Leafy vegetables are an excellent source of bioactive factors, traditionally used as
important medical ingredients. Recently, some leafy vegetables are domesticated
without the use of fertilizer, as well as the assessment of the effect of fertilizer on
their nutritional value. This study aims at testing the effect of three mineral and
organic fertilizers (Cowpat, NPK and NPK + cowpat) on three traditional leafy
vegetables:
Ceratotheca sesamoïdes
,
Sesamum radiatum
and
Justicia tenella
. Their
antioxidant activities were assessed at different harvesting times varying from six (6)
to fourteen (14) Weeks After Transplantation (WAT) using three
in vitro methods:
Ferric reducing antioxidant power (FRAP), 2,2’-Azinobis3-ethylbenzothiazoline-6-
sulfonic acid (ABTS) and 2,2-diphenyl-1-picryl hydrazil (DPPH). The FRAP, DPPH,
ABTS assays were consistent and positively correlated (p < 0.001). Total antioxidant
activities of leafy vegetables depended on species, harvesting time and methods. They
ranged from 32.0 to 45.7 μmol Fe/g DW (for FRAP), with non fertilized
J. tenella cut
at 12 WAT giving the highest antioxidant activity. Percentage of inhibition using
DPPH assay ranged from 11.4 to 87.2 % and showed that
J. tenella fertilized with
NPK and cowpat, and harvested at 9 WAT had the highest antioxidant activity.
Regarding ABTS, the range of 17.6 to 28.9 μmol TE/g DW was recorded, and the
leaves of
C. sesamoïdes harvested at 10 WAT and fertilized with cowpat showed the
highest level. Compared to other species, those studied here may best contribute to
improve human health related to degenerative diseases. Moreover, significant and
positive correlations were observed between the total phenolic compounds content
and antioxidant activities of leaves regardless the methods used. The positive and
significant correlations between the three assays (FRAP, DPPH, ABTS) allow to
suggest the use of only anyone of them to check factors in the study. This paper
highlights the potential of antioxidant capability of the leafy vegetables even
fertilized.
