## 4 Use of Spectroscopic Techniques for Monitoring Changes in Muscle Foods during Processing
### Fish and Other Seafoods
#### 4.1.1 Thermal Treatments
Indeed, the results of fluorescence spectroscopy coupled with multivariate analysis, especially support vector machine, allowed to classify cod fillets, thermally treated in a water bath at 50, 60, 70, and 80 \({}^{\circ}\)C, according to the their received thermal treatments, with an accuracy higher than 92% being obtained. Most of the aforementioned studies were conducted using traditional excitation/emission procedure. Although this approach can be rapid and give valuable information if the fluorophore to be investigated is well-known, it can limit the potential of fluorescence spectroscopy for investigating several fluorophores simultaneously. Fluorescence excitation-emission matrices (EEM), or calledfluorescence landscapes in some references, take longer time to collect but enable scanning over a wide range of excitation and emission wavelengths, giving more information about fluorophores present in the sample. The EEM technique was investigated recently to identify changes of fluorescence behavior of shrimp during different treatments, including ohmic heating [54]. One of the spectroscopic results reported in this study was that the tryptophan fluorescence appeared to be highly dependent on the temperature of the treated shrimp samples. Nuclear Magnetic Resonance (NMR) Spectroscopy: NMR is an important tool for the investigation of the effects of thermal treatments on quality changes of seafood. Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) have been widely used for studying water migration, water mobility changes, and water distribution during food processing [150]. NMR chemical shift and \(T_{2}\) relaxation behaviors are among the widely NMR used parameters for evaluating the state on moisture in the measured samples, and consequently, monitoring structural changes occurring in seafood during cooking or other thermal treatments. For example, \(T_{2}\) parameters were found to be correlated with texture profile analysis (TPA) parameters of sea cucumber (_Stichopus japonicus_) during a two-step heating; pre-heating and post-heating [179]. In another study, NMR and MRI were used to investigate the impact of three cooking methods (frying, boiling, and stewing) of turbot on water mobility and distribution and the relationship with traditional parameters, including texture and color [180]. PCA applied to the NMR data showed a clear discrimination between the samples according to their cooking method, while weighted images of the MRI scans provided visualizations of internal structural information. In a recent study, low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) techniques were used to study the impact of four cooking methods, including boiling, steaming, roasting, and frying on proton dynamics, physicochemical parameters, and microstructure of Spanish mackerel [181]. \(T_{1}\) weighted magnetic resonance images were recorded and a significant decrease of MRI intensity for mackerel samples after roasting and frying was observed, demonstrating that these cooking methods were more drastic in changing the proton states than boiling and steaming. PLSR models applied to LF-NMR data to predict texture parameters (hardness, resilience, springiness, chewiness, gumminess, and adhesiveness) showed good reliability and accuracy with correlation coefficients of more than 0.98 being obtained. The same technique was used recently to monitor water dynamic changes in surf clam during heating [182]. The results of principle component analysis (PCA) and heatmap showed that the clam samples heated at 40-70 \({}^{\circ}\)C were different from those treated at high temperatures (80-100 \({}^{\circ}\)C).