## 4 Use of Spectroscopic Techniques for Monitoring Changes in Muscle Foods during Processing
### Fish and Other Seafoods
#### 4.1.2 Non-Thermal Treatments
These changes were lessened in salmon treated by HPP (300 MPa for 10 min) at low temperature (i.e., at 5 \({}^{\circ}\)C compared to 40 \({}^{\circ}\)C) and the use gelatin-lignin film, which resulted in better salmon quality. Similar uses of FT-IR to examine the protein structure of blue crab meat subjected to HPP treatment [125; 187], palm ruff treated by HPP [188], and shrimp treated by ultrasound processing [186] have been reported. These studies confirmed that HPP treatment (100, 300, and 600 MPa for 5 min at 10 \({}^{\circ}\)C) and ultrasound processing (20-kHz frequency, 400 W for various times at room temperature) resulted in a lower percentage of \(\alpha\)-helix and a higher percentage of \(\beta\)-turn secondary structures compared to untreated samples. Collectively, the above results confirmed the ability of FT-IR as a fast, reliable, and accurate technique for the evaluation of freshness and quality of muscle foods. Fluorescence Spectroscopy: The combination of fluorescence and chemometric techniques can be successfully used as a non-destructive method to evaluate the quality of foods. [PERSON] and [PERSON] [116] evaluated the quality of whiting fillets in MAP (50% N\({}_{2}\)/50% CO\({}_{2}\) or 80% N\({}_{2}\)/20% CO\({}_{2}\)) stored at 4 \({}^{\circ}\)C for up to 15 days using physicochemical properties and front face fluorescence spectroscopy emission spectra. A complete segregation of the treatments was achieved using PCA. Lower lipid oxidation, total volatile basic nitrogen, and better texture attributes were found in the MAP treated samples with the 50% CO\({}_{2}\) showing best protection during the cold storage. Hyperspectral Imaging (HSI): Fresh salmon stored aerobically, under MAP (60% CO\({}_{2}\)/40% N\({}_{2}\)) or 90% vacuum packaging at 4 \({}^{\circ}\)C was investigated using HSI [189]. Spectral differences were observed among the treatments, especially at 606 and 636 nm that were suggested to be related to the oxidation state of hemoproteins. Classification model was obtained (>88%) using wavelengths at 606, 636, 665, 705, and 764 nm. The technique was successful in classifying smoked salmon and separate expired product from saleable product at success rate of 82.7% [190]. Magnetic Resonance Techniques: LF-NMR was used to investigate the freshness and quality of half-smooth tongue sole fillets subjected to edible coating treatment and stored chilled in different packaging systems including MAP [191]. The technique provided valuable information on the moisture status from the transverse relaxation times (bound in \(T_{21}\) range 1.32-6.14 ms, immobilized in \(T_{22}\) range of 28.48-117.38 ms, and free in \(T_{23}\) range of 403.7-3274.55 ms) in the fillets. Significant correlations in the range 0.796-0.898 were found for \(T_{22}\) and H\({}_{2}\)O and fat contents as well as the Ca\({}^{2+}\)-ATPaseactivity in the fillets. Furthermore, significant correlations (0.802-0.966) were found for \(T_{23}\) and lipid oxidation, total volatile basic nitrogen, and K value. The study also employed MRI technique to obtain information on the molecular distribution and internal morphological organization of the sample matrix. Overall, MRI enabled the monitoring of the microstructure of the samples and supported the use of MAP and edible coating to maintain freshness and product shelf life. The use of LF-NMR and MRI enabled the prediction of product quality and shelf life. The ability to detect methylated amines and nucleotide degradation products using \({}^{1}\)H NMR was investigated in fresh sardines stored drilled in various packaging systems (aerobic; MAP (30% CO\({}_{2}\) + 70% N\({}_{2}\); 30% CO\({}_{2}\) + 70% N\({}_{2}\)O and 30% CO\({}_{2}\) + 70% Ar)) [192]. The obtained \({}^{1}\)HNMR spectra were used to determine the concentrations of trimethylamine-N, trimethylamine-O, hypoxanthine, adenosine-5\({}^{\prime}\)-diphosphate, adenosine-5\({}^{\prime}\)-monophosphate, inosine, and inosine monophosphate, all of which are important to calculate freshness in seafood products.