Tilapia is one of the most popular seafood dishes, with annual global production topping 6 million tonnes. However, fish is a highly perishable food with a short shelf-life. As a result, large quantities of fish meat are discarded due to loss of quality between capture and final consumption.
Dr Maria Lucia Guerra Monteiro and colleagues at the Federal University of Rio de Janeiro aim to reduce this waste due to the early loss of quality. They investigate the effect of a new style of packaging on the freshness of tilapia fillets stored under refrigeration, both with and without ultraviolet treatment.
Read their original paper here: https://www.nature.com/articles/s41598-020-61293-8
Image credit: Sofia Pelayo/Shutterstock
Hello and welcome to Research Pod. Thank you for listening and joining us today.
Today we are exploring research related to emerging food technologies to preserve the quality of fish fillets for more extended periods. The study conducted by Dr Maria Lucia Guerra Monteiro, a pPost-doctoral student at the Federal University of Rio de Janeiro, and colleagues, investigates the effect of a new style of packaging, with or without ultraviolet treatment, on the freshness of tilapia fillets stored under refrigeration aiming to reduce the food waste from the early loss of quality.
Fish consumption has increased due to its large amount of nutrients and its relation to health benefits. Tilapia is one of the most consumed species worldwide, mainly in fillet form. However, fish is highly perishable because , as a fresh, moisture-rich food medium, it’s very hospitable to enzymes and bacteria. So, fish rapidly loses quality by undesirable changes in colour, texture, odour, and flavour and the formation of harmful compounds (e.g., ammonia and amines) as they degrade, or go ‘off’. Also, large quantities of fish meat are discarded due to loss of quality between capture and final consumption. These facts are concerns for the consumer’s health and finances of seafood producers .
There are many conservation methods to preserve the fish quality for longer, but the main challenge is finding alternatives that increase the shelf life without negatively affecting the quality of the product.
Now, did you know that UV-C light can reduce the rate of growth of bacteria on fish in refrigerated storage? It’s true, but the action of UV-C light is superficial. Overall, the doses of UV-C needed to prolong the shelf life of fish end up contributing to the production of reactive oxygen species that accelerate oxidative degradation and, consequently, undesirable changes in colour, texture, odour, and flavour. On the other hand, there are preservation technologies that mitigate oxygen-dependent reactions, such as oxygen scavengers or O2 absorbers.
Vacuum packaging is also useful here, as you’ve probably seen on supermarket shelves, but did you know that there can still be up to 0.5% oxygen levels in vacuum packages? By comparison, O2 absorber- containing packaging scores less than 0.01%. This is because vacuum packaging systems do not prevent O2 from penetrating through their film wrapping during storage, while the O2 absorbers use iron oxidation to consume oxygen constantly.
So, individual application of UV-C light and O2 absorbers have previously proven effective in fish and other meat matrices. Therefore, the researchers from Federal University of Rio de Janeiro, and Fluminense Federal University in Brazil asked the following question: Can oxygen removal in the packaging during storage minimise the adverse effects of UV-C light?
To find out, the researchers examined six treatments:
- Treatment 1 being fillets packed in plain air packages,
- Treatment 2 comprising fillets packed with one O2 absorber sachet inside the package,
- Treatments 3 and 4 being fillets packed in air packages and subjected to UV-C light exposure at 0.102 or 0.301 Joules per centimetre squared,
- and then Treatments 5 and 6 comprising of fillets packed with one O2 absorber sachet inside the package and subjected to UV-C light exposure at 0.102 or 0.301 Joules per centimetre squared.
UV-C light at two doses increased the shelf life of refrigerated tilapia fillets over 6 days by reducing bacterial growth rate and formation of compounds from the protein degradation process, such as volatile nitrogenous substances and ammonia. Although the UV-C doses did not affect the formation of biogenic amines, they did accelerate the lipid oxidation, protein oxidation, and discolouration, with the higher the UV-C dose, the more intense the oxidation processes. UV-C light also negatively affected texture properties, but the two doses led to a similar outcome.
O2 absorbers alone also had a positive effect against bacterial growth and formation of protein degradation compounds during storage, extending the shelf life of tilapia fillets stored under refrigeration in 5 days. This treatment also decreased the formation of biogenic amines during refrigerated storage. Although less effective for shelf life extension than UV-C light, O2 absorber alone minimized lipid and protein oxidation, discolouration, and negative texture changes.
And then, what about the combined treatments?
UV-C exposure, either at 0.102 or 0.301 joules per centimetre squared combined with O2 absorber were the most effective of treatments in this study at reducing the bacterial growth rate, formation of compounds from the protein degradation process, and overall increasing the shelf life of refrigerated tilapia fillets. It was extended by 7 days, regardless of the UV-C dose. The formation of biogenic amines was decreased in the same way as O2 absorber alone.
Surprisingly there was no difference in lipid and protein oxidation, discolouration, and negative texture changes between the combined treatments at two UV-C doses and O2 absorber alone, suggesting a potential method to be used in combination with UV-C dose up to 0.3 Joules per centimetre squared in refrigerated fish. This means longer shelf life, which translates to higher safety and convenience for shoppers, with less economic losses in supply chains and less food waste in the environment.
In conclusion, the work of Dr Monteiro and their colleagues demonstrates that, while O2 absorbers alone are effective in delaying the oxidative degradation, they had the least benefit for the shelf life of refrigerated tilapia fillets at just 5 days.
On the other hand, although UV-C doses at 0.102 and 0.301 Joules per centimetre squared have extended the shelf life of refrigerated tilapia fillets by 6 days (more than O2 scavengers alone), these treatments accelerated lipid oxidation, protein oxidation, and discolouration in a dependent manner, in addition to negative changes on texture – in short, not recommended for tilapia fillets stored under refrigeration.
The most effective preservation treatment in increasing the shelf life of refrigerated tilapia fillets was an O2 scavenger combined with two UV-C doses, at 7 days. Also, the O2 scavenger prevented the adverse effects induced by UV-C light, regardless of the dose.
All in all, Dr Monteiro states, “O2 scavengers can be a simple, low-cost and effective alternative to suppress the adverse effects of the UV-C light and make it viable for industrial applications to reach a longer shelf life, while maintaining the original quality attributes in refrigerated tilapia fillets”. She continues “combining O2 scavenger and UV-C light is a promising non-thermal technology to solve one of the main barriers in the fish production chain; economic losses due to high perishability of fish resulting in rapid loss of quality during transport and retail display”.
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