Study On The Construction Of Emulsion-based Food Colloid For Protecting Probiotics In Colon-controlled Release

Dairy and fermented foods are the main vectors of probiotics and consider as ready-to-eat healthy foods for many years.Probiotic viability in food products is passively influenced by various factors,such as the environmental situations in food processing(oxygen levels,temperature,and water activity)or those in the gastrointestinal tract(pH,pepsin,pancreatin,and bile salts).A popular method(spray drying,freeze drying,extrusion,and emulsification)is the construction of probiotics in deliver capsules that can preserve them via the gastrointestinal tract and ultimately release them in the colon.In this paper,a redox initiation system is used to prepare protein-polyphenol complexes through free radical induced reactions,and they are used as emulsifiers to prepare high internal phase emulsions,W₁/O/W₂ double emulsions,multilayer emulsions,and double network emulsion gels.The main research is as follows:(1)The structural properties of whey protein isolate(WPI)and(-)-epigallocatechin-3-gallate(EGCG)complexes by free-radical induction reaction were studied in the pH range of 3-11.More nucleophilic acid groups in WPI were participated in the reaction at pH 9.However,the WPI denaturation under extreme pH values limited the exposure of their active groups,which led to the decrease of the graft amount of EGCG.The CD analyses showed that the secondary structure of WPI were destructed to some extent at all pH values.It can be seen from ¹H NMR spectroscopy,EGCG are easily oxidized to form o-quinones at pH?7,and they further react with nucleophilic groups on the WPI to form complexes.At pH<7,the complexes were formed between carbocation of EGCG and nucleophilic groups of WPI.The WPI-EGCG complexes formed at pH 9 had better digestive enzyme inhibition effect in the digestion fate.(2)In this study,Pickering HIPEs stabilized with the WPI-EGCG complex nanoparticles were used to encapsulate probiotics.The WPI-EGCG complexes formed at pH 9 had smaller particle size and better wettability.Then,the WPI-EGCG-pH 9 complexes were used to stabilize the O/W type Pickering emulsion.The?addition led to an increase in the droplet size and modulus of Pickering emulsions toward to generate gel-like structure.On the other hand,at a constant?value,the droplet size of these Pickering HIPEs reduced with increasing c from 0.5 to 5%,indicating that high particle concentration can stabilize more oil droplets.Encapsulation of Lactobacillus Plantarum powder with the Pickering HIPEs was successful to enhance the viable cell count after 14 days storage and GIT digestion.The protective effect of Pickering emulsions was improved with the addition of the c and/or?value.(3)In this study,WPI-EGCG complexes/gellan gum double network emulsion gels by duo-induction of GDL and Ca Cl₂ were used to encapsulate probiotic powders.Firstly,we fabricated the signal GDL-induced emulsion gels based on the WPI-EGCG complexes stabilized Pickering emulsion.GDL acidification promoted the cross-linking of WPI-EGCG complex particles or particle-coated oil droplets via disulfide bonds formation,which improved the mechanical properties and stability of the signal GDL-induced emulsion gels,such as gel strength,WHC,G?value,storage stability,and temperature stability.Subsequently,we employed a novel one-step continuous cold gelation strategy to product double network emulsion gels.In this double network emulsion gel system,the gellan gum in continuous phase was first induced by Ca Cl₂ to form a gel in a short time.Besides,the GDL(weak acid)was improved covalent cross-linking between WPI-EGCG complex particles or particle-coated oil droplets because of the slowly pH reduction.The first cross-linked gellan gum gels could be more closely integrated into the GDL-induced second gel networks with synergistic role,which promoted the formation of compact and homogeneous networks through hydrophobic interactions and disulfide bonds.In addition,the oil droplets served as active fillers in fabrication of the double network emulsion gels.The double network emulsion gels supplies a colon-controlled delivery carrier for the Lactobacillus Plantarum powders encapsulation into internal oil phase.(4)In this study,W₁/O/W₂ double emulsion stabilized with the WPI-EGCG complex nanoparticles with alginate-Ca-EDTA system were used to encapsulate probiotic strain liquid.W₁/O/W₂ double emulsion illustrated that the compartmented nature consisted of surfaced WPI-EGCG complex nanoparticles and dispersed oil droplets with smaller water droplets.Then,the rheological properties of alginate-Ca-EDTA system in the external aqueous phase of the W₁/O/W₂ double emulsions as the pH changes were investigated.The W₁/O/W₂ double emulsion maintained in the hydrogel state at pH below 4.0 because of Ca²⁺coupled with G residues of alginate.In contrast,the W₁/O/W₂ double emulsion transformed to solution state at neutral pH condition,which caused the dissociation of Ca²⁺from the Ca-alginate hydrogel and resulted in Ca-EDTA chelation.A pH-sensitive carrier based on an alginate-Ca-EDTA system in a set-type W₁/O/W₂ double emulsion model was exploited by regulating the release of Ca²⁺.Based on the pH-sensitive alginate-Ca-EDTA system and middle oil phase resistance,such a double emulsion supplied a colon-targeted release carrier for the Lactobacillus Plantarum strain liquid encapsulation into inner aqueous phase with the functional protection effect.(5)In this study,chitosan and alginate layer by layer self-assembly microcapsule with WPI-EGCG complexes stabilized Pickering double emulsion templates were used to encapsulate probiotic strain liquid.Firstly,we fabricated the W₁/O/W₂ double emulsion by ultrasonic homogenization.The double emulsion formed by ultrasonic treatment at 285 W had a single and narrow distribution with smallest droplet size.The double emulsion particles were then coated with Alg,Chi,and Ca.The formation of multilayer emulsions was quantitatively proved by?-potentials,morphology,and FTIR measurements.The viability of encapsulated Lactobacillus Plantarum after pasteurization/GIT digestion increased with the increasing coating layers.However,the Lactobacillus Plantarum encapsulated in multilayer emulsions was more sensitive to heating treatment than gastrointestinal passage.It could be noted that the deposition of 3 coating layers was the minimum and most available formulation for the Lactobacillus Plantarum encapsulation after pasteurization/GIT digestion.