| Starches from rice,waxy corn,wheat and potato were used to prepare hydrophobic starch particles by octenyl succinic anhydride(OSA)modification.The oil/water(O/W)Pickering emulsions were prepared using different kinds of hydrophobic starch particles.The effects of different starch particles on the stability of emulsions were compared by optical microscope,laser particle size analyzer and rheometer,etc.A better hydrophobic starch particle was selected to study the influence of different temperature on the stability of O/W Pickering emulsions.Physical stability and oxidative stability of O/W Pickering emulsion obtained using hydrophobic starch particles and small molecular surfactants as stabilizers were also studied.The study is important for the design of new functional starch based particle stabilizers,which can be used in the food and related industries.The main research contents and conclusions were as follows:(1)Starch from rice,waxy corn,wheat and potato were used to prepare hydrophobic starch particles by octenyl succinic anhydride(OSA)modification.The O/W Pickering emulsion was constructed by using hydrophobic starch particles as emulsifier and sunflower oil / water system as the research model.The microscopic structures of the emulsions were observed using optical microscope,and the rheological behaviors of the emulsions were also determined by means of rheometer.Different types of hydrophobic starch particles on the stability of emulsions were studied.The results showed that the Pickering emulsion with hydrophobic modified rice starch had the largest cream volume,uniform droplet size distribution,and the best emulsion stability.The emulsion stabilized with potato starch particles separated more oil,so the stability was the worst.Within the storage duration of 14 d,the droplet size increased,and then stabilized.The starch particles adsorbed on the oil / water interface and wrapped in oil droplets,which can reduce the droplet migration rate in emulsion systems by the steric hindrance,electrostatic interaction and the formation of hydrogel structure,to prevent flocculation.The Pickering emulsion with rice starch had the smallest emulsion droplet size,and the Pickering emulsion with potato starch had the largest and heterogeneous emulsion droplet size.Shear experiments showed that viscosity decreased with the increase of shear rate,which characterized by shear thinning behavior.The fluid index was less than 1,so the Pickering emulsion stabilized by starch particles was a typical pseudoplastic fluid.The viscosity of rice starch was the largest,and that of potato starch was the lowest.Dynamic viscoelasticity experiments showed that the emulsion with potato starch had the highest emulsion elastic modulus and tangent,it might be due to the larger size of potato starch particles.The Pickering emulsion stabilized by hydrophobic starch particles had typical gel rheological behavior.Under a certain external force,the interaction between droplets in emulsion liquid system increased with the stronger ability of resist deformation.(2)Considering the factors such as hydrophobic starch particles size,droplet size,emulsion volume and microstructure,hydrophobic rice starch was used as particle emulsifier to prepare Pickering emulsion.The effects of different temperatures(25℃,30℃,40℃,50℃ and 60℃)on the stability of emulsions were researched.Results showed that the cream volumes and the stability of starch particle were better at 50℃ and 60℃.The cream volumes gradually decreased with the storage time increased from 0.5h to 5.0h at the temperatures of 25℃,30℃ and 40℃.The starch particles in emulsion were coated with oil drops at 25℃,30℃,40℃ and 50℃,but some starch particles were gelatinized at 60℃.Partial starch in Pickering emulsion pasted at 60℃.The gelatinization temperature of starch decreased after hydrophobic modification.The emulsion droplet size of the emulsion firstly increased and then stabilized with the storage time increased from 0.5h to 5.0h.(3)According to the previous research,we selected hydrophobic rice starch as particle emulsifier.The physical stability and oxidative stability of Pickering emulsion were studied when rice starch particles were combined with small molecule surfactants.The O/W Pickering emulsions were prepared by 2% hydrophobic starch particles,2% SDS,2% CTAB,2% Tween 20,1% hydrophobic starch +1% SDS,1% hydrophobic starch +1% CTAB,1% hydrophobic starch +1% Tween 20 were studied,respectively.Emulsions were characterized for their physical stabilities by droplet size distribution and droplet microstructure which measured by laser particle size analyzer and optical microscope.The oxidative stability of the emulsions were also investigated by means of Rancimat.The results showed that the cream volume had significantly different.For example,1% hydrophobic starch and 1% SDS cream phase volume was 17.1 m L,and 1% hydrophobic starch and 1% CTAB was 15.8 m L.However,the droplet size distributions of the emulsions with particle-surfactant decreased greatly compared to those only with starch particles(P<0.05).The average particle size of emulsion with 2% hydrophobic starch was 118-128μm,and the average particle size of emulsion with 1% hydrophobic starch and 1% SDS was 0.9-9.9 μm.Microstructures of the emulsions showed that small molecular surfactants and starch particles around of the oil droplets.Rancimat results revealed that the induction periods of the emulsion stabilized by starch particles and particle-surfactants were longer than those of the emulsions stabilized only by small molecular surfactants.The emulsion stabilized by 1 % hydrophobic starch and 1 % SDS had the longest induction period of 13.83 h.All the results showed that the starch based particle emulsifier were compatible with small molecular surfactants and could be used to enhance the stabilities of the emulsions.Moreover they could decrease the oxidation rate of O/W Pickering emulsions. |
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