Investigating carotenoid loss after drying and storage of

1. Sample preparation
Caution! Carotenoids are subject to
photo-oxidation. All operations must be
performed under dim light.
- For fresh sweetpotato roots or fresh
chips, defreeze by soaking the plastic bag
in tepid water (about 30°C). Fresh
samples must be blended to a fine pulp
using a Kenwood FP698 Multi Pro Food
Processor.
- For flour samples milled from dried
sweetpotato chips, put samples at
ambient temperature for about 10-15
minutes. Add 10ml deionised water to rehydrate
sample; measure 20 minutes
before extraction.
2. Sample Weighing
- Homogenise well sample using the long
spatula.
- Weigh 5g in triplicate for dry matter
determination using glass Petri dishes or
ceramic dishes as followed: Tare balance;
weigh tare; report tare weight; add 5g of
sample; report tare + sample weight. Put
samples in oven at 105ºC for 24h
minimum. (In case of power shortage,
leave for one day more).
- Homogenise again sample using long
spatula
- Weigh a portion of the sample for total
carotenoids determination in triplicate in
257
Appendix 3
beakers using the two spatulas. The
weight depends on the carotenoids
content of the sample as shown in the
table below.
Portion of sample weighed (g) for
carotenoids determination
Sweet
potato
variety
Ejumula 1
Kakamega 3
SPK004/1 or
SPK004/1/1
SPK004/6 or
SPK004/6/6
Naspot 1
Fresh Dried
0.5
1
3-6 -
2 -
8-9 -
- Cover with foil and transport to fume
cupboard
3. Extraction
- Pour 50 ml mixture of methanol:
tetrahydrofuran (THF) (1:1) into the beaker
containing the sample; fix on the stand and
homogenise for 60 seconds using Polytron
homogeniser. Rinse the Polytron rod with
deionised water and place it back into the box
to protect apparatus from falling.
- Fix vacuum flask, rubber and sintered glass
funnel on the stand. Add sample solution.
Filter through funnel by vacuum (first
filtration). Rinse beaker with 10-15 ml of
methanol: THF (1:1) mixture receiving the
washing in the vacuum flask through the
funnel (second filtration). Use small spatula
to homogenise solution in the funnel before
filtering for the second time. The residue or
washing must be devoid of colour. If not rinse
beaker again and repeat filtration.