Research On Volatile Compounds Of Grass Carp Meat And Its Influence Factors

The yield of freshwater fish has reached more than 20 million tons in China, accounting for about 50% total output of fisheries production. How to utilize freshwater fish effectively and develop highly value-added products from this valuable resource have become a major research topic. As a resource provided perfect protein, surimi processing has made significant progress which eliminated the problem of fish bone in recent years. However, the unpleasant off-flavor(earthy fish odor) has not been fundamentally resolved, restricting promotion and application of the freshwater fish processing technology. The proportion of aquatic product processing is about 80% in developed countries, while the proportion of deep processing of aquatic products in China is only 30% out of total production. Low percentage of freshwater fish deep processing, which has only about 10%, is mainly because of its unpleasant earthy flavor lack of attraction to many consumers. Thus, the study of earthy taste and odor not only enrich the theoretical knowledge of flavor chemistry, but also provide an effective solution to the current situation of low proportion of fish processing.In this paper, the different parts of cultured grass carp were used as research object. The volatile compounds in different parts of grass carp were compared by electronic nose. The volatile compounds of grass carp were extracted and concentrated by headspace solid phase micro-extraction (HS-SPME). Then the volatiles were identified by gas chromatography-mass spectrometry (GC-MS). The predominant volatile compounds in different parts of grass carp were determined with method of odor activity value. Furthermore, the change of volatile components in different storage conditions, and methods of reducing off-flavor and deep-processing process were surveyed.This study includes: identification and analysis of predominant volatile compounds of all parts of cultured carp (dorsal meat, belly meat, red meat, skin, viscera and gills); the influence of farming season, growth environment and the weight on flavoring among different parts of grass carp; the improvement of flavoring of grass carp meat on temporary cultivation and slaughter measures; identification, analysis and comparison of volatile compounds among uncooked grass carp meat, cooling cooked grass carp meat, cooked grass carp meat, twice cooked grass carp meat; the change of volatile compounds of grass carp among different heating temperatures; the change of volatile compounds of grass carp meat in freeze, room-temperature and cold storage; the effect of washing process on volatile compounds in grass carp surimi. Results were as follows:1. According to the pre-test and reference, optimum operating conditions of the HS-SPME method were determined: 65μm PDMS/DVB SPME fiber, 45℃water bath under the conditions of 40min adsorption; temperature program: initial column temperature 40℃, maintained 2min, to 4℃/min rise to 160℃, and then to 10℃/ min rise to 250℃, maintained 5min.2. According to GC-MS detected data, 42, 41, 43, 48, 45 and 41 volatile compounds were detected in dorsal meat, belly meat, red meat, skin, viscera and gills of cultured grass carp respectively. The volatile components in dorsal meat, belly meat and red meat of cultured grass carp are mostly carbonyl compounds and alcohols, relative concentrations can reach 95.76%, 91.97% and 96.87%, respectively. According to comprehensive evaluation of odor activity values, predominant volatile compounds of each part of grass carp were determined. There are 12 predominant components determine the dorsal meat, including: 1-Octen-3-ol, 2,6-Nonadienal, Nonanal, (E,E)-2,4-Decadienal, (E,Z)-2,4-Decadienal, Hexanal, 2-Nonenal, Octanal, 2-Decenal, Heptanal, Heptanol and 2-Octenal etc. Predominant volatile compounds of belly meat are determined with the 12 species: 1-Octen-3-ol, 2,6-Nonadienal, Nonanal, (E,E)-2,4-Decadienal, (E,Z)-2,4-Decadienal, 2-Nonenal, Octanal, Hexanal,2-Decenal, heptanol,2-Octenal,and Heptanal etc. There are 9 predominant volatile compounds of red meat of cultured grass carp fish were determined: 1-Octen-3-one, (E,Z)- 2,4-Decadienal, (E,E)-2,4-Decadienal, 2,6-Nonadienal, 2-Nonenal, 1-Octen-3-ol, 2,4-Nonadienal, Nonanal, and Hexanal, etc. Predominant characteristic volatile compounds in fish skin has 6 kinds which cluding: 1-Octen-3-one, 2,6-Nonadienal, 1-Octen-3-ol, 2-Nonenal, (E,E)-2,4-Decadienal and Nonanal, etc. Viscera of grass carp predominant volatile compounds are 5 kinds: 1-Octen-3-one, 1-Octen-3-ol, 2,6-Nonadienal, (E,E)-2,4-Decadienal and 2-Nonenal, etc. 7 predominant volatile compounds from gills of grass carp are determined: 1-Octen-3-one, 2,6-Nonadienal, (E,Z)-2,4-Decadienal, (E,E)-2,4-Decadienal, 2,4-Nonadienal, 2-Nonenal and 1-Octen -3-ol, etc.3. Electronic nose could discriminate dorsal meat(belly meat) red meat, skin, viscera and gills of grass carp, but it could not discriminate dorsal meat and belly meat.4. According to GC-MS, 21, 43, 42 and 42 volatile compounds were detected in dorsal meat, 26, 44, 41 and 26 volatile compounds were detected in belly meat, 48, 46, 43 and 53 volatile compounds were detected in red meat of grass carp in spring, summer, autumn and winter respectively. The volatile components are mostly carbonyl compounds and alcohols According to the detection and analysis of the electronic nose, dorsal, belly meat, and red meat of culture grass carp farming in different seasons can be distinguished. The influence of seasonal changes on volatile components of dorsal meat and belly meat is larger than red meat.5. According to the electronic nose, differences can be distinguished from the volatile components of the dorsal meat, belly meat, red meat of wild grass carp and dorsal meat(or belly meat), red meat of cultured grass carp. There are 24, 17, 31, 42, 41 and 43 kinds of volatile compounds were determined in dorsal meat, belly meat and red meat of wild and cultured grass carp respectively. The volatile components in wild fish are mostly carbonyl compounds and alcohols, relative concentrations are above 90%. Analysis of variance of GC-MS results can be inferred that there are significant differences of volatile compounds between wild and cultured grass carp.6. The electronic nose could well distinguish volatile components of the dorsal meat, belly meat, red meat of grass carp with different weight. There are 30, 39, 52, 42, 41 and 43 kinds of volatile compounds were determined in dorsal meat, belly meat and red meat of big and small grass carp, respectively.7. Temporary cultivation can be positively influence the flavor of dorsal and belly meat of grass carp but impact little on red meat. However, more than 3 days temporary cultivation would contribute little to flavor improvement.8. There are 27, 29, 47, 42, 41 and 43 kinds of volatile compounds were identified in dorsal meat, belly meat and red meat of grass carp killed by exsanguinated and knock-head. The results also show exsanguination had effect on the volatile compounds of dorsal meat and belly meat, and little effect on red meat of grass carp. There are 46 kinds of volatile compounds were identified in blood of grass carp, among them 34 kinds are aromatic hydrocarbon and the relative content could be reached to 75.59%. Therefore, the exsanguination was suggested to apply ahead of processing and consumption of grass carp.9. There are 42 volatile components identified and 8 are predominant volatile constituents of cooked grass carp fish under 30℃: 1-Octen-3-ol, Nonanal, Hexanal, Octanal, 2-Pentyl-furan, Heptanal, Heptanol and Decanal. According to samples of grass carp fish at 30℃, 6 predominant volatile components identified from a total of 23 species: 1-Octen-3-one, 1-Octen-3-ol, Hexanal, Nonanal, 2-Nonenal, and Octanal, Furthermore, since odor threshold of high levels of content 2,3-Octanedione cannot not found in the corresponding literature, it might plays an important role in the smell of dorsal meat. When cooked grass carp heated at 95℃, 74 species volatile components identified and their predominant volatile compounds are 13 species: Nonanal, 2,4-Decadienal, 1-Octen-3-ol, 2-Nonenal, Octanal, 2-Decenal, Hexanal, Dodecanal, Decanal, Heptanal, 2- Pentyl-furan, 2-Octenal and Heptanol etc. There are 13 species predominant determined from 59 identified volatile components on the samples reheated cooked meat at 95℃were determined: 2,4-Decadienal, 1-Octen-3 -ol, Nonanal, 2-Nonenal, 2-Decenal, Octanal, Hexanal, Decanal, Dodecanal, Heptanal, Heptanol, 2-Octenal and 2-Pentyl-furan etc.10. In room temperature, the volatile components of fresh grass detected less amount and significant composition changes than those of the cooling grass carp after cooking. The changes in the composition may be the main reason of unpleasant fishy smell of cooled down cooked grass carp. According to the analysis of volatile components of one time and re-heated grass carp fish, twice heated samples enjoyed an increase in alcohols, and decrease aldehydes with large molecule weight, number of compounds and total amount of volatile components. Those transformations may lead to deterioration of re-heated grass carp flavor.11. Temperature affects not only the total amount of volatile components, also affect the composition of volatile components in grass carp meat. As the up of temperature, significantly increased the number of detected compounds; 1-Hexanol and 1-Octen-3-ol changed most significantly in the relative content in different temperature. Relative content of a number of high molecular weight saturated aldehydes and Hexanal are affected by the temperature.12. Frozen treatment has great impact on grass carp fish flavor, mainly increase the number and amount of volatile components, especially the fish in winter. Electronic nose could differentiate back meat and red meat before and after frozen treatment.13. The cold storage experiments showed that the flavor of grass carp meat storage within 3 days were closely to each other, samples storage 5 and 7 days were changed significantly. The samples of dorsal meat storage in 25℃began to degenerate after a day , and the degree of deterioration is larger than that of 7 days under cold storage. The volatile compounds which cause decomposedodour in grass carp meat including Indole, Phenol, Dimethyl disulfide, Acetic acid, 2-Methyl-1-butanamine, Dimethyl trisulfide, Dimethyl tetrasulfide, Trimethylamine etc.14. There are 25, 23, 10 and 10 kinds of volatile compounds in fish meat, washed one times, washed two times and washed three times, respectively. Among these compounds, most of them were volatile carbonyl compounds and alcohols, the respective relative contents are 94.76%, 93.03%, 89.32% and 92.03%. The essential rinse has the significance difference to volatile compounds in grass carp surimi, but samples washed twice and three times have no significance difference.