Size and location of ice crystals in pork frozen by high-pressure-assisted freezing as compared to classical methods.

In high-pressure-assisted freezing, samples are cooled under pressure (200 MPa) to - 20 °C without ice formation then pressure is released (0.1 MPa) and the high super-cooling reached (approx. 20 °C), promotes uniform and rapid ice nucleation. The size and location of ice crystals in large meat pieces (Longissimus dorsi pork muscle) as a result of high-pressure-assisted freezing were compared to those obtained by air-blast and liquid N(2). Samples from the surface and centre of the frozen muscle were histologically analysed using an indirect technique (isothermal-freeze fixation). Air-blast and cryogenic fluid freezing, having thermal gradients, showed non-uniform ice crystal distributions. High-pressure-assisted frozen samples, both at the surface and at the central zones, showed similar, small-sized ice crystals. This technique is particularly useful for freezing large pieces of food when uniform ice crystal sizes are required.