Frozen storage, freezing, thawing; freezing damage; blast-freezer; tempering

Maintaining product quality during freezing and frozen storage

Wageningen Food & Biobased Research investigates how freezing affects food products and how the freezing process can be optimised from product and energy perspective.

Many processed food products – from fish, topastries and fruit – are frozen, either in transit between processing steps or as consumer product. Freezing temporarily prevents food spoilage and therefore increases a product’s shelf life but is also linked to quality problems. Freezing, thawing and tempering (defrosting to -3°C) often lead to irreversible changes in product composition and texture: the formed ice crystals damage cell structures and dehydrate the product, which causes protein denaturation and changes water-binding and water-distribution. Such quality changes are often invisibleto the naked eye. This makes it difficult for food manufacturers and chill/freezeprocessors to optimise the quality and cost of their processing chain. Understanding the effects of freezing process parameters and storage temperature on the formationof ice crystals, the change in water-binding capacity and microbiology isessential.

Freezing, thawing and tempering

Wageningen Food & Biobased Research gives food manufacturers and processors a deeper understanding of freezing processes and its effects on product quality. We follow a unique, integrated approach, examining and explaining effects of freezing, thawing and tempering at different scales fromfreezing tunnel to product micro level. We investigate how freezing process conditions and storage temperature affect a product’s freezing rate, ice-crystal formation, water distribution, liquid-glass transition and resulting water-binding capacity as well as microbiology. Key point is to take into account the composition-dependent freeze concentration: increasing concentration of salts and other solids in thefluid fraction (and subsequent freezing point lowering) during ice crystalsformation. This subsequently leads to physico-chemical, enzymatic and microbialchanges. By combination of product and process level models, we reduce the needfor extensive, expensive experiments.

Optimal freezing process

Wageningen Food & Biobased Research supports a wide range of manufacturers in optimising freezing processes in their production chain. Recently we investigated the impact on product quality of different stages in a fish chain during transport, processing and packaging. For a client in the snack industry we clarified effects of analternative freezing system on product quality. For fruit-processing industry we analysed suitability of alternative tempering methods (based on radio frequencyenergy) for reducing cell damage – and thereby water migration - in soft, vulnerable fruits such as strawberries. We supported other clients in reducing moisture and subsequent quality loss and choosing most appropriate cooling/freezing process.

Publications

  • Esveld, Erik.  Vriesbewaring van levensmiddelen – effect op kwaliteit.  Voordracht themadag KNVvK Dec. 2014.
  • Broeze, Jan. Voedsel inkoelen of invriezen: wat is het effect? RCCK&L Nov 2014 (107) 18-20
  • R.G.M. van der Sman, A. Voda, G. van Dalen, A. Duijster. Ice crystal interspacing in frozen foods. J. Food Engineering. 116(2):622–626 (2013).
  • A. Voda, N. Homan, M. Witek, A. Duijster, G. van Dalen, R. van der Sman,J. Nijsse, L. van Vliet,     H. Van As, J. van Duynhoven. The impact offreeze-drying on microstructure and rehydration properties of carrot. Food Research Int. 49(2): 687–693 (2012)