Study On The Bifidabacterium-Loaded Microcapsule Prepared By Internal Emulsiifcation Method

Bifidobacteria, which confer health benefits to host, have been incorporated into the foodand medicine industry. However, in order for Bifidobacteria to exert these beneficial effects,they must be able to tolerate the acidic conditions of the stomach environment as well as thebile in the small intestine. In this thesis a microencapsulation system was developed with theobjective of enhancing viability during exposure to the adverse conditions of thegastro-intestinal tract and stability over storage.At frist, Bifidobacterium bifidum was encapsulated with alginate by internalemulsification method. Effect of washing medium and the processing parameters on thecharacteristics of the microspheres containing Bifidobacterium bifidum were investigated. Theacid tolerance and enteric solubility were also studied in this thesis. Based on the sizedistribution, encapsulation efficiency, the optimal conditions were determined as follows:1%（v/v） Tween80in aqueous solution as washing medium, the volume ratio of Span80to oil1%(v/v)，the volume ratio of water to oil30:100, stirring speed400r/min，the mass ratio ofCaCO3to sodium alginate7.5:40and the mole ratio of glacial acetic acid to CaCO33.5:1.Under these conditions, the average size of the microspheres reached116μm, and theencapsulation yield of Bifidobacterium bifidum was89.8%. Besides, compared to free cells,the viability of Bifidobacterium bifidum loaded in alginate during exposure to simulatedgastric juice and sequential gastrio-intestinal juice increased two and three log respectively.After the treatment of stimulated intestinal juice for60min, almost all microcapsulesdisintegrated.The research was carried out by coating with polyelectrolytes such as chitosan, wheyprotein and alginate for purpose of increasing stability of the alginate microcapsules. Theinfluence of these treatments on the size of microspheres, encapsulation yield and the viabilityof microencapsulated Bifidobacterium bifidum under simulated conditions of gastro-intestinaltransit were studied. The mean diameter of double layer microspheres ranged from126to172μm, reaching a maxium value when whey protein was used as a coating material. Nodifference was detected in encapsulation yield with different type of microcapsules, whichwas approximately50%. It was observed that the protective effects varied with the type ofmicrocapsules. However, chitosan coating provided the best protection for microencapsulatedcells in simulated gastro-intestinal tract. All microspheres showed good enteric solubility.The molecular weight of chitosan, as well as the concentration and pH of chitosansolution had significant effects on acid-resistance and enteric solubility of microcapsules. Theoptimal conditions for preparing chitosan-coated alginate microcapsules were as follows:molecular weight400kDa,0.4%of chitosan concentration and solution pH5.0. Under theseconditions, the amount of Bifidobacterium bifidum maintained5.53Log cfu/g after120min in simulated gastric juice. The number of Bifidobacterium bifidum increased to7.86Log cfu/gwithin4h in simulated intestinal juice. The ultrastructure of chitosan-algiante microsphereswas characterized by scanning electron microscopy (SEM). After coated with chitosan,chitosan-alginate complex film endowed the beads a relatively dense surface with less andsmaller cracks. Various physicochemical interactions among components and existence stateof components were researched by fourier transform infrared spectroscopy (FTIR) and X-raydiffraction (XRD). The form of Bifidobacterium bifidum loaded chitosan-coated alginatemicrospheres was mainly controlled by the electrostatic interaction between chitosan andalginate.A modified method using resistant starch for the microencapsulation of probioticbacteria was reported in this study. Incorporation of resistant starch did not improvedencapsulation of viable bacteria as compared to when the bacteria were encapsulated withoutthe starch. A preliminary study was carried out in order to monitor the effects ofencapsulation on the survival of Bifidobacterium bifidum in yoghurt over a period of3weeks.This study showed that the survival of encapsulated cultures of Bifidobacterium bifidumshowed no decline in viable count over a period of3weeks, while there was a decline ofabout0.5log in cultures which were incorporated as free cells in yoghurt.