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Heat transfer model tool for the heat absorption capacity of superchilled fresh fishery products (HTM-SFFP Tool)

García, Miriam R.; Suffredini, Elisabetta; Messens, Winy; Bover-Cid, Sara

Introduction

This model was developed and applied by members of the EFSA Working Group on the transport/storage of fresh fishery products during the preparatory work on the BIOHAZ Scientific Opinion on the use of the so called 'superchilling' technique for the transport of fresh fishery products (EFSA-Q-2019-00437) (https://doi.org/10.2903/j.efsa.2021.6378).

A heat transfer modelling approach was used to identify under which initial configurations the fish temperature of superchilled fresh fishery products (SFFP), at any time during the storage/transport, is lower or equal to conventional fresh fishery products (CFPP), when exposed to the same conditions of on-land storage and/or transport. This approach is feasible when the boxes used to transport the fish (e.g. expanded polystyrene boxes) and the storage and transport conditions are the same for the two compared conditions (SFFP and CFFP).

The capacity of the CFFP and SFFP to maintain their temperature depends on their capacity to absorb heat, which is determined by their initial configurations. These are:

  • for CFFP: the initial fish and ice temperatures and the proportion of ice:fish in the box; and
  • for SFFP: the degree of superchilling, i.e. the ice fraction in the fish matrix, which depends on the fish temperature after superchilling and the initial freezing point of the fish.

The tool can be used as part of 'safety-by-design' approach of the food business operator to identify scenarios under which initial configurations the SFFP will be equivalent or have a higher capacity to absorb heat than CFFP.

The ratio (R) between the capacity to absorb heat between both systems can be determined as R=QS/QC. If R ≥ 1, then the SFFP temperatures are lower than those of CFFP. If R < 1, then the SFFP temperatures may be eventually higher than those of CFFP.

 

Description

A MS-Excel spreadsheet tool enables the setting of the degree of superchilling for SFFP that is considered able to maintain fish temperature below or equal to that a given configuration of CFFP regarding the initial fish temperature and the proportion of ice added per mass of fish (ice:fish) in the box (R ≥ 1, corresponding to QS QC). The tool facilitates identification of configurations under which the SFFP cannot be proved to be equivalent or better than CFFP (R < 1, corresponding to QS < QC).

The tool has the following options:

  • To derive if superchilling is able to maintain fish temperature below or equal to that of CFFP at any time of storage before all ice melts, based on
    • the target % of frozen free water in SFFP (option 1)
    • the initial superchilled fish temperature (option 2)
  • To derive the initial superchilled fish temperature and percentage of ice in superchilled fish needed to equal the absorbing heat capacity of CFFP before all ice melts (option 3)
  • To derive the proportion of ice in CFFP to equal the absorbing heat capacity of SFFP before all ice melts, based on
    • the target % of frozen free water in SFFP (option 4)
    • the initial superchilled fish temperature (option 5)

In each option there is the possibility to estimate the initial freezing point of fish and free water of fish from the proximate composition; more in particular, from the fish composition regarding the content of water, protein ash and other than ash, water, proteins or fat (such as carbohydrates).

The reliability of the outcome provided by the tool depends on the accuracy of the input data introduced by the user.

More details about the methodology can be found in section 2.1.1. and results of modelling can be found in section 3.1.1 of the opinion. The uncertainties related to the outcome of the heat transfer model are described in section 3.1.4 of the opinion.  

EU; XLSX; biohaz@efsa.europa.eu
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