Thaw drip loss and protein characterization of drip from air-frozen, cryogen-frozen, and pressure-shift-frozen pork longissimus dorsi in relation to ice crystal size

Abstract

Drip loss from thawed, pressure-shift-frozen longissimus dorsi pork was not different from drip loss from fresh meat samples, while cryogen-frozen (using liquid nitrogen at −70 °C) and air-frozen (−20 °C) pork both had significantly higher drip loss (12%) upon thawing when compared to pressure-shift-frozen and fresh pork (4%). Pressure-shift-frozen pork was discolored, with a significant decrease in CIE redness parameter a*, and showed signs of denaturation upon visual inspection. A high molecular weight protein band (Mw 97,000) characteristic for gel electrophoresis (SDS-PAGE) for drip from fresh, air-frozen, and cryogen-frozen pork was not present in drip from pressure-shift-frozen pork. Ice crystals in the frozen pork, as evaluated by image analysis of cavities in digitized pictures from light microscopy of 14 μm-thick meat slices (cut transverse to the fiber direction) embedded in tissue wax following treatment with Carnoy’s fixative and ethanol, increased in the order: pressure-shift-frozen<cryogen-frozen<air-frozen pork. Meat structure, as evaluated visually following thawing, deviated from fresh meat structure only for pressure-shift-frozen pork. It is accordingly concluded that pressure denaturation of meat proteins is more important for structure appearance than growth of ice crystals, and that protein denaturation increases water-binding capacity in pressure-shift-frozen pork.