|Abstract: ||石斑魚為近年來熱門的養殖魚種，褐石斑 (Epinephelus bruneus) 在台灣俗稱油石斑或闊嘴格仔，其油脂含量較高，肉質清爽不膩；珍珠龍膽石斑 (E. lanceoratus × E. fuscoguttatus) 為龍膽石斑 (E. lanceoratus) 與老虎斑 (E. fuscoguttatus) 雜交繁衍而來。本研究分析養殖之珍珠龍膽石斑與褐石斑之化學組成及呈味成分，並探討其貯存安定性，俾做為養殖業者改善魚貨品質、促銷推廣與加工利用參考。 珍珠龍膽石斑水分含量平均為 76.57%，粗蛋白20.05%，粗脂肪 2.64% 而灰分1.42%；褐石斑水分含量平均為 76.56%，粗蛋白20.89%，粗脂肪1.36%，灰分 1.46%。珍珠龍膽石斑粗蛋白含量略低於褐石斑，而粗脂肪含量則高於褐石斑，水分及灰分差異不大。珍珠龍膽石斑肥滿度以 2009 年 5 月及 2010年 4 月之樣品最高；而褐石斑肥滿度與季節及體重間較無相關。 珍珠龍膽石斑游離胺基酸組成以牛磺酸、甘胺酸、蘇胺酸及絲胺酸等較多，雙胜肽僅 2009 年 5 月樣品檢出微量之甲基肽；褐石斑游離胺基酸組成則是以牛磺酸、甘胺酸、丙胺酸及離胺酸等居多，另有雙胜肽之甲基肽。兩種石斑核苷酸相關化合物含量皆以 IMP 最高，珍珠龍膽石斑核苷酸相關化合物之總量以 2009 年 5 月及 2010 年 2 月採樣者最高，而褐石斑在各季節及體重間無顯著差異。珍珠龍膽石斑與褐石斑游離脂肪酸均以不飽和脂肪酸居多，2009 年 5 月及 2010 年 2 月樣品飽和脂肪酸、不飽和脂肪酸、EPA 與DHA含量較高，其中又以油酸及亞麻油酸為主；此兩種石斑 DHA 含量均較 EPA 高。 珍珠龍膽石斑在 7oC 貯藏至第 12天有腥臭味產生，而在 25oC 貯藏至第 32小時已達腐敗階段；褐石斑在 7oC 貯藏第 12天有腥臭味產生，在 25oC 貯藏第 24 小時已腐敗。在微生物方面，此兩種石斑於 7oC 貯藏至第 12 天尚未超過新鮮魚介類限量之 3 × 106 CFU/g；25oC 貯藏期間，珍珠龍膽石斑於第 24 小時，而褐石斑於第 8 小時超過限量。珍珠龍膽石斑在 7oC 與 25oC 貯藏期間，揮發性鹽基態氮 (volatile basic nitrogen, VBN) 在貯藏第 12 天及第 24 小時含量超過衛生標準限量之 25 mg/100g；褐石斑在第 6 天及 16 小時超過此限量標準。此兩種石斑三甲基胺 (trimethylamine, TMA) 含量於貯藏期間也會隨時間而增加，而 7oC 貯藏期間上升幅度較 25oC緩慢。珍珠龍膽石斑於 7oC 貯藏下，次黃嘌呤 (hypoxanthine, Hx) 之含量在第 6 天顯著上升；25oC 貯藏期間 IMP 含量在第 8 小時便會迅速降解成肌苷 (inosine, HxR) 及 Hx，鮮度下降。褐石斑於 7oC 貯藏期間 HR 及 HxR 含量緩慢上升；在 25oC 貯藏期間，IMP 於 16 小時後便迅速降解成 HxR 與 Hx，K 值在貯藏 16 小時後達到 84.16%。 珍珠龍膽石斑與褐石斑於貯藏 7oC 下能減緩微生物生長及VBN 與 TMA的生成，綜合以上鮮度衛生品質指標，兩者之7oC 貯藏期限分別為 9 天及 6 天；25oC 貯藏期限分別為 24 及 8 小時。|
Grouper has become a popular cultured fish in recent years. Longtooth grouper (Epinephelus bruneus) was known as oil grouper in Taiwan because its muscle contains relatively high oil. Pearl grouper (E. lanceoratus × E. fuscoguttatus) was a hybrid strain from giant grouper (E. lanceoratus) and tiger grouper (E. fuscoguttatus). This study was to understand the biochemical characteristics and storage stability of longtooth grouper and pearl grouper to improve the meat quality and to promote the market and their utilization. The condition factor of pearl grouper was high in May 2009 and April 2010, and that of longtooth grouper shows no significant difference by season. The average moisture, protein, lipid and ash of the muscle in pearl grouper were 76.57, 20.05, 2.64 and 1.42%, respectively. The muscle in longtooth grouper were 76.56, 20.89, 1.36 and 1.46%, respectively. The content of crude protein in pearl grouper was a little lower than longtooth grouper; on the other hand, the content of crude lipid of the former was higher than the latter. There was no significant difference in moisture and ash between both groupers. The predominant free amino acid (FAA) in the muscle of pearl grouper was taurine (Tau), glycine (Gly), threonine (Thr) and serine (Ser). The dipetide of anserine (Ans) was only detected in trace in the sample of May 2009. The predominant FAA in the muscle of longtooth grouper was Tau, Gly, alanine (Ala) and lysine (Lys); and the dipetide of anserine (Ans) was detected in each samples. The dominant nucleotide-related compound of both groupers was inosine 5’-monophosphate (IMP). The total amount of nucleotide-related compounds in pearl grouper was higher in May 2009 and February 2010, and that of longtooth grouper showed no significant difference by season. The major fatty acid composition in these two groupers was unsaturated fatty acid. Saturated fatty acid, unsaturated fatty acid, eicosapentaenoic acid (EPA) and decosahexaenoic acid (DHA) were higher in samples of May 2009 and February 2010 than other months. The dominant fatty acids in the muscle of these two groupers were oleic acid and linoleic acid. The amount of DHA in both groupers was higher than EPA. The perceptible decomposed odor occurred after pearl grouper stored at 7oC for 12 days, and was observed for that stored at 25oC for 32 hours. The perceptible decomposed odor was found for lonhtooth grouper stored at 7oC for 12 days and at 25oC for 24 hours. The values of total plant count (TPC) in these two groupers were lower than the limited value (3 × 106 CFU/g) after 12 days of storage at 7oC. TPC had exceeded the limited value after pearl grouper was stored at 25oC for 24 hours and longtooth grouper for 8 hours. When stored at 7oC and 25oC for 3 days and 24 hours, the amount of volatile basic nitrogen (VBN) in pearl grouper exceeded the limited value (25 mg/100 g); and 6 days and 16 hours were found in longtooth grouper. The amount of trimethylamine (TMA) in these two grpupers was increased with storage time, and the amount at 7oC was lower than at 25oC. The amount of hypoxanthine (Hx) was increased after 6 days in pearl grouper stored at 7 oC. The rapid degradation of IMP to inosine (HxR) and Hx was found after storing at 25oC for 8 hours. The rate of HxR degraded to Hx in longtooth grouper was slow when stored at 7oC. IMP was degraded rapidly to HxR and Hx when stored at 25oC for 16 hours, and the K value was increased to 84.16%. The values of TPC, VBN and TMA were lower in the sample stored at 7oC than those at 25oC. The shelf-life of pearl grouper was 9 days and 24 hours during storage at 7oC and 25oC; and longtooth grouper was 6 days and 8 hours, respectively.