6.2
meq O₂/kg
3.1
mmol O₂/kg
—
3.1
mL
6.2
meq O₂/kg
3.1
mmol O₂/kg
—
3.1
mL
The Peroxide Value (PV) calculator determines the level of lipid peroxides in fats and oils, expressed as milliequivalents of active oxygen per kilogram of sample. Peroxides are the primary products of lipid oxidation — formed when atmospheric oxygen attacks unsaturated fatty acid double bonds through a free radical chain reaction. The peroxide value is the most widely used indicator of oxidative rancidity in the early stages of deterioration. Fresh oils have PV below 1 meq O₂/kg, while values above 10 indicate significant oxidation and flavour deterioration. This measurement is mandatory in food quality regulations worldwide, including Codex Alimentarius, EU, and FDA standards. The iodometric titration method detects peroxides by their ability to oxidize iodide ions to iodine, which is then quantified with sodium thiosulfate.
The peroxide value determination uses iodometric titration. Peroxides in the sample oxidize iodide ions to iodine:
$$R\text{-}OOH + 2KI + H_2O \rightarrow R\text{-}OH + I_2 + 2KOH$$
The liberated iodine is titrated with standardized sodium thiosulfate:
$$I_2 + 2Na_2S_2O_3 \rightarrow 2NaI + Na_2S_4O_6$$
Using starch indicator (blue → colorless endpoint).
The peroxide value is:
$$PV = \frac{(V_{sample} - V_{blank}) \times N \times 1000}{W}$$
where $$V_{sample}$$ is the thiosulfate volume for the sample (mL), $$V_{blank}$$ is for the blank, $$N$$ is the normality of thiosulfate, and $$W$$ is the sample weight (g). The factor 1000 converts from equivalents per gram to milliequivalents per kilogram.
To convert meq O₂/kg to mmol O₂/kg, divide by 2 (since each peroxide bond contains one O-O linkage but liberates 2 equivalents of iodine).
Quality guidelines for peroxide values: Fresh refined oils: < 1 meq O₂/kg — excellent quality, no detectable oxidation. Good quality: 1-5 meq O₂/kg — acceptable for most applications. Codex Alimentarius limit for refined oils: 10 meq O₂/kg. Virgin olive oil maximum: 20 meq O₂/kg (extra virgin: 15). Values above 20 indicate rancid oil unfit for consumption. Important caveat: PV can decrease in advanced oxidation because peroxides decompose into secondary products (aldehydes, ketones). Therefore, a low PV does not always mean fresh oil — it could indicate that oxidation has progressed beyond the peroxide stage. Combine PV with anisidine value or TOTOX value for complete oxidation assessment.
Inputs
Results
PV = (0.9 × 0.01 × 1000)/5.0 = 1.80 meq O2/kg. Good quality, minimal oxidation.
Inputs
Results
PV = (3.1 × 0.01 × 1000)/5.0 = 6.2 meq O2/kg. Oxidation has started — oil should be used soon or discarded.
Peroxide value measures the concentration of peroxide and hydroperoxide groups formed during the initial stage of lipid oxidation. It is expressed as milliequivalents of active oxygen per kilogram of fat (meq O2/kg). Higher values indicate more oxidative damage to the oil.
Peroxides are primary oxidation products that decompose into secondary products (aldehydes, ketones, epoxides) as oxidation progresses. In severely oxidized oils, peroxide breakdown exceeds formation, causing PV to drop. This is why PV alone is insufficient — use anisidine value for secondary oxidation.
TOTOX (Total Oxidation Value) = 2×PV + p-AnV (anisidine value). It combines primary oxidation (PV) and secondary oxidation (anisidine value) into a single number. TOTOX below 10 is considered good quality, above 26 is unacceptable for most applications.
Light (especially UV), heat, oxygen exposure, metal ions (Fe, Cu), and high degree of unsaturation (more double bonds) all accelerate oxidation. Antioxidants (vitamin E, BHT, rosemary extract), dark storage, nitrogen blanketing, and refrigeration slow it down.
Codex Alimentarius sets maximum PV at 10 meq O2/kg for refined oils and 15 meq O2/kg for cold-pressed/virgin oils. The European Union specifies the same limits. Extra virgin olive oil has a stricter limit of 20 meq O2/kg (some PDO standards require < 15).
Oil samples should be protected from light and air exposure. The analysis should be performed immediately after opening. The sample-solvent mixture must be purged with nitrogen, and all reagents must be fresh. Starch indicator should be added only near the endpoint to prevent iodine loss.
For low PV oils (fresh, refined): use 0.01 N thiosulfate for adequate sensitivity. For high PV oils (crude, oxidized): use 0.1 N to avoid excessively large titration volumes. The blank titration should be less than 0.5 mL to ensure reagent quality.
PV has limited usefulness for frying oils because the high temperature rapidly decomposes peroxides into secondary products. For frying oil quality, total polar compounds (TPC) and color tests (TPM test kits) are more reliable indicators than PV.
Since each peroxide (-O-O-) liberates 2 equivalents of iodine in the titration, 1 mmol of peroxide = 2 meq. Therefore, mmol O2/kg = meq O2/kg ÷ 2. Some European standards report PV in mmol/kg, while AOCS uses meq/kg.
Commercial frying operations should test oil quality at least daily, or more frequently during heavy use. While PV is one option, rapid test kits measuring polar compounds or free fatty acids are more practical for routine monitoring in food service environments.
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