台灣黑鮪熟肉現象與初步生化學分析

The Biochemical Property between ＂Sik-Bah＂ and Burnt Meat from Pacific Bluefin Tuna (Thunnus Thynnus Orientalis)

每年4月至7月間是太平洋黑鮪（Thunnus thynnus orientalis）洄游到台灣東海岸的季節，捕捉到的黑鮪魚是台灣重要漁業種類之一。黑鮪口感佳，常做為日本料理高級生魚片等食材，近年由於資源量減少使黑鮪在國際市場上屢刷高價紀錄。黑鮪肉質之顏色與價格有密切關聯，鮮紅的肉質是新鮮與品質的保證。然而東港漁民口中相傳一種肉質呈現蒼白、鬆軟及少許酸味的鮪魚肉稱為「熟肉」（台語發音為Sik-Bah）。熟肉是異常肉的一種，常發生在鮪屬肌肉，特別是黑鮪（Thunnus thynnus）、大目鮪（Thunnus obesus）及黃鰭鮪（Thunnus albacares）容易發生熟肉現象。東港漁民描述熟肉主要特徵為；肉色蒼白、缺乏彈性並略帶酸味。國外文獻記載一種異常肉稱為burnt meat特性與東港漁民所稱之熟肉極為相似，也具有蒼白、缺乏彈性、略帶酸味等特徵。台灣漁民所指熟肉是否與國外所指burnt meat相同？由於台灣無文獻參考及研究所以無法斷定。本論文旨在探討東港地區漁民所指熟肉與國外文獻紀錄burnt meat在生化學上之異同。為了解東港地區漁民所認知之熟肉特性，透過訪談及調查東港鮪魚相關業者30位，針對熟肉特性及可能發生原因作問卷調查，並實際採黑鮪熟肉樣本進行實驗分析，測定了熟肉基本生化特性如pH值、色彩質（L*, a*, b*）、電泳等。調查結果顯示，東港漁民普遍認為熟肉之特徵為蒼白（90%）、柔軟（73%）、酸味（67%）、腐臭味（53%）。產生熟肉可能原因以溫度因素最高（93%）、其次為保存方式（53%）、死亡時間（37%）、日月照射（30%）、性別影響（30%）、黑鮪品系（27%）、死前掙扎（20%）等。實驗結果之數據顯示，熟肉之pH值（5.56 ± 0.1, n=14）低於正常黑鮪肉（5.96 ± 0.2, n=14）。另在色彩值分析結果，亮度（L*）（39.61 ± 3.36 vs 29.07 ± 2.19, n=14）、藍黃度（b*）（12.41±2.88 vs 7.77±2.90, n=14）在熟肉明顯高於正常肉。另在SDS-PAGE電泳分析東港採集黑鮪熟肉中發現在50 kDa附近有蛋白質降解現象。經與Yamashita及Ochiai發表黑鮪burnt meat論文對照確認降解蛋白質是磷酸肌酸（creatine kinase）。由以上所得結果，確認東港漁民所謂「熟肉」即是國外文獻中敘述的異常肉「burnt meat」。經由本次調查及研究結果確認東港黑鮪所採集之熟肉為burnt meat，將可參考國外研究方法，彌補國內無研究紀錄之空白。在鮪魚資源逐漸枯竭之際，希望國內漁政單位注意鮪魚熟肉發生問題，降低漁民損失。

From April to July, the Pacific bluefin tuna (Thunnus thynnus orientalis) will migrate to Taiwan's east coast every year. The bluefin tuna is one of the important fishery species in Taiwan. Since bluefin tuna taste good, it often as sashimi and other Japanese cuisine advanced ingredients. In those years, the reduced amount of resources to make bluefin tuna renew high prices records in the international market. It is important for meat colors of bluefin tunas, red meat is fresh and quality assurance. But the Donggang fishermen legend meat that presents a pale, soft and a little sour of tuna meat known as ＂cooked-meat＂ (pronounced Taiwanese to Sik-Bah). Cooked-meat is an abnormal meat, often occurs in the case of tuna muscle, especially bluefin tuna (Thunnus thynnus), bigeye tuna (Thunnus obesus) and yellowfin tuna (Thunnus albacares). Donggang fishermen describe the main features of cooked-meat as follow; pale flesh, lack of flexibility and sour. Foreign reports ＂burnt meat＂ are very similar to cooked-meat because their features also have pale, lack of flexibility, slightly sour and others. Is the ＂cooked-meat＂ same as ＂burnt meat＂? Because Taiwan have no any references, it is difficult to determine. This paper aims to explore the biochemical property between ＂burnt meat＂ and ＂cooked-meat＂. In order to know the characteristics of cooked-meat, interviews for tuna related worker 30, and sampling cooked meat for laboratory analysis including pH, color quality (L*, a*, b*) and electrophoresis. The results of interview by Donggang fishermen show that the property of cooked-meat including pale (90%), soft (73%), sour (67%), rancid (53%). May cause cooked meat at a temperature factor was the highest (93%), followed by storage mode (53%), the period time of death (37%), sun or moon irradiation (30%), gender impact (30%), species strain (27%), death struggle (20%). The results of the data showed that the pH value of cooked-meat (5.56 ± 0.1, n=14) was lower than normal meat (5.96 ± 0.2, n=14). The color values of brightness (L*) (39.61 ± 3.36 vs 29.07 ± 2.19, n=14), blue and yellow degree (b*) (12.41 ± 2.88 vs 7.77 ± 2.90, n=14) in cooked-meat significantly higher than normal one. The SDS-PAGE electrophoresis analysis for cooked-meat from Donggang collected shown near 50 kDa protein band degradation. To be compared with papers reported from Yamashita and Ochiai, the degraded protein was creatine kinase. From the above results, the conclusion that ＂cooked-meat＂ was the same as ＂burnt meat.＂ In this study, we make sure that ＂cooked-meat＂ was ＂burnt meat.＂ We will design new study by burnt meat references.