Visual determination of oxidation of edible oil by a nanofiber mat prepared from polyvinyl alcohol and Schiff's reagent.

A fiber mat was developed to visually determine the oxidation of edible oils, based on the colorimetric reaction of Schiff’s reagent and aldehydes - the major volatile formed during lipid oxidation. The mixtures of polyvinyl alcohol (PVA) and Schiff’s reagent containing various amounts of glycerol were electrospun to form the fiber mats. The response of the PVA/Schiff’s reagent fiber mats to gaseous hexanal (model aldehyde) was investigated. Oxidized soybean oils were used to evaluate the effectiveness of the PVA/Schiff’s reagent fiber mat for indicating oxidation of the oils. The results showed that the fiber mats obtained had average fiber diameters of less than 100 nm. Upon hexanal exposure, the fiber mats turned from white to purple. Higher amount of glycerol led to larger color change of the fiber mats and shorter response time to hexanal. A linear relationship (R2 = 0.96) was observed between the color change of the mat and hexanal concentration (15–117 μmol L−1). The visual determination limit of the mat for hexanal was 29 μmol L−1. The color change of the PVA/Schiff’s reagent fiber mat was increased with an increase of soybean oil oxidation. Out of the seven soybean oils tested, the PVA/Schiff’s reagent fiber mat was able to correctly indicate the oxidation states of six oils. The result suggested that the visual determination method developed is a promising method to indicate the oxidation of edible oils, which can be performed easily by non-experts. Graphical abstract