## 4 Development of Optical Sensing Techniques for Red Meat Quality Prediction
### Spectroscopic Techniques
#### 4.1.1 Near-Infrared (NIR) Spectroscopy
Over the past several years, research investigating the use of NIR spectroscopy for the examination of red meat sensory characteristics have been published. Tables 1 and 2 summarise the information from various studies on the sensory characteristics of different types of red meat using NIRS. The type of muscles, spectroscopy type, wavelength range, analytical method, measured attribute, and performance of each study are included. In terms of colour analysis (Table 1) in beef, [PERSON] et al. [121; 123], using multiple beef muscles in the range of Vis-NIR, achieved moderate performance values for prediction models, while [PERSON] et al. [124] and [PERSON] et al. [99], using one beef muscle (_longissimus thoracis_), in the same spectral range and with the same statistical method (partial least squares regression), obtained similar performance values. In addition to partial least squares regression (PLSR), [PERSON] et al. [124] also tested SVM, leading to a slight increase in the R\({}^{2}\) values compare to PLSR. Additionally, [PERSON] et al. [125] and [PERSON] et al. [126] achieved higher performance values for the prediction of beef colour than [PERSON] et al. [127], who used different pre-treatment spectral methods and different statistic techniques. In their study, [PERSON] et al. [128] observed similar performances across both the Vis-NIR and NIR spectral ranges in the _longissimus thoracis_ analysis, and [PERSON] et al. [129] showed that in the NIR range, using principal component regression (PCR) obtained higher values for L* and slightly lower compared to PLSR. This could be a result of the different pre-processing methods and the use of Vis-NIR as the visible spectrum is associated with the percentage of oxymyoglobin. This difference between the performance values could also be due to an effect of the different sample set size. In terms of pork meat analysis and colour attributes, [PERSON] et al. [130] achieved higher R\({}^{2}\) values compared to [PERSON] et al. [131], [PERSON] et al. [132] and [PERSON] et al. [133], with the discrepancy likely attributed to the different timing of spectral data collection. In the studies by [PERSON] et al. [131], [PERSON] et al. [132] and [PERSON] et al. [133], spectra measurement was taken in a laboratory, but in the study by [PERSON] et al. [130], the spectra data were collected immediately in the chilling room after quartering the carcass. Concerning the lamb meat analysis, [PERSON] et al. [134] and [PERSON] et al. [135] analysed multiple lamb muscles using the same spectral range and validation method, reporting similar R\({}^{2}\) values for colour. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Source** & **Animal** & **Musde** & \begin{tabular}{c} **Number of** \\ **Samples** \\ \end{tabular}  & \begin{tabular}{c} **Spectroscopy** \\ **Method** \\ \end{tabular}  & \ \begin{tabular}{c} **Wavelength** \\ **Range (nm)** \\ \end{tabular}  & \begin{tabular}{c} **Statistical** \\ **Method** \\ \end{tabular}  & \multicolumn{3}{c}{**Performance of Measured Attribute**} \\ \hline
[21] & \ \begin{tabular}{c} **B**eef \\ **Hersers** \\ \end{tabular}  & \begin{tabular}{c} [PERSON] \\ **Hersers**, [PERSON] \\ \end{tabular}  & 230 & Vis-NIR & 350-1800 & PLSR & \(\mathrm{R}_{\mathrm{CV}}^{2}=0.53\) & \(\mathrm{R}_{\mathrm{CV}}^{2}=0.58\) & \(\mathrm{R}_{\mathrm{CV}}^{2}=0.57\) & - & - \\
[123] & \begin{tabular}{c} **B**eef \\ **Hersers** \\ \end{tabular}  & 336 & Vis-NIR & 350-1800 & PLSR & \(\mathrm{R}_{\mathrm{CV}}^{2}=0.72\) & \(\mathrm{R}_{\mathrm{CV}}^{2}=0.73\) & \(\mathrm{R}_{\mathrm{CV}}^{2}=0.66\) & - & - \\
[124] & \begin{tabular}{c} **B**eef \\ **Hers** \\ \end{tabular}  & 234 & Vis-NIR & 350-1800 & PLSR & \(\mathrm{R}_{\mathrm{CV}}^{2}=0.76\) & \(\mathrm{R}_{\mathrm{CV}}^{2}=0.59\) & \(\mathrm{R}_{\mathrm{CV}}^{2}=0.58\) & - & - \\
[127] & \begin{tabular}{c} **B**eef \\ **Hers** \\ \end{tabular}