Ishikawa, M., Teshima, S., Kanazawa, A., Koshio, S.-1997
Journal of Applied Ichthyology, 13 (1) : 31-35
Abstract:
An attempt was made to measure the apparent digestibility (AD) of cholesterol and fatty acids using 5-alpha-cholestane as a marker (cholestane method) using tilapia, Oreochromis niloticus, and the freshwater prawn, Macrobrachium rosenbergii, as test animals. The results were compared with those obtained by the Cr2O3 method. Casein based test diets containing 0.3% levels of cholestane and chromic oxide as markers were prepared for determination of AD of dietary cholesterol and fatty acids. After 2 weeks of acclimation, the test animals, tilapia (average 3.0g wet weight) and freshwater prawn (average 0.5 g wet weight) were fed the test diets for 1 week, and faecal samples were collected over 6 subsequent days. Lipids in the diets and faeces were extracted with chloroform methanol and saponified with 10% KOH in methanol. Gas liquid chromatography (GLC) on 1.5% OV 17 of the unsaponifiable matters afforded the quantities of 5-alpha-cholestane and cholesterol, whereas that on 5% Shinchrom E 71 of the saponifiable matters provided the quantities of fatty acids. Chromic oxide was determined by a wet digestion method. In tilapia, the AD of cholesterol determined by cholestane and Cr2O3 methods were 78.1% and 73.5%, respectively. The AD of individual fatty acids differed with the types of fatty acids, but those of fatty acids determined by the two methods in this study were similar, except for a slightly higher value of several fatty acids such as 16:1 in the cholestane method than in the Cr2O3 method. This indicates that 5-alpha-cholestane as well as Cr2O3 can be conventionally used as a marker for determining AD of fatty acids and cholesterol. The cholestane method is advantageous as it permits parallel analysis of cholesterol (or fatty acids) and 5-alpha-cholestane by GLC using small amounts of faecal sample. The cholestane method was also useful for analysing digestibilities of cholesterol and total lipids in freshwater prawn. However, slight differences between the cholestane and Cr2O3 methods were observed in the AD of several fatty acids such as 14:0 and 16:1.
(Kagoshima Univ, Fac Fisheries, 4-50-20 Shimoarata, Kagoshima 890 Japan)
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