Comparison of Interfacial and Foaming Properties of Soy and Whey Protein Isolates

A comparative study on the foaming properties and behavior at the air-water interface of soy and whey protein isolates were made, Foams were obtained by the method of gas bubbling. The initial rate of passage of liquid to the foam （vi） and the maximum volume of liquid incorporated to the foam （VLEmax） were determined. The destabilization process of the formed foams was analyzed by a biphasic second order equation. Measurements of equilibrium surface tension （water/air） and surface rheological properties were carried out in a dynamic drop tensiometer. The foaming capacity （vi and VLEmax） and the stability of foams prepared with the whey protein isolates （WPI） were better than those formulated with the soy protein isolates （SPI）. WPI foams were more stable showing the lower values of rate constants of gravity drainage and disproportion. There were significant differences （P 〈 0.05） in the dilatational modulus in the surface rheology measurements, which were higher at the interface with WPI, implying greater resistance of the film formed to collapse and disproportion. In conclusion, WPI formed better and more stable foams than the SPI.

Influence of particle size and ionic strength on the freeze-thaw stability of emulsions stabilized by whey protein isolate

The influence of particle size and ionic strength on the freeze-thaw(FT) stability of emulsions stabilized by whey protein isolate(WPI) was investigated in this study. The destabilization of emulsions during the FT process could be suppressed in a way by decreasing the particle size of the initial emulsions, which was the result of retarding the coalescence between oil droplets. To further improve the FT stability of emulsions, different amounts of Na Cl were added before emulsification. The emulsions with the ionic strength at 30–50 mmol/L exhibited good FT stability. Notably, the ionic strength in this range would not lower the freezing point of emulsions below the freezing temperature used in this study. Salt addition could improve the structural properties of proteins, which was available to strengthen the rigidity and thickness of interfacial layers, sequentially building up the resistance that the destruction of ice crystals to emulsions. Moreover, stronger flocculation between emulsion droplets could promote the formation of a gel-like network structure dominated by elasticity in the emulsion system, which might effectively inhibit the movement of droplets, and improve the FT stability of emulsions eventually. The result was of great significance for the preparation of emulsion-based foods with improved FT stability.

Interaction between whey protein isolate and rose anthocyanin extracts at different pHs:Structure,emulsification and digestibility of complexes

Whey protein isolate(WPI)was dietary protein with various functional properties and nutritional value,while anthocyanins were famous for their biological activities.This study aimed to investigate the effect of the interaction between WPI and rose anthocyanin extract(RAEs)at pH7.0 and pH9.0 on the structure,emulsification,and digestibility of WPI.The results showed that compared with the initial WPI,all WPI-RAEs complexes presented lower hydrophobicity and free SH content,higher absoluteζ-potential,thermal stability,and emulsification.In addition,the interaction of WPI and RAEs could reduce the digestibility of WPI.More importantly,WPI-RAEs complexes may be more effective emulsifiers than the original WPI,which was of great value to the dairy processing industry and food nutrition.

In vitro gastrointestinal model for the elderly: Effect of high hydrostatic pressure on protein structures and antioxidant activities of whey protein isolate

With the increase in global life expectancy,the research on the specific digestive patterns of the elderly is becoming highly essential.We simulated the digestion process of older individuals in vitro and investigated the effects of various high hydrostatic pressure(HHP)treatments on the protein structure,digestibility,and antioxidant activity of whey protein isolate(WPI),as well as the antioxidant peptides produced from its digest.The HHP treatment specifically affected on the secondary and tertiary protein structures along with the free sulfhydryl content of WPI.Protein microstructure revealed a significant increase in the number and depth of pores.Highest in vitro digestibility and cellular antioxidant activity was observed after HHP treatment at 600 MPa for 30 min.In the intestinal digest,15 antioxidant peptides were identified whose characteristics matched those of bioactive peptides.Of these,the LGSDMEDLR peptide sequence had the highest"-CDOCKER Energy"and formed the salt bridge,attractive charge,conventional hydrogen bond,carbon hydrogen bond,and van der Waals with Arg380,Arg415,Arg483,Tyr334 and Asn382,which all located in the binding site of the Keap1-Nrf2 interaction.Overall,HHP appeared to be a potential method for the application of dairy products among the elderly.

Glycation of whey protein isolate and stachyose modulates their in vitro digestibility: Promising prebiotics as functional ingredients

Glycated conjugates have recently been designed to be targeted to probiotic in the colon.However,the underlying mechanisms of regulating the prebiotic properties and digestibility of conjugates through glycation have not been fully elucidated.In this study,WPI-stachyose conjugates were prepared through Maillard reaction and proposed as functional ingredients with prebiotic characteristics.The effect of glycation on the in vitro simulated gastrointestinal fate of WPI-stachyose conjugate was further evaluated.The results showed that the glycated conjugates of stachyose covalently bound to whey protein exhibited a characteristic cross-linked structure,which enhanced their inhibition ofα-amylase activity and retardation of glucose dialysis.Besides,simulated digestion analysis demonstrated that stachyose-conjugated WPI was more resistant to pepsin and trypsin digestion than unconjugated WPI.Compared with native WPI,the protein digestibility and degree of hydrolysis of WPI-stachyose conjugates were reduced by 12.5%±0.66%and 5.30%±1.02%,respectively.In addition,rat intestinal extracts were used to detect the in vitro digestibility of stachyose.The hydrolysis rate of stachyose in the glycated conjugates was 70%lower than that of stachyose.Therefore,the resulting WPI-stachyose conjugate may be used as functional ingredients to achieve the sustained-release effect in the gastrointestinal tract.These findings demonstrate the possibility of modulating proteins and carbohydrates digestibility through glycation,and have implications for the design and manufacture of potential prebiotic molecules with controlled digestibility in food and related healthcare fields.

Combination of microwave heating and transglutaminase cross-linking enhances the stability of limonene emulsion carried by whey protein isolate

In this study,we examined the effect of transglutaminase(TG)cross-linking time(0 h,2 h,4 h,8 h,and 12 h)on the stability of limonene emulsion loaded by microwave-heated WPI(MWPI).Size exclusion chromatography results showed that molecular weight of TG-treated MWPI and WPI was enhanced with the increase in TG cross-linking time(0–12 h).Microwave and TG cross-linking decreased particle size(7.55%)and increasedζ-potential(5.33%)and protein adsorption(4.58%)of WPI emulsion at TG cross-linking time of 12 h.CLSM results showed smaller droplet size of MWPI-TG emulsion and its uniform size.The obtained limonene emulsion loaded by MWPI-TG at 12 h showed the lowest creaming index and the strongest oxidative stability under aerobic conditions after 10th days of storage.Thus,the combination of microwave heating and TG cross-linking effectively enhanced the stability of limonene emulsion stabilized by WPI and facilitating the application of WPI in the fields of food,medicine,cosmetics,and other areas.

Stability of β-carotene microcapsules with Maillard reaction products derived from whey protein isolate and galactose as coating materials

The stability of β-carotene microcapsules using Maillard reaction products（MRPs） derived from whey protein isolate（WPI） and galactose as coating materials, was studied under the varying environmental conditions of temperature, pH, air, incandescent light, and ultraviolet（UV） light.Scanning electron microscopy showed that microcapsules prepared by WPI-galactose MRPs displayed a smooth and less concave-convex surface and that the particle size（D_（50）） of the microcapsules made with WPI-galactose MRPs was smaller than those made with WPI-galactose mixture.The storage stability of β-carotene microencapsulated in WPI-galactose MRPs was remarkably better than that of β-carotene microencapsulated in the WPI-galactose mixture and that of β-carotene crystal, in respect of temperature, pH, air, incandescent light, and UV light measurements.When the storage temperature was increased from 5 to 105 ℃, the retention rate of β-carotene microcapsules significantly decreased（P〈0.05）.When p H values were increased from 1 to 12, the β-carotene retention rate of the microcapsules significantly increased and afterward decreased.Compared with the retention rate of β-carotene microencapsulated in a WPI-galactose mixture, the retention rate of β-carotene microencapsulated in WPI-galactose MRPs was at a maximum between pH 8 and 9.Under the actions of air, incandescent light, and UV light, the retention rates of β-carotene microcapsules in WPI-galactose MRPs and WPI-galactose mixture, as well as in β-carotene crystal, decreased significantly as the storage time increased（P〈0.05）.Therefore, the use of WPI-galactose MRPs as coating materials can aid in improving the storage stability of β-carotene microcapsules.

Gastrointestinal digestive fate of whey protein isolate coated liposomes loading astaxanthin:Lipolysis,release,and bioaccessibility

Whey protein isolate coated astaxanthin-loaded liposomes were prepared in this work.The gastrointestinal digestive fate of whey protein isolate coated astaxanthin-loaded liposomes was evaluated in terms of particle size,size distribution,zeta potential,and morphology during in vitro digestion as a function of time.Analysis on the particle size and morphology of whey protein isolate coated astaxanthin-loaded liposomes showed that the majority of particles maintained spherical shape with a progressive increase of particle size after passage through the digestion.The zeta potential on whey protein isolate coated astaxanthin-loaded liposomes became highly negative after digestion.As compared in uncoated liposomes,the astaxanthin release in whey protein isolate coated liposomes was slower in simulated gastric fluid digestion,while was faster in simulated intestinal fluid digestion.Through in vitro digestion,the bioaccessibility of astaxanthin was improved significantly after whey protein isolate coating.It was also found that the whey protein isolate coating could protect liposomes against destruction and suppress the lateral mobility of pyrene,resulting in lower micropolarity and fluidity of liposomal membrane during the digestion.These findings may guide the potential application of whey protein isolate coated liposomes for improving the bioaccessibility and stability of astaxanthin in nutraceuticals and pharmaceutics.

Physicochemical properties and antibacterial application of silver nanoparticles stabilized by whey protein isolate

Nano metal materials have been widely explored to be applied in medical,environmental,and material science.Among these nanoparticles,especially silver nanoparticles(AgNPs),have drawn increasing attention for antimicrobial applications.Most researchers are keen on the development of the biologically friendly capping reagents for the synthesis of AgNPs,instead of unfriendly organic polymers.In this study,the liquid chemical reduction method was used to synthesize AgNPs with edible whey protein isolate(WPI)as a capping reagent.These WPI-AgNPs had a broad size distribution(average diameter of 138.6 nm),and their dimensions could be readily controlled in the range of 22.5-149.6 nm by introducing different concentrations of chloride.Subsequently,it was confirmed that WPI-AgNPs were formed through two mechanisms,which were respectively reduced in situ(without the addition of NaCl)and ex situ(in presence of NaCl)to yield silver nanoparticles.The WPI-AgNPs synthesized in presence of 10 mM of NaCl as mediation reagent were stable at room temperature or 4℃ up to 3 months.Furthermore,the synthesized WPI-AgNPs had a good antibacterial activity toward pathogens including Gram-negative E.coli and Gram-positive S.aureus.The results shed light on method and capping reagent to stabilize silver nanoparticles,which highlighted the potential of WPI and chloride in metal nanoparticle synthesis.

Effect of small molecular surfactants on physical,turbidimetric,and rheological properties of Pickering nanoemulsions stabilized with whey protein isolate

In the present study,Pickering nanoemulsions(oil-in-water)co-stabilized with whey protein isolate(WPI)and three types of small molecular surfactants were prepared.Hexadecyltrimethylammonium(CTAB),sodium dodecyl sulfate(SDS),and Tween 20 were used as cationic,anionic,and nonionic surfactants,respectively.To investigate effects of small molecular surfactants on physical stability,turbidimetric,and rheological properties of protein-stabilized Pickering nanoemulsions,various treatments mimicking food processing including pH,heat,freeze-thaw,and salt were applied.Results revealed that the droplet size and polydispersity index of the nanoemulsion prepared with WPI alone were increased after heat treatment or at pH condition near the isoelectric point of WPI,indicating a low physical stability.However,nanoemulsions prepared with WPI-SDS or WPI-CTAB maintained their initial state even after heat treatment including autoclave.Furthermore,there was no significant change in the droplet size of the nanoemulsion prepared with WPI-Tween after freeze-thaw and salt treatments.Although Pickering nanoemulsion stabilized with both WPI and SDS had the highest viscosity,Turbiscan stability index(TSI)was the highest.However,the TSI of the nanoemulsions added with CTAB or Tween 20 was lower than that of the nanoemulsions prepared with WPI alone,confirming that the storage stability of protein-stabilized Pickering nanoemulsion was improved by adding small molecular surfactants.