Study Of Poly γ-glutamate-Gelatin Microcapsulation Of Bacillus Thuringiensis

Crystal protein is the key ingredient for the toxicity of Bacillus thuringiensis(Bt) and it has a characteristic of low resistance to heating treatment and UV irradiation which would lead to less activity and instability,and reduced the time of residual toxicity.So,it is important to select appropriate preparation to assure the stability in deposited and to exert the full measure of its effect in the field.Microcapsule preparation was known as one of the best controlled release preparation.It was shown that the resistance to harmful conditions is strengthened,and it would last the effect when it used in the field and could enhance its storing stability.A technology of Bt microcapsule by double phase separation-coacervation and spraying dryness using polyγ-glutamate(γ-PGA) - gelatin was investigated in this paper.The resistance of the microcapsule to UV irradiation and heating treatment was evaluated by the comparison of the survival rate of spore and the lethality rate to Heliothis armigera of Bt technical and the microcapsule.Also the controlled release of crystal protein from microcapsttles was investigated under the conditions of water or soil or the midgut of Bombyx mori.The conclusions have been obtained as follows:1.In terms of encapsulation rate,average diameter,storing stability,virulence test of microcapsules preparation,confirmed that the best technique conditions of the microcapsules preparation with theγ-PGA- gelatin were:the Bt technical 5%,the concentration ofγ-PGA-gelatin 1.8%,the system temperature 40℃,the pH 4.0 and the rotate speed 400 r/min.Its encapsulation rate was 89.2%,and average diameter was 25.5μm.The optimum spray drying conditions were:inlet temperature 190±5℃,outlet temperature 70±2℃,liquid feed rate 25±2 ml/min、atomizing air pressure 0.15 Mpa. The potency of Bt microcapsules was 32105 IU/mg.2.The resistance of the microcapsule to UV irradiation and heating treatment was evaluated by the comparison of the survival rate of spore and the lethality rate to Heliothis armigera of Bt technical and the microcapsule.It was shown that,after UV irradiation for 4 h,the lethality rate to Heliothis armigera of the microcapsule and Bt technical were 53.57%and 16.60%respectively,the survival rate of spore of the microcapsule and Bt technical were 46.63%and 6.90%respectively.It was also illustrated that,after heating treatment at 80℃for 100 min,the lethality rate to Heliothis armigera of microcapsule and Bt technical were 43.42%and 26.11%respectively.In the case of heating treatment at 100℃for 15 min,the survival rate of the microcapsule and Bt technical were 72.53%and 25.50%respectively.The microencapsulation technology can effectively increase resistance of Bacillus thuringiensis formulation to heating treatment and UV irradiation.3 The controlled release of crystal protein from microcapsttles was investigated under the conditions of the water,the soil,the midgut of Bombyx mori respectively.It set up models of controlled release of microencapsulation.The release equation of Bt microcapsule in the conditions of the water,the soil,the midgut of Bombyx mori were M_t=0(t=0～3), M_t=4.7214(t-3) -8.7643(10≥t＞3);M_t=0(t=0～0.5),M_t =10.045(t-0.5) -6.2087(7≥t＞0.5); M_t=177.71t + 2.6548,(t=0-0.167);the unit of M_t is%,the unit of time is d.Using polyγ-glutamate(γ-PGA) - gelatin as the microencapsulation membrane material can effectively balance the inconsistency of the rapid action of Bt and the continuous activity of Bt.