Non-destructive measurement of salt using NIR spectroscopy in the herring marinating process

The salt content is one of the most important quality and safety parameters in the manufacturing process of marinated herring, which needs to be controlled during processing. Standard methods are often destructive and time consuming, and therefore a nondestructive and fast method needed. Near-infrared (NIR) spectroscopy was measured on marinade samples from herring marinating process in order to investigate the potential of NIR as a fast method to determine the salt content in marinade and in fish. The spectral region 1100–1300 nm had the highest positive correlation with the measured salt values. A principal component analysis performed on the NIR spectra showed that the first principal component described the evolution of the spectra according to the determined salt values. A partial least-squares regression model between the selected region of the NIR spectra and the salt content of the fish gave a correlation coefficient of 0.81 and a prediction error (RMSECV) of 0.41 g/100 g with the prerequisite that salt concentration in fish and marinade was in equilibrium. The results indicate that NIR spectroscopy can be used as a fast and non-destructive method for assessing the salt concentration in fish during the herring marinating process in order to ensure product safety.