The Design And Stability Regulation Of The Maltodextrin-dextran Water In Water(W/W) Emulsion

The stabilization of water in water（W/W）emulsions,as a potential candidate for encapsulating water-soluble functional components,remain a significant challenge in food science research.In this work,dextran（DEX）and maltodextrin（MAL）solutions were mixed to obtain the water in water（W/W）emulsion.What was more,the effect of emulsification parameters and phase component on the emulsion microstructure and phase separation behavior was investigated.The bacterial cellulose nanofibers（BCNFs）were modified by using different chemical methods.And the obtained nanoparticles were applied as the particles for the stabilization of W/W emulsion to slow down the phase separation.It could manipulate the complex microstructure of W/W emulsion and enrich the W/W emulsion resource.The main findings of this thesis were as follows:1.The regulation of the phase behavior of the aqueous two phases system composed of DEX and MAL.The phase diagram of DEX-MAL was obtained by using the matrix method to get the phase separation concentrations of the DEX and MAL.In the two phases region,the W/W emulsions were prepared by applying the shear force.The phase behavior of the W/W emulsion were regulated by changing the preparation parameters（emulsification method,stirring time,stirring speed,and the concentration of two-phase substance）.Meanwhile,the DEX phase in the emulsion was stanned by the fluorescein isothiocyanate-dextran（FITC-DEX）to observe the emulsion type.The results showed that the DEX and MAL were incompatible and the mixture underwent the phase separation after 1 d.The upper phase was rich in DEX and the lower phase was rich in MAL.The microstructure and phase separation phenomenon of the W/W emulsion was significantly depended on the polymer concentration.As the mass ratio（φ）of MAL and DEX increased from 1:2 to 4:1,the emulsion type was inverted from MAL in DEX to DEX in MAL and the unstable bi-continuous phase was found atφ=3/1.While the phase inversion did not happen with increasing the polymer concentration in the case of fixingφ.2.The W/W emulsion stabilized by the bacterial cellulose nanocrystalsThe bacterial cellulose nanocrystals（BCNCs）were prepared by using the acid hydrolysis（64%H₂SO₄）.The particles were used to stabilize W/W emulsion.The AFM tests showed that compared to BCNFs,the BCNCs possessed the smaller size.The FT-IR spectrum indicated that there was no change in the chemical components for BCNCs.The emulsion droplet was increased from 2.30±0.63μm to 4.01±0.59μm with increasing the MAL concentration.What was more,the droplets were decreased with increasing the DEX concentration and BCNCs content.The optimized emulsion was stable after 5 d of storege.,The contact angle test indicated that the BCNCs preferred to the continuous DEX phase compared with the MAL phase.Besides that,the tested emulsions possessed the shear-thinning property.The BCNCs particles could enhance the emulsion stability,but the emulsion droplet was easy to flocculation.In addition,the emulsion microstructure was sensitive to environmental factors（p H,Na Cl）.The droplet deformation was severe with increasing the Na Cl concentration in the range of 0-7 m M.Meanwhile,the emulsion droplet was increased and the droplet was deformed at p H 9.0 and 11.0.In short,the emulsion was more sensitive to the alkaline environment.3.The W/W emulsion stabilized by TEMPO-oxidized bacterial celluloseIn order to enhance the emulsion stability,the oxidized-nanofibers were prepared by the TEMPO oxidization and applied to prepare W/W emulsion.The results showed that the modified nanofibers remained the long fiber structure and the group of-COOH was more obvious as increasing the nanofibrils oxidation degree.What was more,the effect of oxidation degree and content of the oxidized-BCNFs on the emulsion structure and rheological properties was studied.It was found that the BCNFs oxidation degree had little effect on the emulsion microstructure.The emulsion droplet was decreased from 3.78±0.79μm to 2.01±0.40μm with the increase of the oxidized-BCNFs concentration.The W/W emulsion was stable after 7 d of storage.The concentration of oxidized-BCNFs required to stabilize the emulsion was less than that of BCNCs and the flocculation phenomenon of the emulsion droplet was not observed.In addition,the W/W emulsion structure was insensitive to environmental factors（p H and Na Cl）.Besides that,the emulsion viscosity,storage modulus and loss modulus were decreased with increasing the BCNFs oxidation degree,and were increased with increasing the oxidized-BCNFs concentration.The SEM and the contact angle test showed that the oxidized-BCNFs preferred to the continuous DEX phase.The oxidized-BCNFs could stabilize the MAL in DEX W/W emulsion by forming a network structure in the continuous phase,and the emulsion droplets were entangled by the oxidized-BCNFs.