Multivariate modelling of fish freshness index based on ion mobility spectrometry measurements

Ion mobility spectrometry based analysis has been found to provide a powerful and reliable tool as a portable gas detector of different chemical compounds and mixtures. The suitability of the spectrometer in food quality assay was studied in a case study, in which fish quality changes during cold storage were modelled. Hexane extracts of gills of vendace (Coregonus albula L.) were analysed by using ion mobility spectrometry. For reference, microbial counts of gills, ATP-breakdown products (K-value) of fish flesh, electrical properties (Torrymeter scores) of fish skin and sensory evaluation scores were determined. Principal component analysis (PCA) was utilised to create an index for quality by compressing the reference data. Relationship between the quality index and the spectral data were modelled with N-mode partial least squares (PLS). Thus, the ion mobility data have three-dimensional nature, since signals from six channels are recorded simultaneously. Reliability of the predictions and ion mobility measurements was of great interest in the development procedure of this novel analytical method. The multivariate statistical process control (MSPC) charts were used to determine the reliability of the ion mobility measurements. The chemical composition of gill extracts changed during the storage period as indicated by the ion mobility spectrum profiles. The dominant variation in the data was related to the length of storage of fish and to seasonal variation. The results of the case study revealed that the spectrometer, with the analytical method, and with chemometric tools form a promising tool for food quality assays.