Measurements of Optical Penetration Depth in Smoked Salmon

Abstract

Optical spectroscopy is a common method used in the determination of quality parameters in groceries. An optical characterization of smoked Atlantic salmon was carried out in this thesis. The optical penetration depth in salmon was found at 531 nm and 632 nm from measurements with lasers as light sources, and from 550 nm to 880 nm with a tungsten halogen lamp as light source. The spectrum of the halogen lamp combined with the absorption spectrum of the salmon made it difficult to obtain results for wavelengths below 550 nm with the halogen lamp. Two variations in the measurements on smoked salmon were performed; measuring on needle insertion versus needle extraction and measuring across several layers of muscle tissue versus measuring along one layer of muscle tissue in salmon. The absorption coefficient and the reduced scattering coefficient of smoked Atlantic salmon was calculated. Significant differences were found dependent on needle insertion or needle extraction, and whether the measurements were made along one layer or across several layers. The penetration depths were found to be 6.79±0.33 mm across several layers and 10.76±1.03 mm along one layer in the measurements with the He-Ne laser. The diffusion approximation was found to be a good approximation for wavelengths from 600 nm to 700 nm. With further development, it may be possible to determine the astaxanthin content of salmon with the method used in this thesis.