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Abstracts
Workgroup: Public Health and Processing
Investigation of Fresh Oyster Flavor Profiles and Changes Following Post-Harvest Treatments
Principal Investigator(s):
Zhimin Xu, Dept. of Food Science, Louisiana State University Agricultural Center, zxu@agctr.lsu.edu
Funding Period: 10/01/01-09/31/03
1) Changes of fresh oyster fatty acids during storage following post harvest treatments
Because lipid oxidation and flavor alteration are closely related to changes of fatty acids, the changes of fatty acids in oysters treated by warm-water chilled water (WWCW) and High Hydro-Pressure (HHP) pasteurization methods were investigated. The total of fatty acids in untreated and the two treated groups decreases significantly during the storage. The polyunsaturated fatty acids (PUFA) were more vulnerable than other fatty acids. The decrease of C16:1, C20:3, C20:4, and C22:6 in WWCW group were significantly lower than either untreated or HPP group. No difference was found for C18:1 and C18:2 among the three groups. The reduction of C16:1, C20:3, and C22:6 in HHP group were significantly higher than in untreated group, except, C20:4. The results indicate that HHP pasteurization method may accelerate lipid oxidation of oyster.
2) Analysis of changes of fresh oyster flavor compounds during storage
A solid-phase microextraction (SPME) method was developed to extract flavor compounds of oyster. GC-MS (Gas Chromatography - Mass Spectrometer) technique was used to identify and quantify the flavor compounds in the extract. The significantly increased volatile compounds during storage were identified as dimethylamine and dimethyl sulfide that are produced from amino acids degradation and hexanal, hexenal, 2-nonenal, 1-octen-3-ol, 1-nonen-3-ol, 2,4-octadienal, and 3,5-octadien-2-one that are produced from lipid oxidation. The advantages of the SPME method with GC-MS analysis are very simple and reliable. It could be applied to monitor the freshness of oyster.
3) Aroma characters of the flavor compounds produced from amino acids degradation and lipid oxidation
The aroma characters of the increased volatile compounds were determined using GC-olfactory method. The odor of dimethylamine and dimethyl sulfide are described as fishy and sulfur smell, respectively. The odor of lipid oxidation compounds, hexanal, hexenal, 2-nonenal, 1-octen-3-ol, 1-nonen-3-ol, 2,4-octadienal, and 3,5-octadien-2-one are described as grass, mushroom, carrot, and watermelon smells. The changes of the volatile compounds may be directly responsible to the oyster flavor alternation during storage.
IMPACTS and/or BENEFITS:
The results of this study will help the oyster industry develop more efficient safety treatments while maintaining original flavors and extending shelf life. Furthermore, the protocols for flavor assessment used in this study could be applied in the oyster quality control.
PROJECT PUBLICATIONS:
The manuscripts for the project publications are being prepared.
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