Studies On Lipolysis, Protelysis And Flavor Compounds During Processing Of Cantonese Sausage

Cantonese sausage is a traditional Chinese meat product that is well accepted by consumers over the world due to its unique qualities. Flavor is considered as one of the most important attributes determining the acceptance of food by the consumer. The development of flavour in meat products is a very complex process, not yet fully understood due to the high number of reactions involved. Lipolysis and proteolysis constitute two of the most important biochemical mechanisms during the processing of Cantonese sausage with relevant consequences for the final sensory quality. The objectives of this work were to identify the predominant volatile components in Cantonese sausage and to track its changes during the ripening and storage. The mechanisms for the formation of these volatile compounds were also discussed. Changes in lipolysis and proteolysis, and substrates released during lipolysis and proteolysis were investigated to evaluate the impact of these changes on the formation of Cantonese sausage volatile compounds. The results will help to understand which substances are responsible for the flavor of Cantonese sausage and the relevant mechanism. This information will be useful to select the technological strategies to enhance flavor characteristics of Cantonese sausage.1. Cantonese sausage was prepared according to traditional practices. Samples were periodically taken at 0th, 6th, 18th, 36th, 54th and 72nd h for analyses. Lean pork and back fat were separated. Total lipids were fractionated, and fatty acids of each fraction were determined. The results indicated that the main triacylglycerols of neutral lipid were POO+SLO+OOO (P: palmitic, S: stearic, L: linoleic, O: oleic) for both lean pork and back fat, the main fatty acid was oleic acid. PC was the most abundant in phospholipids for both lean pork and back fat, and the other fractions were different. The most abundant fatty acid in phospholipids fraction was polyunsaturated fatty acids (PUFA) in lean pork, while monounsaturated (MUFA) in back fat. The lipolysis of phospholipids in lean pork, especially that of PC was the main contributor to the increase of free fatty acids, while in back fat neutral lipid and phospholipids were equivalent to release free fatty acids. Total free fatty acids, whether in lean pork or in back fat, increased (P < 0.05) greatly through the processing of Cantonese sausage. The rate of release of unsaturated fatty acids, especially PUFA was higher than saturated fatty acids.2. Lipase and phospholipases were extracted from Cantonese sausages at different processing periods and to assay their activities. Changes in the main indices during processing were also investigated to evaluate their relationships with lipase and phospholipases activities. The activities of these enzymes decreased throughout processing. Lipolysis influenced by lipase and phospholipasesdue, which remain active all along the process. A highly significant correlation was measured between their activities and salt content, water activity, total carbohydrate content, pH.3. Lipid oxidation was estimated. Results showed that lipid oxidation occurred during processing. The acidity value and TBARS value of Cantonese sausage increased during the process (P < 0.05), and the peroxide value increased at the first stage (P < 0.05), and decreased at the last stage (P < 0.05). The activity of antioxidant enzymes was determined. The activity of catalase and SOD remain active all along the process, indicating that lipid oxidation was retarded. Two peptide fractions (P1 and P2) were isolated from Cantonese sausages at different processing periods and their antioxidant activities were assayed. A good antioxidant activity was observed for each peptide fraction. Peptides with molecular weights more than 5 kDa possess a higher antioxidant activity than peptides with molecular weights less than 5 kDa. A significant (P < 0.05) correlationship between lipid oxidation and antioxidant activity was observed.4. Proteolysis was investigated during Cantonese sausage processing. Changes in the protein composition of Cantonese sausage were illustrated by the progressive decrease in sarcoplasmic and myofibrillar protein fractions, accompanied by an increase in the alkali-soluble and non-protein fractions. Peptides of > 10 and 3–5 kDa were the main WSN fractions, and their contents at final products were 40.66% and 42.05% of total WSN, respectively. A stable balance between the formation and degradation of peptides was observed. The total free amino acid concentration increased during Cantonese sausage processing, especially for hydrophobic amino acids. The discrepancies in changes of individual amino acids were due to restriction Enzyme cutting site of endogenous enzyme and active activities of individual amino acids. 5. Dynamic evolvement of Cantonese sausage protein was estimated. The protein solubility determinations suggested that hydrogen bonds, hydrophobic interactions and disulfide bonds gave rise to a three-dimensional network structure of Cantonese sausage proteins. Heat treatment, protein oxidation and proteolysis were implicated at least in changes of protein surface hydrophobicity of sarcoplasmic proteins and myofibrillar proteins, and further resulting in protein particle size changes. Not only above reasons but also the SH/S-S exchange reaction could lead to changes of myofibrillar proteins particle size. Results from CD suggested that?-helical content markedly decreased, while?-strand increased. Structural changes of myofibrillar proteins from raw muscle and Cantonese sausage at different processing periods were elucidated using Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. Structural changes of myofibrillar proteins were significant. The rebuilding process of myofibrillar proteins secondary structures was observed at the rest stage due to proteolysis.6. The volatile compounds of Cantonese sausage at different stages of processing and storage were analyzed by gas chromatography/mass spectrometry (GC/MS) with solid-phase microextraction (SPME). One hundred and four volatile compounds were identified. Esters and alcohols were the most important chemicals in all the samples, accounting for 16.94–50.12% and 30.01–65.54% of the total area, respectively. Alcohol and lipid oxidation played a key role on Cantonese sausage flavor formation. Amino acid catabolism and microbial action also plays an active role in the formation of volatile compounds. The hierarchical cluster analysis results show that the period of 18–36 h and storage were important to volatile compounds formation. Releases of volatile compounds of Cantonese sausage were influenced by structural changes of Cantonese sausage proteins, the distribution and extents of protein inter- and intra-molecular interactions and lipid content changes.7. The Maillard reaction products (MRPs) were prepared at 90 (M1), 100 (M2), 110 (M3) and 120°C (M4), respectively. The effects of MRPs and mixed starter cultures on Cantonese sausage quality characteristics and flavour were investigated. Addition of MRPs affected lipolysis and lipid oxidation during Cantonese sausage storage. M1 and M3 had an inhibitory action on total free fatty acids levels and extended the induction period. Antioxidant quality of Cantonese sausage treated with M1 and M3 was improved. Cantonese sausages treated with M1 and M2 showed good sensory properties. However, M3 and M4 had a negative (P < 0.05) effect on the flavour of Cantonese sausages compared to control. The residual nitrite content of Cantonese sausage decreased by inoculation with mixed starter cultures (S.condimenti and M.caseolyticus). Mixed starter cultures could accelerate growth of Lactic acid bacteria during initial processing stage and yeast during last processing stage. Inoculation with mixed starter cultures had effective on colour formation and flavour of Cantonese sausages.