Totox indicator – how to check oil quality before you buy it?

The Totox index is a number calculated using the formula (2×PV) + AV, which indicates the total level of oil oxidation – the lower the value, the fresher the product. For fish oils and omega-3 supplements, a safe limit is a result not exceeding 26, according to GOED and Codex Alimentarius standards. However, for olive oil and most vegetable oils, this index does not have a formal, uniform threshold – here, quality is assessed differently, based on the peroxide value and, in the case of olive oil, K232/K270 indices.

In this article, we explain how Totox is calculated, what standards apply to different types of oils, how to check this index when purchasing – both through a certificate of analysis and IFOS certification, as well as home sensory evaluation – and what actually accelerates oil oxidation in your kitchen or medicine cabinet.

1. What is the Totox index?

Totox (Total Oxidation Value) is a numerical index that determines the total level of oil oxidation – both at early and advanced stages. Unlike individual parameters, such as the peroxide value, Totox combines two measurements into a single value, providing a more complete picture of oil freshness than each of them individually.

The index was developed for the fish oil and omega-3 supplement industry, but is now used more broadly – also in the context of vegetable oils, although its interpretation here requires greater caution (as discussed in chapter 3).

1.1. How is the Totox value calculated?

Totox is not measured directly in the laboratory – it is calculated based on two other independently measured parameters using a simple formula:

where:

• PV (Peroxide Value) – expressed in milliequivalents of active oxygen per kilogram of oil (meq O₂/kg)
• AV (Anisidine Value) – a dimensionless value based on absorbance measurement

The peroxide value is multiplied by 2 because, during progressive oxidation, some peroxides break down into secondary compounds already measured by AV. This multiplier partly compensates for the fact that PV itself underestimates the real level of oxidation in oil that has already been partially processed – the method of calculation is confirmed by an analysis published in PLOS One, where Totox was calculated as (2 × PV) + AV.

1.2. What are peroxide value (PV) and anisidine value (AV)?

To understand what a Totox result truly tells us, it's essential to know what its two components measure individually.

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The peroxide value is a measure of primary oxidation because peroxides are the first compounds formed when polyunsaturated fatty acids begin to oxidize. The problem is that peroxides are unstable – over time, they break down into smaller molecules, including aldehydes, which are responsible for the rancid smell and taste of stale oil. It is these secondary compounds that AV detects.

Therefore, an oil that was heavily oxidized and then refined or stored for a long time may have a surprisingly low PV – the peroxides would have already decomposed – while simultaneously having a high AV. PV alone would then give a false sense of freshness. Combining both values into a single Totox index is intended to prevent this.

2. Why is the Totox index important for oil quality?

High Totox is not just an aesthetic issue – stale, heavily oxidized oil loses its nutritional value, tastes worse, and can deliver compounds that, in larger quantities, are harmful to the body.

2.1. What does high Totox mean for health and taste?

From a sensory perspective, it's straightforward: it's the secondary compounds detected by AV – primarily aldehydes – that are responsible for the rancid, "paint-like" or metallic aftertaste and smell of oil that has lost its freshness. During oxidation of fats, unsaturated fatty acids react with oxygen, forming lipid peroxides, which then break down into small, volatile compounds, including aldehydes and ketones, responsible for the unpleasant taste and smell.

From a health perspective, the topic is more complex and requires distinguishing between two situations: oil that has oxidized while at rest (e.g., poorly stored flaxseed oil or omega-3 capsules), and oil subjected to repeated heating at high temperatures (e.g., frying oil used multiple times).

• Polyunsaturated cooking oils subjected to high-temperature frying can generate significant amounts of cytotoxic and genotoxic lipid oxidation products, including aldehydes, which permeate into the fried food and are consumed with it.
• Animal studies suggest that consumption of thermally oxidized cooking oils can adversely affect lipid profiles (increased LDL, decreased HDL, elevated cholesterol), hematological parameters, and increase oxidative stress in the body.
• Lipid oxidation products are linked in the literature to a range of disease processes, including cardiovascular diseases and inflammatory conditions, although these are mainly data from preclinical and observational studies, not conclusive evidence of the scale of risk with typical, moderate consumption.

In the case of omega-3 supplements, there's another aspect – oxidized EPA and DHA lose their structure, and with it, part of the health potential for which they are taken in the first place. That's why the omega-3 supplement industry was the first to introduce strict Totox limits (Chapter 3.1) – here, the freshness of the oil directly translates to the purpose of its supplementation.

2.2. Primary vs. Secondary Oxidation – Why One Number Is Not Enough

Fat oxidation is a complex process occurring in three stages: initiation, propagation, and termination, leading first to the formation of peroxides, and then to more stable oxidation products. In other words – oil oxidation is a dynamic process, not a one-time state, and different parameters "catch" it at different stages:

• Primary oxidation – the first phase, in which peroxides are formed from fatty acids. This is what PV measures.
• Secondary oxidation – peroxides are unstable and eventually break down into aldehydes, ketones, and other carbonyl compounds. This is what AV measures.

From this arises a practical pitfall: PV alone can give a misleading picture of oil quality. In practice, it happens that in fish oil capsules, peroxide values decrease over time, while anisidine values increase – which ultimately still raises the Totox value. A manufacturer who only provides PV may therefore – intentionally or not – conceal the real level of oxidation of their product.

Therefore, combining both parameters into a single index makes practical sense: it allows detecting both fresh oil that is just beginning to oxidize (high PV, low AV), and "old oxidized" oil where most peroxides have already decomposed (low PV, high AV). Neither of these cases would be correctly identified if only one of these two numbers was considered.

3. What Totox value is considered safe?

The answer to this question depends on the type of oil we are talking about. For fish oils and omega-3 supplements, there is one universally cited and strict threshold. For vegetable oils, the situation is more fluid – and this is a key difference that needs to be understood before comparing labels.

3.1. GOED Standard for Fish Oils and Omega-3 Supplements

The fish oil and omega-3 supplement industry was the first to formalize oxidation limits – and at a surprisingly strict level compared to other edible oils. These limits were established by GOED (Global Organization for EPA and DHA Omega-3s), an association of manufacturers in this industry, in the so-called Voluntary Monograph:

• Peroxide Value (PV): maximum 5 meq O₂/kg
• Anisidine Value (AV): maximum 20
• Totox: maximum 26

These limits are calculated using AOCS Official Method Cd 8b-90 for peroxide value and AOCS Cd 18-90 for anisidine value, and Totox itself is the result of the calculation (2 × PV) + AV. The same numerical values (PV≤5, AV≤20, Totox≤26) were later adopted as an international standard by Codex Alimentarius for fish oils in a separate document – CODEX STAN 329-2017 sets a Totox limit below 26 for fish oil, unlike the standard for vegetable oils, which does not have such a threshold.

Importantly, GOED membership is voluntary, and the limits are in the nature of an industry monograph, not food law enforced by regulatory bodies in every country. In practice, this means that a manufacturer can declare compliance with the GOED standard, but there is no single authority that routinely checks every batch of product for this – hence the importance of a certificate of analysis, as discussed in chapter 5.

Actual test results for market products can vary widely. In a database covering over 1900 fish oil samples, 13.9% exceeded the peroxide value limit (5 mEq O₂/kg), and 8.8% exceeded the Totox limit (26). In other words – the mere fact that a product is an omega-3 supplement in a reputable store does not automatically guarantee compliance with the standard.

Omega-3 60 capsules - Vilgain

3.2. Standards for Vegetable Oils (Codex Alimentarius) – Why There Isn't a Single Totox Threshold Here

For vegetable oils, the situation is different from that for fish oil. The international Codex Standard for Named Vegetable Oils (CXS 210-1999) regulates the peroxide value, but does not establish a formal, uniform Totox limit or anisidine value applicable to all vegetable oils:

• Refined oils: peroxide value up to 10 meq active oxygen/kg
• Cold-pressed and virgin oils: peroxide value up to 15 meq active oxygen/kg

The lack of a formal Totox threshold for vegetable oils is not an oversight, but a consequence of the specificity of this category. Dozens of very different oils fall under one standard – from stable coconut oil, through rapeseed or sunflower oils, to omega-3 rich flaxseed oil – and each of them oxidizes at a different rate and with different susceptibility to the formation of secondary compounds. Unifying the Totox limit for all these products would either be too liberal for oils susceptible to oxidation, or unjustifiably restrictive for very stable oils.

For the same reason, it is worth exercising caution regarding marketing comparisons such as "this oil has a Totox of X, meaning it is better than the standard for fish." The Totox specification below 26 established by GOED was developed with omega-3 products in mind and should not be treated as a universal safety criterion for repeatedly heated frying oils, as different types of oils and other food matrices exhibit different oxidation pathways.

In the scientific literature, informal reference points for vegetable oils appear – some authors indicate that high-quality vegetable oil should have a Totox below 10, compared to the limit of 26 adopted for fish oil. However, this is a recommendation from individual scientific publications, not a formal industry or legal standard – unlike the strict GOED/Codex limit for fish oil.

Organic Olive Oil Spray 200 ml - Vilgain

3.3. Comparative Table of Standards

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The most important conclusion from this table: olive oil does not use the Totox index at all. Its quality and freshness are assessed based on the peroxide value and two UV absorption indices – K232, which increases with primary oxidation and peroxide formation, and K270, which indicates advanced secondary oxidation associated with aldehyde and ketone formation. If you are looking for the Totox index on a bottle of olive oil, you simply won't find it there – and this is not a manufacturer's error.

4. How does Totox differ from peroxide value and anisidine value?

Now that we know what the individual parameters are and what standards apply to them, the practical question remains: which indicator should you look at when buying a specific type of oil? The answer depends on what each parameter actually tells you – and what it doesn't.

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The practical rule is as follows:

• If you are buying an omega-3 supplement or fish oil – look directly for the Totox value (and preferably also PV and AV separately) in the certificate of analysis. This is the only category where Totox has a formal, widely recognized limit value.
• If you are buying olive oil – Totox is not present. Instead, check the peroxide value and K232/K270, if the manufacturer provides them.
• If you are buying another vegetable oil (rapeseed, sunflower, flaxseed, grapeseed, etc.) – formally, the peroxide value compliant with the Codex limit for the given processing type (refined vs. cold-pressed) is primarily important. The Totox value, if provided at all, should be treated as additional, supplementary information, not an official requirement.

PV alone can be misleading due to the reason described in section 2.2 – a low peroxide value does not necessarily mean a low level of oxidation, as this could result from an advanced stage of oxidation where primary oxidation products have already converted into secondary products, lowering PV while AV increases. Therefore, where possible – primarily for fish oils and omega-3 – it is advisable to check both parameters together, rather than relying solely on one of them.

5. How to check the Totox index of the oil you are buying?

The Totox number itself is not printed on the label of any product in standard retail sales – these are laboratory data that must be obtained through other means. This method differs for omega-3 supplements and for ordinary cooking oil purchased in a store.

5.1. Certificate of Analysis (COA) – what to look for from a fish oil/omega-3 manufacturer

A Certificate of Analysis (COA) is a laboratory document pertaining to a specific product batch. A reputable omega-3 supplement manufacturer should be able to provide it – some brands publish it on the product page or make it available by scanning a QR code on the packaging, while others send it upon customer request.

When looking for a COA for fish oil or omega-3, pay attention to the presence of three specific values:

• PV (Peroxide Value) – should be stated in meq O₂/kg
• AV (Anisidine Value) – dimensionless value
• Totox – calculated result (2×PV + AV), preferably clearly below the threshold of 26

If the manufacturer only provides PV, omitting AV and Totox, it's a warning sign – as explained in section 2.2, PV alone can give a false sense of freshness if the oil has already passed the stage of peroxide decomposition into secondary compounds. Lack of transparency regarding AV and Totox does not necessarily mean poor product quality, but it prevents its real verification.

5.2. Independent quality certifications (e.g., IFOS) for omega-3 oils

In addition to the manufacturer's own declarations, there are independent certification programs that test omega-3 products in accredited external laboratories. The most recognizable of these is IFOS (International Fish Oil Standards).

IFOS tests products for active ingredient content (whether the product actually contains the declared amount and type of omega-3 fatty acids), contaminant levels, and stability, meaning whether the oil is as fresh as possible and has not oxidized. As part of IFOS testing, acid value, peroxide value, anisidine value, and Totox value are checked, with a reference threshold of ≤5 meq/kg for individual oxidation parameters.

Test results are translated into a clear star rating scale – for a product to receive the highest, five-star IFOS rating, it must simultaneously meet all criteria: compliance with CRN/WHO tests, omega-3 content consistent with the label declaration, oxidation level consistent with CRN standard, PCB level consistent with CRN standard, and dioxin level consistent with WHO standard. Importantly, IFOS test results for each product batch are publicly available online and can be searched by the batch number from the packaging, allowing verification of the specific bottle you hold in your hand, not just a general brand declaration.

The absence of an IFOS certificate on the label does not automatically mean lower oil quality – certification is voluntary and paid, so some reputable, smaller manufacturers simply do not use it. However, it is a convenient shortcut for consumers who do not want to independently analyze certificates of analysis.

5.3. How to assess the quality of vegetable oil when buying?

For ordinary cooking oil – rapeseed, sunflower, flaxseed, or olive oil – the "certificate of analysis + IFOS" path is practically non-existent in the retail market. Here, quality assessment is primarily based on what is visible on the label and packaging:

• Pressing or harvest date – especially for cold-pressed oils and olive oil; the fresher the harvest, the lower the initial oxidation level. The expiry date itself tells less than the pressing date, as it only indicates an upper limit, not the moment of production.
• Type of packaging – dark glass or opaque containers protect against light much better than transparent plastic or glass bottles.
• Display method in the store – oil standing for months on a lit, warm shelf near a window loses quality faster than oil stored in a cool, shaded warehouse.
• Pressing method – cold-pressed oil usually has more natural antioxidants (tocopherols, polyphenols) than refined oil, but at the same time – according to Codex standards in section 3.2 – a higher initial peroxide value is permissible for it.
• Short ingredient list – the oil itself, without additional "stabilizers" or flavorings, also facilitates subsequent home assessment of freshness (see 5.4), as it does not mask any rancid smell.

None of these elements is a direct measurement of Totox, but together they allow for an estimation of the risk that the purchased oil has already been heavily exposed to the main accelerators of oxidation – which are discussed in more detail in section 6.

5.4. Home, approximate assessment of oil freshness

You don't have a laboratory at home to measure PV or AV, but your senses – especially smell – provide a surprisingly good, though only approximate, indication of the oil's condition.

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In the case of refined oils with little inherent aroma, such as rapeseed or sunflower oil, simply pour a small amount onto a teaspoon and smell it – an unpleasant smell reminiscent of crayons, metal, or something sour means that the oil is past its best-before date. Unrefined oils, including extra virgin olive oil, are more difficult to assess because their natural aroma and taste can mask the beginnings of rancidity – therefore, for such oils, a taste test is also recommended, not just a smell test.

A good habit is to remember (or at least note) how the oil smelled and tasted immediately after opening the bottle – this makes it easier to detect a change over time, rather than evaluating the oil without a reference point.

6. What accelerates oil oxidation and increases Totox?

The Totox index indicates the state of the oil at a given moment, but how quickly this state deteriorates depends on several well-known factors. These mechanisms are largely common to all oils – vegetable, fish, and omega-3 – although some categories are significantly more susceptible than others.

6.1. Light, oxygen, temperature, and repeated heating

Four factors drive the oxidation of fats, whether we are talking about a bottle of rapeseed oil in the kitchen or omega-3 capsules in the medicine cabinet:

• Oxygen – any contact of oil with air, including opening and closing the bottle, introduces additional oxygen that initiates oxidation reactions.
• Light – radiation, especially UV, accelerates photochemical reactions that break down the fat structure, which is why transparent packaging promotes faster rancidity than dark glass or opaque containers.
• Temperature – heat (e.g., storing a bottle of oil next to the stove) accelerates the rate of chemical reactions responsible for the formation of peroxides and secondary products.
• Repeated heating – this is the most aggressive factor, as it combines high temperature and prolonged contact with oxygen.

Sequential, autocatalytic oxidative degradation of unsaturated fatty acids during frying leads to the formation of significant amounts of aldehydic and other toxic lipid oxidation products, which penetrate the fried food. The higher the frying temperature and the more heating cycles the same oil undergoes, the higher the concentration of these compounds – and thus the higher the real Totox of the oil used for frying, even if it had a low value of this index at the start.

This is precisely why the choice of oil with appropriate thermal stability is no less important than its initial freshness in the bottle – not all oils are equally resistant to repeated heating. We discuss this topic in more detail in the article Which oil to choose for frying? Ranking and comparison of oils by thermal stability.

6.2. Specificity of fish/omega-3 oils – why they oxidize faster

Fish and omega-3 oils oxidize much faster than most vegetable oils used in the kitchen, not due to poorer production quality, but due to their chemical structure.

Polyunsaturated fatty acids have many double bonds in their structure, and each of these is a potential site for oxygen attack, initiating a chain reaction of oxidation. EPA and DHA – the main fatty acids in fish oil – are among the most unsaturated fatty acids found in the diet, having more double bonds than, for example, linoleic acid dominant in sunflower oil or alpha-linolenic acid from flaxseed oil. The more double bonds, the faster oxidation occurs with the same exposure to oxygen, light, and heat.

This has direct practical consequences: a study by Kolanowski et al. showed that fish oil capsules stored at room temperature, in sealed packaging with limited light exposure, developed peroxide levels up to 20% higher within just 22 days of storage. This demonstrates that even a relatively short period and seemingly proper storage conditions can noticeably degrade the freshness of such a product – which also explains why the GOED standard from section 3.1 is so restrictive compared to limits for regular vegetable oils.

6.3. How to store oil correctly to maintain quality?

Practical storage rules differ slightly depending on whether we are talking about culinary oil in a bottle or an omega-3 supplement in capsules or liquid form.

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None of these rules will lower the Totox value of oil that has already oxidized – as noted in section 5.4, this process is irreversible. Their role is different: to slow down the rate at which fresh oil degrades from the moment of purchase until consumption, and thereby minimize the risk of exceeding the safe thresholds described in section 3.

7. FAQ

7.1. Does a high Totox mean the oil is spoiled and unfit for consumption?

There is no single rigid boundary between "good" and "spoiled" oil – Totox is a continuous scale, not a black-and-white result. Exceeding the standard (e.g., 26 for fish oil) means that the oil does not meet the industry quality threshold and loses some of its nutritional and flavor value, but a single consumption of such a product is not an emergency situation. The real risk is associated with regular, long-term consumption of highly oxidized fats, not with a single serving.

7.2. Do more expensive oils always have a lower Totox than cheaper ones?

There is no direct correlation. The price of oil mainly depends on the raw material, pressing method, and brand, not on the current oxidation level of a specific bottle – this depends primarily on the freshness of the raw material, production conditions, and how long and under what conditions the oil has been on the store shelf or in storage. A more expensive premium oil may have a high Totox if it was stored improperly, while a cheaper one may have a low Totox if it reached the store shelf relatively recently.

7.3. Does freezing oil slow down its oxidation?

Low temperature generally slows down the rate of chemical reactions, including oxidation, so cooling or freezing can theoretically extend the freshness of oil. In practice, however, this is not a routinely used solution for most culinary oils – some of them (e.g., olive oil) become cloudy or partially solidify at low temperatures, which is normal and reversible upon warming to room temperature, but not always convenient for daily use. For liquid omega-3 supplements, manufacturers more often recommend a regular refrigerator than a freezer.

7.4. Is there a home device for self-measuring Totox?

Not in a widely available and reliable form for the consumer. Measuring PV and AV requires laboratory equipment and reagents, and Totox itself is calculated based on them – it cannot be measured with a single simple test at home. The only available home methods are the sensory assessment described in section 5.4 (smell, taste, appearance), which is purely indicative.

7.5. Does the Totox index also apply to butter and lard?

Methodologically, yes – PV and AV can be determined in any fat, including animal fat, because the mechanism of unsaturated fatty acid oxidation is similar. In practice, however, formal, widely cited Totox limits (GOED, Codex for fish oil) apply to liquid oils rich in polyunsaturated fatty acids – for butter or lard, an analogous, established industry threshold does not function.

7.6. How long after opening does oil maintain a low Totox level?

It is impossible to give a single universal number of days or weeks – it depends on the type of oil (the more polyunsaturated fatty acids, the faster the Totox increases), storage method, and frequency of opening the packaging. Oils rich in polyunsaturated fatty acids, such as flaxseed, and omega-3 supplements lose freshness most quickly, which is why manufacturers usually provide a shorter recommended consumption time after opening for them than for more stable oils, e.g., rapeseed or olive oil.

8. Summary

Totox is a calculated value (2×PV + AV) that combines the level of primary and secondary oil oxidation into a single indicator – the lower the result, the fresher the product. For fish oils and omega-3 supplements, there is a strict, widely recognized limit of 26 (GOED and Codex Alimentarius standards), confirmed by certificates such as IFOS. For vegetable oils, the situation is different – formal Codex standards mainly regulate the peroxide value, and olive oil does not use the Totox index at all, only PV and K232/K270 indices.

In purchasing practice, this means three different strategies depending on the product: for omega-3 supplements, it is worth looking for a certificate of analysis or IFOS designation; for olive oil, check the PV and pressing date; and for other culinary oils, pay attention to the packaging, storage conditions, and, if in doubt, your own senses. Regardless of the type of oil, its main enemies remain the same four factors: oxygen, light, heat, and repeated heating – and proper storage is the only way to slow down oxidation before it occurs.

9. Sources

Standards and regulations:

• GOED Voluntary Monograph, Global Organization for EPA and DHA Omega-3s – PV, AV and Totox limits for omega-3 oils
• Codex Alimentarius – Standard for Named Vegetable Oils, CXS 210-1999 – peroxide value limits for vegetable oils
• EEC Regulation No. 2568/91 and International Olive Council standards – quality parameters for extra virgin olive oil (PV, K232, K270), discussed in: study on the oxidation kinetics of EVOO

Scientific studies:

• Fish oil supplements, oxidative status, and compliance behaviour – PLOS One / PMC
• Vegetable oil oxidation: Mechanisms, impacts on quality, and approaches to enhance shelf life – ScienceDirect
• Oxidation in EPA- and DHA-rich oils: an overview – Lipid Technology, Wiley
• Examination of marine and vegetable oil oxidation data from a multi-year, third-party database – ScienceDirect
• Evidence-Based Challenges to the Continued Recommendation and Use of Peroxidatively-Susceptible PUFA-Rich Culinary Oils – Frontiers in Nutrition / PMC
• Potential Adverse Public Health Effects Afforded by the Ingestion of Dietary Lipid Oxidation Product Toxins – Nutrients (MDPI)
• Potential Health Implications of the Consumption of Thermally-Oxidized Cooking Oils – Polish Journal of Food and Nutrition Sciences
• Omega-3 Long-Chain PUFA Content and Oxidation State of Fish Oil Supplements in New Zealand – Scientific Reports
• Food lipid oxidation and health – International Food Information Service
• Why Are Fish Oil Oxidation Values Important to Your Health? – Omega3 Innovations (regarding Kolanowski et al. study)