Study On Physicochemical Property And Antibacterial Activity Of Abalone Shell Calcinate At Different Temperature

The abalone shell was calcined at elevated temperature to modify its physicochemical properties.Those properties and composition of the abalone shell calcinate at different calcination temperature were then used to test the antibacterial activity in vitro,and the according antibacterial mechanism were preliminarily investigated.Firstly,to determine the ranges of appropriate calcination temperature of the abalone shell,pyrolysis characteristics of the calcinate during the heating process were examined with thermal methods.Secondly,the morphology and structure changes of the calcinate were observed with scanning electron microscope energy-spectrum?SEM-EDS?,X ray diffraction?XRD?and Fourier transform infrared spectroscopy?FTIR?,and the variations of mineral elements were detected by inductively coupled plasma mass spectrometer?ICP-MS?.Thirdly,the antibacterial activities in vitro of the calcinate at different calcination temperature were survived through three methods.Consequently,the relationships among the antibacterial activities and the calcination temperature,physicochemical properties and mineral elements variations were compared.Lastly,the antibacterial mechanism of the abalone shell calcinate were preliminarily inquired to provide theory evidence and reference for the further application of this natural antibacterial material.The results are shown as follows:?1?The thermogravimerty curve?TG?of abalone shell showed that the mass fraction reduced gently where the temperature was between 25²50? while the weightlessness rate showed a slowly decent after a slightly rapid decline at 400? when the temperature ranged from 250 to 670?.The curve showed an obviously decrease at the temperate of 670? before the mass fraction almost keep a constant value from 823? to 1000?.Meanwhile the curve of derivative thermogravimetric analysis?DTG?and differential scanning calorimetry?DSC?presented a similar tendency with the curve of TG,however,compared with the DTG and DSC,the curve of TG indicated a distinct effect hysteresis with delaying of almost 20? which means that the max DTG and sharp endothermic peak appeared at the temperature of 800?.Thus,we concluded that the calcination temperature of abalone shellranged from 400 ? to 1100 ? while the temperature programmed rate was 10?/min.?2?The particles of abalone shell calcinate became smaller gradually with the higher temperature such as prominently apparent changes at 600?,particle refining and fritting phenomena at 800? and 900?,respectively.The more even production of calcinate can be generated at 1000? and 1100?.The results of Fourier Transform Infra-red spectrum?FTIR?showed that calcinate owns the characteristic absorption peak of CO₃^2- at the temperature of 0?,400? and 600?,while the peak was disappeared and replaced by noteworthyabsorption of active calcium oxide from 1000? to 1100? after a noticeably weakened tendency at the temperature ranged from 800 ? to 900 ?.The X-ray diffraction analysis shows the similar results with FTIR.The concentration of Ca in calcined abalone shell was highest while the deleterious elements were lowerthan nation criterion.The calcining temperature has clearly concentrating for Cu and Zn with the rise of temperate.?3?There were certain differences between the results of antimicrobial efficacy experimental in vitro which used for testing the antimicrobial activities of abalone shell calcinate.According to the results of Oxford cup method,the calcinate produced at the temperature of ?800? showed the significant inhibition for four active pathogens named?Staphylococcus aureus,Pseudomonas aeruginosa,Escherichia coli and Enterococcus faecalis?respectively.The diameter of antibacterial circle of abalone shell calcinate increased with the rise of temperature while the disc diffusion method was relatively insensitive until the temperature up to 900? where small part of antibacterial activity was generated.Abalone shell calcinate presented the best effect on bacteriostatic activities with the Minimum Inhibitory Concentration?MIC?of 1mg/mL,0.5mg/m L,2mg/m L and 2mg/mL for four active pathogens named Staphylococcus aureus,Pseudomonas aeruginosa,Escherichia coliandEnterococcus faecalisrespectively when the temperature increased to 1100?.?4?The pH value of abalone shell calcinate,tested in the range of antibacterial concentration,were bigger than 12.43 when the calcining temperature more than 800?,and showed the highest value from 1000? to 1100?.Combined with the results such as particle diameter decreasing,specific surface area increasing,active calcium oxide generating and mineralselement concentrating and so on,we surmised that the antibacterialmechanism of abalone shell calcinatemay be connected with the adsorption,higher pH value,active calcium oxide and higher amount of Cu and Zn in the abalone shell calcinate.Meanwhile,electron microscopy results showed that the abalone shellcalcinatedestroyed the cell structure of bacteria,caused in cell wall sag by affecting its permeability and integrity.Thus,we concluded that the antibacterial action sites of abalone shellcalcinate may existed on the cell wall.