## 4 Use of Spectroscopic Techniques for Monitoring Changes in Muscle Foods during Processing
### Fish and Other Seafoods
#### 4.1.1 Thermal Treatments
The authors concluded that the technique can be used as a rapid tool for monitoring thermal treatments during the processing of seafood. Formerly, [PERSON] and collaborators conducted several valuable studies to investigate the potential of NIR spectroscopy for monitoring thermal treatments in several seafood products [159; 161; 163]. Although these studies were conducted at laboratory scales, the obtained results were promising and paved the way for further investigations in this context. In recent years, HSI has matured to become one of the most powerful tools used for quality and control in the food industry. This technique has been frequently used within several spectral ranges, especially NIR, giving spatial information in addition to the spectral features that are usually obtained with traditional spectroscopic techniques. One example is the study conducted by [PERSON] and [PERSON] [164], who used HSI operating in the 900-2500 nm spectral range in order to classify kamaboko, a Japanese seafood, receiving different thermal treatments. The authors applied a partial least square regression (PLSR) model to estimate core temperature and thermal history and linear discriminant analysis (LDA) model to classify samples according to their thermal treatments. Both models achieved good results since R\({}^{2}\)p of 0.86 and 0.83 were obtained for predicting core temperature and thermal history, respectively. The LDA model yielded an overall classification accuracy of 93.75% in both calibration and validation sets. More interestingly, the optimal models were applied to the images in a pixel-wise manner in order to produce prediction and classification maps, visualizing weather the processed product has reached certain thermal conditions just by looking at the color of the generated images. In a more recent study, the performance of two different instruments based on NIR (760-1040 nm), namely a point measurement system and a commercial on-line NIR imaging scanner (QMonitor, TOMRA, Norway), operating in an interactance mode for determining the core temperature of heat-treated fish cases, was compared [153]. Although slightly better results were obtained using the offline point measurement system, as a result of deeper penetration of light into the sample, the on-line imaging scanner was highlighted due to its potential to be adapted for a typical conveyor belt, giving the opportunity to monitor the temperature in all products after heat treatment in the industrial application. Fourier transform infrared (FT-IR) spectroscopy is a biochemical fingerprinting technique that has attracted much attention in recent years due to many desirable features such as high speed, resolution, and sensitivity [158]. Like Raman spectroscopy, FT-IR has been widely used to study changes in the secondary structure of proteins as induced by thermal treatments. Again, the changes of the secondary structures of surimi gels have been studied by FT-IR in order to improve the texture and solve the problem of decreased gel strength of surimi when applying high temperatures to treat the product [158]. The results of FT-IR, along with those of Raman spectroscopy showed that the network structure of the gel surimi undergoes serious damages when treating the surimi at high temperatures (i.e., 100 and 120 \({}^{\circ}\)C). As protein denaturation and aggregation have the main responsibility for physical modifications and other related changes (e.g., cooking loss, changes in water holding capacity) occurring in seafood during thermal processing, FT-IR has been widely used to study these phenomena [157; 158; 165; 166]. For example, [PERSON] and coauthors found that the changes in the amide I band (1700-1600 cm\({}^{-1}\)) are the most useful for studying denaturation in alteration in the secondary structure of protein upon heating [165].