## 4 Development of Optical Sensing Techniques for Red Meat Quality Prediction
### Spectroscopic Techniques
#### 4.1.3 Other Spectroscopic Techniques  
Terahertz (THz) spectroscopy stands out as a promising field among spectroscopic techniques due its unique radiation band. THz waves occupy a relatively uncharted region of the electromagnetic spectrum, spanning the frequency range of 0.1 to 10 THz, and this range lies between the mid-infrared and microwave regions [169]. Terahertz (THz) imaging systems can be categorised into two modes based on the type of source used: pulse and continuous. The pulse mode is similar to terahertz time-domain spectroscopy (THz-TDS) and enables functional imaging, allowing for the acquisition of the refractive index distributions within the substance being imaged, thereby providing detailed information about the internal structure of the object [13]. The system's primary concept revolves around capturing the temporal changes of a brief electromagnetic pulse, which can be transformed into the frequency domain using a Fourier transform [170]. Furthermore, when compared to the frequently utilised optical and near-infrared spectra, the wavelength of the THz spectral band is longer, making it less susceptible to scattering [171]. Terahertz spectroscopy, which is capable of detecting the unique \"fingerprint\" signatures of various biomolecules and covering a wide range of vibrational modes, can be used to distinguish between fresh and spoiled meat. [PERSON] et al. [47], in their study, predict pork freshness using terahertz spectroscopy (R\({}_{\text{P}}\) = 0.84, RMSE = 9.89). The results show a significant correlation between the moisture content and meat quality, suggesting that this technique has potential applications in the detection of meat freshness [13].  
Fluorescence spectroscopy is a non-destructive method that assesses the fluorescence characteristics of an object by extracting data from various fluorophores present in biological samples. This technique is commonly utilised in biological sciences, particularly in the field of food technology [172]. In a study on meat quality assessment, [PERSON] et al. [173] utilised fluorescence spectroscopy to analyse the ATP content and plate count in pork meat. By developing partial least squares regression (PLSR) models, they achieved high determination coefficients, with values of R\({}^{2}\)c = 0.9-0.97 and R\({}^{2}\)cv = 0.84-0.88.  
Nuclear magnetic resonance (NMR) spectroscopy is utilised to gather structural details on organic compounds present in biological samples. The NMR properties are a result of the interaction between an atom and an external magnetic field. More specifically, the nucleus, which carries both angular and magnetic momentum, undergoes a precession movement in response to the magnetic field. Nuclear magnetic resonance (NMR) techniques, including high-resolution NMR (HR-NMR) and low-field NMR (LF-NMR), are commonly used in the food industry for quality assessment, with specific applications in evaluating meat quality [174]. NMR systems are highly sensitive in identifying various meat components due to their strong magnetic fields and reliance on the presence of magnetic atoms in the sample [175]. They are capable of determining key physio-chemical parameters of fresh meat and assessing the impacts of cooking and freezing. To ensure accuracy, NMR is sensitive to temperature changes and thus requires low room temperatures for precise results. Additionally, the need for small sample sizes may lead to sample destruction in some cases [176]. In addition, [PERSON] et al. [177] studied the use of time-domain nuclear magnetic resonance (TD-NMR) to detect beef tenderness. Their study showed a robust correlation (r > 0.65) between the spectral and reference data for assessing tenderness. Finally, [PERSON] et al. [178] utilised NMR technology in their research to study the migration and distribution properties of myofibrillar water within muscle tissues. As water plays a vital role in meat tenderness analysis, this study has demonstrated the potential of NMR technology for non-invasive assessment of meat's tenderness.