Mechanistically derived fluorescence rancidity index for real-time monitoring of olive oil oxidation under thermal, photo, and frying conditions

A fluorescence-based method was developed for rapid, non-destructive monitoring of olive oil oxidation. The fluorescence rancidity index (FRI) was introduced as a ratio-based optical indicator normalized to fresh oil fluorescence. Using a custom-built laser-induced fluorescence system (532 nm excitation), extra virgin and pomace olive oils were evaluated under thermal oxidation (180 °C), UV oxidation, and repeated frying. Oxidation caused progressive attenuation and a blue shift of chlorophyll-associated emission (~675 nm). Under thermal oxidation, FRI showed strong correlations with PAV ( r = 0.92), TOTOX ( r = 0.91), INTOX ( r = 0.92), and CDV ( r = 0.88), whereas no significant correlations were observed under UV oxidation. FRI also increased progressively during repeated frying. These findings support FRI as a rapid, reagent-free optical indicator of olive oil oxidation, particularly under thermal conditions, while highlighting its oxidation-pathway-dependent response.