The Role of Antioxidants in Preserving Food Quality

Every food product that contains fats or oils is at risk of going bad – not from bacteria, but from a chemical process called oxidation. When fats react with oxygen, the result is rancidity: off-flavours, discolouration, loss of nutrients, and even the formation of potentially harmful compounds. Lipid oxidation in polyunsaturated fatty acids leads to rancid off-flavours, reduced nutritional value, and shorter storage periods. Antioxidants are the food industry’s primary defence against this deterioration. They are chemical compounds – both natural and synthetic – that interrupt the oxidation chain reaction and keep food fresh, safe, and palatable for longer.

What is lipid oxidation and why does it matter? 🔗

Lipid oxidation is a chemical process in which unsaturated fatty acids in fats and oils react with oxygen from the air. This process results in rancidity and deterioration of fats, progressing through free-radical propagated chain reactions. It doesn’t happen all at once – it unfolds in three distinct stages.

Initiation 🔗

The process starts when external factors like heat, light, or the presence of metal ions (especially iron and copper) destabilise unsaturated fatty acid molecules. This disruption causes the formation of lipid radicals – highly reactive molecules missing an electron. These radicals are unstable and immediately begin seeking electrons from neighbouring molecules.

Propagation 🔗

Once lipid radicals form, they react rapidly with oxygen to produce peroxy radicals and hydroperoxides. These peroxyl radicals further react with lipids to form additional hydroperoxides, continuing the chain reaction. This is the self-sustaining phase – each reaction generates new free radicals that attack more fat molecules. The more unsaturated (polyunsaturated) a fat is, the more vulnerable it becomes, because its double bonds are prime targets for radical attack.

Termination 🔗

Eventually, hydroperoxides – the primary oxidation products – break down into secondary products such as aldehydes, ketones, and alcohols. These secondary compounds are directly responsible for the stale, rancid smells and off-flavours that consumers associate with spoiled food. This breakdown also diminishes the nutritional value of food, since vitamins sensitive to oxidation are degraded in the process.

How antioxidants work: breaking the chain 🔗

Antioxidants protect food by interrupting the oxidation chain reaction before it can cause widespread damage. The primary mechanism is straightforward: antioxidant molecules donate a hydrogen atom or an electron to a free radical, stabilising it and converting it into a harmless, non-reactive compound. This stops the radical from attacking additional fat molecules.

What makes antioxidants effective is the stability of the radical they form after donating their electron. The high stability of antioxidant radicals compared to food-derived radicals results from resonance delocalisation in the phenolic rings of the antioxidant compounds. In simpler terms, the antioxidant’s molecular structure allows it to absorb and distribute the extra energy from the radical evenly, preventing further reactions.

Different antioxidants can target different points in the oxidation process. Some scavenge free radicals directly (primary antioxidants), while others remove oxygen, chelate pro-oxidant metal ions, or decompose hydroperoxides (secondary antioxidants). This is why food manufacturers often use combinations of antioxidants for comprehensive protection.

Synthetic antioxidants commonly used in food 🔗

Synthetic phenolic antioxidants have been used for decades in the food industry because of their effectiveness, stability, and low cost. The four most widely used synthetic antioxidants are BHA, BHT, propyl gallate, and TBHQ.

Butylated hydroxyanisole (BHA) 🔗

BHA is a white, waxy solid that is highly soluble in fats. It is a mixture of two isomers, with the 3-isomer making up about 90% of commercial BHA and considered the more effective antioxidant. BHA has excellent stability at high temperatures, making it particularly useful in frying applications. It is commonly found in animal fats, cereal products, and confectionery items, especially those made with coconut and palm kernel oil. BHA is often used in combination with other antioxidants to boost its effectiveness.

Butylated hydroxytoluene (BHT) 🔗

BHT works by donating hydrogen atoms to free radicals, neutralising them before they can propagate the oxidation chain. BHA and BHT combinations show a synergistic antioxidant effect, which is why they are frequently used together. BHT is particularly valued for its “carry-through” properties – meaning it remains active even after food has been processed at high temperatures. You’ll find BHT in breakfast cereals, snack foods, chewing gum, and packaged baked goods.

Propyl gallate (PG) 🔗

Propyl gallate contains three hydroxyl groups, which give it a high degree of reactivity and strong antioxidant capacity. However, it has some limitations: it is less soluble in fats, tends to chelate trace minerals like iron, and forms coloured complexes. PG is also less stable at high temperatures – it decomposes at its melting point of 148°C, which makes it unsuitable for frying applications. It works well, however, in products that do not undergo intense heat treatment.

Tert-butylhydroquinone (TBHQ) 🔗

TBHQ is especially effective in vegetable oils and is more heat-stable than many other antioxidants. Synthetic antioxidants like TBHQ are highly effective in preventing lipid oxidation, particularly in high-fat foods prone to rancidity. It is widely used in frying fats, instant noodles, and other processed foods. One point to note: TBHQ, while powerful, is also the quickest among synthetic antioxidants to deplete during processing and storage.

Regulatory status 🔗

These synthetic antioxidants are approved for food use by major regulatory bodies around the world. The U.S. FDA classifies BHA and BHT as “Generally Recognised as Safe” (GRAS), provided the total antioxidant content does not exceed 0.02% of the fat or oil content. The European Food Safety Authority (EFSA) permits their use at specified levels – for instance, BHT is allowed up to 100 mg/kg of fat, while BHA and TBHQ can be used at up to 200 mg/kg.

Natural antioxidants: tocopherols and ascorbic acid 🔗

While synthetic antioxidants are effective and economical, consumer demand for “clean label” products has driven growing interest in natural alternatives. The two most important natural antioxidants used in food preservation are tocopherols and ascorbic acid.

Tocopherols (vitamin E) 🔗

Tocopherols exist in four forms – alpha (α), beta (β), gamma (γ), and delta (δ) – and are found naturally in vegetable oils, nuts, and seeds. Their primary function is to preserve food colours and flavours by slowing deterioration, rancidity, or discolouration caused by oxidation. Gamma-tocopherol is often more effective as a food antioxidant than alpha-tocopherol, even though alpha is the most biologically active form in the body.

Tocopherols work by interrupting the lipid autoxidation chain – they donate hydrogen atoms to peroxy radicals, converting them into stable hydroperoxides and stopping the chain reaction. They are especially effective in protecting polyunsaturated fats, which are the most oxidation-prone type of fat. Commercial tocopherol concentrates, available as mixed tocopherols, are widely used in vegetable oils, baked goods, and snack foods.

Ascorbic acid (vitamin C) 🔗

Ascorbic acid is often included in food products as a preservative, with its antioxidant properties used to prevent discolouration and protect lipid-based products from spoilage. It functions through two main mechanisms: oxygen scavenging (reacting with dissolved oxygen before it can attack fats) and free radical quenching (directly neutralising reactive species).

Ascorbic acid is water-soluble, so it works primarily in the aqueous phase of food systems. However, its fat-soluble form – ascorbyl palmitate – is effective directly within oils and fats. Beyond its own antioxidant action, ascorbic acid plays a critical supporting role by regenerating other antioxidants, particularly tocopherols, after they have been oxidised. This is one of the most important examples of antioxidant synergy.

Antioxidant synergy: why combinations work better 🔗

One of the key principles in food preservation is that antioxidants often perform better in combination than individually. This phenomenon is called synergy, and it occurs through several mechanisms.

The most well-known example is the interaction between tocopherols and ascorbic acid. Ascorbic acid can regenerate α-tocopherol, inactivate metal initiators, and reduce hydroperoxides. When tocopherol neutralises a free radical, it loses its own electron and becomes an inactive tocopheroxyl radical. Ascorbic acid then donates an electron to this spent tocopherol, restoring it to its active form. This recycling mechanism extends the overall antioxidant capacity of the system significantly.

Synergy also occurs when different antioxidants target different stages of oxidation. A free radical scavenger like BHT paired with a metal chelator like citric acid provides protection at both the propagation and initiation stages simultaneously. Pairing antioxidants can achieve excellent antioxidant capability, and synergists such as citric acid, ascorbic acid, phosphoric acid, and lecithin can regenerate oxidised antioxidants, allowing them to remain functional for longer periods.

This is also why BHA and BHT are often used together. Their combined effect on lipid oxidation is greater than what either would achieve alone, providing more robust protection across a wider range of conditions.

Food applications: where antioxidants are used 🔗

Antioxidants are added to virtually every category of food product that contains fats or oils. Here is how they are applied across major food categories.

Fats, oils, and spreads 🔗

Cooking oils, margarine, and shortening are among the most common applications. Oils and fats in processed foods like spreads, baked goods, and snacks are frequently supplemented with antioxidants including tocopherols, BHT, BHA, and propyl gallate. TBHQ is especially popular in vegetable oils because of its strong performance in unsaturated fat systems.

Meat and poultry products 🔗

Processed meats like sausages, ham, and cured products use antioxidants to prevent colour fading, off-flavour development, and fat oxidation. Ascorbic acid serves a dual purpose in meat processing: it acts as an antioxidant and also accelerates the curing reaction with nitrites, helping to develop and fix the characteristic pink colour of cured meats while preventing the formation of harmful nitrosamines.

Cereals, baked goods, and snack foods 🔗

Products like breakfast cereals, crackers, biscuits, and chips contain oils that are vulnerable to oxidation during their relatively long shelf lives. BHT is frequently chosen for cereals because of its carry-through stability, while mixed tocopherols are increasingly used where natural-sounding labels are preferred. Fried snacks often rely on TBHQ, as it withstands the high temperatures of frying.

Dairy products 🔗

Butter, ghee, and anhydrous milk fat also benefit from antioxidant protection. BHA, BHT, and tocopherols are all used in dairy fat products. In fact, the synergistic combination of BHA and BHT has been widely adopted in butter oil and dairy fat spreads for enhanced stability.

The shift towards natural antioxidants 🔗

While synthetic antioxidants remain effective and widely approved, the food industry is seeing a clear trend toward natural alternatives. The U.S. food industry is experiencing a surge in demand for natural antioxidants, driven by consumers seeking clean-label products and avoiding artificial preservatives. Manufacturers are increasingly replacing BHA and BHT with mixed tocopherols, rosemary extract, and green tea extract in vegetable oils, chips, and nut mixes.

Plant extracts rich in polyphenols – particularly rosemary extract containing carnosic acid and carnosol – have emerged as effective natural antioxidants for meat, oil, and baked goods applications. However, natural antioxidants generally have some limitations: they tend to be less heat-stable, shorter-lived, and more expensive than their synthetic counterparts. Balancing performance, cost, and consumer expectations remains an ongoing challenge for food manufacturers.

Factors that influence antioxidant effectiveness 🔗

Not all antioxidants perform equally well in every food system. Several factors determine how effective an antioxidant will be in a given application.

Fat composition: Foods with highly unsaturated fats need stronger antioxidant protection because more double bonds mean more sites for radical attack. Polyunsaturated oils like fish oil or flaxseed oil require particularly robust antioxidant systems.

Processing temperature: Some antioxidants degrade at high temperatures. BHA and TBHQ handle heat well, while propyl gallate and some natural antioxidants do not. Choosing the right antioxidant for the processing conditions is essential.

Solubility: Fat-soluble antioxidants (like BHT and tocopherols) work best in bulk oils and the lipid phase of emulsions, while water-soluble ones (like ascorbic acid) are effective in the aqueous phase. Ascorbyl palmitate bridges this gap as a fat-soluble derivative of vitamin C.

Concentration: More is not always better. Alpha-tocopherol, for example, can actually promote oxidation at very high concentrations – a phenomenon known as the prooxidant effect. Proper dosing is critical.

Timing of addition: Antioxidants should be added as early as possible in food processing. Once oxidation has started, antioxidants cannot reverse the damage already done – they can only slow further progression.

What do you think? As consumers become more aware of ingredient labels, how do you see the balance between synthetic and natural antioxidants evolving in everyday food products? And could emerging plant-based antioxidant sources eventually match the performance of synthetic ones across all food applications?

References

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