Monitoring the quality of frying oils using a nanolayer coated optical fiber refractometer

The analysis of the quality of food oils is of paramount importance, because the degradation of oils can lead to formation of harmful substances to the human organism. With the increase of the degradation of oils an increase of its refractive index occurs. The objective of this work is to develop and to characterize optical fiber refractometers sensitive to variations of refractive index of food oil samples. The optical fiber refractometers thanks to the intrinsic characteristics make them suitable for monitoring the quality of frying oils. They possess the advantages to require small volumes of sample for analysis, do not contaminate the sample, and supply the response in real time. In this work a long period grating (LPG) as refractometer is used because of their sensitivity to refractive index of the external media: degraded and not degraded frying oil samples. The oil samples had been characterized by the analysis of total polar components. The refractive index of oil is above 1.47, this region the LPG does not show enough sensitivity, a nanolayer of an organic material was coated onto the fiber. Using the Langmuir-Blodgett technique the response of LPG is modified according to the refractive index and thickness of the film. The deposition of the film modifies the rates effective modes of cladding, thus improving the response of the changes in the refractive index of the external media higher than that the refractive index of the cladding (n = 1.457).