| The microwave and ultrasonic assisted extraction of total flavonoids from hibiscusmutabilis was studied and tested spectrophotometrically. The influences of the concentration ofethanol, ultrasonic power, microwave power, the ratio of solid to liquid, and the extracting timeon the total flavonoids’ extraction yield from hibiscus mutabilis were investigated by singlefactor and orthogonal experiments. As a result, the extraction rate was6.72%under theoptimum extracting conditions: ethanol55%, ultrasonic power700W, microwave power700W, ratio of solid to liquid(w:v)1:40and extraction time50s.The antioxidant activity of the crude hibiscus mutabilis flavonoids extract was studied andcompared with those of BHT and Vc. The major results obtained from the study were asfollows:(1) In the ability of reducing power, flavonoids of hibiscus mutabilis had some certainability of reducing, which was weaker than vitamin C and stronger than BHT.(2) Theflavonoids had scavenging effects on hydroxyl radical, superoxide anion radical.(3) Themaximum capabilities of inhibiting formation of nitrosamine and scavenging rate of sodiumnitrite were97.38%and88.32%respectively.Bacteriostatic experiments were carried out to analyze the antimicrobial activity in vitro ofextracts from hibiscus mutabilis. Five crude extracts, which were extracted by ethyl acetate,acetone,70%alcohol, petroleum ether from hibiscus mutabilis respectively, were tested theantimicrobial activity to Escherichia coli, Bacillus subtilis, Bacillus licheniformis, Yeast,Aspergillus oryzae, Mortierella isabellina and minimum inhibitory concentration(MIC) andantibacterial circle diameter by disc diffusion method and doubling dilution. The results showedthat the five crude extracts possessed obvious antimicrobial activity to Escherichia coli,Bacillus subtilis, Bacillus licheniformis, and ethanol crude extract achieved the best results. TheMIC of70%alcohol crude extract to Escherichia coil, Bacillus subtilis, Bacillus licheniformiswere50g/L,50g/L,12.5g/L respectively. The above results indicated that flavonoids fromhibiscus mutabilis had antibacterial effect, and it would be probable used in food processing andpreservation.The optimum extraction process on hibiscus leafs’ flavonoids was investigation byorthogonal design. Ultraviolet spectrophotometry was used to determine the total flavonoids.The results showed that the extraction rate was3.91%under the optimum extracting conditions: ethanol20%, ultrasonic power225W, ratio of solid to liquid(w:v)1:40and extraction time60min. |
