Mid‐infrared spectroscopy as a new tool for the evaluation of fish freshness

Summary Frozen fish usually have a much lower market price than fresh fish, hence, adulteration could occur. This paper focuses on the use of mid‐infrared (MIR) spectroscopy combined with chemometric tools to determine whether fish has been frozen–thawed. A total of twenty‐four fish samples (fresh fish (n = 12) and frozen–thawed fish (n = 12)) were investigated. The principal component analysis and the factorial discriminant analysis were applied to the three spectral regions in the MIR of 3000–2800 cm−1, 1700–1500 cm−1 and 1500–900 cm−1. Within the 1500–900 cm−1 spectral region, correct classification (CC) of 100% and 75% was observed for the calibration and validation spectra, respectively. Improved classification was obtained from the 3000–2800 cm−1 spectral region, with CC of 100% and 87.5% of the calibration and validation spectra, respectively. It can be concluded that the 3000–2800 cm−1 and 1500–900 cm−1 spectral regions may provide useful fingerprints allowing the differentiation between fresh and frozen–thawed fish. These regions can be considered as a reliable indicator of fish freshness.