Free Sulphydryl Groups Research Articles

Effects of CaCl2 concentration on fibrils formation and characteristics of soybean protein isolate and β-conglycinin/glycinin

In this study, fibrillation of soybean protein isolate (SPI) and β-conglycinin (7S)/glycinin (11S) in acid-heating with CaCl2 concentration (0–200 mM) was explored. Fibril formation kinetics results showed the fastest fibril formation rate and the most fibrils with 80 mM CaCl2 addition. Fourier-transform infrared (FTIR) spectroscopy, size distribution and Transmission electron microscopy (TEM) results demonstrated SPI fibril structure became more complete and occurred entanglement with CaCl2 concentration increasing from 0 to 80 mM. When CaCl2 addition was above 80 mM, ζ-potential, surface hydrophobicity (H0) and free sulphydryl groups determination proved hydrophobic interaction among fibril built-units was hindered by charges shielded effect, and basic units of 11S were more exposed, aggregate morphology were changed to thicker fibrils or amorphous aggregates. The whole system with CaCl2 has preferable antioxidant property and no cytotoxicity. The study provided a basis for optimizing SPI fibrillation in food industry.

Oxidative and anti-oxidative responses to metal toxicity in an extremophilic alga (Cyanidium caldarium) and a neutrophilic alga (Chlamydomonas reinhardtii)

ABSTRACT Redox metabolism is integral to the functioning of photosynthetic organisms. The highly oxidative reactive oxygen species (ROS) are products of cellular redox processes and can cause major cellular damage. ROS are also produced in the face of environmental and cellular stress, including metal-induced oxidative stress. The degree of ROS production and the subsequent anti-oxidative response will vary according to the tolerance level of the species and the degree and type of stress it experiences. The extremophilic alga Cyanidium caldarium and neutrophilic alga Chlamydomonas reinhardtii have contrasting Zn tolerances, with the EC50 of the extremophile 128 times higher than that of the neutrophile. We examined the oxidative stress responses of these algae to zinc stress, using ROS production to establish the metal-induced oxidative state of the organisms. The anti-oxidative responses measured included total free-sulphydryl groups and total protein content as well as a heat shock protein 70 (HSP70) response assay to explore the role the stress protein HSP70 might play in the contrasting metal tolerance mechanisms in these two species. Results showed that the oxidative response in Cy. caldarium was dose-dependent, while in Ch. reinhardtii the oxidative response was more dependent on the time of exposure to Zn. Cyanidium caldarium managed to regain its base level of protein (i.e. that seen in naïve cells) upon acclimation (long-term exposure) to sub-toxic Zn levels. On the other hand, Ch. reinhardtii showed reduced total protein content upon acclimation. This raises questions about the different roles that ROS signalling might play in metal stress tolerance.

A unique mechanism for thiolation of serum albumins by disulphide molecules.

Protein S-thiolation is a reversible oxidative modification that serves as an oxidative regulatory mechanism for certain enzymes and binding proteins with reactive cysteine residues. It is generally believed that the thiolation occurs at free sulphydryl group of cysteine residues. Meanwhile, despite the fact that disulphide linkages, serving structural and energetic roles in proteins, are stable and inert to oxidative modification, a recent study shows that the thiolation could also occur at protein disulphide linkages when human serum albumin (HSA) was treated with disulphide molecules, such as cystine and homocystine. A chain reaction mechanism has been proposed for the thiolation at disulphide linkages, in which free cysteine (Cys34) is involved in the reaction with disulphide molecules to form free thiols (cysteine or homocysteine) that further react with protein disulphide linkages to form the thiolated cysteine residues in the protein. This review focuses on the recent finding of this unique chain reaction mechanism of protein thiolation.

Oxidant-Antioxidant balance in patients with coronary slow flow.

Objective:Recent studies have focused on the probable role of oxidative stress in cardiovascular diseases. We aimed to assess the oxidant/antioxidant biomarkers in coronary slow flow (CSF).Methods:The study included 51 subjects with CSF and age and sex matched 32 controls. Detailed anamnesis of the patients in the study was taken and routine physical examinations were performed. Routine biochemical blood tests were analyzed. Total oxidative status (TOS), oxidative stress index (OSI) and lipid hydroxyperoxide (LOOH) levels as oxidant biomarkers; paraoxonase (PON1), ceruloplasmin (CP), free sulphydryl (SH) groups, and total antioxidant capacity (TAS) levels as antioxidant biomarkers were studied.Results:Baseline demographic characteristics of the study population did not differ significantly between groups.TOS, OSI and LOOH concentrations were higher in study group than in control group. However, there was no significant difference detected in levels of TAS, PON1, SH and CP. Multivariate logistic regression analysis revealed that TOS, hsCRP and smoking were indepedent risk factors of CSF.Conclusions:Although there was not any significant difference in antioxidant biomarkers (TAS, PON1, SH and CP) in CSF patients, we detected increased TOS, OSI and LOOH levels which have oxidant properties. These data supported the possible involvement of oxidative stress in pathogenesis of CSF as previous studies reported.

Liposomal vesicles-protein interaction: Influences of iron liposomes on emulsifying properties of whey protein

In this study, whey protein (WP) was used as a model protein to interact with ferrous sulfate liposomes (FL). The interaction between FL and WP was researched using circular dichroism, intrinsic fluorescence, surface hydrophobicity, free sulphydryl groups, Fourier transform infrared spectroscopy, zeta potential, particle size, and interfacial tension. These observations indicated that FL interacted with WP via electrostatic force, hydrophobic force, and hydrogen bonds. WP secondary structure and tertiary structure could be changed by the interaction between FL and WP. The emulsifying properties of WP were improved by the interaction between FL and WP. Emulsifying activity index and emulsifying stability index of WP in the presence of FL increased from 39.69 to 65.63 m2/g, from 28.63 to 101.55 min, respectively. And the WP-stabilized emulsion droplet size decreased from 1.64 μm to 0.78 μm in the presence of FL. However, the emulsifying properties of WP were also influenced by liposomal composition, pH, and temperature. The changes of WP emulsifying properties could be attributed to the effects of liposomes on WP secondary structure and tertiary structure, zeta potentials, and particle size. This work provides new insights into the application of liposomes in food.

Effects of amidated low methoxyl pectin on physiochemical and structural properties of polymerized whey proteins

ABSTRACTThis study aimed to investigate effects of amidated low methoxyl (ALM, 0.3%, w/v) pectin on physiochemical and structural properties of polymerized whey proteins (PWP, 10%, w/v) prepared by thermal aggregation at 85°C for 10–30 min. Particle size, zeta potential, isoelectric point (IEP), surface hydrophobicity, free sulphydryl group, rheological properties and the secondary structure of all samples were analysed. ALM pectin increased mean diameter and narrowed size distribution of PWP samples (p < 0.05) regardless of heating time. Addition of ALM pectin shifted the IEP of PWP‒pectin complex to lower pH, which decreased with heating time increased. ALM pectin decreased the surface hydrophobicity of PWP heated for 30 min pronouncedly. Whey protein (WP) complexed with ALM pectin showed decreased gelation time and rheological properties of improved elasticity. ALM pectin had no considerable effect on secondary structure of PWP. Data indicated that ALM pectin could alter physiochemical properties of heat-induced polymerized WPns.

Biochemical Quality Indicators and Enzymatic Activity of Wheat Flour from the Aspect of Climatic Conditions

The contents of free sulphydryl groups (SH), disulphide bonds (SS), and free amino groups (NH2) were determined in order to estimate the extent of climatic condition influence on gluten quality. The analysis included four bread wheat varieties grown in two production years (2011 and 2012) with different climatic conditions in different locations. According to our previously reported results, the working hypothesis was that enzyme activity for breadmaking purpose was insufficient. The aim of this paper was to study the influence of naturally present enzymes on the bread quality by the addition of previously extracted and freeze-dried albumins to the base flour as an additive. The selection of samples was made on the basis of different combinations of proteolytic and α-amylolytic enzymes activity levels. For samples from 2012 production year, the content of SH groups was significantly higher. Regarding the SS content, the obtained results exhibited the opposite trend. Variations in NH2 content were dominantly caused by temperature treatment of tested samples. The addition of freeze-dried albumins to bread improved its specific volume in a lesser extent, while bread crumb texture was significantly improved.

High hydrostatic pressure (HHP) effects on antigenicity and structural properties of soybean β-conglycinin.

In this study, the effect of high hydrostatic pressure (HHP) on antigenicity, free sulfhydryl group (SH) content, hydrophobicity (Ho), fluorescence intensity and circular dichroism data of soybean β-conglycinin was studied. The antigenicity of soybean β-conglycinin was decreased significantly at pressures 200-400MPa. The antigenicity inhibition rate of β-conglycinin declined from 92.72 to 55.15%, after being treated at 400MPa for 15min. Results indicated that free sulphydryl (SH) groups and surface Ho of β-conglycinin were significantly increased at pressures 200-400MPa and 5-15min, whereas these properties decreased at the treatments above 400MPa and 15min. The maximum fluorescence intensity was noticed at 400MPa and 15min. The circular dichroism data analysis revealed that the amount of β-turns and unordered structure significantly increased, while the content of α-helix1 and β-strand1 noticeably decreased. These results provide evidence that HHP-induced the structural modification of β-conglycinin and could alter the antigenicity of β-conglycinin.

Whey protein film properties as affected by ultraviolet treatment under alkaline conditions

The effects of UV radiation treatment on film-forming solutions adjusted to two alkaline pH values (9 or 11) on the properties (water vapour permeability, solubility, mechanical properties, colour and microstructure) of whey protein concentrate films, and on some structural characteristics of proteins (free sulphydryl groups, degree of aggregation, denaturation and secondary structure) were evaluated. UV radiation increased protein aggregation at both pH values. Ultraviolet treatment of pH 9 solutions increased free sulphydryl groups and produced films with higher solubility, tensile strength, elastic modulus, and puncture properties and lower elongation at break; UV radiation at pH 11 decreased free sulphydryl groups and films showed higher solubility and elastic modulus and lower puncture deformation and elongation at break than untreated films. The treatment also affected film colour differently depending on the pH. In conclusion, ultraviolet treatment modifies the properties of the films in different ways depending on the pH of the solutions.

Ultrasound‐induced changes in physical and functional properties of whey proteins

SummaryUse of high‐intensity ultrasound to modify certain functional properties of whey proteins is an alternative to traditional method in food industry. Whey protein isolate (WPI) solutions were treated with an ultrasound probe (20 kHz) at different intensities (20% or 30% amplitude) and durations (10 or 20 min). Results showed that ultrasound treatment changed physical and several functional properties of whey proteins including decreased particle size (from 190.4 nm to 138.0 nm), increased surface hydrophobicity (from 5.13 × 105 to 5.77 × 105), free sulphydryl groups (from 52.64 μmol SH g−1 to 53.64–58.77 μmol SH g−1), solubility (from 74.95% to 89.70%), emulsion activity index (from 3.18 m2 g−1 to 3.59–5.32 m2 g−1) and emulsion stability index (from 62.26 min to 71.44–104.83 min), and changed viscosity (from 5.51 mPa.s to 4.81–5.64 mPa.s). Therefore, we conclude that high‐intensity ultrasound can be potentially applied to whey proteins to improve its specific functions during food processing.

Effects of ultrasound treatment on physicochemical and emulsifying properties of whey proteins pre- and post-thermal aggregation

The aim of this study was to determine the effect of high intensity ultrasound on physicochemical and emulsifying properties of thermally aggregated whey proteins. Whey protein isolate (WPI) solutions were sonicated for 20 min using an ultrasonic probe (frequency: 20 kHz; amplitude: 20%) pre- and post-thermal treatment (85 °C for 30 min). Changes in particle size, zeta-potential, surface hydrophobicity, free sulphydryl group content, turbidity, thermal denaturation properties, rheological properties, and emulsifying properties were studied. Soluble aggregates prepared with ultrasound treated post-thermal aggregation resulted in significantly smaller particle size and broader size distribution compared with those prepared by untreated or ultrasound treated pre-thermal aggregation (P < 0.05). It was suggested that surface hydrophobicity of the soluble aggregates was significantly increased by ultrasound applied post-thermal aggregation (P < 0.05). There was a significant reduction in turbidity of whey protein solutions by ultrasound applied post-thermal aggregation (P < 0.05). The apparent viscosity of whey protein soluble aggregate model systems has been decreased significantly by ultrasound pre- and post-thermal aggregation (P < 0.05). Emulsion activity index and emulsion stability index of soluble aggregates were increased significantly by ultrasound applied post-thermal aggregation (P < 0.05). There were no significant changes in zeta-potential, total free sulphydryl group by ultrasound either pre-or post-thermal aggregation (P > 0.05). We conclude that ultrasound treatment on post-thermal aggregation has improving effect on physiochemical and emulsifying properties of whey protein soluble aggregates for potential industrial applications.

Research Note: Total Free Sulphydryls of Several White and Red Wines

Total free sulphydryl groups were assessed in several white and red wines. Ellman’s method was adapted to wine samples for the determination of total –SH groups. Total –SH groups of white wines, as glutathione, were in the range of 315 to 734 and of red wines in the range of 163 to 467 mg/L. In most cases, white wines exhibited higher values than red wines. The high total sulphydryls of white and red wines indicate their potential contribution to wine antioxidant capacity.

Optimization of arachin extraction from defatted peanut (Arachis hypogaea) cakes and effects of ultra-high pressure (UHP) treatment on physiochemical properties of arachin

A process for the optimization of arachin from defatted peanut cakes had been developed. The process included pre-treatment, extraction by Tris–HCl buffer solution, pH adjustment and final separation by centrifugation. A Box–Behnken design including independent variables such as extraction temperature (x1), extraction pH (x2) and liquid–solid ratio (x3) was used. The variable with the largest effect was extraction pH. The optimum extraction conditions were found to be extraction temperature 56.0°C, extraction pH 8.7 and liquid–solid ratio 14:1, under which the arachin yield could reach 310.4g/kg defatted peanut cakes. The effect of ultra-high pressure treatment on the physiochemical properties of arachin was also evaluated. After processing, solubility, emulsifying activity, emulsifying stability and surface hydrophobicity changed significantly. The content of free sulphydryl groups, which were often associated with aggregation and gelation of proteins, also decreased. All the processes widened the utilization of by-products generated from oil extraction as a source of protein in human diet.

Graded inclusions of sodium metabisulphite in sorghum-based diets: I. Reduction of disulphide cross-linkages in vitro and enhancement of energy utilisation and feed conversion efficiency in broiler chickens

Seven sorghum-based diets containing 0, 1.50, 2.25, 3.00, 3.75, 4.50 and 5.25g/kg of the reducing agent sodium metabisulphite (SMBS) were prepared in which sodium levels were balanced with sodium bicarbonate. A red sorghum (766.4g/kg starch, 78.6g/kg protein) was hammer-milled through a 3.2mm screen prior to being mixed into complete broiler diets containing 195g/kg protein with an energy density12.97MJ/kg, which were steam-pelleted at an 84°C conditioning temperature. Each of the seven dietary treatments was offered to a total of 294 male Ross 308 chicks in seven replicate cages (6 birds per cage) from 10 to 24 days post-hatch to determine the effects of SMBS on growth performance, nutrient utilisation and nitrogen (N) digestibility coefficients in four small intestinal segments. SMBS did not linearly influence (P>0.50) weight gains and feed intakes. However, SMBS quadratically improved (r=0.416; P<0.05) feed conversion ratios and it may be deduced from the quadratic equation that 4.75g/kg SMBS improved FCR by 3.06% (1.424 versus 1.469). At all positive inclusions, SMBS significantly enhanced apparent metabolisable energy (AME) and N-corrected AME (AMEn); at the lowest inclusion, 1.50g/kg SMBS significantly improved AME by 0.36MJ (13.81 versus 13.45MJ/kg; P=0.005), AMEn by 0.45MJ (12.30 versus 11.85MJ/kg; P=0.001) and FCR by 2.47% (1.422 versus 1.458; P=0.025) on the basis of pair-wise comparisons. SMBS linearly decreased concentrations of disulphide bonds (r=−0.775; P<0.001) and linearly increased free sulphydryl groups (r=0.890; P<0.001) and protein solubility of the diets (r=0.943; P<0.001). However, SMBS had little influence on N digestibility coefficients as the sole significant response was a 6.41% increase (0.797 versus 0.749; P<0.01) in the distal ileum at 3.75g/kg and SMBS did not influence small intestinal sites of protein disappearance. Consideration is given to the possibility that the sulphite reducing agent, SMBS, caused oxidative-reductive depolymerisation of starch polysaccharides which may have been responsible for the improvements in energy utilisation and feed conversion efficiency.

Determination of free sulphydryl groups in wheat gluten under the influence of different time and temperature of incubation: Method validation

The aim of the present study was to determine the characteristics of an analytical method for determination of free sulphydryl (SH) groups of wheat gluten performed with previous gluten incubation for variable times (45, 90 and 135min) at variable temperatures (30 and 37°C), in order to determine its fitness-for-purpose. It was observed that the increase in temperature and gluten incubation time caused the increase in the amount of free SH groups, with more dynamic changes at 37°C. The method characteristics identified as relevant were: linearity, limit of detection, limit of quantification, precision (repeatability and reproducibility) and measurement uncertainty, which were checked within the validation protocol, while the method performance was monitored by X- and R-control charts. Identified method characteristics demonstrated its acceptable fitness-for-purpose, when assay included previous gluten incubation at 30°C. Although the method repeatability at 37°C was acceptable, the corresponding reproducibility did not meet the performance criterion on the basis of HORRAT value (HORRAT<2).

Changes in the content of free sulphydryl groups during postharvest wheat and flour maturation and their influence on technological quality

The main aim of this study was to determine the changes in free sulphydryl content during postharvest wheat and flour maturation. The content of free sulphydryl groups was determined from wet gluten over 50 days of wheat postharvest maturation and over 14 days of flour maturation by varying incubation temperatures (30 and 37 °C) and incubation times (0, 45, 90 and 135 min). The amount of free sulphydryl groups increased during postharvest wheat and flour maturation as well as with the increase in temperature and gluten incubation time. The additional aim of this study was to find the interrelation between the content of free sulphydryl groups and selected parameters of technological quality by means of Principal Component Analysis. During wheat/flour maturation, the strengthening of protein structure was observed manifested by the increase in gluten index and Mixolab protein network weakening (C2), and changes in dough resistance as well. The incubation temperature of 37 °C affected the weakening of protein structure manifested by the decrease in gluten index and resistance, and increase in extensibility. Strong differentiation of examined varieties in terms of selected quality indicators was observed upon pre-defined maturation period, probably due to the expression of their intrinsic properties.

Preliminary assessment of including a reducing agent (sodium metabisulphite) in ‘all-sorghum’ diets for broiler chickens

The preliminary assessment was designed to determine appropriate inclusion levels of the reducing agent, sodium metabisulphite (SMBS), in ‘all-sorghum’ broiler diets. Dietary SMBS inclusion levels of 0, 1.25, 2.5, 5.0, 7.5, 10.0, 12.5 and 15.0gkg−1 were investigated with corresponding reductions (923–908gkg−1) in dietary sorghum concentrations. In vitro evaluations included the determination of concentrations of free sulphydryl groups and disulphide bonds in all-sorghum diets. In vivo parameters included growth performance (14–21 days post-hatch), nutrient utilisation and apparent nitrogen (N) digestibility coefficients in four small intestinal sites in broilers at 21 days post-hatch. In addition, the effect of 5.0gkg−1 SMBS on starch digestibility coefficients and sites of starch disappearance along the small intestine were determined. The reducing agent significantly increased free sulphydryl group and decreased disulphide bond concentrations. SMBS significantly depressed feed intakes at 5.0gkg−1 and at higher inclusion levels and there was a linear reduction in feed intakes (r=−0.783; P<0.001). SMBS had cubic effects on weight gain (r=0.588; P<0.001) and feed conversion ratios (r=0.500; P<0.01). It may be deduced from the relevant regression equations that the optimum SMBS inclusions are 2.47gkg−1 for weight gains and 2.14gkg−1 for feed conversion ratios. SMBS significantly increased apparent metabolisable energy (AME) at inclusions of 1.25, 5.0, 10.0 and 12.5gkg−1. At the lowest inclusion of 1.25gkg−1 SMBS increased AME by 0.39MJ (14.80 versus 14.41MJkg−1; P<0.001) and the most profound response of 0.56MJ (14.97 versus 14.41MJkg−1; P<0.001) was observed at 10.0gkg−1. SMBS linearly increased N retention (r=0.592; P<0.001). In the distal jejunum, SMBS significantly depressed N digestibility coefficients at inclusions of 1.25, 2.5, 10.0, and 15.0gkg−1 and in the distal ileum with SMBS inclusions of 1.25, 10.0 and 15.0gkg−1. SMBS did not influence N digestibility in the proximal jejunum (P>0.60) and proximal ileum (P>0.55). At 5.0gkg−1, SMBS increased starch digestibility coefficients by 3.76% in the proximal ileum (0.966 versus 0.931; P<0.01) and 3.27% in the distal ileum (0.980 versus 0.949; P<0.001). Also, SMBS significantly decreased the quantity of starch disappearance in the proximal jejunum, or abruptly digestible starch, by 16.3% (245.6 versus 293.4gbird−1; P<0.01). It is concluded that birds are able to tolerate dietary inclusions of SMBS approaching 5.0gkg−1 and that SMBS has the capacity to enhance energy utilisation of sorghum-based diets by broiler chickens. Consideration is given to the mechanisms whereby SMBS might enhance energy utilisation.

Reduction of aggregation of β-lactoglobulin during heating by dihydrolipoic acid

Prevention of the heat-induced aggregation of β-lactoglobulin (β-Lg) would improve the heat stability of whey proteins. The effects of lipoic acid (LA, or thioctic acid), in both its oxidised and reduced form (dihydrolipoic acid, DHLA), on heat-induced unfolding and aggregation of β-Lg were investigated. LA/DHLA was added to native β-Lg and the mixture was heated at 70, 75, 80 or 85 °C for up to 30 min at pH 6·8. The samples were analysed by Polyacrylamide Gel Electrophoresis (PAGE) and Size-exclusion HPLC (SE-HPLC). LA was not as effective as DHLA in reducing the formation of aggregates of heated β-Lg. Heating β-Lg with DHLA resulted in formation of more β-Lg monomers (due to dissociation of native dimers) and significantly less β-Lg aggregates, compared with heating β-Lg alone. The aggregates formed in the presence of DHLA were both covalently linked, via disulphide bonds, and non-covalently (hydrophobically) linked, but the amount of covalently linked aggregates was much less than when β-Lg was heated alone. The results suggest that DHLA was able to partially trap the reactive β-Lg monomer containing a free sulphydryl (-SH) group, by forming a 'modified monomer', and to prevent some sulphydryl-sulphydryl and sulphydryl-disulphide interactions that lead to the formation of covalently linked protein aggregates. The effects of DHLA were similar to those of N-ethylmaleimide (NEM) and dithio(bis)-p-nitrobenzoate (DTNB). However, the advantage of using DHLA over NEM and DTNB to lessen aggregation of β-Lg is that it is a food-grade compound which occurs naturally in milk.

Effect of freeze–thaw cycles on the molecular weight and size distribution of gluten

Freezing processing is widely used in food industry, but some key scientific issue is still unclear. In this paper, the effects of freeze–thaw cycles on the molecular weight, radius of gyration, free amino group content, free sulphydryl group content and molecular conformation of gluten were investigated by size-exclusion chromatography in conjunction with multi-angle laser light scattering (SEC–MALLS), spectrophotometry and atomic force microscopy (AFM). The results showed that during the freeze–thaw cycles (frozen at −18°C with cycling to 0°C for 12h and then back to −18°C per 10days) the molecular weight and radius of gyration of the gluten proteins decreased with the increase in freeze–thaw cycles, implying a depolymerisation in the high-molecular-weight fraction of the gluten. The free amino group content changed only slightly, and the free sulphydryl group content of the gluten increased from 9.8μmol/g for the control to 13.87μmol/g for the gluten stored for 120days and submitted to 12 times freeze–thaw cycling, indicating that the depolymerisation of the gluten during freeze–thaw cycling was due to the breakage of disulphide bonds. AFM images showed that the gluten chain formed a fibril-like branched network which was weakened with increasing freeze–thaw cycles storage time. Some aggregation of the gluten chains was also observed in the AFM images.

Study on Mechanism of Soy Protein Oxidation Induced by Lipid Peroxidation Products

Oxidative modification of soy protein by lipid peroxidation products, which was potentially present in a lipoxygenase-catalyzed polyunsaturated fatty acid peroxidation system, was investigated in this study. 13S-Hydroperoxy-9Z, 11E-Octadecadienoic acid (HPODE), malondialdehyde and acrolein were selected as representative primary product and secondary byproducts of lipid peroxidation and 2, 2’-azobis-(2-amidinopropane) dihydrochloride (AAPH) -derived peroxyl radical peroxyl radicals were chosen to simulate lipid peroxidation- derived free radical. Incubation of soy protein with increasing concentration of AAPH, HPODE, malondialdehyde and acrolein resulted in gradual generation of protein carbonyl derivatives, loss of free sulphydryl groups, total sulphydryl groups, free amine, available lysine, surface hydrophobicity and formation of oxidation aggregates. The average distribution model of protein accessible groups could explain majority mechanism of lipid peroxidation products-mediated soy protein oxidation. Primary oxidation aggregates further developed into insoluble aggregates by covalent cross-linking also may provide a partial mechanism of lipid peroxidation products-mediated soy protein oxidation.