The yield increased first and then decreased with the increase in rubbing time, and reached the maximum value at the 8th hour (P being less than 0.05). Because in the rubbing process, by applying physical pressure, the tight structure of beef is gradually changed, and the marinating liquid can be better absorbed by the meat. With the extension of rubbing time, the absorption rate of the marinating liquid gradually slows down, which is conducive to the accumulation of salt-soluble protein on the surface of the meat, enhances the ability to prevent water loss and improves the yield. The water holding capacity of beef increases gradually with the extension of rubbing time, probably because myofibrillar protein easily forms a three-dimensional net structure during this period, thus increasing the hydrophilic capacity. The pH value increased with the rubbing process, possibly due to the continuous absorption of the marinade by the beef. With the extension of the rubbing time, the absorption of the marinade was greatly increased, which in turn raised the pH. Zhaoming Wang, Peilei Shi and others also verified the above conjecture in the research on rabbit flesh and goose.
 
2.3.3.2 Effects of different rubbing time on texture and shear force 
 
The effects of different rubbing time on texture and shear force are shown in Tables 2 to 13.
 
Tables 2-13 Texture and shear force of sauced beef under different rubbing time 

 
The hardness and shear force gradually decreased with the extension of rubbing time; the elasticity increased slowly, and the trend of chewiness increased first and then decreased (P being less than 0.05). The same principle was expressed above, that as the rubbing process progresses, the aggregation of salt-soluble proteins reduces water loss and improves the beef’s texture properties and water holding capacity. Rubbing is a processing technology that improves the texture of meat by creating mechanical pressure, and a moderately prolonged operation time is beneficial for reducing chewiness.
 
2.3.3.3 Sensory evaluation of different rubbing time
See Figures 2 to 3 for the sensory evaluation of sauced beef with different rubbing times.
 

Figure 2-3 Sensory evaluation with different rubbing time
 
According to the figure, the sensory evaluation score increased first and then decreased with the increase in rubbing time (P being less than 0.05), and the highest score was 96 at the 8th hour of rubbing. When the rubbing time is short, the muscle tissue is hard, and the shear force, hardness and chewiness are good. When the rubbing time is long, the muscle tissue is loose, which may easily lead to poor appearance, uneven shapes, and heavy taste. After comprehensive consideration, the rubbing time between 7 and 9 hours is more suitable, which can better improve the texture and other characteristics of the sauced beef.
 
2.3.4 Orthogonal test analysis of the rubbing process
According to the single-factor experiment of concentration of ginger juice, proportion of marinating liquids, and rubbing time, a three-factor and three-level orthogonal experiment was designed. The experimental results are shown in Tables 2 to 14. 
 
Tables 2-14 Orthogonal tests for optimization of the rubbing process 

 
It can be seen from Tables 2 to 14 that the optimal process of rubbing and tenderizing is A2B3C3, that is, the concentration of ginger juice is 30%, the proportion of marinating liquid is 21 to 30%, and the rubbing time is 9 hours. The factors that affect the sensory evaluation score of sauced beef  cooked by a sous-vide cooker are as follows: A: concentration of ginger juice > C: rubbing time > B: the proportion of added marinating liquids. In order to verify the accuracy of the orthogonal test, the best group A2B3C3, the second best group A2B3C2 and the third best group A2B2C2 were selected according to the range analysis in Tables 2 to 14 for verification experiments. The test results are shown in Tables 2 to 15. 
 
Tables 2 to 15 Verification results of the best rubbing and tenderizing combination based on sensory scores