| Liquid vegetable oil is limited in food applications due to its easy oxidation and deterioration,storage and transportation difficulties,etc.During the daily processing,solid edible fat is often obtained from vegetable oil after hydrogenation and is widely used in food industry,such as margarine,butter,ice cream,shortening and other processed products.However,such plastic-fat processed foods usually contain a large amount of trans-fatty acids.Long-term or excessive intake will increase the risk of cardiovascular and cerebrovascular diseases or obesity.Therefore,it is of great significance to explore how to directly solidify liquid vegetable oil to avoid the use of trans-fatty acids.The traditional method is to emulsify and solidify the liquid vegetable oil by adding a surfactant,but there are problems such as a large amount of surfactants,a high cost,and a large side effect on the organism.Pickering emulsion solidification of liquid vegetable oil requires only a few parts per thousand particles,whose cost is rather low and has superior anti-coalesence stability.Besides it meets the commercial requirements of green food labeling and has become a research hotspot in recent years.Gelatin and starch have been widely used in food,medicine and other fields due to their excellent biocompatibility,biodegradability,wide source and low cytotoxicity.Based on this,the Pickering emulsion with enhanced stability was prepared by the Schiff’s base reaction between Gelatin nanoparticles(GNPs)and dialdehyde starch nanoparticles(DASNPs)in this paper,which realized the purpose of directly structuring liquid vegetable oil.The results show that GNPs and DASNPs have undergone Schiff’s base reaction on the surface of Pickering emulsion droplets and the interface among the droplets,which could effectively improve the stability of Pickering emulsion,and it has good encapsulation and solidification capabilities for liquid oil.It can still maintain good stability after 6 months of storage.In addition,the dense interface layer formed by Pickering emulsion can preventβ-carotene from diffusing out of the internal phase,indicating that it has the potential to encapsulate and store active nutrients.In summary,Pickering emulsion stabilized by GNPs and DASNPs is a good strategy of liquid oil solidification and can be used as a substitute for hydrogenated vegetable oil.Meanwhile Pickering emulsion is used to encapsulateβ-carotene for release study,which provided a new idea for the delivery of nutrients.Pickering emulsion prepared by this method is expected to be a potential drug carrier.The three main parts of this thesis are as described below:1.Preparation and characterization of gelatin nanoparticles(GNPs):gelatin nanoparticles(GNPs)with small particle size and uniform distribution were prepared by desolvation of acetone under alkaline conditions using type B gelatin as raw material.Genipin of natural plant origin has been used as a crosslinking agent.The morphology and structure of GNPs were characterized by scanning electron microscope,atomic force microscope,and infrared spectroscopic analysis,showing a spherical shape with a smooth surface.The particle size was 163.3±1.0 nm,PDI was 0.039,the potential was-42.8 m V,and the three-phase contact angle was 76.6°.The nanoparticles prepared in the experiment in this section showed good performance and can be used for the preparation of Pickering emulsion.2.Preparation and characterization of dialdehyde starch nanoparticles(DASNPs):dialdehyde starch(DAS)was obtained by specific oxidation of sodium periodate under acidic condition using corn starch as raw material.The oxidation degree of aldehyde group measured by hydroxylamine hydrochloride titration was40.15±0.80%.Cholesterol was grafted onto dialdehyde starch molecular chain to obtain dialdehyde starch nanoparticles(DASNPs)by self-assembly method.The amount of cholesterol added would directly affect the morphology and structure of the nanoparticles.Scanning electron microscope and transmission electron microscope results showed that when the grafting amount of cholesterol was 20%,the prepared nanoparticles were spherical and uniform in size.Infrared spectroscopy analysis also showed that starch was successfully modified by cholesterol.The particle size was 178.8±1.3 nm,PDI was 0.213,the potential was-31.1 m V,and the three-phase contact angle was 64.0 ~o.Various characterization results had indicated that cholesterol could successfully modify starch,and reduced its hydrophilicity and self-assemble nanoparticles.3.Preparation and characterization of GNPs-DASNPs co-stabilized Pickering emulsion:using nanoparticle’s concentration,emulsification time,rotation speed,pH of continuous phase and salt concentration as single variables,the optimal conditions for preparing Pickering emulsion were explored as follows:concentration was 2.0%,emulsification time was 90 s,and rotation speed set as 13000 rpm,pH of continuous phase was 8.0.Synergistically stable Pickering emulsions were prepared according to a certain volume ratio of GNPs and DASNPs.A simple water dispersion method was used to identify Pickering as typical O/W emulsion.The microscopic structure of droplets inside the emulsion was characterized by optical microscopes and fluorescence microscopes.The analysis showed that the cross-linking reaction of gelatin nanoparticles and dialdehyde starch nanoparticles not only occurred on the surface of the droplets but also among the droplets.It was feasible to construct a novel Pickering emulsion with enhanced stability to realize the encapsulation of liquid edible oil through Schiff’s base reaction between the aldehyde group of the dialdehyde of starch molecule and the amino group of the gelatin molecule.The rheological results also confirmed that the gel state of Pickering emulsion could maintain its three-dimensional network structure.Pickering emulsions after 6 months of storage could still maintain high stability,and the droplet diameter inside the emulsion just had a minor change.β-carotene was encapsulated in Pickering emulsion for an in vitro release study,the results showed that the cumulative release of Pickering stabilized by single nanoparticle was up to 40%,while the cumulative release rate of Pickering emulsion stabilized by GNPs and DASNPs was only about 8%,indicating that the stable Pickering emulsions with GNPs and DASNPs could successfully coat nutritional functional biologically active molecules and to facilitate their transportation,storage and application. |
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