The Effect of Sous-vide Cooking on Braised Pork

Braised pork is a well-known meat product in China, but its various processing methods include high-temperature and long-term heating processing steps. Excessive processing methods not only damage the appearance of meat products, but also adversely affect physicochemical properties and the bioavailability of nutrients. With the upgrading of consumer attitudes, consumers expect healthier, nutritious and safer foods. The low-temperature slow-cooking process which uses a lower temperature to heat meat sealed by a vacuum sealer a long time has gradually become the development trend in the food industry. Combining the low-temperature slow-cooking technology with the production of traditional Chinese sauce braised pork makes the production of delicious and nutritious meat products possible. However, the application of sous-vide cooking started late in China, and the research on heating traditional Chinese meat products by sous-vide cooking is even lacking.
 
1. The impact of sous-vide cooking on the edible quality of braised pork
The moisture content of braised pork in different groups was determined by halogen moisture analyzer. The moisture content of groups was significantly higher than that of the traditional processing (CT) group (P being less than and equal to 0.05) except for the groups with a temperature of 70℃ for 12 hours (SV6) and 75℃ 12 hours (SV9), indicating that the low-temperature slow-cooking can significantly increase the moisture content of the product and make the product have a juicy taste, while the groups of a temperature of 70℃ for 12 hours (SV6) and 75℃ 12 hours (SV9) were treated for a long time. The gel mesh in the meat was thermally denatured and the water holding capacity was reduced. With the prolongation of heating time, the shear force of different temperature groups in the low-temperature slow-cooking process showed a trend in increasing first and then decreasing, which was closely related to the shrinkage and denaturation of protein and connective tissue in meat. The fat content increases with the increase in heating temperatures at the same time. At the same temperature, it decreased with the prolongation of heating time, and the trend of fat loss was the same as that of thermal processing loss. Color difference analysis showed that sous-vide cooking can make the braised pork uniformly color like the traditional process. At the same time, it can also make the meat have better brightness, showing a crystal clear color. From the analysis of the integrity of the sarcomere, it can be found that the light band in the traditional processing (CT) group increases and the dark band shortens, which may be caused by the high temperature for heating for a long time, leading to the excessive contraction of myosin and actin. Excessive heating may also lead to the excessive oxidation of myofibrils, resulting in the disintegration of the myofibril structure and the incomplete sarcomere structure. This is also the reason why the shear force of the conventional processing (CT) group is higher than that of the other two groups. Comparing the SV1 group of heating at a temperature of 65℃ for 8 hours and the SV9 group of heating at a temperature of 75℃ for 12 hours, it can be found that the connection between the Z lines of the SV9 group of heating at a temperature of 75℃ for 12 hours is weakened, which indicates that under the slow cooking process, increase in time and heating can cause greater protein structural changes, but the denaturation intensity is still lower than that of the traditional processing CT group. Particle size data suggest that high-temperature stewing may cause excessive protein aggregation, leading to an increase in the size of the protein, which may be caused by the formation of random coils and intertwining of the protein after severe oxidation of the protein due to excessive heating.
 
2. Effects of sous-vide cooking on the nutritional properties of braised pork
The particle size results showed that the Dx(10) and Dx(5o) values ​​of the CT group after digestion with gastric enzymes and pancreatic enzymes were significantly higher than those of the other groups, which may be caused by the excessive denaturation and aggregation of proteins due to high temperature stewing, which reduced the effect on digestive enzymes, so that they cannot be enzymatically decomposed into smaller peptides. The digestibility of traditional processing (CT) group and SV9 group of heating at a temperature of 75℃ for 12 hours after pepsin digestion were significantly lower than other groups, while the digestibility of SV1 group of heating at a temperature of 65℃ for 8 hours was significantly higher than that of other groups (P<0.05).
 
After digestion with pepsin and trypsin, the digestibility of SV1 group of heating at a temperature of 65℃ for 8 hours was still significantly higher than that of other groups (P<0.05), which may be because the low temperature and short-time heating conditions moderately denatured and aggregated the protein, which increased the contact site with pepsin. The value of malondialdehyde showed that the value of the traditional processing (CT) group was significantly higher than all low-temperature slow-cooking groups (P<0.05), which indicates that the increase in heating temperature and time will reduce the content of malondialdehyde, and the low-temperature slow-cooking group also shows obvious regularity, that is, the malondialdehyde of braised pork increased with the extension of heating time at the same temperature. The a-helix structure of the traditional processing (CT) group was significantly higher than the low-temperature slow-cooking group (P<0.05), while the β-sheet content was significantly lower than the low-temperature slow-cooking group (P<0.05), which indicated that the high-temperature and long-term heating caused excessive aggregation of the protein structure and the increase in the content of a-helix structure.

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