## 4 Use of Spectroscopic Techniques for Monitoring Changes in Muscle Foods during Processing
### Meat and Poultry Products
#### 4.2.1 Thermal Treatments
In more detail, samples of breast bovine meat were cooked by microwave oven (800 W for 95 s, or at 650 W for 160 s) or by a traditional oven (165 \({}^{\circ}\)C for 16 min) and analyzed by MIR spectroscopy. The authors observed that the microwaved samples presented lower bands for CH\({}_{2}\) of the methylene group, and carbonyl, probably due to uncompleted Maillard reaction, and increase of \(\beta\)-turns and \(\beta\)-sheets. With the development of technologies and increased research of innovation in the gastronomic sector, novel refined cooking techniques are quite widespread, and deserved to be accounted. An example is the sous-vide approach, often used for cooking muscle food, in particular meat. In a recent study, [PERSON] and collaborators investigated the texture characteristics of pork join which underwent this treatment [207]. NIR spectra were collected on pork loins under vacuum cooked at different times (1, 2, 4, 6, or 8 h). Additionally, other parameters, such as moisture, pH, cooking loss, and collagen were estimated, together with the texture profile and sensory analysis. PCA analysis applied to the texture highlighted sample grouping according to the cooking time; moreover, it indicated that short-cooked samples (<2 h) presented the most parsimonious cooking loss and appeared less tough and fibrous than other samples. The explorative analysis of NIR spectra allowed finding out the variables contributing the most to the PCA model; these were the bands between 880 and 890 nm and those between 910 and 920 nm, associable to C-H bonds, and absorptions between 960 and 980 nm and 1010 and 1030 nm, relatable to O-H and N-H bonds. It is well-known that thermal treatments do not affect only proteins' structures, but also moisture content, which is a relevant quality parameter that strongly affects the organoleptic characteristics of meat. In this regard, [PERSON] and others proposed a valuable study, where an HSI was used to assess moisture distribution in chicken breast [208]. Thirty-six chicken breasts were oven-cooked at three different temperatures (50, 60, and 70 \({}^{\circ}\)C) and then analyzed by HSI. Hyperspectral images were collected in the Vis-NIR range (400-1000 nm) and moisture content was quantified according to the association of official analytical chemists (AOAC) recommendations. Eventually, moisture was also predicted from the hyperspectral data by means of PLSR. The regression model achieved successful results, providing a R\({}^{2}\)p of 0.90. As expected, the water content strongly decreases with the increase of cooking temperature; samples cooked at 50 \({}^{\circ}\)C presented around 70% of the initial moisture, whereas those cooked at 70 \({}^{\circ}\)C had around 63% of it. This outcome is clearly visible in the water dispersion map shown in Figure 3.  
In the bottom plots, red pixels are directly proportional to moisture. From this graphical representation it is evident that, at lower temperatures, moisture is spread all over the breast, in particular in the central area; on the other hand, higher temperature diminishes the water content, which is strongly reduced at 70 \({}^{\circ}\)C. In a similar context lays the work from [PERSON] and coauthors who exploited HSI to investigate moisture distribution in beef during microwave heating [209]. Furthermore, two other relevant studies on this regard can be found in the literature. These works focused on NIR analysis of baked liver pate and sausages during heat treatment [210]. One of the peculiarities of these papers is that they were conducted in industrial conditions or similar environments (conveyor belts). In [210], baked liver pate samples were investigated by a noncontact system collecting spectra in the range 760-1040 nm. NIR signals were used to create a PLS predictive model to estimate the temperature of meat samples; the RMSEP obtained was 2.66 \({}^{\circ}\)C. Similarly, in [211], an in-line NIR device was exploited for the assessment of the core temperature in sausages at the final stage of heating in an industrial oven.