Comparison of the Chemical Constituents, Antimicrobial and DPPH free Radical Scavenging Activities of the Fresh and Air-dried Leaves Essential Oils of Hildegardia barteri (Mast.) Kosterm

Abstract

Due to the ethnomedicinal use of Hildegardia barteri in treating stomach disorders
and some skin issues, we set out to investigate and compare the biological activities
of essential oils from the fresh and air-dried leaves of the plant. Essential oils were
extracted by hydrodistillation using an all-glass Clevenger apparatus and analysed
by GC/MS. Antioxidant activity was by the DPPH scavenging method while
antimicrobial activity was by the agar diffusion method. Essential oils (EOs) from
fresh 0.34% (w/w) and air-dried 0.28% (w/w) leaves of Hildegardia barteri were
colourless with an herbal smell. Both oils had ten (99.99%) and seventeen
compounds (100%) from the fresh and air-dried leaves respectively. The fresh
leaves EO comprised mainly 58.21% unsaturated fatty acids (oleic acid (34.29%),
cis, cis linoleic acid (22.10%), and derivatives (1.82%)), and 38.81% saturated fatty
acids (palmitic acid (24.85%) and stearic acid (13.96%)). The air-dried leaves EO
was mainly 59.15% unsaturated fatty acids (α-Linolenic acid (41.56%), oleic acid
(13.14%), and derivatives (4.45%)), and 30.43% saturated fatty acids (palmitic
acid (21.41%), stearic acid (6.97%), and derivatives (2.05%)). Antimicrobial
activities were tested on Staphylococcus aureus, Salmonella typhi, Escherichia coli,
Pleisomonas shigelloides, Bacillus cereus, Proteus vulgaris, Candida albicans, and
Candida tropicalis at 6.25-50 mg/mL. The EO from the fresh leaves at 50 mg/mL
for some of the organisms tested gave zones of inhibition from 7.3±1.33-11.3±2.73
mm and MIC (0.39-6.25 mg/mL), while the air-dried leaves gave from 8.0±2.00-
15±4.73 mm with MIC (0.39- 6.25 mg/mL). Antioxidant activities at 6.25-200
μg/mL of both oils and ascorbic acid were investigated. At 200 μg/mL, the fresh
and air-dried oils gave the same activity of 66.41% and 66.42%, comparable to
ascorbic acid’s 69.23%. The unsaturated and saturated fatty acids in both oils
could contribute to the plant's antimicrobial and antioxidant activities and its
usage in managing stomach issues and various skin problems.