## 4 Use of Spectroscopic Techniques for Monitoring Changes in Muscle Foods during Processing
### Meat and Poultry Products
#### 4.2.1 Thermal Treatments  
Quality assessment of meat products after the application of thermal treatments is a broad and extensively studied topic. The present overview represents merely a concise survey, organized by spectroscopic technique (Raman, NIR, MIR, Vis, fluorescence, and NMR); other works on this theme are reported in Table 4.  
Raman Spectroscopy: As widely described above, meat products often undergo thermal treatments, such as microwave or ohmic heating, which obviously modify the structure of the aliment, in particular, at the protein structure level. For this reason, the characteristics of meat products during or after the application of thermal treatments are monitored by Raman spectroscopy, which is particularly suitable at inspecting secondary and tertiary protein structures [196] and it is therefore exceptionally useful for the investigation of muscle foods [155]. For instance, [PERSON] and collaborator have used this technique to investigate the changings in meat batters after heating (70 \({}^{\circ}\)C for 30 min) [197]. Analysis of variance (ANOVA) highlighted samples prepared with soybean oil or pork fat present a decrease in \(\alpha\)-helix content and an increase in \(\beta\)-sheet. The same conclusions were also reached by other authors; for instance, by [PERSON] et al. [198] or by [PERSON] and collaborators [199] who focused on the changes in myofibrillar proteins induced by heating, on chicken [198], and pork meat [199], respectively. Furthermore, in the study proposed by [PERSON] and coauthors a deeper inspection of the Raman spectra was allowed by means of PCA. This explorative method disclosed hardness of meat was correlated with the \(\beta\)-sheet and \(\beta\)-turns amount, and anticorrelated with the \(\alpha\)-helix content. Additionally, the scores-plot inspection highlighted there was a clear spread of samples along PC1 according to their heating degree. In a similar scenario, [PERSON] and others applied PCA to Raman spectra in order to investigate the effects of cooking temperature and time on meat proteins [200]; the authors concluded the cooking temperature has a greater repercussion on the tyrosine and tryptophan ratio. Vis/NIR/MIR: The suitability of these approaches is provided by the specificity of MIR, and, to a lesser extent, of NIR, for the proteins and polypeptides structures [201,202]. Although NIR signals are not directly relatable to specific compounds, [PERSON] and [PERSON] [203] showed that it was possible to assess maximum cooking temperatures in heat treated beef with a prediction error of 2.0 \({}^{\circ}\)C in the temperature range 50-85 \({}^{\circ}\)C. More recently, [PERSON] and collaborators demonstrated that the technique can be an efficient tool for investigating the modifications induced by oven-cooking in meat sensory characteristics [204]. In their study, pork loin samples were cooked in an oven at different conditions (150 or 180 \({}^{\circ}\)C, for 45, 60, or 75 min) or confit-cooked for 120, 180, or 240 min. The samples were evaluated by trained panelists and analyzed by NIR spectroscopy. PCA highlighted the possibility of differentiating samples according to the cooking temperature. Moreover, the inspection of the score plots allowed distinguishing between oven and confit cooking procedures regardless of the other conditions, but it did not show grouping tendencies according to the diverse cooking times. Additionally, interesting findings came out by the multiblock [205] analysis of joint sensory and spectroscopic data. In fact, this allowed correlating the quantitative descriptive analysis (QDA) outcome with NIR spectra, providing indications about the positive/negative correlations among sensory attributes and absorption ranges. [PERSON] and [PERSON] used FT-IR to compare the effect of cooking using conventional convective heating and microwave on meat [206].