Preparation And Application Of Starch-based Complex Colloidal Particles On Pickering Emulsions

With the increasing attention for the development of Pickering emulsions,it has become a new trend to develop food grade emulsifiers with green and safe properties.In this research,chitosan hydrochloride-carboxymethyl starch（CHC-CMS）complex colloidal particles were constructed through the formation of amide linkages between the existing amino groups of CHC and the carboxyl group of CMS using1-ethyl-3-（3-dimethyl-aminopropyl-1-carbodiimide）（EDC）as cross-linker The Pickering emulsions were prepared by CHC-CMS nanogels,and its protection and delivery properties ofβ-carotene were investigated.Furthermore,the Pickering emulsions were applied to prepared starch-based Pickering emulsion gels.This study not only enriched the types of granular emulsifiers,but also provided new ideas and methods for the design of low-fat foods.The CHC-CMS nanogels were prepared by covalent cross-linking method.Results showed that the optimal conditions for the formation of complex particles were:pH 4 and 2:1 volume ratio（CHC:CMS）.The average size of CHC-CMS nanogels was 378.2 nm,and the potential was 40.23 mv.Transmission electron microscopy（TEM）displayed that CHC-CMS nanogels had the spherical structure.Fourier transform infrared spectroscopy（FT-IR）confirmed that the amide linkage was formed between CHC and CMS.X-ray diffraction（XRD）data exhibited that the crystalline structure of CHC was destroyed after covalent cross-linking with CMS,which further confirmed that the CHC-CMS nanogels were formed.Besides,the nanogels behaved as viscoelastic solids over the entire frequency range.Meanwhile,the nanogels showed excellent pH-sensitivity.The O/W Pickering emulsions were prepared using CHC-CMS nanogels by high shearing.The three-phase contract angle of CHC-CMS nanogels was 89.3°.The effects of CHC-CMS nanogels concentration,oil phase volume fraction（φ）and environment factors on the stability of Pickering emulsions were evaluated.Results showed that with the increasing concentration of CHC-CMS nanogels from 0.1 wt%to 1.5 wt%,the droplet size of Pickering emulsions decreased from 42.03±0.86μm to7.35±0.16μm.However,with the oil phase volume fraction ranging from 0.1 to0.7,the droplet size of Pickering emulsions increased from 4.43±0.31μm to 17.19±0.87μm.The Pickering emulsions were highly stable at pH 6 and above.When the Na Cl concentration was up to 0.4 M,aggregation of droplets occurred in the Pickering emulsion.Confocal laser scanning microscopy（CLSM）revealed that the CHC-CMS nanogels could be adsorbed on the oil-water interface and formed a densely packed layer at the surface of spherical oil droplets.The Pickeirng emulsions（φ0.5,1.5 wt%）exhibited long-term stability for 3 months storage.Rheological results illustrated that all emulsions showed the typical pseudoplastic fluid characteristics and conformed to the Herschel-Bulkley model.And the storage modulus（G’）was higher than the loss modulus（G″）in Pickering emulsions,which indicating the formation of an elastic gel-like structure.Based on the encapsulating characteristics of Pickering emulsions to bioactive ingredients,the protection and delivery of Pickering emulsions toβ-carotene were explored.Results displayed that the retention ofβ-carotene in Pickering emulsions was higher than that in Tween 80 stabilized emulsions（TEs）and bulk oil during ultraviolet radiation and storage.The size and morphology of Pickering emulsions did not change significantly after thermal treatment.Meanwhile,lipid hydroperoxide（<180.96 mmol/kg oil）and malondialdehyde（<20.64μmol/kg oil）of Pickering emulsions were lower than that of TEs and bulk oil after storage for 15 days.The vitro digestion results suggested that the released free fatty acids（FFA）were below 30%for all Pickering emulsions,which indicated that a physical barrier was formed by CHC-CMS nanogels to restrain the lipid hydrolysis.The bioaccessibility ofβ-carotene in Pickering emulsions（>13.98%）was higher than that of bulk oil（6.01%）.In this study,the Pickering emulsion gels were further prepared based on the low digestibility of Pickering emulsions.Results exhibited that the concentration of curdlan and the volume ratio of Pickering emulsions to curdlan had effects on the hardness,elasticity,water holding capacity（WHC）,swelling degree and rheological properties of emulsion gels.When the concentration of curdlan increased,the hardness and WHC of emulsion gel increased,while the elasticity and swelling degree decreased.However,emulsion gels characteristics mostly showed the opposite trend when the volume ratio of Pickering emulsions to curdlan increased.Degradation behavior ofβ-carotene conformed to a first-order kinetic model,and half-life time(t_1/2)ofβ-carotene increased from 19 days to 30 days with the increasing concentration of curdlan.The vitro digestion results showed that the release of FFA in Pickering emulsions（φ0.1）decreased from 28.81%to 18.66%compared to that in Pickering emulsion gels（φ0.1,3 wt%）,indicating that Pickering emulsion gels might be used for lipid substitutes.