Assemblying Behavior And Regulation Of Gliadin Nanoparticles On Air-Water Interface And Their Applications

Foam endows special structure,appearance,mouthfeel,and taste of food.It is the key point to take into consideration when it comes to the structural design of foam food.The micro/nano size colloidal particles could be adsorbed on the air/water interface and thus playing a role in regulating foam properties.Natural biopolymers have good biocompatibility,biodegradability,non-toxic and harmless properties,and have become the main substrate for preparing colloidal particles.Moreover,the natural biopolymer colloidal particles prepared by self-assembly get more and more attention as foaming agents because of their advantages such as safety,non-toxicity,simple preparation,and easy control.This study was based on the moderate hydrophobicity of gliadin.First,the morphology of gliadin dissolved in different solvents was studied,and the microstructure,surface behavior,and foam properties of gliadin nanoparticles(GNPs)prepared through dissolving in different solvents and different concentrations of gliadin alcohol solutions were investigated.Then,the adsorption and distribution of GNPs at the air/water interface were studied systematically.And the influence of external environmental conditions(p H and heating treatment)on the structure and foam properties of GNPs were discussed.Through the regulation of the microstructure and foam properties of GNPs by protein fibrils,the structure-activity relationship among microstructures-surface structures-foam properties was established.And typical foam food models were used to evaluate the actual application of GNPs.The main conclusions were as follows:1.Gliadin had been first extracted.The molecular weight of gliadin was mostly concentrated at 25-50 k Da,the content of non-polar amino acid was 29.9%,and the secondary structure of gliadin contained the most random coils.The SAXS and USAXS studies found that gliadin dissolved in 70%alcohol solution at low concentration(2mg/m L)was a rod-like structure.With increasing the concentration to 10 mg/m L,gliadin molecular morphology did not change significantly.However,as the concentration further increased to 20 mg/m L,the value of D_f was 2.87,indicating that gliadin aggregated to form an approximately spherical structure.The D_f value of gliadin dissolved in acetic acid solution(20 mg/m L)was 3.32,which also indicated that gliadin aggregated in acetic acid solution to form a spherical structure.GNPs could be prepared by solvent evaporation method and anti-solvent method,but the particles prepared by anti-solvent method were more uniform,stable,and controllable than that of solvent evaporation method.The nanoparticles prepared by dissolving gliadin in 70%alcohol solution had better foam properties than that of dissolving in acetic acid solution(the foamability was about 2.5 times).2.Edible gliadin nanoparticles were fabricated using simple and green anti-solvent method.They possessed unique high foamability and foam stability.An increasing concentration of GNPs accelerated their initial adsorption speed from the bulk phase to the interface and raised the viscoelastic modulus of interfacial films.High foamability(174.2±6.4%)and foam stability(75.5±2.03%)was achieved at the very low concentration of GNPs(1 mg/m L),which was much better than that of ovalbumin and sodium caseinate.Three stages of adsorption kinetics at the air/water interface were characterized.First,they quickly diffused and adsorbed at the interface,resulting in a fast increase of the surface pressure.Then,nanoparticles started to interact and fuse into a film,and finally,the smooth film became a firm and rigid layer to protect bubbles against coalescence and disproportionation.These results explained that GNPs had good foamability and high foam stability simultaneously.That provides GNPs as a potential candidate for new foaming agents applied in edible and biodegradable products.3.Foaming behavior strongly depends on the structural characteristics of protein nanoparticles.These characteristics may be modified by means of changes in p H value or temperature.In this paper,the foaming and surface properties of GNPs treated by different p H values(3.0-5.8)and heat temperatures(25-70°C)were investigated.First,decreasing of the p H value(from 5.8 to 3.0)is a process that p Hs stay away from isoelectric point(p I?6.5)of gliadin.Accordingly,zeta potential of GNPs rose from+16.3to+22.0 m V with decreasing the p H from 5.8 to 3.0.But the particle size of GNPs decreased slightly.Meanwhile,the foamability(FA)and foam stability(FS)of GNPs significantly decreased,evidenced by the slow initial adsorption rate and low viscoelastic modulus at the air/water interface.Heating induced a growth of GNPs particle size,however,the zeta potential remained unchanged.The FA and FS of GNPs after heat treated at different temperature values(25-70°C)kept at the high values and the bubble size maintained the same level.To compare the effect of p H and temperature on GNPs surface behavior,our results found that the zeta potential played leading role on the adsorption rate of GNPs onto the air/water interface instead of particle size and morphology.Besides,for the foaming properties of GNPs,sensitivity of p H and non-sensitivity of heating give an instructor for further applications.4.?-Lactoglobulin fibrils could serve as a surface-active component and form adsorption layers at the air/water interface.In this study,the physical parameters,foam and surface properties of?-lactoglobulin fibrils treated by different p H values(2-8)were first investigated.Then,?-lactoglobulin fibrils added into the GNPs system to further study the effect of p H on the structure and foam properties of GNPs-?-lactoglobulin fibril complexes.Results showed that an increase of p H(?-lactoglobulin fibrils)from 2 to 5 led to a rise of the viscoelastic modulus of the surface adsorption layer and half-life time(t_1/2)of foams,but it decreased foamability.When the p H was close to its isoelectric point(5.2),fibrils had the lowest electrostatic repulsion and entangled at the air/water interface resulting in a tightly packaged adsorption layer around bubbles to prevent coalescence and disproportionation.When the p H(7-8)of?-lactoglobulin fibrils was higher than the p I of fibrils,the negatively charged?-lactoglobulin fibrils possessed good foamability(?80%)and high foam stability(t_1/2?8 h)simultaneously even at low concentration(1mg/m L).It first demonstrated that?-lactoglobulin fibrils with negative charges presented a good foaming behavior.The?-Lactoglobulin fibrils were introduced into the GNPs system and it was found that GNPs-?-lactoglobulin fibril complexes had different microgel structures at different p Hs.The surface charge of complexes was closer to 0,the pores of the microgels were smaller.The addition of?-lactoglobulin fibrils to GNPs could significantly increase the foamability.The surface structure of foams stabilized by GNPs-?-lactoglobulin fibril complexes was compact at p H 5.0,and result found that?-lactoglobulin fibrils could inhibit the fusion rate of GNPs at the air/water interface.The GNPs-?-lactoglobulin fibril complexes had excellent foamability and high foam stability,and could be a potential new foaming agent in the food industry.5.GNPs possessed unique high foamability and foam stability.Applications in baked food and foam beverages of GNPs were studied.In the application of replacing egg white as a foaming agent of cake,results found that the foamability of samples was gradually increased as rising GNPs proportion.At a concentration of 10 mg/m L,100 g GNPs produced 755±44 m L of foam,significantly better than that of egg white(100 g egg white produced 525±35 m L of foam).Compared with 100%egg white,the added ratio(0-50%)of GNPs did not affect the appearance,color,and internal structure of cake.That provides GNPs as a foaming agent for replacing at least 50%of egg white in the actual production of cakes.This study successfully loaded citral inside GNPs and the loading capacity of GNPs for citral up to 28.6±0.1%.Results showed that Cit-GNPs(ratio of 1:0.01)not only had better foam properties,but also had a special lemon flavor.Cit-GNPs not only significantly improved the foaming properties of dark beer,but also imparted a special flavor to the dark beer.