| Summary: | 碩士 === 國立澎湖科技大學 === 食品科學系碩士班 === 105 === Gymnothorax favagineus (GF) and Gymnothorax pseudothyrsoideus (GP) are two major eels in Penghu. However, few studies have been done the effect of size on two species moray eel muscle and skin, this study was to investigate the chemical composition of two group (Small: 905-971 g and Large: 1776-2420 g). Result presented the GF have more meat yield (79-80%) than GP (75-77%), but GP have higher condition factor (2.43-2.79). Two eels content of moisture, ash, crude protein and crude fat were between 75-78%, 1.19-1.32%, 18-21% and 0.75-2.49%, respectively. The GF muscle and skin are positive correlations lipid content between two difference sizes, but GP had a negative correlations with lipid.
The major nucleotide-related compound in the muscle was inosine monophosphate (IMP), average between 5.18 to 6.71 μmol/g. A total amino acid content of 286 to 365 mg/100 g, and taurine and threonine were major free amino acid in muscle, and GP have more TMAO than GF. No matter what size these two types of eels are, the dominant fatty acids were palmitic acid (C16: 0), stearic acid (C18: 0), palmitoleic acid (C16: 1), oleic acid (C18: 1n9c) and docosahexaenoic acid (C22: 6n3) in muscle and skin, but large GF had a large amount of PUFA (287.06 mg/100 g muscle) in muscle and GP had a large amount of PUFA (2430.64 mg/100 g skin) in skin. The n-3/n-6 ratio should be greater than 1, and two different types of eels n-3/n-6 ratio were better, it is between 2.84 to 4.39 in muscle. In addition, GF and GP had abundant vitamine A, E, B2 and B3, these two types of eels are all full of richest nutrition fishes.
Total plate counts (TPC) of GF and GP stored in 4℃, exceeded the limit value of 6.47 log CFU/g fish muscle after 6 days of storage, while pH value also increased significantly. On day 6, the total volatile basic nitrogen (TVBN) and trimethylamine (TMA) only reached 11.36-12.84 mg/100 g and 0.85-1.14 mg/100 g, respectively, but both of them were low than the unaccepted limit. Based on sensory analysis, the perceptible decomposed odor occurred at 6 days. Although K value of GF and GP increased with storage time, major accumulated nucleotide-related compound of GF was IMP and still showed the fresh state on the end of storage. Where the K value used, with GP it increased very rapidly at 3 day. This is due to accumulation of a large quantity of HxR relative to the quantity of Hx produced. Therefore, K value is not suitable freshness indicator for GF and GP. Our results suggested that the GF and GP muscle kept acceptable quality during at least 6 days under the experimental conditions of this study.
The non heme iron contents were 0.36 and 0.38 mg/100 g in the muscle of GF and GP on 0 day, and increased to 0.54 and 0.58 mg/100 g, respectively, when stored for 18 day at 4℃. Peroxide value (POV) and thiobarbituric acid reactive substances value (TBARS) and yellowness (b＊) also increased significantly with duration time. A similar trend with a much more remarkable response was noted for the skin in GP samples. Phospholipid content increased with increasing storage time which corresponds to the release of free fatty acid (FFA) increased by the end of the storage period for the skin in GF and GP. The rancid odours was detected at day 10 of storage for GP and a higher intensity than GF.
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