| Jinhua ham is famous for its special and characteristic flavor, and it is produced using a traditional and special dry-cured method in China. It is widely favored by consumers both at home and abroad for its aroma, produced from long ripening period. Its yield has increased annually to three to four million pieces. However, the main mode of its consumption is direct cooking. Its product is seldom in the market. There are various meat products in China and the demand for meat flavoring is quite large. Ham flavoring is rare in the Chinese market and it is universally considered to have lower olfactory quality compared to the original ham aroma. The famous Jinhua ham was chosen as the raw material and its characteristic aroma components as the main evaluation index in this thesis. Inartificial and high quality Jinhua ham flavoring base was prepared by supercritical-CC>2 fluid extraction, enzymatic hydrolysis and Maillard reaction to intensify the aroma.Three extraction methods for volatile flavor components of Jinhua ham were optimized and compared in order to choose optimum method and avoid the deviation of different methods. For simultaneous distillation extraction (SDE), ether was the optimum solvent and extraction time was 2h. For solid-phase microextraction (SPME), the optimum conditions were: 75 μ m CAR/PDMS as optimum absorption fibre, absorption time 40min and temperature 60℃, while desorption was 2min at 250℃. For the thermal desorption (TD) method, -30℃ cold trap was beneficial to condense the low boiling point volatile components while absorption was carried out at 60℃ for 40min. However, this study did not concern itself with samples containing high water vapor, and more investigations need to be done. Under each optimized condition, 81, 79 and 60 compounds were identifiable in SPME, SDE and TD, respectively. The mean relative square standard deviation in SPME was lowest at 16.14%. The other values were 18.29% and 24.10% for TD and SDE, respectively. The analysis results are relevant for the cooked Jinhua ham flavor because of the high temperature cooking in SDE procedure, while SPME and TD experimental results may represent the volatile flavor components of the raw Jinhua ham. One hundred and thirteen (113) Jinhua ham flavor compounds were identified when the three methods are used to complement each other.The characteristic flavor of Jinhua ham was investigated in order to establish the quality evaluation index of Jinhua ham flavoring base. The flavor components of Jinhua ham, salted pork and fresh pork were compared by SPME and SDE, respectively. The odor-active components in Jinhua ham aroma extract prepared by the two methods were identified and characterized by gas chromatography- olfactometry (GC-O). The characteristic SPME Jinhua ham flavor components contain 17 volatile compounds. They include 2-methyl-propanal,3-methyl-butanal, 2-methyl-butanal, 3-(methylthio)-propanal, phenyl acetaldehyde, methanethiol, dimethyl disulfide, dimethyl trisulfide, methyl-pyrazine, 2-heptanone, 2,3-pentanedione, 2-methyl-butanoic acid, 2,6-dimethyl-pyrazine, 2-pentyl-furan, ethyl acetate, l-octen-3-ol. The other compounds, such as hexanal, heptanal, octanal, nonanal, butanoic acid, also contributed to the whole SPME profile.The characteristic SDE flavor components contained 15 volatile compounds. They include 3-methyl-butanal, 2-methyl-butanal, (E)-2-pentenal, heptanal, 3-(methylthio)-propanal, benzaldehyde, octanal, phenyl acetaldehyde, 2,6-dimethyl-pyrazine, 2-pentyl-furan, 5-pentyI-dihydro- 2(3H)-furanone. The other compounds, such as hexanal, 2-hexenal, (Z)-2-heptenal, nonanal, (E, E)-2,4-decadienal, 2-undecenal, ethyl acetate, also contributed to the whole SDE profile of Jinhua ham.Aroma extract dilution analysis (AEDA) was used to quantify the contribution of each odor-active component to the whole ham flavor profile. The order according to significance to the ham aroma was ?2,6-dimethyl-pyrazine, 3-(methylthio)- propanal;(2) hexanal;(3) 2-heptanone, ethyl acetate;? 5-pentyl-dihydro-2(3H)- furanone, (E, E)-2,4-decadienal, 2-pentyl-furan, (Z)-2-heptenal, 3-methyl-butanal, 2-methyl-butanal;(5) 2-undecenal, phenyl acetaldehyde, octanal, l-penten-3-ol;? 2,3-pentanedione, 1-octen- 3-ol;? nonanal;(8) (E)-2-pentenal, benzaldehyde, heptanal, 2-hexenal.The volatile ham components were extracted by supercritical-CO2 (SC-CO2) fluid firstly. Single-factor and orthogonal tests were done for the optimum extraction parameters: extraction pressure 35Mpa, extraction temperature 65°C, extraction period 3 hr and high pressure pump frequency of 24Hz. Evaluation of the effect of operation condition on extraction efficiency should include two parts. The first was the total volatile aroma compounds quantity change (including the weight of extract and the yield of total volatile components). The second was the whole aroma profile change (including mean square deviation and sensory evaluation). As a whole the mean square deviation (MSD) and sensory evaluation were consistent. When the order sum in sensory evaluation was higher, the MSD was lower, and vice versa. This result proved significantly that MSD was feasible completely to evaluate the effect of SCFE operation on the products flavor profile. Meanwhile, the optimized SC-CO2 extraction of the ham provided 85% aroma extracts with high olfactory resemblance to the original Jinhua ham.The operation conditions for the taste components and flavor precursors extraction by enzymatic catalysis using a combination of Protamex and Flavourzyme were optimized by single factor experiment and surface response analysis. The results indicated that the optimum conditions were: the ratio of sample to water 1:7, reaction temperature 50'C, initial pH 7.5, thedose of Protamex 1.6% and Flavourzyme 5.0% (w/w, Enzyme/Protein). The two enzymes were simultaneously added followed by incubation for 1.85h. Under such experimental conditions, the total nitrogen recovery (TNR) was 86.9%;the degree of hydrolysis (DH) was 24.1% and the product gave a good taste. The nitrogen-containing components in the extract had relative molecular weight distribution lower than 1000. The products were enriched in free amino acids to 26.325% relative to total dry material. Glutamic acid in the enzymatic products was 16.9 fold as high as in the raw ham. The other umami amino acid -asparagine was 81 fold as in the raw ham. The umami taste was significantly enhanced by enzymatic hydrolysis and the product had an enjoyable complex, mostly umami, including saltly, sweet and bitter taste.The Maillard enhancing aroma reaction was investigated for the enzymatic hydrolysate in order to improve its aroma intensity. The optimum conditions for the Maillard reaction optimized by the single factor experiments and Lig(37) orthogonal tests were as follows. The ratio of the ham hydrolyte: xylose: hydrochloric cysteine: thiamine: fat of ham was 100: 5: 10: 5:1. The solution had a concentration of 30% while the system pH and the reaction time were 5.0 and 30min at 120°C, respectively. The free amino acids analysis results before and after the aroma enhancing reaction indicated that cysteine was the most active amino acid in Maillard reaction and was the most important flavor precursor. The umami amino acids were expended less and umami intensity was not decreased during the Maillard reaction.The three flavoring bases were supercritical fluid extract (SFE), the aroma enhancing enzymatic hydrolysate product and a mixture of both. The aroma compositions of the three flavoring bases were analyzed by GC-MS. SFE closely resembled the original flavor of raw Jinhua ham. The Sulfur-containing and heterocyclic compounds produced during Maillard reaction had low aroma threshold and strong meaty flavor. The mixed product had high olfactory resemblance to the original ham as determined by sensory evaluation. The GC flavor profile analysis objectively proved that the mixture flavor profile was consistent with that of raw ham.
|
PDF Full Text Request