The Effect of Sterilization, pH, Filler and Spore Inoculum Concentration on the Preparation of Alginate Pellets

Alginate encapsu lation of an atoxigen ic strain of Aspergillu s ̄ avus was studied in order to optimize encapsu lation of fungal inocula with alginic acid . Steriliza tion by autoclav ing is known to depolymerize sodium alginate . Buffered solution s (pH 5 7± 8) reduced this effect . Autoclaving the alginate solutio n with a ® ller/nutrien t further inhibite d the depolymerization reaction . Autoclaving under optimal conditions allowed a less expensive alginate (medium viscosity ) to be used at a lower concent ration (1%) to produce a stable product . The lowest cost pellets resulted from use of 1% medium viscosit y sodium alginate with 10% cotton-seed meal. Further saving s may be achieved by performing fermentation s directly in alginate ± nutrien t mixture s and thus eliminating the mixing and blending steps. In such formulations , the nutrien t compositio n and length of fermentatio n must be adjuste d to preven t alginate hydroly sis. The ultimate composition of alginate pellets is in ̄ uenced by the diffusion of nutrient s during gelation . Up to 65% of water-soluble nutrient s were lost from alginate pellets during gelation . Once pellets are introduced into the environment, organisms other than the formulated agent compete for pelleted nutrient s. A minimum concentr ation of the biocontrol agen t must be presen t to ensure the agent exclude s competitor s and successfully converts the nutrients to biomass. For A. ̄ avus , 5000 spores g 2 1 were required.