Study of the oxidative degradation of farmed salmon lipids by means of Fourier transform infrared spectroscopy. Influence of salting

Abstract

Farmed salmon fillets were dry-salted for 24 h. Both salted and unsalted samples were submitted to oxidative conditions at 50• C in an oven with circulating air. Lipids of both samples were extracted daily from aliquots and studied by Fourier transform infrared spectroscopy. The infrared spectra of salmon lipids are similar to those of vegetable edible oils, with differences in the frequency and absorbance of some bands due to their different acyl group compositions. The infrared spectra of salted and unsalted fish lipid samples remain unchanged during a period of time, which is shorter for the salted salmon. After this period, changes in the frequency and absorbance of some bands of the spectrum are observed owing to the presence of oxidation products. Therefore the reduction in the oxidative stability of farmed salmon lipids caused by the dry-salting process is proved and the usefulness of this technique for studying the oxidative stability of fish lipid samples as well as their oxidation degree is shown.

Effect of refrigeration time on the lipid oxidation and fatty acid profiles of catfish (<em>Arius maculatus</em>) commercialized in Cameroon

“…Generally, the FTIR spectrum exhibited similar regions of functional group vibrations as reported previously for mackerel fish lipids (Giménez et al 2011), farmed salmon fillet lipids (Guillén and Cabo 2004), as well as for some vegetable oils (Vlachos et al, 2006).…”

“…These bands were also found by Guillén and Cabo (1999). According to Guillén and Cabo (1997), the peaks at 1250 cm -1 and 1150 cm -1 would be associated with the stretching vibration of the C-O ester group and the bending vibration of the CH 2 group, both related to the proportion of saturated acyl groups in the oil sample. Figure 4 shows the effect of refrigeration on select IR regions taken from the spectra of the lipids extracted from catfish.…”

“…Lazzari and Chiantore in 1999 found similar bands when analyzing the oxidative degradation of linseed lipids. The peak at 3010 cm -1 , related to the C-H stretching vibration of the cis-double bond (=CH), appeared at the same wave number in salmon lipids (Guillén et al, 2004). The two peaks just below 3000 (2924 and 2853 cm -1 ) can both be assigned to absorption caused by asymmetric and symmetric stretching vibrations of methyl groups, and the peak at 1750 cm -1 is related to absorption caused by stretching vibrations of ester groups.…”

“…The band associated with the overtone of the glyceride ester carbonyl absorption showed a maximum absorbance near 3448 cm -1 (Guillén et al, 2004). The weak band associated with hydroxyl groups newly formed during oxidation appears in the figure near 3350 cm -1 .…”

“…Recently, the evaluation of volatile compounds has become an additional indicator of lipid oxidation in fish samples (Ross and Smith, 2006). With respect to instrumental methods, infrared spectroscopy has been demonstrated to be a useful tool to monitor oxidative changes in edible oils (Guillén et al, 2004), due to the high information content of infrared spectra and the possibility of assigning specific absorption bands to particular functional groups.…”