## 3 Results and Discussion  
### Changes of Volatile Flavours in Cooked Marinated Pork Kunckle During Processing  
There were 20 compounds in raw meat (T1), including 3 aldehydes, 2 ketones, 4 alcohols, 4 esters, 4 acids, and 3 alkenes in Table 1. It is worth noting that the content of 1-nonanol was the highest in the T1 stage, which was decreased in the marinade stage (T2), and even not detected in the brine soup stage (T3) and finished product stage (T4). It suggested that the 1-nonanol is from raw meat and is easily decomposed, which has a pleasant aroma of rose and orange. In addition, vinyl hexanoate is a sweet-smelling substance unique to black pork and has a well-rounded, pineapple-scented aroma. Methyl heptanone, with a fruity and fragrant flavour, has the effect of enhancing the aroma of meat, and it is mainly derived from raw meat. Compared with raw meat, the types and contents of volatile compounds increased significantly (\(p<0.05\)) in the T2 stage, in which the pork knuckle underwent a marinade process using salt and spices [16; 17]. There were 33 compounds measured in T2, including 5 aldehydes, 2 ketones, 8 alcohols, 6 esters, 4 acids, 1 furfural, 3 phenols, and 4 alkenes. Furfural and 2-furan methanol were not found in raw meat. This indicated that they are the characteristic flavour compounds of soy sauce. There were 40 compounds measured in T3, including 9 aldehydes, 3 ketones, 10 alcohols, 6 esters, 5 acids, 3 phenols, 1 furan, 1 furfural, and 3 alkenes. There were 60 compounds measured in T4, including 15 aldehydes, 6 ketones, 14 alcohols, 8 esters, 9 acids, 3 phenols, 1 furan, 1 furfural, and 3 alkenes. The types and contents of flavour compounds increased significantly (\(p<0.05\)) after heating. The degradation of protein, the Maillard reaction of flavour precursors, and the Strecker degradation of amino acids through heating are the factors that contributed to this result. In addition, spices play an important role in the processing of cooked marinated meat products, which can not only give meat products unique flavour and improve the flavour of meat products but also restrain and correct the unpleasant odour in meat products. The active ingredients in spices affect the formation of fat oxidation products. Meanwhile, spices can also react with raw meat components to produce volatile flavour substances. For example, some volatile compounds are from spices, and benzaldehyde has bitter almond, cherry, and nutty aromas derived from anise, cinnamon, and syzygium aromaticum; 4-Methoxy-benzaldehyde, which provides a long-lasting hawthornaroma, derives from anise and verum; Linalool has floral, woody, berry and other aromas, and is from anise, verum, cinnamon, syzygium aromaticum, nutmeg, peppercors and coriander seeds; \(\alpha\)-Terpineol is from anise, verum, cinnamon, nutmeg, peppercors, coriander seeds, and amomum tsao-ko; Eucalyptrol is from verum, nutmeg, cinnamon, peppercors, coriander seeds, and amomum tsao-ko; Terpinen-4-ol equipped with peppery is present in verum, nutmeg, cinnamon, peppercors, and coriander seeds. And 4-Terpineol is from syzygium aromaticum. In particular, the content of anethole in T3 was high to 647.56 \(\mu\)g/g, which has a spicy and licorice smell mainly from anise, cinnamon and verum in the spices. Still its content declined significantly (\(p<0.05\)) in the T4 stage, which indicates that it is easily soluble in water and easy to be enriched in the brine soup. In addition, the components of anise and verum would affect the fat oxidation products such as hexanal and octanal in raw meat [18].