STUDY OF CAROTENOIDS BY RAMAN SPECTROSCOPY AND COLORIMETRIC CHANGES IN IRRADIATED SALMON FILLETS (Salmo salar)

Irradiation is a physical method that can be applied to increase the shelf life of foods. It is effective in reducing microorganisms. However, it can cause undesirable changes, especially in foods rich in lipids. It may promote the formation of free radicals which can induce oxidation reactions. This study aimed to investigate the effect of irradiation on coloration and carotenoid pigments in chilled salmon fillets (1°C). The samples were irradiated with doses of 1 and 3 kGy, using a source of 60Co. Control samples (0 kGy) were also prepared. The irradiated samples and the control remained at refrigeration temperature throughout the irradiation process until color analysis, using ice for this. For a preliminary analysis of carotenoids, mapping by Raman spectroscopy was used. Aliquots of approximately 2 g were used for this analysis. These were dried for 24 h, without any additional treatment, and then analyzed. Color analysis was performed 24 h after irradiation using a CM-600D colorimeter (Konica Minolta®, Japan). Color coordinates L*a*b* (CIELAB) were obtained, in which L* indicates luminosity (black=0/white=100); a* is the red (+)/green (-) coordinate and b*the yellow (+)/blue (-) coordinate. All analyzes were performed in triplicate. With the use of Raman spectroscopy, spectra were obtained in the region from 200 cm-1 to 2200 cm-1, in which three characteristic peaks were identified, at the wavenumber 1013 cm-1, 1164 cm-1 and 1526 cm-1. According to the literature, these wavenumber are the three main indicators associated with carotenoid pigments and, as they showed a reduction in intensity with the increase of the irradiation dose, it can be inferred that the irradiation reduced the content of these pigments (Schulz, Baranska and Baranski., 2005). The literature reports the feasibility of applying Raman spectroscopy for detection and monitoring of carotenoids and oxidation in foods. In the color analysis, there was a significant (p<0.05) reduction in the intensity of red, and an increase in luminosity in the irradiated samples compared to the control. This color decrease is probably associated with the oxidation tendency of total carotenoids, corroborating the results obtained in Raman Spectroscopy. Control salmon samples irradiated at 1 and 3 kGy showed values of L*= 51.01 (±0.67), 56.03 (±2.37) and 62.51 (±0.98); a*=18.57 (±0.70), 11.56 (±1.01) and 3.01 (±0.30); and b*=23.17 (±1.35), 24.78 (±1.10) and 21.78 (±1.01), respectively. Thus, it can be concluded that the red-orange coloration of salmon decreased with the use of irradiation. The results obtained, although preliminary, can be used as a basis for future work.
Schulz H, Baranska M, Baranski R. Potential of NIR-FT-Raman spectroscopy in natural carotenoid analysis. Biopolymers. 2005 Mar;77(4):212-21. doi: 10.1002/bip.20215.