Investigating carotenoid loss after drying and storage of

161
7. Involvement of enzymes
carotene by peroxidase in the presence of linoleic acid can be explained by the use of
linoleic acid peroxide as substrate (Preston and Barrett 1987) and the production of
small amounts of H2O2 from the oxidation of linoleic acid that are used by the
horseradish peroxidase.
The instantaneous bleaching of β-carotene by horseradish peroxidase highlighted that
peroxidases could potentially degrade carotenoids in sweet potato, hypothetically in
using phenols, present in sweet potato (Woolfe 1993), to generate free radicals.
7.3.4. EDTA assay
Prevention of !-carotene autoxidation in presence of linoleic acid using metal ion
chelator EDTA was tested under dim light conditions (Figure 7-1).
Relative absorbance at 450nm
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Blank
LA+ 5%EDTA
LA+ 10%EDTA
LA+ 15%EDTA
LA+ 20%EDTA
LA
0 5 10 15 20 25 30
Incubation time (min)
Figure 7-1: Effect of EDTA concentration on !-carotene autoxidation by linoleic
acid (LA) in solution at 40ºC and at pH 7.4 during 25 minutes
Substrates: Blank: deionised water; Linoleic acid (LA) 0.4mM (representing 5% of
solution); EDTA (ethylene diamine tetra acetic acid) (variable concentration 0-20%
equivalent to 0-1.5mM in solution)
Fifty percent of β-carotene lost after 25 minutes in presence of linoleic acid by
autoxidation confirmed that autoxidation was an important phenomena. EDTA had