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.     

Characteristics and antioxidant activity of ultrafiltrated Maillard reaction products from a casein–glucose model system

Maillard reaction products (MRPs) were prepared from casein–glucose by refluxing for 130 min at 102 °C and initial pH 12.0 without pH control to investigate the characteristics of casein–glucose Maillard reaction and the antioxidant activity difference among different fractions of MRPs. Browning and intermediate products increased, however, the pH of the system decreased with increase in the heating time. Free amino group content decreased 78% during first 10 min and did not change nearly thereafter. Amino acid analysis indicated that lysine and arginine decreased significantly, and casein was partially hydrolysed to peptides or free amino acid. High molecular weight compounds were dominant in the MRPs, determined by high performance gel-filtration chromatography. After ultrafiltration, antioxidant activity of each MRPs fraction was investigated by DPPH radical-scavenging activity, reducing power, Fe²⁺ chelating activity and lecithin oxidation assay. MRPs of different molecular weight exhibited distinctly different antioxidant activities.     

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.     

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.     

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.     

Fabrication and evaluation of physicochemical properties of probiotic edible film based on pectin–alginate–casein composite

The objective of this study was to develop a casein-based edible film for the entrapment of probiotic Enterococcus faecium Rp1. Casein, pectin, sodium alginate and glycerol were used to prepare the film. In this study, the physicochemical and morphological properties of casein-based edible film and its impact on the stability of probiotic were evaluated. Surface morphology and properties of the film were tested using a scanning electron microscope, fluorescence microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Probiotic-incorporated casein-based edible film showed significant improvement in the antimicrobial and antioxidant properties and enhanced the structural, optical and thermal properties. Furthermore, the film was found to be desirable to carry probiotics, with the viability of 10⁷ CFU mL⁻¹ rate up to 30 days of storage at 4 °C. Hence, the current study suggests a probiotic-incorporated casein-based edible film for active packaging of food products.     

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.     

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.     

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.     

Interfacial and foaming properties of bovine β-lactoglobulin: Galactose Maillard conjugates

In this paper, the effect of the initial and advanced steps of glycosylation by Maillard reaction (MR) (glycation) of β-lactoglobulin (β-Lg) with galactose on the interfacial and foaming (foamability and foam stability) properties of this protein has been studied at both pH 7 and pH 5. Hardly any effect of glycation was observed at pH 7. However, a pH 5, due to its increased solubility, β-Lg glycated at 50 °C during 48 h (advanced steps of MR) presented the best dynamic of adsorption which lead to an increase of the surface dilatational modulus of adsorbed film. This resulted in a better foaming capacity, as well as higher stability of foams of β-Lg glycoconjugates with respect to native and control heated protein. These results could extend the applicability of β-Lg as a foaming agent, particularly in acid foods.     

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.     

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.     

Mechanism of pyrazole formation in [13C-2] labeled glycine model systems: N–N bond formation during Maillard reaction

Studies with ¹³C-2 labeled glycine in model systems containing 3-hydroxy-2-butanone or glyceraldehyde have indicated that the β-dicarbonyl compounds, the immediate precursors of pyrazoles, are produced in Maillard model systems through two pathways. One pathway involves dehydration of α,β-dihydroxy carbonyl compounds with elimination of the α-hydroxyl group and the other through aldol condensation of an α-hydroxy carbonyl compound with simple aldehydes to produce α,β-dihydroxy carbonyl moiety that can undergo the above-mentioned dehydration to produce β-dicarbonyl structures. The conversion of β-dicarbonyls into pyrazoles can be achieved through 1,3-diimine formation by reaction with either two ammonia molecules or with a primary amine and an ammonia. After imine–enamine isomerizations the resulting dienamine can be oxidized to form pyrazole rings similar to the oxidation of two thiol moieties into disulfide linkages. The α-dicarbonyl species can serve as hydrogen acceptors since in their absence no pyrazole formation was detected. Glycine/3-hydroxy-2-butanone system generated 3,4,5-trimethyl-pyrazole (associated with the aroma of tequila) and 1,3,4,5-tetramethyl-pyrazole whereas, glycine/glyceraldehyde generated 1,5-dimethyl and 1,3,5-trimethyl-pyrazoles.     

Study of nonenzymic browning in α-amino acid and γ-aminobutyric acid/sugar model systems

The reactivities, in nonenzymic browning, of γ-aminobutyric acid (GABA), a non-protein amino acid with wide natural occurrence and potential health benefits as it occurs in foods, and of the α-l-amino acids arginine, glutamic acid, glutamine, leucine, lysine, and phenylalanine were investigated by heating equimolar mixtures of glucose and the cited amino acids at 110 °C at pH 6.0 for different times (0–4 h). Linear regression analysis indicated that the colour development in a GABA/glucose mixture was slower than that of a lysine/glucose mixture and comparable to that of a phenylalanine/glucose mixture. High-performance anion-exchange chromatography (HPAEC) with integrated pulsed amperometric detection (IPAD) showed that the decrease in GABA levels (ca. 10% after heating for 4 h) as a function of heating time was smaller than that of glucose (ca. 30% after heating for 4 h). At the same time, glucose to fructose isomerisation took place. After 20 min of heating at pH 6.0, all mixtures showed a fructose peak, the area of which increased with heating time. However, after correcting for fructose isomerisation, glucose losses were still higher than amino acid losses. In contrast to its precursor glutamic acid, GABA was stable during heating of a solution containing it alone. Heating of GABA-containing d-sugar solutions (xylose, fructose, glucose, maltose and sucrose) showed that the relative order of colour yield was pentose > hexose > disaccharides. As well as glucose to fructose isomerisation, HPAEC–IPAD allowed monitoring of the different isomerisation reactions occurring, and also disaccharide hydrolysis in the different GABA/sugar mixtures.     

Gel mechanical properties of milk whey protein–dextran conjugates obtained by Maillard reaction

The effect of Maillard reaction on the mechanical properties of whey protein isolate (WPI) heat-induced gels was evaluated. WPI and dextran (15–25 kDa) conjugates were obtained by controlled dry heating during storage at 60 °C and 63% relative humidity for 2, 5 and 9 days. Changes in browning intensity and content of free amino groups were used to estimate the Maillard reaction. A decrease in free amino groups of WPI was observed when increasing polysaccharide concentration and reaction time. An increase in both a* and b* CIE Lab colour parameters indicated the development of a reddish-brown colour, typical of the Maillard reaction. Uniaxial compression and stress relaxation tests were performed to measure the mechanical properties of mixed and conjugate gels. Maillard reaction significantly modified the mechanical properties of WPI/DX gels, and even prevented fracture when conjugate gels were subjected to 80% deformation in uniaxial compression test.     

Inhibitory effects of curcumin and piperine on fluorescent advanced glycation end products formation in a bovine serum albumin–fructose model

This study investigated the inhibitory effects of curcumin and piperine on fluorescent advanced glycation end products (fAGEs) formation in a bovine serum albumin (BSA)–fructose model. Model systems of BSA and fructose were prepared, and curcumin or piperine was added. fAGEs and BSA oxidation product (dityrosine, kynurenine and N'-formylkynurenine) contents were determined. The results showed that fAGEs content decreased with increasing concentration of curcumin and piperine (P < 0.05). Addition of curcumin and piperine at 160 µg mL⁻¹ could inhibit fluorescent AGEs by 100% and 93% respectively. Dityrosine and N'-formylkynurenine contents decreased as curcumin and piperine concentration increased (P < 0.05). Furthermore, the result of principal component analysis indicated that curcumin and piperine markedly impeded BSA oxidation, resulting in a lower level of fAGEs in model systems. Therefore, adding curcumin and piperine may facilitate reduced fAGEs levels in BSA–fructose model.     

Effects of heat moisture treatment on the structural,physicochemical and digestibility properties of potato starch–soybean peptide complexes

In this study, potato starch (PS) was complexed with soybean peptides (SPTs) with different molecular weights under heat moisture treatment (HMT) at different moisture contents. The results showed that PSSPT complexes formed under HMT were characterised by weaker and fuzzier polarised cross patterns, and more agglomerates. After HMT, higher gelatinisation temperatures and lower enthalpies were observed for PSSPT complexes. In particular, higher gelatinisation temperatures were observed when moisture levels were higher during HMT. Compared with physically mixed counterparts, the PSSPT complexes under HMT displayed higher pasting temperatures and lower swelling power, and peak viscosity. Higher moisture content during HMT led to a less thermodynamically stable B-polymorphic structure converting to a more stable A-type polymorph. Higher SDS content was found in the PSSPT complexes subjected to HMT with lower moisture content, while relatively higher RS content was associated with higher moisture content of HMT. These results could be attributed to restructuring of the amylose/amylopectin chains, the physical barrier of SPT and interactions between the negatively charged groups in PS and the side chains in SPT. This study will advance our understanding of food multicomponent interactions, as well as guidance for the application development of low-glycaemic index foods containing SDS and RS in the field of fine food processing.