Thermal aggregation properties of whey protein glycated with various saccharides

Improved Physicochemical Properties of Curcumin-Loaded Solid Lipid Nanoparticles Stabilized by Sodium Caseinate-Lactose Maillard Conjugate

To improve the water solubility, antioxidant activity, and chemical stability of curcumin, solid lipid nanoparticles (SLNs) were fabricated using equal masses of propylene glycol monopalmitate and glyceryl monostearate as the lipid matrix and sodium caseinate-lactose (NaCas-Lac) Maillard conjugate as the emulsifier. The entrapment efficiency was more than 90% when curcumin was 2.5% and 5.0% of lipid mass, and the SLNs were stable during 30-day storage. SLNs stabilized by NaCas-Lac showed better physicochemical properties than those prepared with NaCas, including higher sphericity and homogeneity; higher entrapment efficiency; better stability against pH, ionic strength, and simulated gastrointestinal digestions; and more controlled release. SLNs also greatly enhanced the antioxidant activity of encapsulated curcumin and the retention of curcumin during storage. Therefore, the present SLNs may find applications to deliver lipophilic compounds in functional foods and beverages.

Obtaining glycoconjugates of marine origin via Maillard reaction and their cytotoxic effect: an alternative for the use of animal byproducts

BACKGROUND

Protein glycation by Maillard reaction is commonly used to improve the functional and bioactive properties of food proteins. It is also known that this glycation method can be accelerated by heat without the need for chemical reagents that could be harmful to health. In this study, glycoconjugates were obtained from a mixture of connective tissue proteins (CTP) from jumbo squid (Dosidicus gigas) and two different sugars, dextran (DEX; 10 kDa) and glucose (GLU), using protein-to-carbohydrate ratios of 1:2 and 1:3, in solution at 50 °C for 6 h. The glycation products were characterized by means of their physicochemical properties and cytotoxic effect.

RESULTS

The intensity of the browning measured at A_420nm and A_294nm in glycoconjugates showed no significant difference (P < 0.05). CTP-DEX (1:2) and CTP-DEX (1:3) were those products with the greatest fluorescence related to the intermediate stage in the Maillard reaction, and also with the highest degree of glycation, which was confirmed using o-phthaldialdehyde assay and Fourier transform infrared analysis. The values of cellular viability for CTP-GLU (1:3), CTP-DEX (1:2, 1:3) as well as CTP (0, 6 h) were around 92-103%.

CONCLUSIONS

The operational parameters used in the glycation process achieved the formation of glycoconjugates from proteins of D. gigas, showing no cytotoxic effect on the HaCaT cell line. This research proposes an alternative for the modification of proteins and opens the way to future investigations regarding the bioactivity of these macromolecules to have applications for the use of byproducts in food science and technology. © 2020 Society of Chemical Industry.

Influence of ultrasound pretreatment on the subsequent glycation of dietary proteins

The influence of ultrasound treatment on the subsequent glycation process of proteins is controversial. Glycation behaviors of bovine serum albumin (BSA), β-lactoglobulin (β-Lg) and β-casein (β-CN) after ultrasound pretreatment (UP) were compared by both evaluating glycation kinetics and analyzing structural changes of proteins. UP resulted in both unfolding and aggregation behavior in protein samples, which altered the accessibility of the Lys and Arg. Five cycles of UP up-regulated the glycation degree of BSA and β-Lg, possibly due to the unfolding behavior induced by UP, which exposed additional glycation sites. In contrast, 30 cycles of UP induced a dramatic increase (by 97.9 nm) in particle size of BSA, thus burying portions of glycation sites and suppressing the glycation process. Notably, UP had minimal influence on glycation kinetics of β-CN, due to its intrinsic disordered structure. Based on proteomics analysis, the preference of Lys and Arg during glycation was found to be changed by UP in BSA and β-Lg. Four, 3 and 3 unique carboxyethylated lysine residues were identified in glycated BSA after 0, 5 and 30 cycles of UP, respectively. This study suggests that the protein glycation can be affected by UP, depending on the ultrasonication duration and native structure of the protein.

Gum Arabic-Mediated Synthesis of Glyco-pea Protein Hydrolysate via Maillard Reaction Improves Solubility, Flavor Profile, and Functionality of Plant Protein

Pea protein hydrolysate (PPH) is successfully conjugated with gum arabic (GA) through Maillard-driven chemistry. The effect of cross-linking conjugation on the structure, solubility, volatile substances, emulsification, and antioxidative activity of glyco-PPH is investigated, and found to improve all properties. The formation of glyco-PPH is confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), Fourier-transform infrared (FTIR), and scanning electron microscopy (SEM). Size exclusion chromatography-multi angle light scattering (SEC-MALS) unveils that the maximum molecular mass of glyco-PPH occurs after 1 day of conjugation and approximately 1.2 mol of gum arabic conjugates on one mole of PPH. Headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS) reveals the odor changes of glycoprotein before and after cross-linking. We have also prepared oil-in-water emulsions using glyco-PPH, which have enhanced physical stability against pH changes and chemical stability against lipid oxidation. The mechanism proposed involves Maillard-driven synthesis of the cross-linked PPH-GA conjugates, which increase the surface hydrophilicity and steric hindrance of glyco-PPH. These findings could provide a rational foundation for tailoring the physicochemical properties and functionalities of plant-based protein, which are attractive for food and functional materials applications.

Maillard-Reacted Whey Protein Isolates and Epigallocatechin Gallate Complex Enhance the Thermal Stability of the Pickering Emulsion Delivery of Curcumin

In this study, whey protein isolates (WPI), lactose (Lac) Maillard-reacted products, and epigallocatechin gallate (EGCG) complex were used to enhance the thermal stability of the Pickering emulsion delivery of curcumin. Atomic force microscopy combined with Fourier transform infrared spectroscopy were employed to study the morphological characteristics and structural changes of WPI-Lac/EGCG nanoparticles. Results proved that WPI-Lac and EGCG were combined by hydrogen bonding and hydrophobic interaction. The mechanism underlying WPI-Lac/EGCG-stabilized Pickering emulsion was further characterized by confocal laser scanning microscopy. The optimal binding ratio of WPI-Lac to EGCG was 1:1 (w/w) at pH 3.0. The particle size and zeta potential of the WPI-Lac/EGCG nanoparticles were about 110 nm and 27 mV, respectively. Analysis of microstructure and droplet size distribution revealed that the glycated WPI-Lac/EGCG-stabilized emulsions exhibited more uniform droplet distribution, stronger thermal stability, and higher curcumin percentage retention than WPI. These results indicate that the WPI-Lac/EGCG nanoparticles are potential stabilizers for Pickering emulsion requirements. This study provides a basis for the construction of Pickering emulsion systems while carrying pro-/hydrophobic bioactive components.

A glycated whey protein isolate–epigallocatechin gallate nanocomplex enhances the stability of emulsion delivery of β-carotene during simulated digestion

A glycated whey protein isolate–epigallocatechin gallate (EGCG) nanocomplex-stabilized emulsion was used to encapsulate β-carotene.

Application of Glycation in Regulating the Heat-Induced Nanoparticles of Egg White Protein

Due to the poor thermal stability of egg white protein (EWP), important challenges remain regarding preparation of nanoparticles for EWP above the denaturation temperature at neutral conditions. In this study, nanoparticles were fabricated from conjugates of EWP and isomalto-oligosaccharide (IMO) after heating at 90 °C for 30 min. Meanwhile, the effects of protein concentration, temperature, pH, ionic strength and degree of glycation (DG) on the formation of nanoparticles from IMO-EWP were investigated. To further reveal the formation mechanism of the nanoparticles, structures, thermal denaturation properties and surface properties were compared between EWP and IMO-EWP conjugates. Furthermore, the emulsifying activity index (EAI) and the emulsifying stability index (ESI) of nanoparticles were determined. The results indicated that glycation enhanced thermal stability and net surface charge of EWP due to changes in the EWP structure. The thermal aggregation of EWP was inhibited significantly by glycation, and enhanced with a higher degree of glycation. Meanwhile, the nanoparticles (<200 nm in size) were obtained at pH 3.0, 7.0 and 9.0 in the presence of NaCl. The increased thermal stability and surface net negative charge after glycation contributed to the inhibition. The EAI and ESI of nanoparticles were increased nearly 3-fold and 2-fold respectively, as compared to unheated EWP.

Maillard-Reacted Whey Protein Isolates Enhance Thermal Stability of Anthocyanins over a Wide pH Range

The poor thermal and acid stabilities of anthocyanins greatly limit their industrial applications as functional food ingredients. This work investigated the ability of the Maillard reaction products (MRPs) of whey protein isolates and glucose to enhance the thermal stability of anthocyanins over the pH range of 2.0-7.0. Anthocyanin dispersions were subjected to up to 120 min of thermal treatment at 80 °C. The improvement in the color stability and antioxidant capacity of the anthocyanin dispersions indicated that MRP remarkably inhibited anthocyanin degradation. Fluorescence spectroscopy results suggested that anthocyanins and MRPs form complexes through hydrophobic interactions. These complexes effectively attenuated anthocyanin degradation under heat treatment at pH 6.0. The particle sizes of MRPs alone or in complex with anthocyanins remained unchanged after heating. The novel protein delivery system proposed in this study expands the applications of anthocyanins as acid- and heat-stable functional food ingredients.

Dry heating of whey proteins leads to formation of microspheres with useful functional properties

Modification of whey protein isolate (WPI) powders is used in the food industry to enhance the functional properties of WPI. We investigated the impact of severe dry heating (DH) at 100 °C for up to 36 h on an alkaline-treated (pH 9.5), spray dried (water activity of ~0.24) WPI powder. Dry heated powders and their reconstituted suspensions were analysed. DH for 0-6 h led to 47% loss of native proteins, increases in the levels of soluble aggregates (×2.2) and of advanced glycation end-products of the Maillard reaction (at least ×2.7) and to powder browning (at least ×3) with a 95% decrease in free lactose content. DH for at least 12 h led to a decrease in soluble aggregates with concomitant formation of large, stable and insoluble microparticles. These microparticles had a microsphere structure, contained 98% of water phase and were made of insoluble powder particles resulting from protein cross-links during DH. Microparticle size could be altered by varying the pH of the suspension: at pH 6.5, microsphere size was 3-5 times larger than powder particle size, but decreased as the suspension pH neared the isoelectric point. DH could be a useful method for producing functional protein ingredients as these microparticles had very high water retention properties and high viscosity values.

Systematical characterization of functional and antioxidative properties of heat-induced polymerized whey proteins

Effects of pH (6-8), protein concentration (6-11%, w/v), heating temperature (70-95 °C) and time (5-30 min) on functional and antioxidative properties of heat-induced polymerized whey protein were systematically investigated. All samples were determined for solubility at pH 4.6, emulsion capacity and stability, and antioxidative properties involving 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis(2-ethylbenzothiazoline-6-sulfonate) (ABTS) scavenging abilities. Heating resulted in significant loss in solubility, emulsion capacity and stability for whey protein, p < 0.05. Heating decreased DPPH but enhanced ABTS scavenging ability for whey protein significantly, p < 0.05. Changes caused by pH variation were much stronger than those observed for other factors. Both protein concentration and heating time had negative effects while heating temperature had positive effect on emulsion capacity of whey protein. Data indicates that functional and antioxidative properties of whey protein could be altered by factors including pH, protein concentration, heating temperature and time.

Maillard-Reaction-Functionalized Egg Ovalbumin Stabilizes Oil Nanoemulsions

Egg white proteins are an excellent source of nutrition, with high biological and technological values. However, their limited functional properties prevent their widespread industrial applications. In this study, the ovalbumin functionality was improved via glycation by Maillard reaction with d-lactose. The free amino groups and sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile were determined, confirming that glycation occurred between ovalbumin and lactose. The emulsification of the conjugate was 2.69-fold higher than that of ovalbumin at pH 7.0 after glycation. The thermal stability also improved remarkably. The glycated protein products were used to form an oil-water nanoemulsion for polymethoxyflavone-rich aged orange peel oil. The resulting nanoemulsion showed good pH, thermal, and storage stabilities.

Fucoidan improves the structural integrity and the molecular stability of β-lactoglobulin

β-lactoglobulin (β-lg) was covalently bonded with fucoidan through Maillard reaction at 60 °C for 96 h under 79% RH condition. The molecular characters of the conjugate were investigated using fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and circular dichroism (CD) spectroscopy. And, its thermal properties, surface activity, and zeta-potential were compared with intact β-lg, β-lg-fucoidan mixture, and fucoidan under different pH conditions. AFM indicated that the conjugate was nano-structured, regular spherical-shaped and generally large sized compared to β-lg-fucoidan mixture. CD spectra and FT-IR showed that tertiary structure of β-lg slightly unfolded, but little change in secondary structure occurred. This explained that glycation under Maillard condition resulted in a molten globule state of β-lg. Differential scanning calorimetry (DSC) data exhibited that fucoidan shifted the temperature of phase transition and improved thermal stability of β-lg molecule. In addition, the conjugate prominently decreased the surface tension with pH-dependency.

Physicochemical Properties of Bovine Serum Albumin-Glucose and Bovine Serum Albumin-Mannose Conjugates Prepared by Pulsed Electric Fields Treatment

The pulsed electric fields (PEF) treatment is a novel method for obtaining glycated proteins by way of a Maillard reaction between proteins and polysaccharides but its effect on the preparation of protein–monosaccharide conjugate has not been explored. This study aimed to prepare bovine serum albumin (BSA)–glucose and BSA–mannose conjugates using PEF in pH 10.0 at an intensity of 10 or 20 kV/cm, frequency of 1 kHz, pulse width of 20 μs and 73.5 pulses. The conjugates were evaluated for physicochemical properties. The results indicated that PEF not only promoted Maillard reaction between BSA and glucose or mannose but also alleviated the undesirable browning. PEF treatment favored the increased surface hydrophobicity and emulsifying activity in BSA but reduced surface hydrophobicity and foaming stability and improved foaming capacity in BSA–glucose and BSA–mannose conjugates. These findings provided useful considerations in the application of PEF treatment as a potential method to prepare BSA–monosaccharide conjugates by Maillard reaction.

Heat stability improvement of whey protein isolate via glycation with maltodextrin without control of the relative humidity

The reduction of protein aggregation and their improved heat stability in solutions are often achieved through glycation.

Glycation of bovine serum albumin with monosaccharides inhibits heat-induced protein aggregation

Glycation with Xyl/Gal could hinder the heat-induced BSA aggregation, and the hindrance effect was enhanced with high glycation degree.

Stable nanoparticles prepared by heating electrostatic complexes of whey protein isolate-dextran conjugate and chondroitin sulfate

A simple and green method was developed for preparing the stable biopolymer nanoparticles with pH and salt resistance. The method involved the macromolecular crowding Maillard process and heat-induced gelation process. The conjugates of whey protein isolate (WPI) and dextran were produced by Maillard reaction. The nanoparticles were fabricated by heating electrostatic complexes of WPI-dextran conjugate and chondroitin sulfate (ChS) above the denaturation temperature and near the isoelectric point of WPI. Then, the nanoparticles were characterized by spectrophotometry, dynamic laser scattering, zeta potential, transmission electron microscopy, atomic force microscopy, and scanning electron microscopy. Results showed that the nanoparticles were stable in the pH range from 1.0 to 8.0 and in the presence of high salt concentration of 200 mM NaCl. WPI-dextran conjugate, WPI, and ChS were assembled into the nanoparticles with dextran conjugated to WPI/ChS shell and WPI/ChS core. The repulsive steric interactions, from both dextran covalently conjugated to WPI and ChS electrostatically interacted with WPI, were the major formation mechanism of the stable nanoparticles. As a nutrient model, lutein could be effectively encapsulated into the nanoparticles. Additionally, the nanoparticles exhibited a spherical shape and homogeneous size distribution regardless of lutein loading. The results suggested that the stable nanoparticles from proteins and strong polyelectrolyte polysaccharides would be used as a promising target delivery system for hydrophobic nutrients and drugs at physiological pH and salt conditions.

Antioxidant Activity and Functional Properties of Polymerized Whey Products by Glycation Process

The antioxidant properties of sweet and acid whey products were incremented by polymerization of their proteins by glycation of whey protein concentrates (WPC) and their hydrolyzates (WPCH) with ribose and glucose in individual experiments under similar concentration. Heating at 50°C during 20 h maximum and pH 7 and pH 9 were used in all tests. The higher activity was found in WPC glycosylates products with ribose at pH 7 and heating during 10–15 h. In comparable form, antioxidant activity in WPCH was incremented by prior hydrolysis to glycation with 25–45% of hydrolysis degree. Further functional properties of whey proteins (solubility, emulsion, and foam) were also improved by the polymerization with ribose. The color of polymerized products due to Maillard reactions was associated with antioxidant activity of each compound; however comparative color in glycosylates products with glucose and ribose did not show this effect.

Characterisation of bovine serum albumin-fucoidan conjugates prepared via the Maillard reaction

Bovine serum albumin (BSA)-fucoidan conjugates were prepared by the Maillard reaction (60 °C and 79% relative humidity for 96 h), and were then identified by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and size-exclusion chromatography (SEC). Molecular characteristics of the BSA-fucoidan conjugates were investigated, using atomic force microscopy (AFM), dynamic light scattering (DLS), fluorescence spectroscopy, and circular dichroism spectroscopy. SDS-PAGE patterns provided evidence for the covalent bonding between BSA and fucoidan. SEC profiles showed that about 1.5-2.0 mol of fucoidan were covalently linked to 1 mol of BSA, resulting in high-molecular-weight compositions (conjugates). AFM images and DLS results indicated that most particles in the conjugates were nano-structured and more spherical than those of a regular BSA-fucoidan mixture. The fluorescence intensity and maximum emission wavelength of the conjugates together revealed that the BSA molecules had converted from an ordered conformation into a partially folded molten globule state.