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Freeze-thaw effects in frozen fish fingers Detection by desk-top NMR

R. HANS TROMP*, JANNY VAN GIJSSEL1, ANN C. STIJNMAN1, NOBUHIKO DOMOTO2
*Corresponding author
1. NIZO food research, PO Box 20, Ede, 6710 BA, The Netherlands
2. Nippon Suisan (Europe) B.V, Nieuwe Kanaal 7J, Wageningen, 6709 PA, The Netherlands

Abstract

A relatively simple method is described for monitoring changes in frozen products due to periods of insufficientfrozen conditions. The case studied is the effect of such “thermal abuse” on the crust of microwaveable fish fingers. Themethod makes use of low-field table top nuclear magnetic resonance (NMR). The water mobility in the crust is determined.This is done on crust material during frozen storage at the preferred temperature of -25oC with and without a period at -5oC.The most important physical process taking place due to imperfect frozen conditions and leading to quality loss such as lossof crispness was found to be transport of mobilized water from the core to the crust of the fish fingers. This method couldin principle be applied in practice, for assessing the amount and moment in time of exposure to too high temperatures ofproducts which have been stored and/or transported in the frozen state.


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