Pressure Shift Freezing of Pork Muscle: Effect on Color, Drip Loss, Texture, and Protein Stability

Abstract

Cylindrical specimens (50 mm diameter and 160 mm length) of fresh pork muscle (boneless rib portions) packed in plastic bags were frozen by pressure shift freezing (PSF) at 100, 150, and 200 MPa, air blast freezing (ABF), and liquid immersion freezing (LIF). Temperature and phase transformations of the muscle tissue were monitored during the freezing process at three locations: center, midway between the center and the surface, and near the surface. Pork muscle quality changes [color, drip loss (both thawing and cooking), texture (shear force), and protein stability (DSC thermal profiles)] were evaluated after thawing the frozen samples at room temperature (20 degrees C). Employing pressures above 150 MPa caused very significant (P < 0.01) color changes in pork muscle during the PSF process. The PSF process reduced thawing drip loss of pork muscle but did not cause obvious changes in total drip loss following thawing and subsequent cooking. PSF at 150 and 200 MPa resulted in considerable denaturation of myofibrillar proteins of pork muscle. The PSF process also caused an increase in the pork muscle toughness as compared with that of unfrozen, ABF, and LIF samples.

Protein Denaturation in Pork Longissimus Muscle of Different Quality Groups

“…Thermal Transitions and Enthalpy of Denaturation Zhu et al 2004;Deng et al 2002). Total denaturation enthalpy (ΔH total ) of the RFN samples was 3.91±0.44 J/g (mean ± SD).…”

“…Therefore, assessing the level of protein denaturation in pork could indicate some underlying mechanisms for the difference in color, texture, and exudation among some of the quality groups including PFN. Differential scanning calorimetry (DSC) is by far the most common and widely used method to study thermal transitions and protein denaturation of muscle tissues (Deng et al 2002;Fernandez-Martin et al 2000;Zhu et al 2004;Brunton et al 2006;Tironi et al 2009). Myosin, which constitutes about 43% of the myofibrillar (contractile) proteins in the muscle tissue (Keeton and Eddy 2004), is the least heatstable protein and generally denatures in the temperature range of 40-60°C (Brunton et al 2006;Li et al 2009).…”

“…In previous DSC studies of whole porcine muscle, three peaks were distinguished in the generated thermograms. These peaks represent thermal denaturation of myosin (about 56°C), sarcoplasmic proteins (about 65°C), and actin (about 79°C; Zhu et al 2004;Fernandez-Martin et al 2000).…”

Recent Advances in the Use of High Pressure as an Effective Processing Technique in the Food Industry

“…However, Fernández-Martín (2004) vehemently argued against the use of light microscopy, suggesting that this technique could not determine the level of understanding which was implied in the conclusions of Martino et al (1998) and that a combination of transmission electron microscopy (TEM) and differential scanning calorimeter (DSC) would be more adequate. Zhu et al (2004) used DSC tests to show that PSF treatment at or above 150 MPa caused considerable denaturation of myofibrillar proteins, which may have increased the toughness of pork muscle during the PSF process, especially for the 150 and 200 MPa PSF samples. Futher, using both TEM and DSC, pressure-induced changes to myofibrillar proteins during PSF of raw pork meat were found by Fernandez-Martin et al (2000), which, when coupled with the compaction caused by the formation of ice, irreversibly reduced the water holding capacity of the meat samples.…”

Freezing/Thawing

“…Rapid nucleation results in small even ice crystals. However, studies on pork and beef (Fernandez -Martin et al 2000 ) and on pork (Zhu et al 2004 ) failed to show any real commercial quality advantages, and an increase in toughness was found in the later study.…”