Preparation Of Microspheres Loaded With Potassium Diformate By Emulsification/external Gelation And Study On Slowed-release Antibacterial Properties

In recent years,potassium diformate（KDF）has been widely used as a good substitute for antibiotics in animal feed additives.However,its directed feeding can cause the utilization rate to be low.Therefore,this study aimed at improving the utilization rate of KDF in the gastrointestinal tract and prolonging the action time.The KDF/sodium alginate（ALG）microspheres and KDF/type A molecular sieve（zeolite A）/ALG microspheres were prepared by emulsification/external gelation method.On the basis of single factor experiment,experiment design was optimized by using response surface method（RSM）,the optimized structure of the microspheres were characterized by FT-IR,XRD,SEM and TGA and so on.The drug slow-release effect of potassium diformate microspheres and the release behavior,as well as the microspheres of Escherichia coli,Staphylococcus aureus in vitro antibacterial properties were studied.The results of KDF/ALG microspheres and KDF/zeolite A/ALG microspheres were as following:（1）The prepared KDF/ALG/Ca²⁺microspheres and KDF/ALG/Zn²⁺microspheres were characterized and analyzed by FT-IR,SEM and ZEISS tests,which Ca²⁺and Zn²⁺were used as cross-linking agents,the results showed that the optimized KDF/ALG/Ca²⁺microspheres and KDF/ALG/Zn²⁺microspheres both effectively encapsulated KDF.The microspheres were spherical in morphology,rough in surface,and the particle sizes were 2-10μm and 10-50μm,respectively,and the particle size distribution was uniform.The results of TGA showed that KDF/ALG microspheres were stable at physiological temperature,and the weight loss of KDF/ALG/Ca²⁺microspheres（58%）was greater than that of KDF/ALG/Zn²⁺microspheres（54%）.（2）Zeolite A with good crystallinity was prepared by hydrothermal synthesis method,and KDF/zeolite A/ALG microspheres were prepared by using it as carrier loading KDF.Zeta potential analysis showed that zeolite A exhibited different potential characteristics at different p H values,and zeolite A had positive charge on its surface,which could effectively adsorb HCOO^-separated from KDF in the solution under acidic conditions.FT-IR analysis of KDF/zeolite A/ALG microspheres showed that there were characteristic absorption peaks of KDF and zeolite A by comparing the KDF/ALG microspheres.The XRD results showed that the structure of zeolite A was not destroyed after loading KDF.SEM and TEM analysis showed that the surface of the microspheres was rough,and the EDS energy spectrum further indicated that zeolite A and KDF were encapsulated in the microspheres.The encapsulation rate（EE%）and loading rate（LC%）of KDF/ALG microspheres and KDF/zeolite A/ALG microspheres were calculated,the results showed that the encapsulation rate and loading rate of KDF/ALG microspheres were lower than those of KDF/zeolite A/ALG microspheres,which proves that the addition of zeolite A can improve the encapsulation rate and loading rate of microspheres.（3）The results of in vitro simulated gastrointestinal release of microspheres showed that the addition of zeolite A could effectively slow down the in vitro release rate of KDF with good slowed-release effect,and the release rate of microspheres in the stomach was significantly faster than that in the gastric tract system.The equilibrium time of KDF/zeolite A/ALG/Ca²⁺microspheres prepared was 5 h in the stomach environment（p H=1.2）and 4 h in the intestinal environment（p H=7.4）.The equilibrium time of KDF/zeolite A/ALG/Zn²⁺microspheres was 6 h when p H=1.2,and in intestinal environment was 5 h.The study on the release mechanism of microspheres in the gastrointestinal tract showed that the best fitting models of KDF/zeolite A/ALG/Ca²⁺microspheres in the gastric fluid environment were Hixon-Crowell model and first-order kinetic model,and the KDF/zeolite A/ALG/Zn²⁺microspheres followed the first-order kinetic model and Higuchi diffusion model.In simulated intestinal fluid environment,the KDF/zeolite A/ALG/Ca²⁺microspheres mainly followed the first-order kinetic model and Hixon-Crowell model,while the KDF/zeolite A/ALG/Zn²⁺microspheres mainly followed the first-order kinetic model.（4）In vitro antibacterial test results showed that bacteriostatic microspheres had a good antibacterial effect against Escherichia coli and Staphylococcus aureus.With the gradual increase of KDF concentration,the antibacterial effect was enhanced.When the concentration of KDF/zeolite A/ALG/Ca²⁺microspheres was 96 mg/mL,the inhibition rates of KDF/zeolite A/ALG/Ca²⁺microspheres against E.coli and Staphylococcus aureus were 89%and 85%,respectively,and the minimum inhibitory concentrations were 12 mg/mL and 6 mg/mL.While the inhibitory rates of KDF/zeolite A/ALG/Zn²⁺microspheres against E.coli and Staphylococcus aureus were 88%and 87%,respectively,and the minimum inhibitory concentrations were 24mg/mL and 12 mg/mL.