碩士 / 國立臺灣海洋大學 / 食品科學系 / 101 / Trimethylamine oxide (TMAO) could be degraded to equal mole of dimethylamine (DMA) and formaldehyde by the action of trimethylamine N-oxide demethylase (TMAOase). It has been reported that formaldehyde is sometimes added inappropriately in seafoods for extending its shelf-life, and formaldehyde residue in seafoods cause a threat to human health. Little study has been done on biochemical charateristics of leatherjacket. The objective of this study is to analyze the chemical compositions of unicorn leatherjacket (Aluterus monoceros) and black scraper (Thamnaconus modestus), and to investigate their changes during storage. The formation of formaldehyde and DMA induced by fish visceral TMAOase was also studied to differentiate that formaldehyde occurs naturally or artificially.
The protein content of unicorn leatherjacket and black scraper muscle ranged from 19-20%, and the fat is about 0.1%. The moisture and ash of both leatherjackets are 78% and 1.3-1.4%, respectively. The predominant free amino acids (FAA) in the muscle of unicorn leatherjacket and black scraper are taurine (Tau), glycine (Gly), and alanine (Ala). The dominant nucleotide-related compound of both leatherjackets was inosine 5’-monophosphate (IMP).
The pH value in two leatherjackets decreased and then increased during storage at 25℃ and 7℃. The total plate count (TPC), total volatile basic nitrogen (TVB-N), and ammonia contents in both leatherjackets increased gradually with storage time. TPC had exceeded the limited value of 3 x 106 CFU/g after unicorn leatherjacket was stored at 25℃ and 7℃ for 16 hours and 9 days, respectively. When stored at 25℃ and 7℃ for 8 hours and 9 days, the amount of TVB-N in unicorn leatherjacket exceeded the limited value 25 mg/100 g. TPC had exceeded the limited value after black scraper was stored at 25℃ and 7℃ for 8 hours and 3 days, respectively. When stored at 25℃ and 7℃ for 16 hours and 6 days, the amount of TVB-N in black scraper exceeded the limited value. The increase of TMA-N was coincidental with the decrease of TMAO in leatherjackets, and DMA-N in both leatherjackets increased with storage time. The K value reached 60% after leatherjackets storing at 25℃ and 7℃ for 8 hours and 6 days, respectively. The shelf-life of leatherjacket was 8 hours and 6 days during storage at 25℃ and 7℃. The total plate count, TVB-N, and K value can be used as freshness indicators for leatherjacket during storage.
Among the crude extracts of different organs of unicorn leatherjacket, spleen extract contained the highest activity of TMAOase with 13.01 unit/100 g. TMAOase in spleen and bile crude extracts of black scraper was 10.30 and 10.92 unit/100 g, respectively. TMAOase in lizardfish kidney crude extract possessed the highest activity with 57.63 unit/100 g. The formation of DMA and formaldehyde in unicorn leatherjacket and black scraper meat induced by lizardfish kidney crude extract resulted in an increase of DMA and formaldehyde. The ratios of DMA to formaldehyde in unicorn leatherjacket and black scraper were 2.47 and 2.64, respectively. The ratios of the meat added with the crude extract of lizardfish kidney and 200 ppm formaldehyde were 0.42 and 0.67, respectively. The ratio of DMA to formaldehyde could be used as indicator to differentiate that formaldehyde occurs naturally or artificially.
| Identifer | oai:union.ndltd.org:TW/101NTOU5253056 |
| Date | January 2013 |
| Creators | Li-Yin Lin, 林俐吟 |
| Contributors | Chyuan-Yuan Shiau, Min-Lang Tsai, 蕭泉源, 蔡敏郎 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 78 |
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