Preparation Of Natamycin Microcapsules Form Layer-by-layer Assembly And Performance Testing

Natamycin(NA) is the secondary metabolites of Actinomycetes, which is also a kind of difficult soluble solid compound with the broad-spectrum bactericidal effect. However, the molecular structure of NA is the polyene macrocyclic lactone that is susceptible to UV light and loss the activity, which limits its application in the control field of plant diseases.In order to improve the photostability of NA, different release rate of NA MCs was prepared by using LbL assembly and characterized, and their performance was determined.Firstly, using the reverse electric potential of assembly as evaluation standard, the optimal assembly conditions were studied by the orthogonal experiments with sodium alginate/chitosan or gelatin/sodium lignosulphonate for wall materials. NA MCs with layer number of 3, 7, 11, 15 and 19 were made with two wall materials. Secondly, overall distribution and surface morphology structure of MCs was observed by optical microscope and scanning electron microscope. Their particle size distribution was determined by laser particle size distribution analyzer. Third, the drug loading(DL) and entrapment efficiency(EE) of MCs were measured, which showed that the DL and EE was reduced with an increase of the layer number of assembly, DL and EE of MCs with gelatin/sodium lignosulphonate for wall materials was lower than that of MCs with sodium alginate/chitosan for wall materials. Fourth, the release performance of MCs was studied by using the release test in vitro. For sodium alginate/chitosan as wall materials, 10% drug release time of MCs with three, seven, eleven, fifteen and nineteen layers were 1.47, 2.17, 2.79, 3.53 and 4.11 times more than uncoated NA. But, for gelatin/sodium lignosulphonate as wall materials, the MCs were easily broken in the process of release. Fifth, the photolysis of NA MCs was investigated by using the inhibition zone and high performance liquid chromatography(HPLC). The drug photostability was distinctly improved after microencapsulation of NA, and the times of the relative activity of NA MCs decreased by 50% under UV light were 1.99, 3.07, 3.51, 3.87 and 4.02 fold more than that of uncoated NA. Sixth, the efficacy of NA MCs for controlling Blumeria graminis was tested on the melon in the greenhouse, which was better than that of uncoated NA and 25% of pyraclostrobin EC, the control efficacy of 11 layer MCs was better than the others. Thus, the drug release rate will have a large impact on the drug Anti-photolysis and diseases control. The suitable release rate of MCs can play the best role for pesticide efficacy.