Comparison of visible-near infrared and short wave infrared hyperspectral imaging for the evaluation of rainbow trout freshness

The freshness of rainbow trout is one of the most important quality parameters to attract customers. Common methods to detect fish freshness are usually subjective to the skill of a quality evaluator and are time consuming and destructive. Therefore, an automatic, nondestructive, accurate and quick method is needed. Hyperspectral imaging has demonstrated its efficiency in the meat and fish industries for quality control purposes. This method is nondestructive, fast and automatic. In this study, two setups for hyperspectral imaging named "Visible-Near Infrared" (Vis-NIR) and "Short Wave Infrared" (SWIR) are used to determine fish freshness. Eighty fresh rainbow trouts were divided into four batches which were separately preserved in ice for 1, 3, 5 and 7days, respectively. Principle Component Analysis (PCA) and Partial Least Squares-Discriminate Analysis (PLS-DA) were used as unsupervised and supervised techniques for the evaluation of rainbow trout freshness. Results obtained by PCA technique indicated that four classes of samples can be detected using the Vis-NIR mean spectrum by applying a second derivative (D2) preprocessing method. The R_CV² and R_Pre with D2 preprocessing were 0.97 and 0.98 for Vis-NIR and 0.84 and 0.67 for SWIR, respectively. The corresponding values of RMSE_CV and RMSE_Pre were 0.16 and 0.14 in Vis-NIR and 0.44 and 0.76 in SWIR, respectively. Classification model achieved an overall correct classification of 100% and 75% for Vis-NIR and SWIR, respectively. The obtained results using both PCA and PLS-DA methods indicated that the Vis-NIR imaging system performs better than SWIR. Among all applied preprocessing techniques, the second derivative preprocessing achieved the best performance.