Fatty acid analysis
The fatty acid composition of the butter samples was analysed
according to Christie (1989). Fatty acid methyl esters of butterfat
samples were prepared using 2 M methanolic potassium hydroxide
solution and extracted with 15 mL of N-hexane and dried over
anhydrous CaCl2 salt. An aliquot of the supernatant was analysed
for free fatty acids using gas chromatography (GC1000, DANI
Instruments SPA, Pavia, Italy) equipped with flame ionisation
detector and a polar capillary column: ECTM-5 (30 m 0.32 mm
0.25 mm film) with a mobile phase of 5% phenyl and 95% methylpolysiloxane.
The column length was 30 m. The operational conditions
were: injector temperature 210 C, detector temperature
260 C and the column temperature was initially adjusted to 50 C
for 2 min, and then increased by 4 C per minute until it reached
250 C after which it was held for 15 min. The carrier gas used was
nitrogen at a flow rate of 1 mL per min. The analysis was conducted
in the Chemistry Department of Addis Ababa University. A total of
three samples were used and each sample was analysed in
triplicate.