The influence of filtration and light exposure on the long-term storage of extra virgin olive oil and its phenolic content — A. Castillo-Luna and F. Priego-Capote
Researchers studied how light exposure, filtration, and storage time affect the phenolic compounds in extra-virgin olive oil. They compared filtered and unfiltered EVOO stored either in darkness or exposed to light for 48 weeks. The biggest finding was clear: light exposure caused far more phenolic degradation than filtration did. ScienceDirect
After 48 weeks, total phenolic content fell by about 78–80% in oils exposed to light, compared with roughly 50–55% in oils stored in the dark. Statistical analysis found that light exposure accounted for 93.8% of the variation in phenolic degradation, while filtration accounted for only 2.2%.
Protecting extra-virgin olive oil from light is critical to preserving its phenolic compounds and long-term quality. In this study, EVOO stored in darkness remained above the study’s European phenolic health-claim threshold throughout the full 48-week period, while EVOO exposed to light dropped below that threshold after about three months. ScienceDirect
The researchers also concluded that filtration can improve medium- and long-term stability by removing water and suspended material that can contribute to hydrolysis, but the effect of filtration was much smaller than the effect of light. Their practical recommendation was to prioritize opaque packaging and filter EVOO before bottling when long-term storage is expected.
The study used one specific EVOO blend produced in Córdoba, Spain, made from 50% Picual, 40% Hojiblanca, and 10% Picudo olives, so the exact rate of phenolic loss should not be assumed to apply identically to every olive oil. The strongest practical conclusion is about storage conditions: light exposure substantially accelerated phenolic degradation.