1. The chain reaction behind autoxidation

Unsaturated fatty acids can oxidize through radical reactions under conditions involving heat, light, or catalytic metals. Reaction with oxygen forms lipid hydroperoxides (LOOH), primary oxidation products that can later decompose into a variety of secondary products. Their structures depend on fatty-acid double-bond positions and the surrounding conditions. Kato’s 2026 review covers radical, enzymatic, and singlet-oxygen pathways and explains how hydroperoxide formation and decomposition lead to structurally diverse products.

2. Why one peroxide measurement cannot describe all rancidity

Hydroperoxides are formed during oxidation but can also break down over time. A single measurement of a primary oxidation product therefore cannot describe the complete oxidation history or sensory quality. Interpretation depends on the sample, its heating and storage history, oxygen exposure, and analytical method. Oxidation also affects the food being cooked, not only the oil: nutrients and sensory properties may change with cooking duration and conditions.

3. What the potato-frying comparison found

Santos and colleagues intermittently deep-fried potatoes in extra-virgin olive, peanut, and canola oils at 175°C, for up to 8 hours per day and 28 hours in total. They compared chemical components and sensory properties of the potatoes. With longer use, vitamin C and other measured potato nutrients declined regardless of oil type. Potatoes fried in canola oil contained more aldehydes derived from polyunsaturated-fat oxidation, while those fried in olive oil were enriched in phenolic compounds. Under the tested conditions, acrylamide did not vary with oil type or frying hours. These findings should not be generalized unchanged to other foods, oils, or fryers.

4. Expert perspective: distinguish a mechanistic review from a cooking trial

Kato’s review synthesizes mechanisms of lipid-hydroperoxide formation and decomposition; it does not set a household rule for how many times frying oil can be reused. Santos’s experiment, conversely, compared a particular potato variety and three oils under a defined intermittent-frying schedule; it did not test every pathway of lipid oxidation. Read together, the sources help separate molecular mechanisms from outcomes measured in a specific food experiment.

In practice, quality cannot be judged from oil type alone. Consider heating duration, repeated use, temperature management, and the condition of both the raw material and the cooked food. The study’s 175°C and 28-hour schedule describes its experiment, not a consumer safety limit or discard time. Nor does an oxidation marker by itself quantify a health risk.

References: Fried Potatoes: Impact of Prolonged Frying in Monounsaturated Oils / Mechanistic Principles of Lipid Oxidation: From Hydroperoxide Formation to Secondary Oxidation Reactions