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Lipid Oxidation – Why Does my Food Taste Rancid?

We’ve all experienced biting into ‘aged food’, and while certain cheeses may age like a fine wine, rancid meat does not provide the same pleasant experience!

Oxidation is a chain reaction that occurs in the presence of oxygen and is responsible for the deterioration in the quality of food and food products. This includes off-flavours, changes in texture and foul-odours. Beyond that, rancidity in food can also potentially be highly dangerous.

So, let’s explore lipid oxidation and what can be done to counter it!

What is Oxidation?

At the most fundamental level, oxidation is the loss of electrons during a reaction by a molecule, ion or atom. The oxidation of lipids is also known as Lipid Peroxidation and involves free radicals removing electrons from the lipids located in cell membranes, thereby causing damage to the cells.

It most commonly affects polyunsaturated fatty acids as they contain multiple double bonds with methylene (-CH2-) bridges in between, which contain highly reactive hydrogen atoms. The reaction generates a range of chemical products that are classified as lipid peroxides or lipid oxidation products.

Mechanisms of Oxidation

There are many catalytic systems that can propagate the oxidation of lipids. A few examples are temperature, light, metals, microorganisms, and enzymes. As mentioned in the previous section, these reactions (usually) involve free radicals and a reactive oxygen species (ROS).

As with any reaction involving free radicals, there are three major stages involved in lipid peroxidation: initiation, propagation, and termination.

Initiation: The first step involves production of a fatty acid radical. A ROS (commonly OH- or HOO-) initiates the reaction through combination with a hydrogen atom, producing H2O and a fatty acid radical.

Propagation: The newly produced fatty acid radical is unstable, so will readily react with molecular oxygen (O2) and create a peroxyl-fatty acid radical. As this is also an unstable radical species, it will also react with another free-fatty acid to produce another free fatty acid radical alongside lipid peroxide (or a cyclic peroxide). This cycle continues until…

Termination: When the proportion of free radical species is high enough that free radicals are likely to collide and react with other free radicals, a non-radical species is produced, and the oxidation reaction ends.

Oxidation in food and antioxidants

As lipids in foods oxidise, hydroperoxides are produced. As the reaction propagates, lots of secondary reaction products can form, such as acids, alcohols, aldehydes, and ketones. In the vast majority of cases, these products adversely affect the qualities to which food is judged like flavour, aroma, taste and nutritional value.

These side products have also been found to be potentially dangerous for humans and can cause toxic effects, therefore it is critical to minimise the oxidation of food in order to maximise quality and lifespan of products.

So how is it done?

One of the most commonly employed tactics is the addition of antioxidants in foods. There are a wide variety of antioxidants, that generally fall into a few different categories.

  • Nutrient antioxidants (Vitamins A, C and E)
  • Mineral antioxidants (Copper, Zinc and Selenium)
  • Non-nutrient antioxidants (Phytochemicals – such as Lycopenes and Anthocyanins)

Antioxidants essentially ‘mop up’ free-radical species and prevent or greatly slow down oxidation by doing so.

Minimising the interaction of the catalytic systems previously mentioned with foodstuffs also has a positive impact on their lifespan and curtails oxidative reactions.

VELP Oxitest

When it comes to food science, it’s clear that understanding the impact of oxidation on a food product is absolutely critical in order to accurately predict shelf life and quality. We at a1-envirosciences are proud to offer the top-of-the-range VELP Scientifica line of products, including the OXITEST Oxidation Stability Reactor.

Whether you work in Food & Feed, Pharmaceuticals, Cosmetics or Petrochemicals, the OXITEST reactor is able to accurately accelerate the lipid oxidation process and provide fast and reliable results every time!

Whether the sample is solid, liquid or doughy, the OXITEST stability test ensures representative results without a large amount of sample preparation! And with the OXISoft™ software, full control of up to 4 separate OXITEST reactors can occur from the same PC at once!

Click this link to learn more about the OXITEST: https://a1-envirosciences.co.uk/products/velp-products/oxitest-oxidation-stability-reactor/

Conclusion

Although there is (currently) no sure-fire additive or technique to stop oxidation of food permanently and safely, through the addition of antioxidants and proper storage containers and conditions we can greatly increase shelf-life. Regular and stringent testing of food products both prior to and post release for sale is critical for accurate shelf-life and safety and should continue to be employed in the sector.

If you require a top-of-the-range oxidation stability tester or are interested in discussing our wide range of VELP products, give us a ring on 0845 873 8181 or get in touch with us by email: sales@a1-envirosciences.co.uk