| Summary: | 碩士 === 國立臺灣海洋大學 === 食品科學系 === 99 === 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.
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