| A sensor system consisting of an array of semiconducting metal oxide (SMO) chemiresistive sensors is presented which can quantitatively measure the freshness of Atlantic salmon (Salmo salar), haddock ( Melanogrammus aeglefinus), and Atlantic cod (Gadus morhua ). A variety of SMO films were tested, including films containing oxides of copper and tin, and commercially available tin-based SMO films. Experiments were performed with these films to determine if they were sensitive to trimethylamine (TMA) and/or dimethylamine (DMA), known fish degradation products. The electrical resistance of the films before and during exposures to concentrations of the amines was monitored. The sensor temperatures were varied to determine the operating conditions for sensitivity and selectivity to one or both gases. The most promising films were then used to monitor the degradation of Atlantic salmon, haddock, and Atlantic cod.; Analytical testing of the fish samples was performed in conjunction with SMO sensor testing of the volatile gases emitted from the degrading fish. Testing included the use of a sensory evaluation panel and tests incorporating TMA colorimetric methods, pH analyses, percent fat content, bacterial aerobic and anaerobic plate counts, and total volatile base nitrogen (TVB-N). Sensory analysis, TMA content, pH, aerobic and anaerobic plate counts provided results that correlated well with each other and with SMO sensor results. Percent fat content and TVB-N results did not correlate well with degradation. A radial basis function neural network was designed and used to classify the fish type, salmon, haddock, or cod, and the day of degradation (1 through 21) from the SMO sensor array response as compared with the analytical results. |
