Optimization of ultrasonic assisted extraction of polyphenol from Euryale ferox seed shells and its antimicrobial activity against Staphylococcus aureus

【Objective】The extraction technology of polyphenols from Euryale ferox seed shell was optimized, and its inhibition and stability to Staphylococcus aureus were analyzed to provide basis for resource utilization of E.ferox seed shell.【Method】The ultrasonic assisted extraction method was used to extract the polyphenols from E.ferox seed shell.The single factor experiment and response surface experiment with extraction yield of polyphenols(Y) as the evaluation index, and the ultrasound time(X₁), ultrasound temperature(X₂) and soild-liquid ratio(X₃) as three factors were carried out to determine the best extraction process, then the extract was preliminarily purified by macroporous resin.The inhibitory activity and the minimum inhibitory concentration(MIC) of E.ferox seed shell polyphenols on S.aureus was studied by agar diffusion method.The effects of temperature, pH and metal ion concentration on the stability of polyphenols were also investigated.【Result】The effects of three factors on yield of polyphenols from E.ferox seed shell were:ultrasound temperature> solid-liquid ratio> ultrasound time, the results showed that the solid-liquid ratio, and the interaction between ultrasound temperature and solid-liquid ratio had significant effects on yield of polyphenols(P< 0.05), while the ultrasound temperature had extremely significant effects(P< 0.01) on the extraction rate of polyphenols from E.ferox seed shell.The regression equation was obtained:Y=14.57+0.064X₁+0.26X₂+0.11X₃+0.079X₁X₂-0.018X₁X₃-0.18X₂X₃-0.11X₁²-0.54X₂²-0.19X₃².The optimum extraction process was:ultrasound time was 39 min, ultrasound temperature was 72℃, solidliquid ratio was 1:41.Under these conditions, the extraction rate was 14.479%, which was close to the predicted value(14.630%). E.ferox seed shell polyphenol had certain inhibitory effect on S.aureus, the MIC was 0.1625 mg/mL.The temperature and Ca²⁺, Mg²⁺, K⁺ and Na⁺ metal ions had no significant effect on the inhibition of S.aureus reproductive activity by E.ferox seed shell polyphenols(P> 0.05), but with the increase of pH, the bacteriostatic activity of E.ferox seed shell polyphenols was inhibited.【Conclusion】The polyphenols in the shell of E.ferox can be effectively extracted by the optimized ultrasonic assisted method, and the polyphenols has a good and stable inhibitory effect on the growth of S.aureus.