ฤทธิ์ต้านเชื้อ Staphylococcus aureus ที่่ก่อโรคอาหารเป็นพิษของสารสกัดจากใบและผลกระทุ (Rhodomyrtus tomentosa) และการประยุกต์ใช้กับน้ำสลัด

Abstract

The aim of this study was to evaluate the antibacterial activity of the ethanol, acetone, and water extracts of Rhodomyrtus tomentosa leaf and fruit on Staphylococcus aureus isolated from foods. By disc diffusion method, all extracts demonstrated antibacterial activity against all bacterial strains with the zone of inhibition ranging from 8.5-15 mm. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the extracts were ranging from 7.8125 - >1000 and 15.625 - >1000 pg/ml, respectively. The result of time-kill study showed that the ethanol extract of leaf produced killing activity at concentration of 8MIC, 4MIC, and 2MIC within 8, 10, and 10 h, respectively. The viable cells were decreased more than 3 log CFU/ml (>99.9%) when compared with the untreated cells at the beginning. Both leaf and fruit ethanol extracts exhibited antioxidant by DPPH assay (ICso 4.6 and 17.99 mg/ml). FRAP assay (FezSO equivalent 2.86 and 2.36 M FezSO/mg sample), total phenolic content assay (1512.43 and 1958.1 mg of gallic acid/mg of extract), and total flavonoid content assay (19.2 and 61.2 mg of catachin/mg of extract). In the sub-chronic toxicity study of leaf and fruit ethanol extracts, there were no significant adverse effects on food consumption, body weight, organ weights, mortality, clinical chemistry, and hematology of rats at 5, 50, and 300 mg/kg body weight. The leaf ethanol extract was incorporated into homemade salad dressing and examined for its sensory properties. The results indicated that the salad dressing contained 12.5 mg/ml of the extract showed the best results by 9-point hedonic scaling with appearance, color, odor, flavor, bitterness, and overall acceptance scales of 7.13, 7.20, 7.07, 7.03, 6.97, and 7.10, respectively. The salad dressings contained the extract were investigated for their anti-S. aureus activity during storage at 4 and 10 °C for 21 days. The result revealed that the salad dressings contained 25 and 50 mg/ml of the extract displayed bactericidal activity within the first day of storage at 4 and 10 °C. Meanwhile, at concentration of 12.5 mg/ml, a reduction in S. aureus were decreased more than 3 log CFU/ml (>99.9%) at day 3 and the bactericidal activity was detected at day 21.