## 3 Results and Discussion
### The Flavor Profile and Comparison of Meat Sausage Analogue  
Flavor is also considered an important sensory characteristic of meat products and largely determines the purchase intent of the consumer. Proteins have little flavor, but many studies have reported their ability to bind and retain flavor compounds [25; 26]. Naturally fermented sausages, such as the Harbin dry sausage, are well known and very popular among the people of northeast China because of their mouthfeel, distinctive flavor and short natural fermentation period (15 days). To explore a greater range of applications, a dry-fermented sausage based on MMSA was also developed by hanging sausages and drying them at 25 \(\pm\) 2 \({}^{\circ}\)C for 15 days (30% relative humidity). To portray the flavor profile, the volatile substances in both MMSA and the dried MMSA (DMMSA) were extracted and analyzed by HS-SPME combined with GC-MS.  
A total of 64 volatile compounds from the MMSA and DMMSA samples were identified and quantified, and they were grouped as esters, aldehydes, ketones, phenols, acids and other compounds. To view the differences of volatile substances in the sausages comprehensively, the number and contents of different chemical classes are exhibited in Figure 5. Generally speaking, the number of different classes in DMMSA was greater than that in MMSA except for ketones and phenols. The contents of volatile compounds from the different classes showed a great difference. 10.372 \(\upmu\)g\(\cdot\)g\({}^{-1}\) and 276.603 \(\upmu\)g\(\cdot\)g\({}^{-1}\) volatile compounds were detected in MMSA and DMMSA, respectively. The content of each class in DMMSA was much higher than that in MMSA, because more volatile compounds had been generated during the dry fermentation processing. The complexities of lipid oxidation and bacterial metabolism are responsible for the abundance of volatile flavor substances that contributed to the aroma profile. The number of volatile substances identified in the MMSA and DMMSA samples was 27 and 45, respectively (Table 3). Hexanal, described as the fat odor, was the most abundant of all the volatile substances in MMSA at 1.931 \(\upmu\)g\({}^{-1}\), and is the most typical of the aldehydes generated by lipid autoxidation [27]. Other aldehydes with certain off-flavors, such as heptanal, 2-heptenal (fat), octanal (fat), 2-octenal (green), 2-nonenal (fat), 2,4-nonnadienal, 2-decenal (tallow), 2,4-decadienal (fat) and 9-octadecenal, are also associated with lipid oxidation, and they were not detected in the MMSA sample, except for 1-nonanal with its green odor found at a low level, which might cause deterioration in meat quality and an unpleasant taste [28; 29]. Alcohols accounted for 17.26% of all the volatile compounds in DMMSA, with linalool (floral, sweet) being the most abundant alcohol at 17.138 \(\upmu\)g\(\cdot\)g\({}^{-1}\). The content of linalool and limonene (50.853 \(\upmu\)g\(\cdot\)g\({}^{-1}\)) in DMMSA increased significantly compared with the unfermented MMSA, as reported in a previous study  
Figure 4: (**A**) Principal component analysis plot and (**B**) cluster analysis of mushroom-based meat sausage analogues comparing different formulations and commercial products. on dry-fermented sausages. The contents of other compounds originating from spices such as alpha-terpineol, cinnaldehyde, phellandrene, alpha-terpineol, alpha-curcumene, bisabolene and alpha-pinene were also at a high level in DMMSA and may contribute to oxidation and the microbial enzyme metabolism [30]. The results for DMMSA agreed with [PERSON]'s, work which reported that the contents of volatile compounds from spices were higher in air-dried sausages than in other types [31]. Limonene was the second most abundant volatile compound detected in MMSA, mainly originating from the spices [32]. The odor of 2-heptanone, with its spicy, blue cheese odor and high threshold, was present at 0.943 \(\mathrm{\SIUnitSymbolMicro g}^{-1}\) in MMSA, which might result in an adverse contribution to the aroma profile.