| Cooked Chinese Nanjing duck was one of the traditional Chinese featured meat products, It was famous for its delicate processing, savory, and tender and umami-like flavour and so on. In resent years, many factories which process ducks usually applied many different post-production heat treatments into duck products after packing, especially 121℃group ducks. The flavour and sensory were influenced much, furthermore the market for these ducks following post-production heat treatments was also influenced. Therefore, we should figure out which heat treatments group ducks could reserve the most part of its flavour in order to modify the processing steps of cooked Chinese Nanjing ducks. The studies on the impact of flavour in meat products during post-production heat treatments were less nowadays. The contents and results were as follows:1 The optimization on the analysis methods of volatile compoundsThis chapter was that we have done more to improve and perfect the volatile analysis technology (SPME-GC-MS) of cooked Chinese Nanjing ducks in order to entirely analyze the main volatile composition in duck meat. We have done a series of SPME fibers optimizations experiments including bipolar 75μm CAR-PDMS, moderate polar 50/30μm CAR/DVB/PDMS and polar 85μm PA fibers separately based on non-polar DB-5MS column and polar DB-innowax column. We found that volatiles in ducks were formed by mainly non-polar compounds, whereas polar compounds were only a small part of duck meat. So we should apply on both a bipolar fiber 75μm CAR-PDMS using a non-polar DB-5 (30 m×0.25 mm i.d.) column and a moderate polar fiber 50/30μm CAR/DVB/PDMS using a DB-innowax (30 m×0.25 mm i.d.) column in order to analyze the volatile composition in ducks comprehensively. There were mainly 67 volatile compounds (alkanes, aldehydes, kenones, alcohols, N-containing and benzezes, furan, acids, esters alkenes et al) identified in duck meats. 2 The changes of volatile compounds and sensory in duck groups following various post-production heat treatmentsThe changes in volatile compounds of traditional cooked Chinese Nanjing ducks during different post production heat treatments groups (Control,99℃,108℃, Microwave, 121℃) were analyzed by headspace solid phase microextraction (HS-SPME) combined with GC-MS. We also carried out comprehensive sensory analysis in these 5 group ducks, whereas triangle sensory analysis between 108℃group ducks and microwave group ducks. Results indicated that mainly 76 volatile compounds were identified, including acids (3 kinds), ketones (14 kinds), aldehydes (20 kinds), alcohols (11 kinds), esters (5 kinds), alkanes (7 kinds), furans (1 kind), N-,S-,benzene- containing compounds(11 kinds) and alkenes (4 kinds) in duck meat.57,56, and 59 kinds of volatile compounds were identified in control group ducks and post production heat treatment at 99℃and 108℃respectively, and higher than microwave (51 kinds) and 121℃(52 kinds) heat treatment group. Control group ducks had the higher relative contents of total peak from major volatile compounds (87.27%) compared with other post production heat treatment groups (99℃,83.27%; 108℃,81.6%; microwave,84.06% and 121℃,84.33%). Compared with microwave and 121℃group ducks,108℃group had higher score in the sensory analysis, but in triangle sensory analysis, The difference between 108℃group and microwave group ducks was not significant. Combined with sensory analysis, we could conclude that flavour of 108℃group was more similar to control group.3 The change of taste compounds and sensory in duck groups following various post-production heat treatmentsTaste compounds including free amino acids, succinic acid and 5'-nucleotides and chemical factors including moisture, pH, protein, crude fat and sodium chloride were evaluated in Cooked Chinese Nanjing ducks following different heat treatments including Control group,99℃group,108℃group, microwave group and 121℃group. Heat treatments decreased (P<0.05) the contents of Alamine, moisture and muscle pH value, but increased (P<0.05) the contents of protein and 5'-nucleotides. The 99℃group had significantly lower content of crude fat compared with other groups (P<0.05). The control group had significantly higher succinic acid content than 121℃group (P<0.05). Higher heat (108℃, microwave,121℃) treatment groups had similar equivalent umami concentrations (EUC), contents of 5'-nucleotides, free amino acids, and the derived contents bitter, sweet taste components compared with other treatment groups.108℃, microwave,121℃group ducks had more umami-taste compared with other treatment group ducks. The contents of soluble sugars were higher in 108℃, microwave,121℃group ducks, but the minor amounts of sugar could not impact final flavour of duck meat. The thiamine content in ducks following post-production heat treatments increased significantly, and the control and 108℃group ducks had the least amount of thiamine content probably due to thiamine thermal degradation excessly and more flavour formation.Based on these results, the control and 99℃group ducks were more light and tasty. The microwave group had more umami-like taste compounds. It appears important not to further process at higher temperatures, there may be some opportunities for modifying the primary processing steps to improve the content of important contributing umami-taste like compounds 5'-nucleotides.4 The change of fatty acids, fat oxidation, triglycerides in duck groups following various post-production heat treatmentsThe main fatty acids in 5 group ducks were methyl palmitate (C16:0), methyl stearate (C18:0), methyl oleate (C18:1), methyl linoleate (C18:2), and methyl arachidonic (C20:4) the main triglycerides in these ducks were LLO, OOO, POO, SOO, POS and PPS. Compared with control group ducks, the carbonyl value, peroxide value and PUFA content increased in these treatment groups. From the data obtained from NL and PL fractions in ducks, we found that the percentages of C16:0, C16:1 and C18:1 decreased whereas C18:2, C18:3 and C20:4 increased, and the increasing tendency of PUFA level in Neutral lipids (NL) was more significant. The percentage of Methyl linoleate (C18:2) in control and 99℃group was significantly (P<0.05) lower than other group ducks. Methyl linolenate (C18:3) in control,99℃and 108℃group ducks were significantly lower (P<0.05) than other treatment groups. About free fatty acids, the percentages of methyl linoleate (C18:2) in control group was significantly lower (P<0.05) than from other treatment ducks, methyl linolenic (C18:3) in control and microwave groups were significantly (P<0.05) lower than other groups. The percentages of triglycerides composed of 3 unsaturated fatty acids in these treatment group ducks were significantly higher (P<0.05) than other group ducks, such as OOO, POO and POP, whereas the triglycerides composed of 2 or 1 unsaturated fatty acids were significantly lower (P<0.05), such as SOO, POS, PPS and SSO. The impact of oxidation reactions and formation of off-flavour induced by TGs were less than fatty acids, In a word, the content of polyunsaturated fatty acids in ducks would be increased following various post-production heat treatments and these treatments could cause auto-oxitation in meat and also induce the formation of off-flavour such as (WOF) and sensory deteriorations in final meat products. |
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