Monitoring of lipid oxidation using a fluorescent sol-gel functionalized material

The food industry lacks rapid, easy-to-use and non-toxic analytical methods to assess the oxidation level of lipid-rich products. A new fluorescent sol-gel sensing material was developed for the fast and simple monitoring of carbonyls secondary products of lipid oxidation. This paper defines the sensor's range of applicability, specifically examining the impact of the nature and structure of the detected carbonyl compounds, as well as the effects of pH and the nature of the food-simulating medium on its response. The material exhibited high fluorescence intensity, which was quenched upon interaction with carbonyls. The size and hydrophobicity of the analyte (propanal, hexanal, nonanal, 1-penten-3-one and 1-octen-3-one) impacted the kinetics and the percentage of fluorescence quenching as well as the limit of detection and the saturation limit of the sensor. Additionally, the solvent nature had a significant impact on fluorescence: fluorescence intensity was higher in ethanol compared to the more polar ethanol/water (10/90, v/v) mixture used as a food simulant. Finally, the optimal pH range to operate the sensor was determined to be from 7 to 9. This study thus validated the feasibility of using this new sensor for the fast (less than 5 min) and simple (no sample preparation) monitoring of food oxidation level without using any toxic reagent compared to conventional methods. The sensor enables global carbonyl content determination within an operative pH range and a range of detection that would cover the entire shelf-life of lipid-rich food products.