Bioactivities of plant extracts collected in Halmahera, Indonesia: A bioprospection study of underexplored plant species

The discovery of new antibiotics to overcome the growing resistance problem, as well as the discovery of new natural and safe antioxidants to combat oxidative stress, are still urgently needed. Medicinal plants are known to produce potential therapeutic substances which are more biologically selective than synthetic compounds. Therefore, we explored the bioactivities of 35 ethanolic extracts from 24 underexplored plant species collected in Halmahera island, Indonesia, to find potential sources for antibacterial and antioxidant agents. Dried plant parts were extracted using ethanol 96%. Thin layer chromatography-direct-bioautography (TLC-DB) and minimum inhibitory concentration (MIC) determination were used to evaluate the antibacterial effect. Antioxidant activity was determined against 2,2-Diphenyl1-picrylhydrazyl(DPPH) using TLC-DB and microdilution assay. Total phenolic content (TPC) was determined using Folin-Ciocalteu’s method. The ethanolic plant extracts from Halmahera island exhibited moderate to weak antibacterial activity against Escherichia coli and Staphylococcus aureus. However, 14 extracts from the leaf, stem, or stem bark of 10 underexplored plant species from Halmahera Island, Indonesia, displayed strong to very strong antioxidant activities against DPPH with antioxidant activity index (AAI) values between 1.12 to 13.42. A strong correlation between TPC and antioxidant activity with r=0.8712, p<0.0001 was observed. This strong correlation between TPC and
antioxidant activity exhibited a prominent role of phenolic compounds in the
plants’ antioxidant properties. These findings indicate that collected plants
from Halmahera are potential to be studied and developed further as potential
sources for novel antioxidants.