Interface Modification Of Cinnamaldehyde On Whey Protein Isolate Stabilized Emulsion Matrix

Protein-stabilized emulsions are a kind of common and important food matrix.They can be liquid or gel systems.Proteins are sensitive to environmental conditions(temperature,pH,and ionic strength),which can cause instability in protein-stabilized emulsion and reduce food quality.Coacervate and aggregation are the main reasons to destabilize the emulsion systems.The stability of emulsion systems could be improved by modulating the properties of protein interfacial layer(viscoelasticity,layer thickness).Modifications of emulsifier,interfacial layer and emulsion structure are commonly utilized.Based on the literatures,whey protein isolate was used as the emulsifier.Cinnamaldehyde was introduced in the oil phase.Schiff base reaction between cinnamaldehyde and whey protein isolate was used to achieve the interfacial modification of the emulsion.The physical and chemical stability of the modified emulsion,the hydrolysis process of the lipid,and the stability mechanism of the emulsion were investigated.Then the influence of the interface modification on the properties of the gel-like emulsion system was investigated.The main findings are as follows:1.Effect of cinnamaldehyde(CA)on physical stability and lipid hydrolysis properties of micron-sized whey protein isolate-stabilized emulsions was investigated.When cinnamaldehyde was present in the oil phase(medium-chain glycerides,MCT),the color of the whey protein isolate emulsion changed from milky white to light yellow or yellow.The yellowish color darkened during storage.After adding cinnamaldehyde,the particle size of the emulsion decreased,and the initial particle sizes of the MCT,MCT/CA,and CA emulsions were around 9 ?m,7 ?m,and 6 ?m,respectively.Due to Ostwald ripening,the particle size of pure cinnamaldehyde emulsion increased during storage,and phase separation occurred.The stability of MCT/CA-pH3.0 emulsion was the best.The results of Optical microscopy showed that cinnamaldehyde promoted the adsorption of whey protein isolate at the oil-water interface.In vitro gastrointestinal digestion experiments demonstrated that the MCT/CA-pH7.0 emulsion had the highest digestion rate,and the lipolysis degree reached 93.4 ± 0.1%.2.Effect of cinnamaldehyde on the preparation and environmental stability of whey protein isolate-stabilized nanoemulsion was studied.The preparation parameters of nanoemulsion were optimized as: 5 wt% total oil phase,1 wt% protein,mass ratio of MCT and CA as 7:3.The pH,ionic strength and temperature were used to evaluate The stability of the nanoemulsion against pH,ionic strength and temperature was evaluated.The results showed that the modified whey protein isolate emulsion has better tolerance to ionic strength and heat treatment.When the NaCl concentration was increased from 0 mM to 500 mM,the particle size of the unmodified whey isolate protein emulsion increased to ~1000 nm,while the particle size of the modified emulsion particles remained stable.The modified whey protein isolate emulsion remained stable after heat treatment at 85°C without and with 100 mM NaCl.SDS-PAGE and interfacial adsorption experiments showed that the interaction between cinnamaldehyde and protein promoted the adsorption of whey protein isolate by 4%.3.Effect of cinnamaldehyde on the physicochemical properties of gel-like whey protein isolate emulsion was studied.Adsorption of free protein by cinnamaldehyde promoted the reduction of the protein in the aqueous phase and reduces the strength of the calcium-induced protein emulsion gel.Micrographs show that the gel structure changed from massive to granular.Heat treatment increased the impact of cinnamaldehyde on gel strength.Fluorescence microscopy and SEM results showed that the addition of cinnamaldehyde and heat treatment(85 ?)promoted the formation of a more compact and uniform gel network structure.The microrheological results showed that t cinnamaldehyde addition and heat treatment increased the viscoelasticity of emulion gel.The results of in vitro digestion experiments showed that the viscoelastic emulsion gel effectively inhibited the particle aggregation in the oral digestion process.