| Summary: | 碩士 === 國立海洋大學 === 食品科學系碩士在職專班 === 89 === European eel, Anguilla anguilla is a very important fish species of automatic recirculating and intensive culture system in Taiwan. This study focuses on the analysis of characteristics of raw materials and nutrition composition. The optimal processing condition of smoked product and the information regarding chemical change before and after the smoking process as well as the shelf life are also established to serve as the reference for producing smoked eel.
European eel was rich in fat, which was increased with the weight while moisture decreased. However, in the case of a fish weighted more than 300g, moisture and crude fat remained constant regardless of the size. Crude protein and ash also showed no obvious correlation with fish size. Fatty acid was mainly comprised of oleic acid and palmitic acid, which together accounted for 55% of the total fatty acid. DHA and EPA were also high and accounted for 7% and 2.5 % respectively. The main free amino acid (FAA), comprises histidine (His), β-alanine (β-Ala) and taurine (Tau). An extraordinary feature was that this fish contained a very high level of dipeptide carnosine (Car). Amino acid was mainly composed of glutamic acid (Glu), aspartic acid (Asp) and lysine (Lys). His was low in fish with small size, and Tau decreased while the size increased. Other FAA, Car, amino acid and fatty acid were irrelevant to fish size.
The acceptability of smoked eel was higher by immersing in brine with the concentration of 6~8%. Smoked eel had fewer moisture, higher crude protein and ash, while the crude fat had no significant difference. Fatty acid remained unchanged during processing, while amino acid and FAA increased when the smoking duration was longer. Lys showed the greatest loss after the processing. β-Ala and His increased, while Car was reduced. With the longer smoking duration, phenolic compound in fish was significantly increased. As for the color variation, eel with longer smoking duration or one-phase smoking had deeper brown color. Muscle protected by epidermis was not apparently influenced. The appearance, flavor, texture, and acceptability of 4 kinds of smoked products were not significantly different (p>0.05), and the acceptability of all products were ranked in medium or higher.
After storing for 8 weeks at 4℃, the FAA of smoked eel increased by 37%, Car decreased by 55.3%, while fatty acid, pH value, volatile basic nitrogen (VBN), thiobarbituric acid (TBA) and NH3 had no significant difference during storage. Peroxide value (POV) was slightly increased. The aerobic plate count (APC) did not reach the ready to eat criteria of 105 CFU/g until the fourth week, but it was beyond the criteria after 6 week storage. Thus, the shelf life of refrigerated smoked eel was proposed as 4 weeks. No significant changes in fatty acid and quality indexce were found in vacuum-packaged smoked eel after storage for 9 months at -20℃. No odor was found. The APC decreased to the level less than 10 CFU/g until the fourth month. After storing for 9 months, FAA increased by 7.7%, and Car decreased by 6.8%. The variation was significantly lower than the situation of storage under the temperature of 4℃. From the results of this study, it was concluded that the vacuum-packaged smoked eel could be stored in the refrigeration environment for at least 9 months.
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