Monitoring the Spoilage of Fresh Sterlet (Acipenser ruthenus) During Storage at 4 °C by Mid-Infrared and Fluorescence Spectroscopies Coupled with Chemometric Tools

Sterlet is a perishable product; therefore, its freshness monitoring and shelf-life evaluation are important. In this study, a series of analytical techniques named physicochemical, microbiological, sensory, colorimetric, and mid-infrared and fluorescence spectroscopies were applied on Sterlet (<i>Acipenser ruthenus</i>) samples during 18 days of storage at 4 °C. The water content increased from 72.8 g/100 g on day 1 to 77.81 g/100 on day 14. Regarding the peroxide value (PV), the initial value was 4.17 meq/kg of Sterlet on day 1, reaching a maximum on day 4 (4.9 meq/kg of Sterlet), and then it decreased gradually, attaining a value of 0.7 meq/kg of Sterlet on day 18. Generally, the thiobarbituric acid reactive substance (TBARS), total viable count (TVC) and psychrotrophic count (PTC) increased during the storage time and increased from 0.03 to 0.13 MDA eq./kg of Sterlet sample, 2.27 to 9.09 log10 CFU/g, and 2.18 to 9.15 log10 CFU/g, respectively, on day 1 and 18, respectively. The microbiological and sensory analyses indicated that Sterlet samples were acceptable for human consumption up to 7 days of storage at 4 °C. This result was confirmed by fluorescence measurements, since the principal component analysis (PCA) applied to the NADH and MIR spectra allowed for a clear differentiation between Sterlet samples aged 7 days or less from the others. This trend was confirmed by the factorial discriminant analysis (FDA) applied to the NADH and MIR spectra, since a correct classification with leave-one cross-validation of 94.44% was observed. In addition, the heatmap of the Pearson correlation coefficients showed high correlations between overall acceptability and microbiology parameters and the structural properties of Sterlet samples during storage, indicating that the modifications observed at the macroscopic level were related to those notedat the molecular scale.