New paper published
The paper “A novel approach for subsurface through-skin analysis of salmon using spatially offset Raman spectroscopy (SORS)” authored by Nils Kristian Afseth, Matthew Bloomfield, Jens Petter Wold, and Pavel Matousek, is published in Applied Spectroscopy 68 (2), 2014, pages 255 – 262.
In the present study the possibility of employing SORS in the qualitative and quantitative characterisation of quality parameters of salmon through the skin has been explored. A laboratory based SORS set-up comprising an 830 nm laser was employed, and intact samples and model samples made of salmon tissue constituents were used to investigate the penetration of Raman signals through the dark and light part of salmon skin. Intact salmon samples with both dark and light skin were measured at different spatial offsets. When using spatial offsets in the range of 5 – 6 mm, the results clearly show that information regarding fatty acid composition and carotenoid content could be obtained from both dark and light parts of the skin. Similar information could not be obtained using conventional backscattering Raman spectroscopy. Model samples of ground salmon spiked with either solutions of carotenoids or a range of vegetable oils were also measured, and at a spatial offset of 5 mm, a clear relationship between Raman carotenoid band intensities and carotenoid concentrations in the model samples was revealed. In addition, high correlations for the estimation of iodine values (i.e. fatty acid unsaturation) could be obtained for SORS measurements through light and dark parts of the salmon skin. A crude estimate suggested that information from around 5 mm beneath the surface area of the salmon skin could be obtained. The choice of a laser line in the near-infrared region is a major prerequisite for successful through-skin analysis of salmon. This feasibility study could pave the way for future Raman analysis of intact salmon.