## 4 Use of Spectroscopic Techniques for Monitoring Changes in Muscle Foods during Processing
### Meat and Poultry Products
#### 4.2.2 Non-Thermal Treatments  
Although heat treatments cause huge modifications in muscle foods, other physical processes can also affect the characteristics of these aliments. The effects of the main non-thermal treatments (HPP, MAP, cold-plasma, and ultrasound) on meat have been mainly studied by FT-IR and NMR, taking advantage of their already explained characteristics. Some studies have also investigated the potential of Raman spectroscopy for monitoring changes occurring during the use of non-thermal treatments. For example, resonance Raman spectroscopy was used to investigate the color changes in pork upon treatment with HPP (600-700 MPa) [220]. Using a 413 nm excitation probe the authors found that the band frequencies in the 1300 and 1700 cm\({}^{-1}\) region are important to elucidate the coordination and oxidation state of iron in hemoproteins. An upshift in frequencies at 1473 and 1564 cm\({}^{-1}\) to bands at 1493 and 1581 cm\({}^{-1}\) upon HPP treatment indicated a transition of deoxymyoglobin from the five-coordinated high spin to a six-coordinated low spin configuration. Other upshifts reported HPP treated meat are from 1356 cm\({}^{-1}\) to 1359 and 1363 cm\({}^{-1}\) and from 1524 cm\({}^{-1}\) to 1552 and 1558 cm\({}^{-1}\) (for both 600 and 700 MPa, respectively). The impact of HPP on meat has been investigated by many authors using IR-spectroscopy; for instance, by [PERSON] and collaborators who analyzed raw, cooked (85 \(\pm\) 2 \({}^{\circ}\)C for 10 min), and HPP (two-different conditions: 300 or 600 MPa, for 1 or 15 min) pork chops by FT-IR spectroscopy and colorimetry [221]. This latter technique showed that the pressure was directly correlated with discoloration of the meat. On the other hand, IR-analysis highlighted pressure and its time of application decrease the presence of \(\alpha\)-helix and \(\beta\)-sheet structures; nevertheless, the lowest amounts were found in cooked samples. This outcome regarded both spectra collected on meat and on juices. Moreover, it was observed that the intensity of absorption bands associated to collagen type I (between 1655 and 1454 cm\({}^{-1}\)) decreases with the increase of pressure, probably due to the move of denaturated collagen to the juices. On the other hand, in spectra collected on juices, the absorption peak at around 1394 cm\({}^{-1}\) (relatable to CH\({}_{3}\) in proteins and lipids) increased with the pressure. FT-IR analysis was exploited also in the study by [PERSON] and coauthors who investigated the spoilage of ham, either HPP treated or not, stored in diverse packages and for different periods of time [222]. Microbiological analysis of TVC and lactic acid bacteria (LAB) were evaluated on the same samples. PLS was used to fit TVC and LAB to IR-spectra. In the literature it is possible to find several papers investigating modifications induced by storage and packaging by use of spectroscopy (Table 4). FT-IR plays a key role in this context; for example, in the study proposed by [PERSON] and others, FT-IR was exploited for monitoring the spoilage of beef meat contained in different packaging (aerobically, MAP, and using an active packaging) [223]. Among the other outcomes, the authors pointed out that FT-IR coupled with chemometrics could be a suitable tool for predicting the spoilage of beef samples; additionally, they highlighted the spectral variables that contributed the most to this prediction: the peak around 1550 cm\({}^{-1}\) (associable to the C-N stretching), the one around 1458 cm\({}^{-1}\) (relatable to CH\({}_{2}\) scissoring in lipids), and the absorptions bands at 1311 and 1246 cm\({}^{-1}\), respectively, probably due to the C-N stretching in amines.