Decrease In Free Amino Groups Research Articles

Esculin protects human blood cells from bioallethrin-induced toxicity: An ex vivo study

Bioallethrin, a household insecticide, is a member of the pyrethroid family and is known for its adverse effects on human health. Human exposure to pyrethroids is unavoidable due to their widespread use in controlling several fatal vector-borne diseases, mostly in developing nations. Bioallethrin is known to induce oxidative stress in target cells, including erythrocytes. Here we have studied the protective effect of dietary antioxidant esculin on bioallethrin-induced damage in isolated human erythrocytes. The cells were incubated with 200 μM bioallethrin, without or with different concentrations of esculin (200, 400 and 600 μM), and the results compared to the untreated control samples. Bioallethrin-treated erythrocytes showed a significant increase in oxidative stress markers, like protein and lipid oxidation, accompanied by decrease in free amino groups and ratio of reduced to oxidized glutathione. There was enhanced generation of reactive oxygen and nitrogen species with changes in plasma membrane integrity. Bioallethrin oxidized hemoglobin to methemoglobin, which cannot transport oxygen. It altered the activities of antioxidant enzymes and lowered the electron donating and free radical quenching ability of erythrocytes. The cell morphology and redox system of erythrocyte membrane were also altered by bioallethrin. Treatment with esculin, prior to incubation with bioallethrin, led to significant restoration in all these parameters in an esculin concentration-dependent manner. Thus esculin attenuated the biolletherin-induced oxidative damage to erythrocytes. Esculin can, therefore, be an effective chemoprotectant against xenobiotic-induced toxicity in human erythrocytes.

Impact of process conditions and type of protein on conjugate formation with pectin by vacuum drying

Plant proteins exhibit low solubility and functionality, limiting their use as emulsifiers. Maillard reaction-based conjugation with polysaccharides, e.g. pectin, is a strategy to improve their functionality. The commonly applied batch process involves economically unviable freeze-drying as a pre-treatment. Vacuum drying was therefore investigated as a novel approach combining the drying process and conjugate formation.First, the process parameters (time and temperature) were altered to determine the optimum conditions for conjugation between potato protein and high methoxylated pectin. Then, the conjugation between the pectin and various plant proteins (soy, pea, rapeseed) was tested to assess the impact of protein type. Conjugate samples were analysed by dry matter, decrease in free amino groups, browning index and molecular weight. Emulsifying properties were evaluated by oil droplet size and emulsion stability. Process parameters of 100 °C and 3 h were identified to favour conjugation. Corresponding potato protein conjugates had high molecular weight and improved emulsion stability at the pI of the protein. Soy protein conjugates showed the highest decrease in free amino groups and enhanced emulsion stability with prevented coalescence. Rapeseed protein conjugates exhibited the most stable emulsions with narrow oil droplet size distribution but were hampered by their inherent colouration.The results confirm that all plant proteins can be used for conjugation with pectin and the obtained conjugates are suitable as emulsifiers for food systems. However, differences in the amino acids content, chemical structure, and overall composition of plant proteins affect conjugation and must be considered in process design.

Improving ACE inhibitory activity of hazelnut peptide modified by plastein: Physicochemical properties and action mechanism

The plastein reaction can increase the activity of angiotensin-converting enzyme (ACE) inhibitory peptides, but the underlying mechanism is unknown. Hence, hazelnut protein hydrolysate and hazelnut peptide YLVR were used as substrate to explore the effect of plastein on physicochemical properties and the mechanism of structural change. The increase in turbidity and particle size and the decrease in free amino groups indicated that the reaction occurred via condensation. The modified products of YLVR were identified by NANO-HPLC-MS/MS, indicating that the N-terminal homologous amino acid aggregates in the plastein. Novel ACE inhibitory peptide YYLVR, YLLVR, and YYLLVR were synthesized and their inhibition rates were 66.35, 72.61, and 89.10 %, respectively, which were higher than that of YLVR (52.58 %). MD simulation showed that YYLLVR exhibited the lowest binding energies of −35.98 ± 2.30 kcal/mol to ACE. Taken together, plastein reaction is a promising strategy for inducing structural modifications to improve the activity of peptide.

Effects of high‐intensity ultrasound treatment on physiochemical properties of caseins‐cyanidin‐3‐galactoside conjugates

SummaryThe application of protein‐polyphenol complexes is increasing and broadening in recent years. Due to their unique properties, these complexes are attracting increased research interest. In this study, the cyanidin‐3‐galactoside was grafted to the caseins using free radicles induced by ultrasound. The formation of conjugation between caseins and cyanidin‐3‐galactoside was confirmed by the decrease in free amino groups and sulfhydryl content. Conjugation with cyanidin‐3‐galactoside resulted in aggregation of caseins, which also led to increase in particle size, relative fluorescence intensity and random coil. Conjugation also disrupted the hydrogen bonds and decreased the electrostatic repulsion and hydrophobic interactions between caseins. The caseins‐cyanidin‐3‐galactoside conjugate had better emulsifying, gelation properties and lower thermal stability than that of caseins.

Effect of Maltodextrin Dextrose Equivalent on Electrospinnability and Glycation Reaction of Blends with Pea Protein Isolate

Compared to commonly applied wet and dry heating procedures, a combination of electrospinning and heat treatment can facilitate glycation of proteins with reducing polysaccharides. This study investigates how the amount of reducing carbonyl groups (i.e. dextrose equivalent, DE) of different maltodextrins influences electrospinnability and subsequent glycation in blends with pea protein isolate (PPI). In the first step of the study, maltodextrin-PPI dispersions were electrospun. The concentrations of PPI and maltodextrin DE 2 were kept constant in the aqueous spinning dispersion. The addition of 0.05 or 0.1 g/mL maltodextrin DE 12 or 21 slightly affected the electrical conductivity and dynamic viscosity of the spinning dispersions, however, fiber production rate and morphology were dominated by the presence of maltodextrin DE 2 (0.8 g/mL). In the second step of the study, fibers were heated (60 °C, 75% rel. Humidity, 0–24 h). SDS-PAGE analysis and the measurement of free amino groups confirmed the covalent attachment of maltodextrin carbonyl groups to free amino groups of PPI. The fastest glycation and the lowest relative amount of free amino groups (49.70 ± 6.54%) after 24 h heating was measured for the fibers with the highest amount of reducing carbonyl groups. The fibers with the lowest amount of reducing carbonyl groups showed no significant (p < 0.05) decrease of free amino groups after heat treatment. The results suggest that within the boundaries of electrospinnability, the degree of glycation can be adjusted by varying the amount of reducing carbonyl groups in the fibers.

Antioxidant and Antimicrobial Enhancement by Reaction of Protein Hydrolysates Derived from Shrimp By-Products with Glucosamine

Shrimp cooking juice and shrimp carapaces are interesting sources of protein which are habitually disposed of at large quantities by crustacean industries. In this work, protein obtained from the cooking juice and carapaces of Pacific white shrimp (Litopenaeus vannamei) was hydrolyzed by an enzyme extract of Enterococcus faecalis DM19 isolated from raw camel milk. The hydrolysates were afterwards heated separately with glucosamine (GlcN) at 100 °C for 0, 40, 60,120 and 180 min. The reaction was followed by measuring the change in absorbance at 294 and 420 nm and also by fluorescence (λexc = 340 nm; λem = 440 nm). Browning and intermediate products increased with heating time showing a concomitant decrease in free amino groups, while the pH decreased as well. Amino acid analysis showed that the amounts of lysine, arginine, and histidine decreased significantly after heating for 180 min. The infrared spectra suggested the appearance of new molecules after heating, presumably Schiff bases and/or aromatic compounds. The antioxidant and antimicrobial activities of the heated hydrolysates were compared to those of the native hydrolysates. Interestingly, the reducing ferric ion activity was improved 22-fold after conjugation. Meanwhile, both scavenging radical and metal chelating ion activities were increased sevenfold. Besides, the shrimp carapace hydrolysate heated in presence of GlcN exhibited a good antibacterial activity against gram positive and gram negative bacteria. To conclude, protein hydrolysates derived from the shrimp by-products studied in this work could be heated in presence of GlcN at 100 °C and be potentially used as antioxidant and/or antibacterial ingredients for different purposes.

Changes in myofibrillar protein gel quality of porcine longissimus muscle induced by its stuctural modification under different thawing methods

The effects of thawing methods (refrigeration thawing (RT, 4 °C), water immersion thawing (WT, 18 °C), vacuum thawing (VT, 25 °C), ultrasonic thawing (UT, 20 °C) and microwave thawing (MT)) on the conformation and gel qualities of myofibrillar protein (MP) obtained from porcine longissimus muscle were investigated. The results showed that MP conformation and gel qualities of porcine longissimus muscles by VT and UT were insignificantly changed compared to fresh meat (FM). A significant decrease in free amino groups of MP from MT illustrated that MT induced protein aggregation and oxidation (P < 0.05). The results of circular dichroism (CD) spectra analysis and fluorescence spectroscopy indirectly proved that thawing can cause protein cross-linking and degradation, secondary structure destruction, non-hydrophilic domain exposed and conformational change of samples. The largest changes in solubility, surface hydrophobicity and particle size were obtained with MT. The effects on the conformation and gel quality of MP were verified during thawing process.

Plastein reaction enhanced bile-acid binding capacity of soybean protein hydrolysates and whey protein hydrolysates

Plastein reaction is a modification reaction that can improve the functional properties of protein hydrolysate. The product of the reaction is a thixotropic aggregation of peptides. This study investigated the formation condition of soybean-whey plastein and bile acid binding capacity of plastein. Soy protein and whey protein were hydrolyzed by pepsin. The mixture (1:1, w/w) of two hydrolysates was modified by pepsin again. After the reaction, the decrease in free amino groups and the turbidity of the modified hydrolysate were measured to obtain appropriate reaction condition. Results showed that the concentration of hydrolysates 40% (w/v), enzyme ratio of 2.0KU/g protein, pH 5.0, 37°C, reaction time of 3.0h respectively, were showed maximum changes in protein hydrolysates. Tricine SDS-PAGE analysis under denaturing conditions revealed that whey protein was more sensitive to pepsin and yielded different polypeptides (PPs) of molecular weight ranged from 3.5-17 kDa. However, a high molecular weight PP was completely hydrolyzed while PPs of 14.2-26 kDa were partially digested after pepsin treatment. Native page analysis further revealed the presence of a high-molecular weight PP in crude and purified plastein product. The bile acid binding capacity was improved by the plastein reaction. The amount of binding sodium deoxycholate, sodium taurocholate, and sodium cholate were 0.75, 2.0 and 1.87μmol/100mg respectively.

Glycation Induced Physicochemical Changes in Low-Density Lipoprotein and Its Role in Promoting Cholesterol Accumulation in Macrophages along with Antiglycation Effect of Aminoguanidine

The present study aimed at investigating physicochemical changes in modified LDL by sugars specifically fructose due to recent reports on its involvement in cardiovascular diseases and also glucose and their role in subsequent in vitro accumulation of cholesterol in macrophages. Antiglycation action of aminoguanidine was also investigated. LDL isolated from human blood was incubated with fructose or glucose and aminoguanidine where indicated. The physicochemical changes in modified LDL were detected by electrophoretic, spectroscopic and chemical analysis. Accumulation of cholesterol and its inhibiton in human monocyte-derived macrophages incubated with modified LDL was determined by HPLC. Results showed increased relative electrophoretic mobility, hyperchromicity at 280 nm, development of AGE fluorescence, decrease in free amino groups and increased carbonyl content in glycated LDL as compared to native LDL. Also total cholesterol accumulated in macrophages was more for glycated LDL as compared to native LDL. The magnitude of changes was more prominent in case of fructose as compared to glucose. Aminoguanidine showed remarkable restriction of glycation-induced alterations in LDL and also in accumulation of cholesterol in macrophages. The study thus proclaims that LDL-AGEs formed by fructose may contribute to accelerated initiation of diabetes induced atherosclerosis via foam cells generation and aminoguanidine may have therapeutic potential against it.

Glycation of human high density lipoprotein by methylglyoxal: Effect on HDL-paraoxonase activity

ObjectiveMethylglyoxal (MG), a reactive carbonyl compound formed primarily from triose phosphates, appears to be involved in the molecular mechanisms of diabetes, end-stage renal disease and neurodegenerative diseases. Methylglyoxal exerts several biological activities. Among these it promotes advanced glycation end products (AGEs), which are crucial in pathogenesis of human disease. Previous studies have demonstrated that MG reacts with proteins and compositional modifications reflect loss of biological activity. The aim of the study was to investigate the effect of in vitro MG-induced glycation on human high density lipoprotein (HDL) and on the activity of the enzyme paraoxonase-1 (PON1). MethodsHDL was incubated in the absence or in the presence of MG (0.2mmol/L and 1.0mmol/L) (MG-HDL) for different times (3, 6, 24h) at 37° C. We evaluated apoprotein compositional changes, in both control and MG treated HDL, using intrinsic fluorescence of tryptophan and monitoring the decrease of free amino groups. Furthermore we evaluated fluorescent advanced glycation end products (Ex=370nm, Em=440nm) and the activity of HDL-paraoxonase. ResultsWe demonstrated that human HDL is susceptible to glycation by MG (0.2mmol/L and 1mmol/L). The decrease of free amino groups and of intrinsic fluorescence of tryptophan demonstrates HDL apoprotein modifications in HDL incubated with MG. The compositional changes are associated with a significant increase in fluorescent advanced glycation end products and with a significant decrease of paraoxonase-1 enzyme activity associated with the HDL surface. ConclusionsHDL-associated paraoxonase is responsible for the anti-inflammatory and anti-oxidative properties of HDL and detoxification against homocysteine-thiolactone. Therefore, modifications of apoprotein composition and the decrease of paraoxonase-1 activity in MG-treated HDL could affect the protective effect exerted by HDL against oxidative damage and could contribute to complications in patients affected by diseases associated with aging and oxidative stress.

Ace Inhibition and Enzymatic Resistance In Vitro of a Casein Hydrolysate Subjected to Plastein Reaction in the Presence of Extrinsic Proline and Ethanol- or Methanol-Water Fractionation

Casein was hydrolyzed by alcalase to a degree of hydrolysis of 10.9% to obtain a hydrolysate having ACE-inhibition in vitro with an IC50 value of 52.6 μg/mL. The prepared hydrolysate was modified by alcalase-catalyzed plastein reaction with extrinsic proline added at 0.4 mol/mol free amino groups (on the basis of the hydrolysate), and fractionated by ethanol- or methanol-water solvents in proportions of 3:7, 5:5, or 7:3 (v/v), respectively. With the decrease of free amino groups of the modified hydrolysate as the response, the optimized plastein reaction conditions were alcalase addition of 3.1 kU/g peptides, substrate concentration of 50% (w/v), and reaction temperature of 25°C. Four modified hydrolysates prepared with different reaction times exhibited higher ACE-inhibitory activities than the original hydrolysate. The evaluation results showed that solvent fractionation of the modified hydrolysate with the maximum activity (IC50 = 13.0 μg/mL) yielded the separated soluble fraction's higher activity but the precipitate fraction's lower one. Further enzymatic digestion of the modified hydrolysate with the maximum activity and its two fractionated products by four proteases in vitro caused damage to the activities, but the residual activities of the final digests were higher than that of the original hydrolysate, indicating that the plastein reaction could confer casein hydrolysate protease resistance.

Small dense LDL is more susceptible to glycation than more buoyant LDL in Type 2 diabetes

Glycation of apoB (apolipoprotein B) of LDL (low-density lipoprotein) increases its atherogenicity. Concentrations of both serum glyc-apoB (glycated apoB) and SD-LDL (small dense LDL) (syn LDL3; D=1.044-1.063 g/ml) are increased in diabetes and are closely correlated. We studied whether SD-LDL is more susceptible to glycation in vitro than more buoyant LDL in statin- and non-statin-treated Type 2 diabetes mellitus. Serum SD-LDL apoB and glyc-apoB on statins was 20±2 (means±S.D.) and 3.6±0.41 compared with 47±3 and 5.89±0.68 mg/dl in those not receiving statins (P<0.001 and <0.01, respectively). There was a dose-dependent increase in glycation on incubation of LDL subfractions with glucose, which was accompanied by an increase in LPO (lipid peroxide) and electrophoretic mobility and a decrease in free amino groups. SD-LDL was more susceptible to these changes than more buoyant LDL. Both SD-LDL and more buoyant LDL from statin-treated patients were less susceptible to glycation. There were fewer free amino groups on LDL subfractions from statin-treated patients, which may contribute to this resistance. In conclusion, greater susceptibility of SD-LDL to glycation is likely to contribute to the raised levels of circulating glyc-apoB in diabetes. Statins are associated with lower levels of both SD-LDL and glyc-apoB.

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.

Effect of phenolic compounds on protein cross-linking and properties of film from fish myofibrillar protein

The effects of several phenolic ocmpounds (caffeic acid, catechin, ferullic acid and tannic acid) at various concentrations (1, 3 and 5% based on protein) on cross-linking and properties of film from myofibrillar proteins of bigeye snapper (Priacanthus tayenus) were investigated. Among all phenolic compounds used, tannic acid exhibited the highest cross-linking ability on myofibrillar protein as evidenced by higher decrease in free amino groups with coincidentally lower band intensity of myosin heavy chain (MHC). In addition, the extent of protein cross-linking increased with increasing concentration of phenolic compounds. Addition of phenolic compounds could enhance mechanical properties of the resulting films. As phenolic compounds content increased, Young's modulus (E) and tensile strength (TS) of the films increased, while their elongation at break (EAB) decreased (P<0.05), suggesting stronger and stiffer film structure. At the same concentration used, tannic acid rendered the film with higher mechanical properties, compared to others. Phenolic compounds decreased film transparency and affected color of the films differently, depending on types and concentrations used. Films from myofibrillar proteins with and without polyphenol generally had the excellent barrier properties to UV light at the wavelength of 200–800nm. Therefore, it could potentially be used as inner packaging material for high-fat foods to prevent the lipid oxidation and thus prolonging the shelf-life of foods during storage.

Preparation of Alcalase-catalyzed casein plasteins in the presence of proline addition and the ACE-inhibitory activity of the plasteins in vitro

Casein hydrolysates were prepared by hydrolysis of casein with alkaline protease Alcalase for 6 h and showed the highest ACE-inhibitory activity in vitro with an IC50 value of 47.1 μg mL−1. Casein hydrolysates prepared were subjected to Alcalase-catalyzed plastein reaction in the presence or absence of proline addition to prepare casein plasteins. Some optimal reaction conditions of plastein reaction in the presence of proline addition were studied using response surface methodology with the decrease in free amino groups in the casein plasteins as response. When the concentration of casein hydrolysates was fixed at 35% (w w−1) and reaction time at 6 h, the optimal conditions were reaction temperature 48 °C, addition level of proline 0.54 mol/mol free amino groups of casein hydrolysates and addition level of Alcalase 9.5 kU g−1 proteins. With these conditions, the maximal decrease in free amino groups in casein plasteins was 195.7 μmol g−1 proteins. The ACE-inhibitory activities of twelve casein plasteins in vitro, prepared in the presence or absence of proline addition with different reaction extents, were evaluated and compared. The results showed that the ACE-inhibitory activity of the casein plasteins prepared in the presence of proline addition changed irregularly, different to that of the casein plasteins prepared in the absence of proline addition, and might relate to the different linking of proline to the peptides in casein hydrolysates during plastein reaction. When the casein plasteins prepared in the presence of proline addition had a decrease in free amino groups 195.7 μmol g−1 proteins, the IC50 value of the casein plasteins was lowered to 0.2 μg mL−1.

Neoformation of antioxidants in glycation model systems treated under subcritical water extraction conditions

Abstract In this work, the possibility of finding newly formed Maillard reaction products produced as a result of the subcritical water extraction (SWE) conditions is explored. Simplified powdered glycation model systems were prepared mixing amino acid (Lys, Arg or Ala) and glucose in a molar ratio 1:4. Samples constituted by glucose or amino acids alone were also prepared as controls. SWE was carried out at room temperature, 100 °C and 200 °C and 100 bar of pressure for 20 min. Different assays were performed in order to determine the extent of glycation by analyzing the decrease of free amino groups and/or the formation of Maillard reaction products (early, advanced and end products). Namely, formation of early colorless Maillard reaction products, Amadori compounds, was detected by ESI-MS; advanced glycation end products (AGEs) were detected by measuring the fluorescence intensity (λex = 360 nm, λem = 460 nm) while end brown products were detected by reading the absorbance at 360 and 420 nm. Besides, the antioxidant capacity of the aqueous extracts was determined by using ABTS and ORACFL assays. Results obtained indicated the occurrence of the Maillard reaction under our specific extraction conditions. Early, advanced and end products were detected in the samples. Caramelization of sugar also occurred. As expected, the extent of the non-enzymatic browning depended on the intensity of the thermal treatment. Additionally, data on antioxidant activity suggested the formation of neoantioxidants. These compounds were predominantly formed at 200 °C. In conclusion, this report demonstrates the formation of antioxidant compounds in simplified glycation model systems under SWE conditions.

Preparation and radical scavenging activity of papain-catalyzed casein plasteins

The aim of this study was to prepare papain-catalyzed casein plasteins and to demonstrate the influence of the plastein reaction on the radical scavenging activity. Casein was initially hydrolyzed with papain under selected conditions to give a degree of hydrolysis of 9.6%. The casein hydrolysates were then subjected to papain-catalyzed plastein reaction to prepare casein plasteins. The formation of plasteins in the prepared casein plasteins was confirmed by size exclusion chromatography. The optimal conditions for the plastein reaction, determined by response surface methodology using the decrease of free amino groups in the casein plasteins as the response variable, were as follows: papain addition level was fixed at 500 U·g−1 proteins, reaction temperature 30 °C, concentration of casein hydrolysates 50% and reaction time 5.6 h. Six different casein plasteins were prepared and the radical scavenging activity on two radicals, 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethyl-benzothiazoline-6-sulfonic acid) (ABTS), was evaluated by the Trolox equivalent antioxidant capacity (TEAC). Analysis showed that all casein plasteins had improved radical scavenging activities. Compared to casein hydrolysates, the scavenging activity of the casein plasteins on DPPH radical had a seven- or ninefold increase, as TEAC increased from 10.45 to 73.41 or 90.31 mmol·g−1 proteins, while a onefold increase was detected on ABTS+ (TEAC increased from 8.33 μmol·g−1 to 15.09 or 16.45 μmol·g−1 proteins). The results of this study clearly showed that the papain-catalyzed plastein reaction could be applied to prepare casein antioxidant peptides with higher activity, and that the plastein reaction may have a new application in dairy science.

An approach to improve ACE-inhibitory activity of casein hydrolysates with plastein reaction catalyzed by Alcalase

The preparation method of casein hydrolysates with high ACE-inhibitory activity was studied by Alcalase-catalyzed hydrolysis coupled with plastein reaction. Casein hydrolysates with an IC50 value of about 47 μg mL−1 were first prepared by hydrolysis of casein with Alcalase and then modified with plastein reaction catalyzed by the same enzyme. The impacts of four reaction conditions on plastein reaction of casein hydrolysates were studied, and then optimal conditions were determined using response surface methodology with the decrease of free amino groups in the reaction mixture as response. When the concentration of casein hydrolysates was fixed at 35% by weight, the maximum decrease of free amino groups in the reaction mixture of 181.8 μmol g−1 proteins was obtained. The optimum conditions for the above decrease were found to be an E/S ratio of 7.7 kU g−1 proteins, reaction temperature of 42.7 °C and reaction time of 6 h. Analysis results showed that ACE-inhibitory activity of casein hydrolysates prepared could be improved significantly by plastein reaction. When casein hydrolysates were modified by plastein reaction, with a decrease of free amino groups in the mixture of about 154.7 μmol g−1 proteins and 181.8 μmol g−1 proteins, their IC50 values could be decreased to 0.6 and 0.5 μg mL−1.

Antioxidant properties of Maillard reaction products obtained by gamma-irradiation of whey proteins

Abstract The radiation processing of sugar–amino acid solutions results in formation of Maillard reaction products (MRPs). In the present study, the efficacy of gamma-irradiation in the formation of MRPs from whey protein powder was investigated. The formation of MRPs in whey protein suspension was studied by monitoring spectrophotometeric and chemical changes. A dose-dependent increase in UV absorbance and development of fluorescence was observed. Formation of brown pigments was established by increased A420 nm and Hunter colour upon irradiation. These MRPs exhibited antioxidant activity as measured by 1,1-diphenyl-2-picrylhydrazyl and β-carotene bleaching assays. Reducing power and iron-chelating abilities of MRPs also increased upon irradiation. These MRPs were able to scavenge hydroxyl and superoxide anion radicals under in vitro conditions. Dose-dependent decrease in free amino groups and lactose suggested the formation of glycated proteins upon irradiation treatment. SDS–PAGE analyses indicated formation of crosslinked proteins upon irradiation.

Bovine Serum Albumin-Sugar Conjugates through the Maillard Reaction: Effects on Interfacial Behavior and Emulsifying Ability

Bovine serum albumin (BSA) was employed as a model protein emulsifier to conjugate with aldohexose (D-glucose (Glc) or D-allose (All)) and sugar fatty acid ester (6-O-octanoyl-D-glucose (GlcC8)) through the Maillard reaction. It was found during the reaction that rate of decrease of free amino groups in BSA was almost the same for the BSA-sugar mixtures whereas browning and protein aggregation developed in the following order: Glc < All < GlcC8. It was thought that the rate of degradation of the Amadori compound could have been influenced by the OH-group stereochemistry at the C3 position of aldohexose, while denaturation of BSA by GlcC8 enhanced the browning and protein aggregation. To understand the emulsifying ability of the BSA-sugar conjugates, hexadecane-water interfacial tension and the oil droplet size of emulsions prepared by homogenizing hexadecane and aqueous solution of the conjugates were examined. BSA-GlcC8 showed greater improvement in interfacial and emulsifying activity than did BSA-Glc and -All. However, no improvement in emulsion stability was observed for any of the BSA-sugar conjugates, suggesting the weakness of the film formed at the oil droplet interface.