Abstract

Journal of Near Infrared Spectroscopy
Volume 17 Issue 2, Pages 77–87 (2009)
doi: 10.1255/jnirs.827

Prediction of ice fraction and fat content in superchilled salmon by non-contact interactance near infrared imaging

Silje Ottestad,^a,b Martin Høy,^a Astrid Stevik^c and Jens Petter Wold^a
aMatforsk AS— Norwegian Food Research Institute, Osloveien 1, N-1324 Ås, Norway
^bNorwegian University of Life Sciences, Department of Chemistry, Biotechnology and Food Science, P.O. Box 5003, N-1432 Ås, Norway. E-mail: silje.ottestad@matforsk.no
^cSINTEF Energy Research, Kolbjørn Hejes vei 1D, N-7465 Trondheim, Norway

It has been shown that superchilling can increase the shelf life of fish and meat products without the reduction in quality encountered with normal freezing. The shelf life and quality achieved depend on the fraction of water frozen and how it is preserved in the product. In this paper we report the possibility of using non-contact near infrared (NIR) interactance spectroscopy in combination with multi-spectral imaging as a rapid non-destructive way to predict the average ice fractionas well as the spatial distribution of ice in superchilled salmon fillets. For average ice fraction calibrations samples in the range of 0% to 30% ice were investigated. Partial least square regression (PLSR) models with high explained variance (R² ≈ 0.98) and root mean square error of cross-validation (RMSECV) between 1.6% and 2.4% were obtained. The time of NIR measurement after superchilling (0, 1/2, 2 and 24 hours) did not seem to affect the prediction ability significantly. The spatial ice distribution as predicted by PLSR modeling was affected considerably by the fat distribution. This was avoided by the use of multivariate curve resolution (MCR) at pixel level and calibration against the amount of ice divided by the total amount of water in both liquid and solid state. Excellent images of ice distribution were achieved and allowed observation of changes during storage and thawing. The ability to predict fat content in superchilled salmon fillets was also investigated. Fat content predictions were affected by ice fraction, but were observed to be independent of time of measurement after freezing.

Keywords: superchilling, near infrared spectroscopy, ice fraction, ice distribution, multi-spectral imaging, curve resolution

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