Microstructure of high-pressure vs. atmospheric frozen starch gels

The aim of this study was to find out whether the ice crystal size of a starch gel, a model food system, could be reduced by high-pressure freezing compared with freezing at atmospheric pressure. The size and number of pores in thawed gels was determined by light microscopy and image analysis, and was taken as an indirect measure of ice crystals formed during the different freezing processes studied. The pore size and the total area occupied by the pores were clearly reduced by high-pressure freezing at 150-240 MPa compared with freezing at atmospheric pressure at the same cooling rate. The pore size in the high-pressure (nor in the atmospheric) frozen gels did not increase during a storage time of 3 months at -24 °C (still air) at atmospheric pressure. Industrial relevance High-pressure processing at subzero temperatures is not yet industrially applied. More evidence on the benefits of high-pressure freezing or thawing on the quality of real food materials as well as development of processing equipment is needed for commercialization of the processes. This study demonstrates that the pore size of frozen and thawed starch gels can be reduced by high-pressure freezing compared with freezing at atmospheric pressure. The reduced pore size was assumed to be a result of smaller ice crystals formed in the high-pressure freezing process. Based on this study, no conclusions can be drawn on the possibility of high-pressure freezing to improve the quality of real foods of a more complex composition and structure