potentially be used to authenticate different cheeses.
Meat and seafood products
Meat and seafood products are highly perishable, due to oxidation, enzymatic autolysis, and microbial growth. Therefore, meat and fish products must be well preserved to ensure that they are safe to consume.
Meat contains some naturally occurring fluorophores, for example, the amino acid tryptophan, nicotinamide adenine dinucleotide (NADH), porphyrin, vitamin A and riboflavin. One parameter of meat which can be studied by fluorescence spectroscopy is the presence of collagen in adipose tissue or connective tissue within the meat. This is more for quality purposes, as collagen is linked to tenderness and other textural aspects of meat.
One study found that it was possible to use fluorescence spectroscopy to study the tenderness of beef. In another study, it was possible to monitor the texture of frankfurters produced by using varying ratios of fat/lean meats by utilizing tryptophan as the fluorophore.
One way in which meat and meat products can be spoiled is the oxidation of lipids and proteins within the meat. Here, thiobarbituric acid reactive substances, a reference for lipid oxidation index, and fluorescence spectra of meat products were shown to be a good measure for the oxidation of meat, and this method could be used to see how different processing and storage affected the rate of oxidation of the meat products.
For example, one study showed that when packaged in a high oxygen environment, turkey samples showed oxidative damage after 7 days in storage.
Seafood including fish also has naturally occurring fluorophores, including amino acids, NADH, vitamin A, and riboflavin, as well as oxidation products. As with meat products, oxidation is a cause for seafood products to become spoiled, and this can also be analyzed by fluorescence spectroscopy.
Dufor and co. investigated whether fluorescence spectroscopy could be used to monitor the freshness of mackerel, salmon, cod, and whiting by using amino acids including tryptophan and NADH as the fluorophores. The fish were stored for 1, 5, 8, and 13 days on ice, and the authors found that there was a difference in fluorescence spectra from the various samples. This means that there is potential to use fluorescence spectroscopy to monitor the freshness of fish.
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How can microbial contamination of food be detected by fluorescence spectroscopy?
One major factor leading to spoilage of food is microbial contamination. This not only affects food quality but can also be harmful to humans who consume the food. Therefore, ensuring that microbial contamination of food is kept to a minimum is vital.
Fluorescence spectroscopy has the potential to be used as a technique to analyze microbial contamination on food. For example, studies using fluorescence spectroscopy were able to predict the number of viable microorganisms found on pork and poultry. It has been suggested that fluorescence spectroscopy may even be able to distinguish between different microorganisms found on poultry.
A different study showed that the various lactic acid bacteria found on sausages could be identified using fluorescence spectroscopy. These studies show the potential of fluorescence spectroscopy to monitor microorganisms found on food, to ensure that the food is safe to consume.
- Karoui, R. and Blecker, C. (2010) Fluorescence Spectroscopy Measurement for Quality Assessment of Food Systems—a Review. Food Bioprocess Technol DOI 10.1007/s11947-010-0370-0
- Hassoun, A. et al. (2019) Fluorescence spectroscopy as a rapid and non-destructive method for monitoring quality and authenticity of fish and meat products: Impact of different preservation conditions. LWT https://doi.org/10.1016/j.lwt.2019.01.021
- He, H.-J. and Sun, D.-W. (2015) Microbial evaluation of raw and processed food products by Visible/Infrared, Raman, and Fluorescence spectroscopy. Trends in Food Science and Technology https://doi.org/10.1016/j.tifs.2015.10.004