Investigating carotenoid loss after drying and storage of

5. Spectrophotometric reading
- Switch on Spectrometer 5 minutes before
reading. Absorbance reading is at 450nm.
- Make blank in Petroleum Ether. (Rinse
blank cuvette with Petroleum Ether and
ensure that cuvettes are clean and wipe
them if necessary using delicate wipe
paper).
- Homogenise sample solution and take
sample reading three times (changing
solution in the same cuvette). Absorbance
should be comprised between 0.2-0.8, range
measured with standard.
- Solutions are diluted in petroleum ether if
the sample absorbance was not included in
the range.
Petroleum Ether is a volatile solvent and
reading had to be carried out quickly in
order to prevent bias.
- Concentrations are determined by comparison
to a standard curve using pure beta carotene,
SIGMA, UK. The curve was established prior to
analyses in November 2006 and repeated in
February 2007.
259
Beta carotene content in solution (mg/L)
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
y = 3.7529x
R 2 = 0.9934
Appendix 3
0 0.2 0.4 0.6 0.8 1
Absorbance
Beta carotene standard curve
Genesys 10UV Spectro.
KARI, Uganda (Feb. 2007)
Sample concentration in solution (mg/L)
is calculated by multiplying the sample
absorbance by the trend-line coefficient
(here 3.7529)
- Sample concentration per weight
deducted by dividing carotenoids content
in the 50ml volumetric flask by the initial
sweetpotato sample weight (fresh or
dried).
Total carotenoids content (!g/g) =
Absorbance x 3.7529 x 50
Sample mass (g)
Poster Author: Aurelie Bechoff- April 2007