## 1 Introduction  
Chinese sausage is a kind of meat product with Chinese characteristics which refer to the meat as raw material, which is broken into small pieces that, together with the excipients, is poured into the animal casings for fermentation and converted to dry meat products. Sausage is one of the largest varieties of Chinese meat products, and the main origins of sausage include China's Guangdong, Zhejiang, Shandong, and other places, of which Cantonese sausage is one of the most famous. With the exception of slightly different materials, the production method of all varities of sausage is roughly the same. Therefore, the non-destructive detection of sausages is of great significance to the quality identification and the protection of trademark rights. The Cantonese sausage grade identification method requires the detection of some of the major components in the sausage, including protein, oil, acid value, nitrite, POV(peroxide value), and so on. Every measurement involves a number of chemical reagents, and the measurement cycle is long. Traditionally, some measurements use the national standard method to measure the physical and chemical properties of sausage. In the study of the effects of Flavourzyme on proteolysis, antioxidant capacity, and sensory attributes of Chinese sausage, ISO-2917 method was used to determine the moisture content, water activity, pH of the sausage, and the protein [1; 2]. Both methods need to dissolve the sausage, and also involve complex pretreatment. Acid and peroxide value can be regarded as detection indices of Cantonese sausage which is stored with changes to the physical and chemical characteristics, such as baking, traditional sun, and so on [3]. The acid value is measured by crushing the sausage and dissolving it with petroleum ether first and then titrating free fatty acid content by potassium hydroxide. Pretreatment is complex and time-consuming, and extensive use of chemical reagents leads to environmental pollution. At the same time, these methods cannot achieve rapid, accurate and comprehensive quality identification of sausage. Gas chromatography-mass spectrometry (GC-MS) is a commonly used method for the determination of components in food flavor substances [4; 5]. It is suitable for the analysis of complex environments containing many organisms. For meat products, GC-MS can effectively detect organic compounds, such as aldehydes, esters, and so on [6; 7]. And the solid phase micro extraction process (SPME)-GC-MS method is usually used to explore volatile components in naturally dried sausage [8]. First, the volatile ingredients were extracted with SPME and then identified with GC-MS. The results showed that the main volatile substances in sausage were hexanal, ethyl, 2-pentanone, D-limonene, and hexanoic acid ethyl ester. The formation of these volatile substances may be due to of fat oxidation, alcohol, microbial activity, spices, and the interaction among them. GC-MS has a high degree of precision, but the detection steps are complex and costly, and it is difficult to extract samples for unevenly distributed mixtures and is, therefore, not suitable for practical production. Traditional chemical detection methods are complex and time-consuming, and extensive use of chemical reagents leads to environmental pollution. At the same time, these methods cannot be fast and accurate for sausage quality identification. Near-infrared spectroscopy is the most commonly used nondestructive testing technique in food detection and classification because it does not require direct contact with the measured object [9; 10; 11; 12]. It can accurately determine the composition and content of fat, protein, and water in meat [13; 14; 15]. [PERSON] used near infrared spectroscopy (NIR) to model fat, moisture, and protein in smoked meat sausage which is pretreated by slicing and crushing [16]. The correlation coefficients of fat, moisture, and protein in sausage processed by slicing were 0.98, 0.93, 0.97.