Structure and antioxidant activity of Maillard reaction products from α-lactalbumin and β-lactoglobulin with ribose in an aqueous model system

Comparative study of antioxidant activities of Allium sativum (a novel variety, HG17) and Allium ampeloprasum (SMG): Revealing the higher potential of HG17 and analyzing its phytochemicals

Garlic, belonging to the genus Allium, is renowned for its rich antioxidant potential. Snow Mountain garlic (SMG) (Allium ampeloprasum) has been traditionally used for medicinal purposes because of its higher antioxidant potential. Considering its potential in medical therapies, we compared the antioxidant activity of SMG with a novel variety of Allium sativum, Hisar garlic 17 (HG17). Comparative antioxidant activity data (2,2-diphenyl-1-picrylhydrazyl and 2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) revealed the higher antioxidant activity of HG17 than SMG, which prompted us to conduct a comprehensive phytochemical investigation to elucidate the factors contributing to antioxidant potential of HG17. To get a detailed antioxidant and phytoconstituents profiling, we differentially extracted HG17 by processing it in different forms (fresh, dry, heated, and aged) with two solvents (50% methanol and n-butanol). Our data (antioxidant activities, total phenolics, and flavonoids) showed that dry garlic methanolic extract (DgM) had maximum potential than other HG17 forms/solvents, which concludes that different extraction techniques had direct impact on the phenolics/flavonoids and antioxidant potential of the extracts. Further, phytochemical analysis of HG17 extracts by high resolution liquid chromatograph mass spectrometer quadrupole time of flight validated the maximum potential of DgM. LCMS revealed the presence of garcimangosone C, osmanthuside A, and protoaphin aglucone polyphenols exclusively in DgM compared to other HG17 extracts, which possibly contributing in its high antioxidant potential. The overall differential extraction and LCMS data of HG17 strongly depict that it may be used as an alternative of SMG under diverse medical applications. HG17 higher antioxidant potential and rich array of unique phytochemicals make it valuable for food and pharmaceutical industries to integrate into functional foods/therapeutics. PRACTICAL APPLICATION: Garlic unique phytochemical composition and its remarkable ability to scavenge different radicals make it valuable therapeutic asset to mitigate diseases associated with oxidative stress. SMG is well known for its anti-arthritic and anti-inflammatory properties. HG17 showed higher antioxidant potential than SMG and can be used as an alternative of SMG for anti-arthritic properties.

Maillard Reaction Process and Characteristic Volatile Compounds Formed During Secondary Thermal Degradation Monitored via the Change of Fluorescent Compounds in the Reaction of Xylose-Corn Protein Hydrolysate

Until now, no effective method has been found to monitor the Maillard reaction process for complex protein hydrolysates. Dynamic changes in the concentration of α-dicarbonyl compounds, fluorescence intensity, and browning degree were investigated during the Maillard reaction of corn protein hydrolysates. When the fluorescence intensity reached the peak, deoxyosones would continue to be increased by ARP's degradation. However, the reaction node with the highest fluorescence intensity coincided with the turning point of the browning reaction, and the subsequent browning rate remarkably increased. Therefore, the change in fluorescence intensity could be used to monitor the degradation of ARP and the formation of browning melanoidin at different stages of the Maillard reaction of complex systems, thus effectively indicating the process of the Maillard reaction. When Maillard reaction intermediates (MRIs) with maximum fluorescent compounds were heated, the most abundant pyrazines were subsequently achieved. However, furan compounds would be progressively increased during the thermal process of MRIs with continuously enhanced browning.

Light-Colored Maillard Peptides: Formation from Reduced Fluorescent Precursors of Browning and Enhancement of Saltiness Perception

The browning formation and taste enhancement of peptides derived from soybean, peanut, and corn were studied in the light-colored Maillard reaction compared with the deep-colored reaction. The fluorescent compounds, as the browning precursors, were accumulated during the early Maillard reaction of peptides and subsequently degraded into dark substances, which resulted in a higher browning degree of deep-colored Maillard peptides (MPs), especially for the MPs derived from corn peptide. However, the addition of l-cysteine in light-colored Maillard reaction reduced the formation of deoxyosones and short-chain reactive α-dicarbonyls, thereby weakening the generation of fluorescent compounds and inhibited the browning of MPs. Synchronously, the peptides were thermally degraded into small peptides and amino acids, which were consumed less during light-colored thermal reaction due to its shorter reaction time at high temperature compared with deep-colored ones, thus contributing to a stronger saltiness perception of light-colored MPs than deep-colored MPs. Besides, the Maillard reaction products derived from soybean and peanut peptides possessed an obvious "kokumi" taste, making them suitable for enhancing the soup flavors.

Characteristics and antioxidant activity of Maillard reaction products from β-lactoglobulin and isomaltooligosaccharide

Starch-derived isomaltooligosaccharide (IMO) is potentially used as prebiotics in infant formulas. Given that they are non-digestible carbohydrates rich in reducing substrates, it's crucial to understand if they can interact with β-lactoglobulin (β-LG) to produce Maillard reaction products (MRPs) and how these MRPs might influence the nutritional properties of β-LG. In our investigation, we conjugated β-LG with IMO to generate MRPs. Using a spectrophotometer, we identified the intermediates and assessed browning. We also evaluated changes in free amino groups and structural alterations. The antioxidative activity of the resulting compounds was assessed using DPPH and the ferric reducing/antioxidant power (FRAP) assay. Our data revealed increased visible absorption and fluorescence intensity, suggesting the formation of intermediate and browning products. The content of free amino groups diminished by 33%, supporting the conjugation of IMO with β-LG. However, circular dichroism results indicated no significant alterations in the secondary structure of β-LG. Notably, the β-LG-IMO MRPs exhibited enhanced 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging activity and ferric reducing/antioxidant power (FRAP). The findings provide insights into the characteristics and antioxidant activities of the conjugates derived from IMO and dairy protein in infant formula.

Characteristics and Functional Properties of Maillard Reaction Products from α-Lactalbumin and Polydextrose

The characteristics and the functions of Maillard reaction products (MRPs) produced by polydextrose (PD), a new type of prebiotic, and α-lactalbumin (α-LA) were valued. PD and α-LA were incubated at 60 °C and 79% relative humidity for up to 72 h to prepare MRPs. The results showed that the absorbance and fluorescence intensity of heated α-LA-PD increased, and the amount of free amino groups reduced as the reaction progressed, which confirmed the formation of different stages of MRPs. Electrophoresis revealed an increase in molecular mass and the degree of covalent cross-linking. The secondary structure of MRPs experienced no significant changes with the measurement of circular dichroism (CD), while the tertiary structure gradually unfolded, exposing hydrophobic groups. Furthermore, a significant increase was detected in the radical-scavenging activity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and the ferric reducing/antioxidant power (FRAP) of MRPs. The findings offer a foundation for understanding the structural and functional features of MRPs in formula milk powder.

Antioxidant Stability of Moringa Leaves Extract Powders Obtained by Cocrystallization, Vacuum Drying, and Plating

Cocrystallization, vacuum drying, and plating are three potential applications to preserve the antioxidant activity of moringa leaves. Moringa leaves extract was incorporated with sucrose at the same concentration (7 : 100, solid : solid) for all applications and stored for 30 days. This study aims to examine the effects of each application on the antioxidant stability of moringa leaves extract powders. Morphological properties by SEM showed that cocrystallized powders exhibited porous, agglomerated crystals, vacuum dried powders exhibited agglomerated crystals, and plated powders exhibited layered crystals. Based on XRD and hygroscopicity results, cocrystallization produced powders with the highest crystallinity, i.e., 69.11%, and the lowest hygroscopicity, i.e., 0.26 × 10−4 ± 0.02 × 10−4 g H2O/g solid/minute due to the slow water intake of the crystalline structure. Powders with the strongest initial antioxidant activity were obtained from cocrystallization, i.e., 3647.96 ± 20.29 ppm and followed by vacuum drying, i.e., 4378.51 ± 26.29 ppm. The least antioxidant activity was obtained from plating, i.e., 4733.46 ± 31.91 ppm. During 30 days of storage, powders obtained by cocrystallization maintained the most stable antioxidant activity (91.81–91.12%). The results indicated that the high temperature used in the process was likely to impact crystalline structure through the pore formation, which entrapped bioactive compounds and resulted in strong antioxidant activity. While, vacuum drying resulted in powders with a lower but increased antioxidant activity (84.06%–86.43%). In contrast to the other two applications, plating resulted in a decreased antioxidant activity (83.77–82.25%). This study suggests that application of cocrystallization produced moringa leaves extract powders with the strongest and most stable antioxidant activity during storage. Preserving the antioxidant stability of plant extract has been one of the major drives in the development of food encapsulation technology. Cocrystallization and vacuum drying are two relatively novel, less common techniques offering a simpler and more cost-effective method, but their effect on the antioxidant stability of moringa leaves extract has not yet been studied. This study discloses the effects of cocrystallization, vacuum drying, and plating (alternative extract incorporation method) on the antioxidant stability of moringa leaves extract powders. The results indicated that the three methods produced powders with high crystallinity and stable antioxidant stability during storage. Among the three methods, cocrystallization was the method that resulted in powders with the strongest and most stable antioxidant activity.

Characterization and functional properties of Maillard reaction products of β-lactoglobulin and polydextrose

The Maillard reaction products (MRPs) between polydextrose (PDX), a popular polysaccharide in formula powder, and β-lactoglobulin (β-LG), a major whey protein, were studied in aggregation degree, structure, hydrophobic, antigenic and antioxidant activity changes of β-LG. Incubation of PDX and β-LG (60 ℃, 79% relative humidity) for up to 72 h yielded MRPs with increases in furosine, UV absorbance, fluorescence intensity and loss of free amino groups. High molecular weight β-LG-PDX MRPs were observed by SDS-PAGE. Circular dichroism spectroscopy revealed negligible change in β-LG secondary structure. Changes in the tertiary structure of β-LG were detected by tryptophan fluorescence spectroscopy consistent with an increase in surface hydrophobicity of heated β-LG-PDX. Antigenicity reduction of β-LG in β-LG-PDX reached its peak when heated for 24 h. After heating for 72 h, DPPH radical-scavenging activity of β-LG-PDX increased by 7.4-fold, and the ferric reducing antioxidant power reached 61.1 µmol ascorbic acid/g protein.

Protein-polysaccharide interactions for the fabrication of bioactive-loaded nanocarriers: Chemical conjugates and physical complexes

As unique biopolymeric architectures, covalently and electrostatically protein-polysaccharide (PRO-POL) systems can be utilized for bioactive delivery by virtue of their featured structures and unique physicochemical attributes. PRO-POL systems (i. e, microscopic /nano-dimensional multipolymer particles, molecularly conjugated vehicles, hydrogels/nanogels/oleogels/emulgels, biofunctional films, multilayer emulsion-based delivery systems, particles for Pickering emulsions, and multilayer coated liposomal nanocarriers) possess a number of outstanding attributes, like biocompatibility, biodegradability, and bioavailability with low toxicity that qualify them as powerful agents for the delivery of different bioactive ingredients. To take benefits from these systems, an in-depth understanding of the chemical conjugates and physical complexes of the PRO-POL systems is crucial. In this review, we offer a comprehensive study concerning the unique properties of covalently/electrostatically PRO-POL systems and introduce emerging platforms to fabricate relevant nanocarriers for encapsulation of bioactive components along with a subsequent sustained/controlled release.

Evaluating the effect of conjugation on the bioactivities of whey protein hydrolysates

In this study, the ability of a whey protein hydrolysate to exhibit the antimicrobial, antioxidant, and antihypertensive behavior after combining with a reducing carbohydrate was studied. Whey protein hydrolysates with varying degrees of hydrolysis (WPH10, WPH15, and WPH20) were determined for their antimicrobial, antioxidant, and antihypertensive activities. Of these, hydrolysate (WPH10) exhibited the highest antimicrobial activity (with 10-11.2 mm zone of inhibition) against tested microorganisms: Listeria innocua, Staphylococcus aureus, and Bacillus coagulans. Also, the WPH10 exhibited the highest antioxidant (866.56 TEAC µmol/L) and antihypertensive (67.52%) attributes. Hence, based on the highest bioactivity, hydrolysate WPH10 was selected for conjugation with maltodextrin, and the effect of conjugation on the bioactivities was evaluated. The conjugated WPH10 solution demonstrated higher antimicrobial (17.16 mm) and antioxidant activity (1044.37 TEAC µmol/L), whereas a slight decrease in the antihypertensive activity (65.4%) was observed, as compared to WPH10 alone. The conjugated solution was further spray dried and alternatively, freeze-dried. The dried WPH10 conjugate exhibited even higher antimicrobial (18.5 mm) and antioxidant activity (1268.89 TEAC µmol/L) while retaining the antihypertensive activity (65.6%). Overall, the results indicate the ability of the WPH10-maltodextrin to retain the bioactive behavior after combining with a reduced carbohydrate. PRACTICAL APPLICATION: Whey protein hydrolysates upon conjugation with carbohydrates retain the bioactive properties of whey protein, which provides opportunities for application as an ingredient to develop novel health formulations.

Effect of free amino acids and peptide hydrolysates from sunflower seed protein on the formation of pyrazines under different heating conditions

Most research concerning pyrazine formation in the Maillard reaction is mainly focused on free amino acids (FAAs), but limited information is available on the effect of peptides and proteins. In this study, three Maillard model systems (i.e., glucose and native sunflower seed protein, hydrolyzed peptides or FAAs, respectively) were prepared, and their effect on the formation of volatiles were further compared at different heating conditions by using of headspace solid-phase microextraction equipped with gas chromatography/mass spectrometry (HS-SPME-GC/MS). It was found that pyrazines were the characteristic volatile compounds in tested Maillard models, and with increasing heating temperature and time, the varieties of pyrazine formation significantly increased. The optimum reaction condition for pyrazine formation was at 140 °C for 90 min, which was subsequently applied to all sets of Maillard models. Further analysis showed that the short chain peptides generated by hydrolyzing sunflower seed protein (SSP), especially the molecular weight ranging from 1.2 to 3.0 kDa, significantly promoted the formation of pyrazines, which highlights the important role of peptides in the Maillard reaction models and is expected to intensify aroma promotion in sunflower seed oil.

Exploring the effect of heating temperature and time on the formation of pyrazines; revealing the potential roles of FAAs and hydrolyzed sunflower seed peptides in the Maillard reaction model.

Preparation, Bioactivities and Applications in Food Industry of Chitosan-Based Maillard Products: A Review

Chitosan, a biopolymer possessing numerous interesting bioactivities and excellent technological properties, has received great attention from scientists in different fields including the food industry, pharmacy, medicine, and environmental fields. A series of recent studies have reported exciting results about improvement of the properties of chitosan using the Maillard reaction. However, there is a lack of a systemic review about the preparation, bioactivities and applications in food industry of chitosan-based Maillard reaction products (CMRPs). The presence of free amino groups in chitosan allows it to acquire some stronger or new functional properties via the Maillard reaction. The present review aims to focus on the current research status of synthesis, optimization and structural identification of CMRPs. The applications of CMRPs in the food industry are also discussed according to their biological and technological properties such as antioxidant, antimicrobial activities and inducing conformational changes of allergens in food. Some promising directions for future research are proposed in this review, aiming to provide theoretical guidance for the further development of chitosan and its derivatives.

Covalent β-lactoglobulin-maltodextrin amyloid fibril conjugate prepared by the Maillard reaction

The surface modification of β-lactoglobulin amyloid fibrils (AFs) was investigated by performing the Maillard reaction with the free anomeric carbon of the maltodextrin in water at pH 9.0 and 90 °C. The bonding of maltodextrin to fibrils was confirmed by determining the free amino group content and the presence of final products from the Maillard reaction. The secondary structure of AFs was preserved as observed by circular dichroism analysis. Atomic force microscopy evidenced that prolonged heat treatment caused hydrolysis of the attached polysaccharide and consequently lowered the height of the fibrils from 8.0 nm (after 1 h) to 6.0 nm (after 24 h), which led to the reduction of hydrophilicity of resulting conjugate. Increasing the reaction time, however, resulted in the improvement of colloidal stability and decrease in turbidity ascribed to the increment of glycation degree, as well as, a decrease in the isoelectric point of the protein-based supramolecular object.

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.

Impact of whey protein hydrolysates on the formation of 2,5-dimethylpyrazine in baked food products

Peptides have been reported to serve as precursors in the generation of alkylpyrazines, key aroma compounds in heated foods. Most previous studies, concerned with the generation of pyrazines via the Maillard reaction, were conducted using model systems of varying complexities. However, the formation of pyrazines in real food systems has received less attention. The aim of this study was to investigate the impact of adding protein hydrolysates as precursors for the generation of alkylpyrazines in baked food products such as bread and cookies. Two whey protein hydrolysates, obtained using either trypsin or proteinase from Aspergillus melleus, were used in the presented study. 2,5-Dimethylpyrazine was produced in both food systems. Therefore, its formation was quantitatively monitored using a stable isotope dilution assay. Additionally, sensory evaluation was performed. Results demonstrated that the addition of the protein hydrolysates were effective in promoting the generation of 2,5-dimethylpyrazine and other aroma compounds in two well-known food products.

Characteristics and antioxidant activity of Maillard reaction products from α-lactalbumin and 2'-fucosyllactose

The characteristics and antioxidant activity of Maillard reaction products (MRPs) from 2'-fucosyllactose (2'-FL), a human milk oligosaccharide, and α-lactalbumin (α-LA) were investigated. MRPs were prepared by reacting 2'-FL with α-LA at 60 °C and 79% relative humidity for up to 72 h. The absorbance and fluorescence intensity of heated α-LA-2'-FL increased as the heating time increased, while the free amino group content decreased, confirming that 2'-FL reacted with α-LA and produced various MRPs at different incubation stages. Conjugates of 2'-FL and α-LA and aggregation of α-LA were observed by SDS-PAGE. The secondary structure of α-LA did not change significantly after reacting with 2'-FL. In terms of antioxidant activity, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity and reducing power of α-LA-2'-FL increased significantly when compared with the protein only sample (p < 0.05). The findings provide a foundation for the characterization and functional analysis of MRPs in dairy products.

Mechanism of aroma compounds changes from sea cucumber peptide powders (SCPPs) under different storage conditions

A rapid and sensitive measurement technique was used to investigate the mechanism of aroma compounds changes in SCPPs under the storage conditions with hygroscopicity and no-microorganism (HNM), nonhygroscopicity and no-microorganism (NHNM) and hygroscopicity and microorganism (HM) by HS-GC-IMS. The types and signal of aroma compounds increased obviously at the 5th day under the storage condition (HNM and HM). The signal of majority of aroma compounds decreased gradually since the 5th day. However, during the storage of SCPPs for 15 days, the total signals of aldehydes, ketones and alcohols gradually increased and reached a maximum. Thereinto, the saturated aldehydes such as hexanal had been produced as an off-flavor. These off-flavor compounds principally including aldehydes and ketones could be generated through Maillard reaction, while alcohols could be generated by microbial fermentation. The study discovered moisture adsorption and microorganism during storage could affect aroma compounds of SCPPs and the effect of moisture absorption was greater than microorganisms.

Reduced IgE/IgG binding capacities of bovine α-Lactalbumin by glycation after dynamic high-pressure microfluidization pretreatment evaluated by high resolution mass spectrometry

Dynamic high-pressure microfluidization (DHPM) pretreatment and glycation with lactose were employed to modify α-Lactalbumin (α-LA) with respect to the IgE/IgG binding capacities. No significant difference on incorporation ratio value of glycated α-LA was observed with and without DHPM pretreatment. However, IgE/IgG binding capacities of α-LA were decreased after glycation and DHPM pretreatment promoted the reduction. The lowest IgE/IgG binding capacities of glycated α-LA were obtained by DHPM pretreatment at 110 MPa. Native α-LA was mainly glycated at K62, K94, K98, whereas glycation sites and degree of substitution per peptide (DSP) were added after DHPM treatment. Therefore, the reduced IgE/IgG binding capacities of α-LA was attributed to the characteristics of glycated sites, including the amount, location, and DSP values. Interestingly, K98 played the most important role in decreasing IgE/IgG binding capacities of α-LA. The study revealed that glycation combined with DHPM was a promising way to decrease the allergenicity of proteins.

Characterization and Antioxidant Activity of Products Derived from Xylose-Bovine Casein Hydrolysate Maillard Reaction: Impact of Reaction Time

The characterization and antioxidant activity on Maillard reaction products (MRPs) derived from xylose and bovine casein hydrolysate (BCH) was investigated at 100 °C and initial pH 8.0 as a function of reaction time. The pH values and free amino groups contents of xylose-BCH MRPs remarkably decreased with the reaction time up to 8 h, whereas their browning intensities significantly increased (p < 0.05). After 4 h of heat treatment, the fluorescence properties of xylose-BCH MRPs reached the maximum. There was a production of higher and smaller molecular substances in xylose-BCH MRPs with an increased reaction time, as analyzed by size exclusion chromatography. The 2,2-diphenyl-1-picryl-hydrazyl (DPPH) free radical scavenging capacity and ferrous reducing activity of xylose-BCH MRPs gradually increased with the reaction time extended from 0 to 8 h.

Antioxidant potential and antimicrobial activity of chitosan-inulin conjugates obtained through the Maillard reaction

Chitosan (1%) was glycated with inulin (0.5, 1, and 2%) via the Maillard reaction at various initial pH values (5, 5.5, and 6). Higher pHs led to a greater pH drop and increase in the intermediate products and browning intensity (BI). The chitosan-inulin conjugates were then classified into three levels of low, medium, and high BI through K-means clustering in order to investigate the effect of BI development on the antioxidant and antimicrobial attributes of the conjugates. Covalent linkage between chitosan and inulin was confirmed by fourier transform infrared spectroscopy. High BI chitosan-inulin conjugate had significantly higher antioxidant property compared to chitosan and other conjugate fractions. In addition, the conjugates obtained at low pH values mainly presented greater antimicrobial activities than those prepared at high pHs. It can be concluded that chitosan-inulin Maillard-born conjugates can be used as novel antioxidant and antimicrobial prebiotic-based ingredients for food applications.

Effect of Methylglyoxal-Induced Glycation on the Composition and Structure of β-Lactoglobulin and α-Lactalbumin

Glycation, and particularly reactions between aldehydes and nucleophiles (thiols, amines), can initiate changes in the structure, solubility, composition, hydrophobicity, conformation, function, and susceptibility to proteolysis of proteins. This can have adverse consequences for mammals, plants, foodstuffs, and pharmaceuticals. Low-molecular-mass dialdehydes such as methylglyoxal (MGO) are much more reactive than parent glucose and therefore potentially highly damaging. These are present at significant levels in some foods. This study investigated whether and how MGO exposure, with or without concurrent heat exposure, affected the major whey proteins β-lactoglobulin and α-lactalbumin. MGO diminished the formation of heat-induced, reducible, intermolecular disulfide cross-links for both proteins, with this being associated, at least in part, with alternative thiol consuming reactions of MGO. At long incubation times, nonreducible protein cross-links were formed in a dose-dependent manner, with LC-MS/MS and UPLC analysis showing the presence of methylglyoxal-lysine dimers (MOLD). UPLC analysis revealed MGO-dependent consumption of specific amino acids in the order Cys > Arg > Lys > Trp for both proteins, with α-lactalbumin affected to a greater extent than β-lactoglobulin. SDS-PAGE revealed altered protein mobility consistent with modification of charged residues. MGO exposure also resulted in increased binding of the hydrophobic dye, 8-anilino-1-naphthalene sulfonic acid, consistent with limited protein unfolding. Overall, these data are consistent with rapid reaction of MGO residues at Cys residues (when available) and surface accessible Arg and Lys residues, with formation of adducts and cross-linked materials. These alternative reactions of dialdehydes diminish direct heat-induced (disulfide) cross-link formation and result in limited protein unfolding.

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.

A New Compound Isolated from the Reduced Ribose-Tryptophan Maillard Reaction Products Exhibits Distinct Anti-inflammatory Activity

In this study, a compound of 532.24 Da named BF-4 was separated from the ribose-tryptophan Maillard reaction products by solvent extraction and purified through reverse phase high performance liquid chromatography. The purified compound BF-4 was identified as 3-((1 H-indol-3-yl)methyl)-8-(5-((1 H-indol-3-yl)methyl)-6-oxomorpholin-2-yl)-9-hydroxy-1,7,4-dioxazecan-2-one in accordance with 1D- and 2D-NMR spectra and LC-ESI-MS/MS analysis. BF-4 significantly reduced the production of nitric oxide (NO), interleukin-6 (IL-6), and tumor necrosis factor α (TNF-α) in lipopolysaccharide-stimulated RAW 264.7 cells. It inhibited nuclear factor κB (NF-κB) activation and mitogen-activated protein kinase (MAPK) phosphorylation through suppressing phosphorylation of IκBα, P65, P38 and c-Jun N-terminal kinase (JNK). The anti-inflammatory activity of BF-4 was comparable to dexamethasone, and more importantly, BF-4 showed less cytotoxicity than dexamethasone on the normal human liver cell LO2. The results indicate that BF-4 is a promising anti-inflammatory agent with pharmaceutical potential.

Ultrasonic Pretreatment Combined with Dry-State Glycation Reduced the Immunoglobulin E/Immunoglobulin G-Binding Ability of α-Lactalbumin Revealed by High-Resolution Mass Spectrometry

Bovine α-lactalbumin (α-LA) is one of major food allergens in cow's milk. The present work sought to research the effects of ultrasonic pretreatment combined with dry heating-induced glycation between α-LA and galactose on the immunoglobulin E (IgE)/immunoglobulin G (IgG)-binding ability and glycation extent of α-LA, determined by inhibition enzyme-linked immunosorbent assay and high-resolution mass spectrometry, respectively. The IgE/IgG-binding ability of glycated α-LA was significantly decreased as a result of ultrasonic pretreatment, while the average molecular weight, incorporation ratio (IR) value, location and number of glycation sites, and degree of substitution per peptide (DSP) value were elevated. When the mixtures of α-LA and galactose were pretreated by ultrasonication at 150 W/cm², glycated α-LA possesses seven glycation sites, the highest IR and DSP values, and the lowest IgE/IgG-binding ability. Therefore, the decrease in the IgE/IgG-binding ability of α-LA depends upon not only the shielding effect of the linear epitope found to be caused by the glycation of K13, K16, K58, K93, and K98 sites but also the intensified glycation extent, which reflected in the increase of the IR value, the number of glycation sites, and the DSP value. Moreover, allergenic proteins and monosaccharides pretreated by ultrasonication and then followed by dry-state glycation were revealed as a promising way of achieving lower allergenicity of proteins in food processing.

Glycation of whey proteins: Technological and nutritional implications

Whey proteins are globular proteins that have received much attention due to their high nutritional value and characteristic functional properties. In addition to being part of the protein system in milk, they constitute the main proteins in whey and whey protein products. Interaction of whey proteins with reducing sugars and carbohydrates via Maillard reaction have been extensively studied in milk and in model systems. Glycation of individual whey proteins results in variable increases in their solubility, thermal stability, antioxidant activity, and emulsion and foam stabilization. Limited glycation of whey protein products particularly whey protein isolates (WPI) using polysaccharides has been studied with the aim to produce conjugates with modified functional properties and acceptable sensory properties. An overview is presented here on the effect of glycation on individual whey proteins and whey protein products and the potential uses of the glycated whey proteins.

Improved Antioxidant Activity and Glycation of α-Lactalbumin after Ultrasonic Pretreatment Revealed by High-Resolution Mass Spectrometry

High-resolution mass spectrometry was performed to investigate the relationship between bovine α-lactalbumin (α-LA) subjected to ultrasonication and glycation treatment with respect to antioxidant activity. After α-LA was pretreated by ultrasonication combined with glycation, the treated α-LA showed low intrinsic fluorescence emission and high antioxidant activity at increased ultrasonic power levels. Prior to ultrasonic pretreatment, three glycated sites were identified, whereas the number of glycation sites was increased to four, four, five, and six after ultrasonic power at 60, 90, 120, and 150 W/cm², respectively, for 15 min. Thus, no obvious difference was found among the glycation sites at the ultrasonic power of 60 and 90 W/cm². The average degree of substitution per peptide molecule of α-LA was used to evaluate the glycation level per glycation site. All the samples pretreated by ultrasonication exhibited a higher glycation level compared with the untreated samples. Ultrasonic power at 150 W/cm² showed the most highly enhanced glycation extent and antioxidant activity. Therefore, the intensified glycation extent and the conformational changes of protein were responsible for the increase of antioxidant activity of α-LA. Moreover, high-resolution mass spectrometry is an efficient technique to understand the mechanism of the improved antioxidant activity.

Implications of the Maillard reaction on bovine alpha-lactalbumin and its proteolysis during in vitro infant digestion

This study investigated the functionality and digestibility of Maillard reaction products (MRPs) of alpha-lactalbumin (α-la), a major whey protein and component of infant formulas. The impact of different carbohydrates (glucose, galactose or galacto-oligosaccharides (GOS)) and heating duration was studied. SDS-PAGE, UV and color measurements monitored reaction extent, which varied between carbohydrates whereby galactose reacted more readily than glucose. Surface hydrophobicity and antioxidant capacity were found to be significantly (p < 0.05) higher following Maillard conjugation, with GOS-based MRPs elevating antioxidant capacity ∼50-fold compared to α-la. In addition, the digestive proteolysis of MRPs was evaluated using an infant in vitro gastro-duodenal model. SDS-PAGE analyses of digesta revealed Maillard conjugation generally increased α-la's susceptibility to proteolysis. Interestingly, GOS-based MRPs presented an optimization challenge, since heating for 12 h delayed proteolysis, while extended heating resulted in the highest susceptibility to proteolysis. Proteomic analyses further demonstrated the differences in enzymatic cleavage patterns and helped identify bioactive peptides rendered bioaccessible during the digestion of α-la or its MRPs. Bioinformatic mining of the proteomic data using PeptideRanker also gave rise to two potentially novel bioactive peptides, FQINNKIW and GINYWLAHKALCS. Finally, antioxidant capacity of luminal contents, measured by DPPH, revealed Maillard conjugation increased the antioxidant capacity of both gastric and duodenal digesta. Overall, this work draws a link between the Maillard reaction, digestive proteolysis and the bioaccessibility of bioactive peptides and antioxidant species in the infant alimentary canal. This could help rationally process infant formulas towards improved nutritional and extra-nutritional benefits.