Abstract :
[en] The traditional stewed pork is a famous sauce pickled product in China and often produced by stewing the fresh pork in aged brine. Here, the aged brine included water and various ingredients such as salt, sugar, spices, soy sauce and cooking wine. Because of its unique sensory characteristics, for example tender texture, bright colour and rich flavour, the stewed pork is appreciated by consumers. However, the traditional stewed pork also has faced a number of potential problems in recent years. Among them, the most important is the volatilization and loss of flavour compounds. In order to solve this problem, the flavour compounds in the stewed pork were fully analysed and a new processing technology were proposed.
Firstly, the flavour compounds profile and odour-active compounds in the stewed pork from four local brands, Dahongmen (DHM), Daoxiangcun (DXC), Henghuitong (HHT) and Tianfuhao (TFH), were evaluated by GC-MS/O and E-nose combined with chemometrics analysis. A total of 62 volatile compounds were identified and quantified in all pork samples, and 24 of them were considered as odour-active compounds because their OAVs were greater than 1. According to principal components analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) of GC-MS/O and E-nose data, the stewed pork samples were divided into three groups (DHM, HHT, and DXC-TFH). The PLS-DA result showed that 9 odour-active compounds (heptanal, nonanal, 3-carene, D-limonene, β-phellandrene, p-cymene, eugenol, 2-ethylfuran and 2-pentylfuran) were confirmed to the potential flavour markers for the discrimination of stewed pork products.
Secondly, the effects of different pork breeds on the aroma profiles of boiled pork were investigated. The three varieties of pigs are Tibetan, Sanmenxia and Duroc × (Landrace × Yorkshire). The volatile compounds and odour-active compounds in boiled pork from three different breeds of pigs were identified and quantified using gas chromatography-olfactometry-mass spectrometry (GC-MS/O) and odour activity values (OAVs). A total of 61 volatile compounds were identified, among which 25 compounds were selected as odour-active compounds in boiled pork. Hexanal, nonanal, 1-octen-3-ol, dimethyl disulphide, heptanal, 2-pentylfuran and 2-ethylfuran were the important contributors to the whole flavour of boiled pork. The flavour profile was determined by E-nose based on principal component analysis (PCA). This result showed that boiled pork from the three pig breeds could be clearly distinguished. The radar chart of response value of E-noes sensors displayed the boiled pork from different pig breeds had significantly different flavour, and that boiled pork from the fore leg and hind leg muscles of pigs had similar aroma compositions. The above analyses showed the different pig breeds had a greater influence on flavour of boiled pork than pigs in different parts, and the GC-MS/O combined with E-nose was a feasible method to determine and distinguish the volatile profiles of different varieties of pork samples.
Besides, the influence of different seasoning recipes (SP1: stewing pork in water, SP2: stewing pork with water and salt, SP3: stewing pork with water, salt and spices, SP4: stewing pork with water, salt, spices and soy sauce, SP5: stewing pork with water, salt, spices, soy sauce and sugar, SP6: stewing pork with water, salt, spices, soy sauce, sugar and cooking wine) on volatile profiles and sensory evaluation of stewed pork were studied. The GC-MS/O and two-dimensional gas chromatography combined with time-of-flight mass spectrometry (GC × GC-TOFMS) were applied to detect the flavour profile in stewed pork form different seasoning recipes. The stewed pork processed using SP1 and SP2 had the most abundant volatile compounds, especially aldehydes. Which indicated that the cooked pork with water and salt promoted lipid oxidation and amino acid degradation. Samples SP3, SP4, SP5 and SP6 were close each other in PC1-PC2, whereas samples SP3 was located on the opposite side of samples SP4, SP5 and SP6 in PC1-PC3 using PCA. It was showed that the addition of spices had a significant influence on the flavour of stewed pork. Sensory evaluation revealed the stronger spicy odour, caramel odour and soy sauce odour were presented in samples SP3, SP4, SP5 and SP6. These results were consistent with the results of partial least squares regression (PLSR).
Finally, the volatile compounds and non-volatile compounds of stewed pork with different processing methods (TS: traditional stewing, TSE: traditional stewing with enzymatic degradation, TSE: traditional stewing with enzymatic degradation and Maillard reaction, HS: high-temperature stewing, HSE: high-temperature stewing with enzymatic degradation, HSEM: high-temperature stewing with enzymatic degradation and Maillard reaction) were analysed. The high-temperature stewed pork (HS, HSE and HSEM) had a higher content of volatile composition than traditional stewed pork (TS, TSE and TSEM), especially sample HSEM. The traditional and high-temperature stewed pork samples clearly distinguished by E-nose method. The contents of umami amino acids (UAAs), sweet amino acids (SAAs) and bitter amino acids (BAAs) of high-temperature stewed pork were higher significantly (P < 0.05) than those of traditional stewed pork, of which the content of Asp and Glu related to umami taste were the most in sample HS and HSEM. The high-temperature stewed pork showed the lower contents of 5’-nucleotides and fatty acids (FAs) than traditional stewed pork. It was concluded that the pork with high-temperature stewing (HS, HSE and HSEM) could be used as an effective method to improve the taste and odour of stewed pork, moreover, sample HSEM had a great advantage in the formation of odour compounds.
