Termodinamica

Journal of Food Engineering 79 (2007) 124–136 www.elsevier.com/locate/jfoodeng

Frost formation on frozen products preserved in domestic freezers
O. Laguerre
b

a,*

, D. Flick

b

a ´ UMR Genie Industriel Alimentaire Cemagref-ENSIA-INAPG-INRA, BP. 44, 92163 Antony Cedex, France ´ UMR Genie Industriel Alimentaire Cemagref-ENSIA-INAPG-INRA, 16 rue Claude Bernard, 75231 Paris, FranceReceived 9 September 2005; accepted 16 January 2006 Available online 9 March 2006

Abstract Frost formation inside food hermetic packages preserved in domestic freezer was studied. The influence on the product weight loss and on air and product temperature fluctuations of the following parameters was studied experimentally: refrigerator characteristics, product characteristics and packageinsulation. The frost deposits particularly on the product located in the central zone of the box and on the bottom horizontal surface of the box. An interpretation of the results was carried out by a simplified heat and water transfer model. This model shows that frost develops in the zone where the temperature is low in the box and/or where the temperature variation is low. This is the case at thebottom of the box (thermal stratification) and at the centre (thermal inertia). Ó 2006 Elsevier Ltd. All rights reserved.
Keywords: Natural convection; Frost; Domestic freezer; Food; Weight loss

1. Introduction When foodstuffs are preserved in a freezer, ice crystals develop gradually in the package. These phenomena take place when the product surface temperature is lower than the dew temperature ofneighbouring air. In a domestic freezer, the compressor ‘‘on’’ and ‘‘off’’ cycles contribute to temperature fluctuations of air, packages and products. Furthermore, there is a difference between the amplitude of air temperature variation and that of a product due to thermal inertia. This leads to frost formation, which is often accompanied by surface dehydration for certain products. This dehydrationmay induce colour modification, rancidity and destruction of ascorbic acid (Martins, Almeida, & Silva, 2005). 1.1. Influence of temperature on packed product quality during storage in domestic freezers In domestic freezers, the average temperature, amplitude and frequency of temperature fluctuations exert a
*

Corresponding author. Tel.: +33 140 966 121; fax: +33 140 966 075. E-mail address:onrawee.laguerre@cemagref.fr (O. Laguerre).

great influence on product weight loss and quality degradation. Several studies were carried out to investigate these influences on several packed foods: Poovarodom, Letang, Bouvier, and Billiard (1990) on chopped steak, Bak, Anderson, Anderson, and Bertelsen (1999) on shrimps, Bustabad (1999) on meat and Martins et al. (2005) on green beans. These authorsreported that the higher the average temperature, the amplitude of fluctuations and the lower frequency lead to more rapid quality deterioration. To our knowledge, Poovarodom et al. (1990) and Bak et al. (1999) are the only researchers, who have quantified the packed product weight loss due to frost formation during storage. They observed that the weight loss increases rapidly with storage time (6%after a 9-month storage period at À20 °C, Poovarodom et al., 1990). Then, the weight becomes stable due to crust development on the product surface, which is a barrier to water sublimation. These authors also observed a small quantity of frost when the storage temperature is low; the amplitude of fluctuation is small and the frequency is high. However, neither the mechanisms of product qualityloss, nor the frost formation are clearly explained.

0260-8774/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2006.01.036

O. Laguerre, D. Flick / Journal of Food Engineering 79 (2007) 124–136

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Nomenclature C Cp D Lchar m P R Rv S t T DT thermal conductance (W KÀ1) product specific heat (J KÀ1) thermal diffusivity (m2 sÀ1) characteristic length (m)...