||日本鰻(Anguilla japonica)養殖為臺灣重要產業，因鰻苗短缺導致產業衰微，鱸鰻 (A. marmorata) 成為新興替代魚種，惟生化學相關資料闕如。本研究採樣不同大小之養殖鱸鰻，分析其生化學組成，並探討其儲藏期間鮮度指標與生化學組成之變化，以了解其儲存安定性，另分析鱸鰻不同抽出液之抗氧化能力，並評估其加工利用方式，以協助業者產製新產品。
鱸鰻肌肉一般成分中蛋白質含量為15.2%~20.3%，粗脂肪為3.54~13.3%，一般成分與魚體大小無相關性。游離胺基酸(Free amino acid, FAA)總量為 93.8~176 mg/100 g，以牛磺酸、麩胺酸、甘胺酸、丙胺酸及離胺酸含量較高，小分子胜肽類則以雙胜肽之肌肽(Carnosine, Car)為主，含量高達 207-355 mg/100 g。鱸鰻死後ATP降解速度快，蓄積之核苷酸化合物主要為肌苷酸(Inosine 5’-monophosphate)。肌肉中脂肪酸含量最高者為油酸(C18:1)，其次為棕梠酸( C16:0)，且皆具高含量之DHA (C22:6)與EPA (C20:5)，不飽和脂肪酸所占比例也高於飽和脂肪酸。鱸鰻肉富含礦物質鉀、磷和鋅以及維生素A和E。
鱸鰻肉儲藏期間，pH值先降後升，而氨含量則漸上升，於7°C儲藏至3天、25°C儲藏至24小時，魚肉好氧性總生菌數(Total plate count, TPC)接近限量之3×106 CFU/g，揮發性鹽基態氮(Volatile basic nitrogen, VBN)分別在12天及16小時超過標準(25 mg/100 g)，三甲胺(Trimethylamine, TMA) 與 K 值亦隨時間增加而上升，依官能檢測、TPC、VBN 及K 值判斷鮮度品質，鱸鰻肉7°C之儲藏期限為3天，25°C為8小時。鱸鰻肉Car含量在儲藏期間下降，相對地其組成分之胺基酸b-丙胺酸(b-Ala)與組胺酸(His)含量逐漸上升，顯示Car會分解為b-Ala與His，低溫貯藏與放血處理可防止Car之分解。
||The culture of Japanese eel (Anguilla japonica) is an important sector in Taiwan, but the shortage of eel fry disintegrated this sector. Giant mottled eel (A. marmorata) becomes an alternative species for aquaculture by degrees. However, few studies have been done on its biochemical characteristics and compositions. This study was to investigate the biochemical compositions in different sizes of giant mottled eels. Changes in chemical compositions and freshness index of giant mottled eel during storage were also studied to reveal the storage stability. In addition, the antioxidative activities of the tissue extracts were investigated in this study. Based on results of biochemical characteristics and functional compositions, the suitable utilization and processing of giant mottled eel was evaluated to develop new products.
Crude protein in the muscle were ranged from 15.2~20.3%, and crude fat were 3.54~13.3%. The total amount of free amino acids (FAA) in the muscle was 93.8~176 mg/100g, and the major FAA were taurine, glutamic acid, glycine, alanine and lysine. The major nucleotide-related compound in the muscle was inosine 5’- monophosphate (IMP). Carnosine (Car) was the predominant small peptide, and its level reached 207~355 mg/100 g. The dominant fatty acid in the muscle was oleic acid (C18:1), followed by palmitic acid (C16:0). In addition, the contents of DHA (C22:6) and EPA (C20:5) were also high. The ratio of unsaturated fatty acid to total fatty acid was higher than that of saturated fatty acid. Giant mottled eel also contained abundant amount of minerals potassium, phosphorus and zinc, and vitamins A and E.
The muscle pH value decreased at the early storage period and then increased after elongated storage. The total plate count (TPC) was closed to the limit value of 3×106 CFU/g during storage at 7°C and 25°C for 3 days and 1 day, respectively. For the limit value (25 mg/100 g) of volatile basic nitrogen (VBN), the storage time was 12 days and 16 hours, respectively. Trimethylamine (TMA) and K value also increased with increasing time. According to the results of organoleptic evaluation, TPC, VBN, K values, the self-life of giant mottled eel meat was 3 days and 8 hours during storage at 7°C and 25°C, respectively. During storage Car decreased, but b-alanine (b-Ala) and histidine (His) increased. Results showed that Car was degraded into b-Ala and His. Refrigeration storage and bleeding treatment could decrease the degradation rate.
The methods including the scavenging effect of DPPH free radical, reducing power, chelating ability of Fe2+ and SOD activity are used to detect the antioxidative activities of giant mottled eel meat and its essence. Results showed that both extracts of tricholoacetic acid and phosphate buffer of eel meat and its essence possessed antioxidative activities. Eel essence had higher scavenging effect of DPPH free radical and reducing power than eel meat, but the latter had higher SOD activity.
The roasted and seasoned products of giant mottled eel, Japanese eel and short-finned eel produced by the same factory showed VBN and TPC complied with national sanitation standards. According to the results of sensory evaluation, Japanese eel product had a higher score among three roasted products, but no significant difference was found. As compared with raw materials, the processed products of giant mottled eel had lower amounts of Car, His and β-Ala, but had higher amounts of glutamic acid, aspartic acid and total FAA. Seasoning sauce resulted in this difference. There were remarkable differences in total FAA amount and flavor intensity among different size of giant mottled eel products. Processing and seasoning conditions should be adjusted to obtain balanced seasoning products.
Results of this project provided the data regarding the biochemical and functional properties of giant mottled eel for market promotion, and the reference for improving the quality of eel products. In addition, it also provided useful ways for suitable utilization and new product development.