Study on the Bacteriostatic Activity and Stability of Ethanolic Extract from Yunnan Litsea cubeba

In this study, the antibacterial effects of five different ethanolic concentrations (0%, 55%, 75%, 95%, 100%) EELC (Ethanol extract of Yunnan Litsea cubeba) on two kinds of pathogenic bacteria were determined. Ethanol extracts which had the strongest antibacterial activity and their stability were analyzed. The inhibition zone diameter of different concentrations in ethanolic EELC against E.coil and S.aureus were determined by KB paper method. At the same time, using TTC (2,3,5-triphenyltetrazolium chloride) method detected the MIC of EELC to screen out the best antibacterial activity of EELC. At the end, the temperature, heat treatment time, pH and UV light stability of EELC were further studied. The results showed that 55% and 75% EELC had the best inhibitory effect on S.aureus and E.coli, with MIC of 19 and 819 μg/mL, respectively. 55% EELC treated at 40 ℃, the OD₆₀₀ was 0.118, which had the optimal antibacterial activity. Furthermore, the antibacterial activity remained stable after treatment for 1~5 hours at this condition. There was no significant difference in antibacterial activity between the two groups after irradiation with 30W UV light for 10~60 min (P>0.05). The bacteriostatic activity decreased at pH4, while it remained at a stable level at pH6~10. 75% EELC was treated at 100 ℃, the retention rate of antibacterial activity reaching 92.88%, and no significant difference was found in antibacterial activity after heating at this temperature for 1~5 h (P>0.05). The antibacterial activity was significantly decreased at pH4~8 (P<0.05), but it showed increasing trend at pH10. UV light irradiation for 10~60 min had no significant effect on the inhibitory activity (P>0.05). It was suggested tha, the 55% EELC had a high stability and low action concentration against S.aureus, while 75% EELC had a stable inhibition effect against E.coil. The results would provide a theoretical basis for the comprehensive utilization and development of Yunnan Litsea cubeba.