Development of a low-cost non-destructive system for measuring moisture and salt content in smoked fish products

Abstract

In this study, a new method to assess salt content in smoked fish products using impedance spectroscopy has been developed. Two fish species (salmon and cod) from two different brands were analyzed. The analyses carried out were moisture, lipid, and salt contents, as well as aw. Impedance measurements were performed directly in different locations on smoked product by using a coaxial needle. The modulus and phase of the spectra of impedance were acquired between 1Hz and 1MHz, for 50 values of frequency. The impedance modulus and phase values were used to predict the studied physico-chemical parameters, by using the PLS method. In general, the highest lipid contents and the lowest moisture values were observed in salmon samples, independently of the brand and the batch analyzed. The results showed a high variability between batches of a same product, regarding to moisture and salt content. Prediction models were established for all the samples studied and also individually for each product. A higher accuracy of prediction was obtained for the PLS models established for each product compared with the model applied for all samples. In general, the highest R2 was obtained for prediction of aw parameter, followed by moisture content. The best correlations were obtained for smoked cod samples independently of the brand. These results can be explained by the isolating effect of the fat. Due to the differences in the raw material composition, a single model cannot be applied for all the products. A previous characterization of the raw material would improve the accuracy of the developed methodology. These results show the feasibility of the impedance spectroscopy to determine salt and moisture contents.