Structure and antioxidant activity of high molecular weight Maillard reaction products from casein–glucose

Maillard reaction products (MRPs) were prepared from a casein–glucose reaction and ultrafiltrated to provide six fractions. The high molecular weight glycated proteins (melanoprotein) were further purified with a Sephadex G-75 column. Two fractions were obtained and analysed for their reducing power and Fe²⁺ chelating activity. Results obtained from the first fraction, analysed by Fourier transform infrared spectroscopy (FT-IR) indicated that the amide I, II and III bands of casein were changed by the Maillard reaction. The obtained samples were also hydrolysed with pepsin and trypsin in vitro, and the proteolytic hydrolysates were evaluated for their antioxidant activities. Non-hydrolysed melanoproteins exhibited the highest reducing power, but peptic hydrolysates of different MRPs were more efficient in radical-scavenging activity.     

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

Maillard reaction products (MRPs) were prepared from aqueous model mixtures containing 3% (w/w) ribose and 3% (w/w) of the dairy proteins α-lactalbumin (α-LA) or β-lactoglobulin (β-LG), heated at 95 °C, for up to 5 h. The pH of MRPs decreased significantly during heat treatment of α-LA-Ribose and β-LG-Ribose mixtures from 8.4 to 5.3. The amino group content in MRPs, derived from the α-LA-Ribose and β-LG-Ribose model system, was decreased noticeably during the first hour and did not change thereafter. The loss of free ribose in MRPs was higher for β-LG-Ribose than for α-LA-Ribose. During the Maillard reaction, the concentration of native and non-native α-LA, or β-LG, decreased and the formation of aggregates was observed. Fluorescence intensity of the β-LG-Ribose MRPs reached maximum within 1 h, compared to 2 h for α-LA-Ribose MRPs. Meanwhile, modification of the UV/vis absorption spectra for α-LA and β-LG was mainly due to a condensation reaction with ribose. Dynamic light scattering showed a significant increase in the particle size of the MRPs. Size exclusion chromatography of MRPs revealed the production of both high and low molecular weight material. Electrophoresis of MRPs indicated polymerization of α-LA and β-LG monomers via inter-molecular disulfide bridge, but also via other covelant bonds. MRPs from α-LA-Ribose and β-LG-Ribose exhibited increased antioxidant activities, therefore theses MRPs may be used as natural antioxidants in food products.     

Biological activities and physicochemical properties of Maillard reaction products in sugar–bovine casein peptide model systems

The purpose of this study was to evaluate the biological activities and physicochemical properties of Maillard reaction products (MRPs), derived from aqueous reducing sugar (ribose, galactose and lactose) and bovine casein peptide (BCP) model systems. The fluorescence intensity of ribose-BCP MRPs reached the maximum value within 1 h, while it took 3 h for galactose-BCP MRPs. Size exclusion chromatography of all the MRPs indicated molecular rearrangements and production of new smaller molecules, as a function of the heating time. The consumption of ribose and amino groups was the highest in the ribose-BCP MRPs. BCP lost its known angiotensin-I-converting enzyme (ACE) inhibitory activity by the Maillard reaction with reducing sugars. Ribose–BCP MRPs had the lowest ACE inhibitory activity, but they showed the highest 2,2-diphenyl-1-picryl-hydrazyl (DPPH) radical scavenging activity and ferrous reducing power among all the MRPs. Galactose-BCP MRPs inhibited, slightly the growth of Caco-2 cells, while ribose-BCPand lactose-BCP MRPs had no cytotoxicity.     

Biological activities of Maillard reaction products (MRPs) in a sugar–amino acid model system

The various biological activities of Maillard reaction products (MRPs) from sugar (fructose and glucose) and 20 amino acid model systems were evaluated. Colour development, in vitro antioxidant, α-glucosidase inhibitory, antihypertensive, and antiproliferative activities of aqueous solutions of MRPs produced by heating at 130 °C for 2 h were measured. The fructose–amino acid mixture showed higher UV-absorbance and browning intensity than the glucose–amino acid mixture. The fructose–amino acid model MRPs showed higher DPPH and ABTS radical scavenging and ACE inhibitory activities than the glucose–amino acid model MRPs. The α-glucosidase inhibitory effect of MRPs derived from fructose– and glucose–tyrosine showed higher α-glucosidase inhibitory activity than that of other MRPs. Sugar–amino acid model MRPs inhibited the growth of HCT116 colon cancer cell in a dose-dependent manner (from 0.5 to 1.5 mg/ml). Glucose MRPs showed slightly higher antiproliferative activity than fructose MRPs. In particular, sugar–tryptophan and –tyrosine MRPs exerted higher biological activities than the other MRPs.     

Effect of Maillard reaction conditions on browning and antiradical activity of sugar–tuna stomach hydrolysate model system

The antiradical activity of Maillard reaction products (MRPs) made from sugar–tuna stomach hydrolysate model system was tested. The antiradical activity of the MRPs derived from ribose was 11-fold higher than that of MRPs derived from glucose due to the acyclic form of the ribose. The activity reached the plateau at a 30 mg/mL ribose concentration. The ribose caramelization contributed to the antiradical activity and browning reactions at 95 °C and 115 °C. The increase in DPPH radical scavenging of MRPs is attributed not only to the temperature but also to the buffer type and buffer concentration. Phosphate buffer showed the most efficient compared to citrate or Tris–HCl buffers. A positive correlation (R² = 0.98) was observed between the antiradical activity, the browning and the phosphate concentration. The MRPs obtained under these mild experimental conditions exhibited no toxicity towards Vero cells and 3T3 cells, despite their high antiradical activity.     

Isolation and characterisation of an α-glucosidase inhibitory substance from fructose–tyrosine Maillard reaction products

An α-glucosidase inhibitory substance was isolated and characterised from fructose–tyrosine Maillard reaction products (MRPs) and the inhibition mode of the active substance determined. The ethyl acetate fraction of fructose–tyrosine MRPs showed strong α-glucosidase inhibitory activity; this fraction was isolated and purified using silica gel column chromatography and semi-preparative RP-HPLC. The structure of the purified compound was determined using spectroscopic methods. The isolated compound was identified as 2,4-bis (p-hydroxyphenyl)-2-butenal (C₁₆H₁₄O₃, HPB242). This is the first report of baker’s yeast α-glucosidase inhibitory activity of HPB242 isolated from fructose–tyrosine MRPs. The IC₅₀ value of HPB242 on α-glucosidase inhibition was 4.00 ± 0.09 μg/ml. Kinetic data revealed that HPB242 inhibits the p-NPG hydrolysing activity of baker’s yeast α-glucosidase noncompetitively with a K_i value of 0.870 mM.     

Structure and antioxidant activity of β-lactoglobulin-glycoconjugates obtained by high-intensity-ultrasound-induced Maillard reaction in aqueous model systems under neutral conditions

Sonication is a new processing technology in the dairy industry. The aim of this study was to test glycation of β-lactoglobulin (BLG) in Maillard reaction (MR) induced by high-intensity ultrasound in aqueous solution under neutral conditions at 10–15 °C, which is not favourable for the MR. BLG was sonicated in the presence of glucose, galactose, lactose, fructose, ribose and arabinose. Formation of Maillard reaction products (MRPs) was monitored by mass spectrometry, spectrophotometry and fluorimetry. Ultrasound treatment resulted in formation of MRPs with all tested carbohydrates. Ribose induced the highest degree of modification resulting in 76% of BLG modified and an average of three anhydroribose units attached. Circular dichroism spectra analyses indicated only minor alterations in secondary and tertiary structures. MRP obtained by ultrasound exhibited 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity and possessed increased iron-chelating activity and reducing power. High-intensity ultrasound efficiently promotes BLG-glycoconjugates formation by MR in aqueous solutions under non-denaturing conditions.     

Improvement of emulsifying properties of Maillard reaction products from β-conglycinin and dextran using controlled enzymatic hydrolysis

A novel emulsifier was prepared by conjugating soy β-conglycinin and dextran (MW 67 kDa) under dry-heated Maillard reaction followed by trypsin hydrolysis with the degree of hydrolysis (DH) at 2.2% and 6.5%. The emulsifying properties of β-conglycinin, β-conglycinin–dextran conjugates and hydrolysates of β-conglycinin–dextran conjugates (DH 2.2% and DH 6.5%) were investigated using zeta-potential, droplet size and creaming index of the emulsions. The results showed that hydrolysates of β-conglycinin–dextran conjugates (DH 2.2%) were capable of forming a fine emulsion (d₄₃ = 0.62 ± 0.04 μm, pH 7.0) which remained stable during 4 weeks of storage. A variety of physicochemical and interfacial properties of β-conglycinin, β-conglycinin–dextran conjugates and hydrolysates of β-conglycinin–dextran conjugates were investigated. Hydrolysates of β-conglycinin–dextran conjugates (DH 2.2%) had a much higher fraction of protein adsorption (F_ads) and a significantly lower saturation surface load (Γ_sat) compared with β-conglycinin, β-conglycinin–dextran conjugates and hydrolysates of β-conglycinin–dextran conjugates (DH 6.5%). This might be due to its higher molecular flexibility, which benefited the adsorption and unfolding of peptide molecules at the droplet interface. These might explain its markedly improved emulsifying capability. The conjugation of β-conglycinin and dextran effectively enhanced the hydrophilicity of the oil droplets surfaces and improved the steric repulsion between the oil droplets. Therefore the emulsions were still stable after 4 weeks of storage against pH, ionic strength and thermal treatment. This study demonstrated that controlled enzymatic hydrolysis of protein–polysaccharide conjugates could be an effective method for preparing favourable emulsifiers.     

Physical changes induced by the Maillard reaction in a glucose–glycine solution

Some physical changes associated with the development of Maillard reaction in a glucose–glycine aqueous solution were detected by means of thermal and rheological analysis as well as by more conventional determinations. The increase in water content, water activity (A_w) and enthalpy of ice melting (ΔHm) during the reaction reflects both the formation of new water molecules and the consumption of low molecular weight species. The concomitant arrangement of more complex molecular structures was indicated by changes in the glass transition temperature of the maximally freeze-concentrated solution (Tg′) and of the freeze-dried solution (Tg _(dry)) as well as in the estimated unfrozen water (UFW). After fractionation of the samples by solid phase extraction, the non-polar fractions exhibited much higher Tg_(dry) than the non-fractionated samples. The Tgs_(dry) of samples at increasing heating time were treated with the Gordon–Taylor equation and results were discussed. The expected increase in viscosity due to polymerisation was compensated by the formation of water, but it could be detected when viscosities were measured on samples equilibrated at a same A_w     

Antioxidative potential of melanoidins isolated from a roasted glucose–glycine model

The antioxidative activity of the total water soluble fraction (sol A), high molecular weight (HMW; MW>12,400 Dalton), low molecular weight (LMW) and the insoluble fraction (IS) of a glucose–glycine model system roasted at 120°C was studied in hydrophilic solutions (PBS buffer, fruit juices; addition: 0.01–0.1%) at ambient temperature and lipophilic (coconut fat, triolein and corn oil; addition: 0.01–0.5%) matrices at 60°C and frying conditions at 200°C. The hydrophilic reducing power in the water-soluble fractions was evaluated with the ABTS [2,2′-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid)] method. Fat stability was determined by observing the development of the peroxide value and conjugated dienes. All fractions increased the hydrophilic reducing power in the water-soluble fractions as a matter of concentration with highest effects for the 0.1% enrichment. In PBS buffer the HMW was most effective, in fruit juices the IS. A slight antioxidative effect in fats was observed only for 0.5% IS and 0.5% sol A in corn oil. Neither in coconut fat at 200°C nor in triolein at 60°C Maillard reaction products (MRPs) were able to extend shelf life. The results performed describe MRPs as highly antioxidative in water-soluble but less effective in water-insoluble fractions.     

Antioxidative properties of a chitosan–glucose Maillard reaction product and its effect on pork qualities during refrigerated storage

The objective of this study was to evaluate the antioxidative properties of a chitosan–glucose Maillard reaction product (CG-MRP), and its effect on pork qualities during refrigerated storage. Chitosan (1%), which was dissolved in acetic acid (1%) with 1.0%, 1.5%, or 2.0% glucose, pH adjusted to 6.0, autoclaved (121 °C, 15 min) and cooled, was prepared. The results showed that the 2,2-dipheny1-1-picrylhydrazy1 (DPPH) radical scavenging activities, ferrous ion chelating abilities, and reducing powers of various CG-MRP solutions were not significantly different. Pork loins soaked in the CG-MRP solutions or deionized water for 10 min and without dipping were stored at 4 °C for 7 days. Little influence was observed on the L∗, a∗, and b∗ colour values of the samples. Dipping in CG-MRP tended to retard the increases in volatile basic nitrogen (VBN) and thiobarbituric acid-reactive substances (TBARS) values, and resulted in lower microbial counts during storage. No detrimental influence on the sensory characteristics was found.     

Binding,stability, and antioxidant activity of curcumin with self-assembled casein–dextran conjugate micelles

This work studied the potential of self-assembled micelles of casein–dextran conjugates (CD) as a protective carrier for bioactive curcumin. CD was prepared through the Amadori rearrangement of the Maillard reaction. In casein micelles and CD micelles, the addition of curcumin can quench the intrinsic fluorescence of casein gradually. According to the double logarithm equation, the binding constants were determined as 3.9 × 10⁴ and 1.8 × 10⁵ M^?1 for the binding of curcumin with casein micelles and CD micelles, respectively. The higher affinity of hydrophobic binding of curcumin with CD micelles was ascribed to the more hydrophobic and compact structure of casein core surrounded by the hydrophilic dextran shell, which was supported by the fluorescence spectrum and fluorescence anisotropy of curcumin. Furthermore, CD micelles were found to be superior to casein micelles for improving the stability and radical scavenging activity of curcumin.     

Ethanol in food: liquid–vapour partition in model systems containing Maillard reaction products

The effect of Maillard reaction products (MRPs) with different browning degree on the liquid–vapour partition of ethanol was studied in model systems. In particular, glucose–glycine aqueous solutions subjected to different heat treatments, which consequentely had different water activity values, were added to increasing amounts of ethanol and analysed for ethanol vapour pressure. In order to study the effects of the water activity change and of melanoidins' formation on the ethanol partition, experiments were also carried out on samples equilibrated at the same water activity. Ethanol vapour pressure decreased as the Maillard reaction proceeded. This result was attributed to the increase in water activity rather than to binding effects of melanoidins towards ethanol. Changes in water activity were mainly due to reagent consumption, water molecule formation and melanoidin production.     

Nε-(carboxymethyl)lysine formation from the Maillard reaction of casein and different reducing sugars

Food Science and Biotechnology - Dietary advanced glycation end products (AGEs) are involved in the pathogenesis of diabetic complications, atherosclerosis, and kidney disease. Formation of...     

Temperature effect on the non-volatile compounds of Maillard reaction products derived from xylose–soybean peptide system: Further insights into thermal degradation and cross-linking

Solutions of soybean peptide with or without xylose were heated over a range of temperatures (80–130 °C) for 2 h to investigate the characteristics of Maillard reaction and the effect of temperature on amino acids and peptides. It was found that both peptide degradation and peptide cross-linking occurred in the Maillard reaction. The critical temperature for peptide degradation was 100 °C, and above it, peptides degraded quickly in thermal degradation system. However, in Maillard reaction system, peptides cross-linked rapidly when the temperature reached 110 °C. Bitter amino acids and peptides below 1000 Da decreased 18.44% and 28.49%, respectively, after Maillard reaction at 120 °C. On the other hand, peptides between 1000 and 5000 Da were increased significantly, nearly doubled compared to its initial hydrolysates after Maillard reaction at 120 °C. Moreover, the increase of macromolecule products was also accompanied with severe browning and pH decrement.     

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

Food Science and Biotechnology - 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...     

Inhibitory effect of melanoidins from glucose–asparagine on carboxypeptidases activity

This paper shows the effect of melanodins obtained from a glucose/asparagine system and also the effect of excess of substrate on the activity of the carboxypeptidase A (CPA) and carboxypeptidase B (CPB) enzymes. It was found that the substrate might have an inhibiting effect at high concentration. The presence of melanoidins has an inhibitory effect on both enzymes, with the value of the maximum reaction rate of the enzymatic reaction decreasing with the increase in melanoidins, so that for CPA, a value of nil was obtained for the above-mentioned maximum reaction rate for melanoidin concentrations of 0.042% (w/v), while the maximum reaction rate value for CPB is nil for a concentration of 0.077% (w/v).