## 4 Use of Spectroscopic Techniques for Monitoring Changes in Muscle Foods during Processing
### Fish and Other Seafoods
#### 4.1.2 Non-Thermal Treatments  
The determination of the freshness and quality of packaged food is problematic since direct contact with food is not visible and use of the sample in destructive way carries a significant cost. This issue is commonly encountered with products treated with emerging technologies, such as irradiation and HPP that aim at treating packaged products. Non-destructive spectroscopy techniques enable the examination of freshness and determination of the quality of packaged muscle foods. Thus, enable making proper decisions regarding their shelf life without compromising the product's integrity. Raman Spectroscopy: Little has been reported on the use of Raman spectroscopy for monitoring changes in fish and other seafoods following non-thermal treatments. One of the scarce examples available in the literature is the study conducted by [PERSON] and others who applied resonance Raman spectroscopic to investigate smoked salmon meat after HPP (up to 600 MPa) [183]. The technique provided novel insights to understand structural changes occurring in astaxanthin and myoglobin (the key components of smoked salmon flesh) as well as the degradation mechanisms of the carotenoid, which is the origin of the color attenuation of smoked salmon after the pressure-treatment. Fourier-Transform Infrared (FT-IR) Spectroscopy: The technique was found to be useful to monitor changes in lipid oxidation (formation and decomposition of free fatty acids and hydroperoxides) in muscle foods. For example, FT-IR spectra contain bands showing vibration of the C-O group and bending vibration of the CH\({}_{2}\) groups at wavelength of 1162.79 and 1215.70 cm\({}^{-1}\), respectively, are associated with saturated acyl groups, cis C=C at 1657.16 cm\({}^{-1}\) that is assigned to unsaturated acyl groups, a stretching vibrational band for the C=O carboxylic group at wavelength of 1739.29 cm\({}^{-1}\) that represent free fatty acids, and a band at wavelength of 3341.52 cm\({}^{-1}\) representing hydroperoxides. The detection of formed FFA and hydroperoxides in striped catfish oil samples demonstrated the synergistic effect of modified atmospheric packaging (MAP, 60% N\({}_{2}\)/35% CO\({}_{2}\)/5% O\({}_{2}\)) and tannic acid addition to control lipid oxidation in chilled striped catfish [117]. FT-IR wavelengths in regions from 1752 to 1735 cm\({}^{-1}\), from 1560 to 1245 cm\({}^{-1}\), and from 1160 to 1025 cm\({}^{-1}\) were used in a PLSR model to predicate freshness, TVC, and some specific microorganisms in fresh salmon stored under various packaging systems (aerobic, MAP (50%N\({}_{2}\)/40%CO\({}_{2}\)/10%O\({}_{2}\))) at 3, 8, and 30 \({}^{\circ}\)C [184]. The TVC and psychotrophs, lactic acid bacteria, molds, and yeasts, _Brochothrix thermosphacta_, _Enterobacteriaceae_, _Pseudomonas_ spp., and H\({}_{2}\)S producing bacterial counts were successfully with R\({}^{2}\) in the range of 0.61-0.87. The technique was proven to be very useful in investigating the effect of HPP treatment on the protein structure [185]. The C=O stretching vibration representing the amide I band in 1600-1700 cm\({}^{-1}\) wavelength range was suggested to be a useful indicator of the secondary structure of protein. In particular, bands at 1652 and 1683 cm\({}^{-1}\) are related to \(\alpha\)-helical and intramolecular antiparallel \(\beta\)-sheet structures, respectively, in salmon [185]. Slightly different wavelengths have been reported for shrimp where the wavelengths related to \(\beta\)-sheets in the amide I region were found at 1613-1637; 1682-1696 cm\({}^{-1}\), for \(\alpha\)- helices at 1645-1662 cm\({}^{-1}\), for turns at wavelengths 1662-1682; 1630 cm\({}^{-1}\) and for unordered structure at 1637-1645 cm\({}^{-1}\)[186]. FT-IR confirmed structural changes in the secondary and tertiary structures of protein upon HPP treatment above 200 MPa.