1.1 Overview
As early as the Spring and Autumn Period, China formed a relatively mature segmentation and cooking skills for meat; after continuous evolution, in the Qin, Han and Southern and Northern Dynasties, traditional braised meat in sauce has become one of the daily commodities sold in restaurants and markets; during the Northern Wei Dynasty, "Qi Min Yao Shu" written by Sixie Jia made a detailed record of the early braised meat in sauce, and introduced them from the aspects of production technology, preparation formula, and necessary storage conditions. In the Tang and Song Dynasties, many excellent historical documents kept detailed records of braised meat in sauce, such as the "Shi Jing" in the Tang Dynasty and "Dongjing Menghua Lu" in the Song Dynasty. The processing technology of traditional braised meat in sauce has been developed and inherited from generation to generation, and is perfected and finalized. There are more than 200 kinds of ingredients, with a wide range of ingredients, exquisite cooking skills, and standardized production processes. There are two main classification methods for traditional braised meat. According to the processing technology, meat is divided into boiled meat, braised meat in sauce, and fermented meat. Meat is classified into sauced meat, braised meat, sweet meat, sweet and sour meat, fermented meat and boiled meat based on the seasonings used. There are classic dishes such as boiled chopped chicken, salted duck, sauced beef, sauced pork ribs, sauced elbow, wined chicken, and Suzhou goose with distillers' grains.
 
1.2 Research progress on the quality of braised meat
The quality of braised meat in sauce is presented by physical and chemical properties such as color, appearance, texture characteristics, tenderness, palatability, nutrients, and safety. The specific indicators for judging quality are color, yield, cutting, chewiness, elasticity, hardness, water holding capacity, tissue state, sensory evaluation, etc. According to market research and analysis, consumers pay more attention to the taste, flavor and convenience of carrying products. Among them, the indicators related to texture characteristics have a greater impact on consumers and are the key factors affecting consumers' second purchases. Sensory evaluation is one of the important ways to evaluate the quality of braised meat, which can directly feedback the comprehensive level of braised meat. Instrumental testing methods are also often used. Because the testing methods are simple and less affected by external and human factors, the data are more accurate and convincing. Currently, they are usually combined with sensory evaluation for quality evaluation of meat. Physical property meters, color difference meters, tenderness meters and pH meters are the main instruments for evaluating the quality of meat. They have good sensitivity and can balance the shortcomings of sensory evaluation.
 
Many experiments combine sensory evaluation and instrumental measurement. Herrero and others studied the correlation between twist-breaking strength and texture index of fermented sausage. Kovacevic and others studied the correlation among the color, physicochemical properties and texture of fermented sausages. Although there are a lot of analyses on the texture characteristics of meat, due to the great differences between different kinds of meat, and the many texture indicators and the complex correlations between them, the analysis is extremely difficult and lacks sufficient theoretical support. Principal composition analysis can be used to reduce the dimensionality of the indicators, and screen out the main indicators that have the most significant impact on the results as an intuitive means to analyze the quality of meat. Herrero and others used principal composition analysis to reduce the dimensionality of texture indicators of sausage, such as cohesion, hardness, elasticity, and stickiness, which simplified the analysis process.
 
Yoshida and others determined three main indicators to determine the quality of meat dumplings through principal composition analysis. The first principal composition is the flavor and texture derived from meat; the second is the flavor due to condiments, and the third is juiciness. The heat treatment of meat is to make the cooked meat delicious and easy to digest, and at the same time, it can kill certain microorganisms; the quality will be greatly affected in this process. Raw meat will lose a lot of water in the sauce making process, and the color will also change from being light to dark, which is related to myoglobin denaturation and Maillard reaction. When the raw meat is heated, the protein is denatured and solidified, and the juice is lost, which makes the muscle fibers of the braised meat shrink, the water holding capacity decreases, the tissue state becomes more compact, and the texture hardened. In addition to water, the lost juice is also accompanied by many nutrients, which also gives the sauce and braised meat a unique flavor. Therefore, it can be inferred that heating the meat in a sealed bag is a key step that affects the quality. Many scholars at home and abroad have conducted analysis and research to demonstrate this. Berto and others found that heating temperature and steak thickness are the main factors affecting the tenderness and flavor of the steak. Tornberg and others found that heat treatment can shrink collagen fibers and denature proteins in meat, thereby affecting texture. Jiang and others found that with the increase in heating temperatures, the protein content of bighead carp showed an overall upward trend, and its meat microstructure also changed significantly. Mohamed and others showed that the heating temperature has a great influence on the microstructure of camel sausage. The impact on the quality of meat is mainly focused on the influence of heating temperatures and time, but it is rare to see the systematic quality impact at each time and temperature in the traditional heating process.