Study On The Construction Of Maltodextrinpoly(ethylene Oxide)water-in-water Emulsion For The Encapsulation And Culture Of Lactobacillus Plantarum

When water in water(W/W)emulsion is used as the delivery system,the stabilization of W/W emulsion is the prerequisite for its related applications.In this paper,an aqueous two-phase system(ATPS)based on polyethylene oxide(PEO)and maltodextrin(MD)was constructed to prepare W/W emulsion.The W/W emulsion was stabilized with cellulose nanocrystals(CNCs),Tempo-oxidized bacterial cellulose nanofibrils(TOBCNFs)and chitosan(CS).In addition,the probiotics were encapsulated and cultured by selecting the appropriate W/W emulsion system.The main results of this work are as follows:1.W/W emulsion stabilized by cellulose nanocrystalsThe PEO-MD ATPS phase diagram was prepared by cloud point method and lattice method.The I-W/W emulsion(PEO/MD=4.5 wt%/3.5 wt%)with MD rich droplets dispersed in the PEO rich phase and the II-W/W emulsion after phase inversion(PEO/MD=0.6 wt%/28.0 wt%)were obtained based on the two-phase region in the diagram.The time for phase separation of the two emulsions was 3 d and 6 h,respectively.When the concentration of MD was increased(2.5 wt%-4.5 wt%),the average droplet size of I-W/W emulsion was increased from 4.22±0.97μm to 7.14±1.70μm.Meanwhile,the phase separation time was shortened from 74 h to 20 h.However,increasing the concentration of PEO caused no obvious effect on the droplet size of emulsion,which increased the viscosity of emulsion thus prolonging the phase separation time to 68 h.The width and height of CNCs obtained by hydrolysis of MCC with 64 wt%sulfuric acid were 38.9±5.2 nm and3.9±1.4 nm respectively,and the overall length of CNCs was less than 300 nm,which were needle-like nanoparticles.Pickering emulsion could be obtained by preparing II-W/W emulsion with CNCs involved.CNCs could form a barrier at the W/Winterface to inhibit the coalescence of the droplets,and the average droplet size of the emulsion was decresed from 20.07±9.73μm to 5.80±1.05μm.However,emulsion will still complete phase separation in a short time(36 h).The addition of Na Cl caused the aggregation of CNCs,and inhibitd the phase separation of the emulsions.The results of frequency sweep showed that the storage modulus and loss modulus of emulsion increased with the increase of the concentration of CNCs and Na Cl.When the concentration of CNCs was higher than 0.400wt%,a weak gel structure could be formed.However,the rapid aggregation of CNCs would influence the interfacial adsorption of CNCs.The average droplet size of the emulsion containing 50 m M Na Cl and 0.20 wt%CNCs was decreased from 6.13±1.45μm to 16.68±5.26μm。2.W/W emulsion stabilized by combining cellulose nanocrystals and oxidized bacterial cellulose nanofibrilsCompared with CNCs,Tempo oxidized bacterial fiber nanofibrils(TOBCNFs)had long and flexible fibrils,which can form three-dimensional network structure to inhibit the movement of droplets and phase separation.When the concentration of TOBCNFs reached0.10 wt%,The average droplet size ofⅡ-W/W emulsion could be decreased to 16.01±5.29μm and no phase separation was observed within 7 d.The emulsion showed shear thinning behavior,and the frequency sweep results indicated that the strength of the fibrous network was increased with the increase of TOBCNFs concentration.However,droplet deformation would take place as TOBCNFs concentration was above 0.05 wt%.StableⅡ-W/W emulsion was obtained by adding 0.20 wt%CNCs and 0.10 wt%TOBCNFs in one-step preparation.The shape of emulsion droplets was regular and the droplet size was reduced to 6.63±1.56μm with no phase separation within 7 d.3.Chitosan-stabilized W/Wemulsion and its application in the encapsulation and culture of probioticsChitosan(CS)could increase the viscosity of emulsion and acted as a steric hindrance to inhibit droplet coalescence,thus stabilizing W/W emulsion.Lactobacillus plantarum was prone to MD phase.Therefore,CS-based I-W/W emulsion was selected to encapsulate Lactobacillus plantarum,and the emulsion was not sensitive to Na Cl(<200 m M).Due to the change of CS dissolution state,the stability of the emulsion was increased with the increase of p H,which could be maintained for at least 30 days at p H 6.The embedded lactobacillus plantarum was cultured by adding 1.0 wt%MRS broth.The growth curve showed that viable cells could reach 1.09×10~9 CFU/m L,the p H of the system dropped to3.6.Additionally,the microscopic images dsiplayed that the living bacteria will increase in the MD droplets.Based on I-W/W emulsion,Lactobacillus plantarum could be embedded first and then cultured.