Abstract

• Croton oblongifolius Roxb., a middle size tree as medicinal plants, was chosen to investigate phytochemical constituents, nutritional values, screening of antimicrobial, total phenolic contents, total flavonoid contents and antioxidant activities. Preliminary phytochemical investigation of Thak-ring-kri bark revealed the presence of flavonoids, phenolic compounds, glycosides, saponin, terpenoids, steroids, carbohydrate, tannin, starch and α-amino acid. Alkaloids and cyanogenic glycoside were not detected in the sample. The AOAC method was used to determine the nutritional values such as moisture, ash, protein, crude fiber, fat, carbohydrate and energy value. The content of these values are 6 %, 10 %, 5.73 %, 11.45 %, 7.43 %, 59.4 % and 327 kcal/100g, respectively. The antimicrobial activity of pet-ether, dichloro methane, ethyl acetate, ethanol, methanol and watery extracts was determined by agar well diffusion method against six species of microorganisms such as Bacillus substilis, Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus pumilus, Candida albicans and E. coli. It was found that all extracts showed antimicrobial activity against all tested microorganisms. Its watery extract showed less activity (12 mm) and pet-ether extract was observed the most pronounced antimicrobial activity (16~35 mm) against all microorganisms tested. Total phenolic contents was determined by spectrophotometric method using Folin-Ciocalteu reagent. Ethanol and watery extracts of the total phenolic contents were found to be (197.50 ± 0.01) µg GAE/mg and (41.42 ± 0.00) µg GAE/mg respectively. Total flavonoid contents was studied by spectrophotometric method. The ethanol extract contain flavonoid content (115.34 ± 0.01) µg QE/mg higher than watery extracts (70.00 ± 0.00) µg QE/mg. From the screening of free radical scavenging activity of Thak-ring-kri stem bark by DPPH assay, it was found that ethanol extract (IC50 = 5.9 μg/mL) showed the higher radicalscavenging activity than watery extract (IC50 = 18.5 μg/mL).