Abstract:
There has been burgeoning interest in plant-based feed additives following restrictions
placed on the use of antibiotic feed additives in many countries. Phytogenic feed additives
are recommended to have a range of useful properties to support the growth and
development of poultry to a similar level as that obtained by supplementing feed with
antibiotics. The aim of this study was to evaluate the antibacterial, anti-lipoxygenase and
antioxidant activity, and in vitro safety of fractions and isolated compounds from leaves
of Senna singueana. Antibacterial activities of the fractions and isolated compounds
were determined against a panel of bacteria using a two-fold serial microdilution assay
and qualitative bioautography assays. Anti-lipoxygenase activity was evaluated using
the ferrous oxidation-xylenol orange (FOX) method. Antioxidant activity was assessed
qualitatively and quantitatively using radical scavenging assays. Dichloromethane and
ethyl acetate fractions from solvent-solvent partitioning had the best antibacterial activity
with MIC values ranging from 156 to 313µg/ml. Fractions obtained from column
chromatography had significant to weak antibacterial activity with MIC values ranging
from 50 to 1,250µg/ml. Bioautography showed clear bands of bacterial inhibition,
indicating the presence of a number of active compounds in several fractions. The ethyl
acetate fraction and all the tested column fractions had potent anti-lipoxygenase activity
with IC50 values of ≤2.5µg/ml which were lower than that of quercetin (positive control),
indicating anti-inflammatory potential. The ethyl acetate fraction and several column
fractions had powerful antioxidant activity with IC50 values of ≤5µg/ml in the ABTS assay.
Cytotoxicity values against Vero kidney cells ranged from LC50 = 40.0–989.3µg/ml.
Bioassay-guided fractionation led to the isolation and identification of a known bioactive
compound, luteolin. S. singueana is a promising candidate for the development of poultry
phytogenic feed additives.
