High-pressure thawing of pork: Water holding capacity, protein denaturation and ultrastructure

Highlights

• The differences between high pressure thawing, air thawing and water thawing were evaluated.

• The ultrastructure of muscle was changed during high pressure thawing.

• A high pressure of 140 MPa showed the lowest thawing loss and was suitable for pork thawing.

Abstract

The effects of high-pressure thawing at 70 MPa (35 min), 140 MPa (29 min), and 210 MPa (25 min) were studied for their affect on the water holding capacity, protein denaturation and ultrastructure of porcine longissimus dorsi muscle that was frozen for 24 h at −18 °C. For comparison, water thawing at 20 °C and air thawing at 4 °C were used as control groups. The results showed that thawing losses at 140 MPa were significantly lower (P < 0.05) than those for atmospheric water thawing and the other two high-pressure conditions. However, pressing losses at 70 and 210 MPa were higher. The cooking losses and the degree of protein denaturation increased as the pressure increased. At 210 MPa, the endothermic transition temperature was higher, and the enthalpy of myosin protein denaturation was lower (P < 0.05) than the other treatment groups. At this pressure, the actin peak disappeared. Shrinkage of the sarcomere was observed in the high-pressure thawing groups, and the greatest sarcomere shrinkage was observed at 210 MPa. The H band began to appear blurry at 70 MPa and almost disappeared at 140 and 210 MPa. At the same time, the Z lines became coarser and the I band became considerably wider and white at 210 MPa.

Introduction

As the most commonly used method of storage, freezing has an important role in meat preservation and meat product processing, but the decreased quality of raw meat caused by freezing also results in significant economic losses (Coleen et al., 2012; Lagerstedt et al., 2008; Pietrasik et al., 2009). To minimize this problem, raw meat must be of higher quality, and the freezing and thawing process must be optimized (Huff-Lonergan et al., 2005; LeBail et al., 2002). A number of freezing processes have been studied, but the thawing of frozen meat has received less attention (Farag et al., 2009). The complex heat and mass transfer process, and the biological and physicochemical mechanism of the protein denaturation is not yet fully understood (Zhu et al., 2003).

In the 1990s, high-pressure thawing began to be applied to food. This thawing method had the advantage of a higher thawing rate, lower thawing losses and having little impact on food quality compared to other thawing methods (Angsupanich et al., 1998; Castro et al., 2017; Fuchigami et al., 1998a). The theoretical basis of high-pressure thawing considers the following two processes. First, from 0 to 210 MPa, the phase transition temperature of water decreases as pressure increases, dropping to −21 °C at 210 MPa. The temperature gap between frozen material and thawing material significantly increases due to freezing point depression. Plank's equation also shows that thawing time is inversely proportional to the temperature gap; therefore, high-pressure thawing can considerably improve the rate of thawing and shorten thawing time (Cheftel et al., 2000; Kalichevsky, 1995; Wu et al., 2017). Second, a decrease in the specific heat capacity and enthalpy of a heated ice-containing solution, as well as an increase in the thermal conductivity of ice at high pressure, can help improve the rates of high-pressure thawing (Knorr et al., 1998; Loc et al., 2014; Sun et al., 2013). High-pressure thawing involves three variables (temperature, time, pressure), which differ from the factors that influence traditional thawing. By regulating the three variables together, high-pressure thawing has the potential to improve the quality of food (Biniam et al., 2014; LeBail et al., 2002). Takai et al. (1991, pp. 1951–1955) studied high-pressure thawing of tuna and found that it can be done at <5 °C with a higher rate of thawing. However, the texture and color of the tuna was affected by the high-pressure thawing. These changes may have been associated with protein denaturation caused by the high pressure (Li et al., 2019; Takai et al., 1991, pp. 1951–1955). Deuchi and Hayashi (1992) found that 50 MPa was more suitable for thawing beef, as the influences on color and drip loss were relatively small. Zhao et al. (1998) compared the influence of high-pressure thawing and air thawing on ground beef quality and found that drip loss, cooking loss, shear force, and color did not change significantly at 210 MPa, showing that high-pressure thawing of beef may be beneficial. Preliminary investigations have been done of the influence of high-pressure thawing on water retention, color, structure and other quality aspects of fish, shellfish, strawberries and other foods (Eshtiaghi et al., 1996; Fuchigami et al., 1998b; Lakshmanan, 2003). These studies showed that the changes in the quality of food processed with high-pressure thawing were probably due to a combination of factors and depended on the original composition of the food (Galazka, 1995; Zhu et al., 2003).

Per capita pork production and consumption accounted for >50% of total meat production and consumption in China, indicating that pork continues to be a primary source of meat, although African Swine Fever may change these numbers. However, this may also lead to the use of more imported frozen meat. Studies of high-pressure thawing have mainly focused on fish, shellfish and other seafood. High-pressure thawing has been used, particularly in Japan, to thaw fish. The objective of the present study was to learn more about the application of this technology to pork.