Study on the characteristic of bovine serum albumin-glucose model system, treated by ultrasonic

Pulsed electric field enhances glucose glycation and emulsifying properties of bovine serum albumin: Focus on polarization and ionization effects at a high reaction temperature

Previous studies demonstrated that the non-thermal effects of pulsed electric fields can promote protein glycation below 40 °C, but it does not always enhance the emulsifying properties of proteins, such as in the bovine serum albumin/glucose model. Therefore, the aim of this study was to investigate the impact of non-thermal effects on the glucose glycation and emulsification properties of bovine serum albumin at 90 °C. The results of circular dichroism, surface hydrophobicity, and molecular dynamics simulations showed that the polarization effect increased the degree of glycation of bovine serum albumin-glucose conjugates from 12.82 % to 21.10 % by unfolding protein molecule, while the emulsifying stability index was increased from 79.17 to 100.73 compared with the control. Furthermore, the results of principal component analysis and Pearson correlation analysis indicated that the ionization effect and the free radicals generated by pulsed electric fields significantly (p < 0.05) inhibited browning and reduced free sulfhydryl content. This study demonstrated that pulsed electric fields combined with heating can prepare glycated proteins with good emulsifying properties in a short period of time and at temperatures lower than conventional heating while reducing energy consumption. This processing strategy has potential applications in improving the emulsifying performance of highly stable proteins.

Effects of ultrasound on functional properties, structure and glycation properties of proteins: a review

Protein is an indispensable part of life. It provides nutrition for human body and flavor for food. The role of protein depends largely on the functional properties of the protein. Therefore, the elucidation of protein structure and functional properties needs to be further explored. The effects of structural and functional properties of proteins under different ultrasonic treatment conditions were reviewed. The structural changes of protein were studied by hydrogen-deuterium exchange mass spectrometry combined with fluorescence spectrometry and proteomics, and the mechanism of action was determined. The glycation site, the glycation degree, and the glycation characteristics of different sugars were determined. The protein was modified by ultrasound, and the influence of protein structure, physicochemical properties, protein glycation characteristics, and the action mechanism were analyzed by biological mass spectrometry.

Recent advances of ultrasound-assisted Maillard reaction

Maillard reaction (MR) is one of the most important chemical reactions in the food science domain with a long history of more than 100 years. As for ultrasound-assisted MR (US-MR), it has gradually drawn attention in a recent decade. Purpose of this paper is to provide a systematic review on recent advances of US-MR in model systems, glycation of protein, and food processing. Fundamental studies on simple MR model systems (i.e. reducing sugar and amino acid) have reported a promoted generation of colored and volatile MR products (MRPs). Critical steps influenced by US and possible mechanisms have been elucidated simultaneously. Other studies focused on modification of proteins which undergoes a glycation between proteins and saccharides as the initial stage of MR. Since the MR rate is extremely low in the presence of protein and saccharide, US becomes a promising mean of promoting the glycation. As a result, a number of functional properties of glycated protein obtained by US are significantly promoted, which extend their utilization in the food industry. The rest of studies reviewed in this article are concentrated on applying US to process real foods. Many attributes changed during US-assisted processing are induced by MR. Positive aspects brought by the promoted US-MR include enhanced antioxidant capacity and organoleptic properties (e.g. desirable color, low bitterness, enhanced flavor, etc.), as well as inhibited hazards (e.g. advanced glycation end-products, acrylamide, etc.) formed in the processed foods. Meanwhile, the promoted MR by US may also inevitably bring some negative aspects to the processed foods due to unfavored yellowish/browning colors, off-flavors and hazard components.

Influence of ultrasound pretreatment on the subsequent glycation of dietary proteins

The influence of ultrasound treatment on the subsequent glycation process of proteins is controversial. Glycation behaviors of bovine serum albumin (BSA), β-lactoglobulin (β-Lg) and β-casein (β-CN) after ultrasound pretreatment (UP) were compared by both evaluating glycation kinetics and analyzing structural changes of proteins. UP resulted in both unfolding and aggregation behavior in protein samples, which altered the accessibility of the Lys and Arg. Five cycles of UP up-regulated the glycation degree of BSA and β-Lg, possibly due to the unfolding behavior induced by UP, which exposed additional glycation sites. In contrast, 30 cycles of UP induced a dramatic increase (by 97.9 nm) in particle size of BSA, thus burying portions of glycation sites and suppressing the glycation process. Notably, UP had minimal influence on glycation kinetics of β-CN, due to its intrinsic disordered structure. Based on proteomics analysis, the preference of Lys and Arg during glycation was found to be changed by UP in BSA and β-Lg. Four, 3 and 3 unique carboxyethylated lysine residues were identified in glycated BSA after 0, 5 and 30 cycles of UP, respectively. This study suggests that the protein glycation can be affected by UP, depending on the ultrasonication duration and native structure of the protein.

Mechanochemically Induced Controlled Glycation of Lysozyme and Its Effect on Enzymatic Activity and Conformational Changes

Protein glycation through heating of a mixture of protein and reducing sugars is one of the most commonly used methods of protein modification; however, in most cases, this approach can lead to uncontrolled glycation. The hypothesis that mechanical energy supplied through ball milling can induce glycation of proteins was tested using a well-characterized enzyme lysozyme. The Q-TOF/MS analysis of the milled samples has indicated that the milling of sugar-protein mixtures in stainless steel jars for 30 min and at a frequency of 30 Hz generated mainly monoglycated proteins even with the highly reactive ribose. Increasing the sugar concentration or the milling time did not influence the overall yield or generate more glycoforms. Enzymatic activity measurements, FTIR, and fluorescence spectroscopic studies have indicated that milling of lysozyme alone leads to a significant loss in enzymatic activity and structural integrity in contrast to milling in the presence of sugars.

Physicochemical Properties of Bovine Serum Albumin-Glucose and Bovine Serum Albumin-Mannose Conjugates Prepared by Pulsed Electric Fields Treatment

The pulsed electric fields (PEF) treatment is a novel method for obtaining glycated proteins by way of a Maillard reaction between proteins and polysaccharides but its effect on the preparation of protein–monosaccharide conjugate has not been explored. This study aimed to prepare bovine serum albumin (BSA)–glucose and BSA–mannose conjugates using PEF in pH 10.0 at an intensity of 10 or 20 kV/cm, frequency of 1 kHz, pulse width of 20 μs and 73.5 pulses. The conjugates were evaluated for physicochemical properties. The results indicated that PEF not only promoted Maillard reaction between BSA and glucose or mannose but also alleviated the undesirable browning. PEF treatment favored the increased surface hydrophobicity and emulsifying activity in BSA but reduced surface hydrophobicity and foaming stability and improved foaming capacity in BSA–glucose and BSA–mannose conjugates. These findings provided useful considerations in the application of PEF treatment as a potential method to prepare BSA–monosaccharide conjugates by Maillard reaction.

Liquid Chromatography High-Resolution Mass Spectrometry Identifies the Glycation Sites of Bovine Serum Albumin Induced by d-Ribose with Ultrasonic Treatment

Ultrasonication is an emerging technology applied in food processing and biological experimental pretreatments. Cavitation phenomena induced during ultrasonic treatment can generate localized high temperature and pressure, which can result in glycation reaction between protein and reducing sugars. In this study, the mixture of bovine serum albumin (BSA) and d-ribose was treated under 600 W for different times. Interestingly, a large amount of carbonized black materials appeared after ultrasonication, while the UV absorbance and intrinsic fluorescence spectra reflecting conformational changes were not obvious. Only 12 sites (11 lysines and 1 arginine) of the BSA with ribose under ultrasonic treatment for 35 min were identified through liquid chromatography high-resolution mass spectrometry (LCHR-MS). K547, K548, R359/R360, and K587 were the most reactive glycated sites, with the average degree of substitution per peptide molecule (DSP) value ranging from 15 to 35%. The glycated modification was distributed not only in domain III, but also in domains I and II. The glycated modification could occur during ultrasonic treatment, thereby influencing the properties of biomacromolecule after extraction.

Comparative Studies on Physicochemical Properties of Bovine Serum Albumin–Glucose and Galactose Conjugates Formed by Glycation Combined with Ultrasonic Pretreatment

The effects of ultrasonication on the physicochemical properties of bovine serum albumin (BSA)–glucose and the galactose conjugates formed by glycation was investigated. Fourier transform ion cyclotron resonance mass spectra analysis showed that the conjugates had a higher molecular weight than the native and ultrasonicated BSA. Ultrasonicated BSA had significantly higher emulsifying and foaming properties than native BSA. The browning intensity, surface hydrophobicity, emulsifying property and foaming capacity of the conjugates were substantially improved while the free amino groups, intrinsic fluorescence emission and foaming stability were decreased compared to native and ultrasonicated BSA. The results of this study indicate that ultrasonication is an efficient technique to improve the physicochemical properties of proteins. The glycation between ultrasonicated BSA and monosaccharide can effectively improve the physicochemical properties of BSA, and the glycation rate order is galactose \gt glucose. It also shows the critical role of monosaccharide conformational changes in improving the glycation and physicochemical properties of proteins.

Glycation of β-lactoglobulin under dynamic high pressure microfluidization treatment: Effects on IgE-binding capacity and conformation

The effects of dynamic high-pressure microfluidization (DHPM) (80, 120, and 160MPa) treatment and glycation with galactose on the IgE-binding capacity and conformation of β-lactoglobulin (β-Lg) were investigated. The binding capacity of immunoglobulin E (IgE) from patients' sera with cow's milk allergy on β-Lg glycated with galactose decreased after DHPM treatment. β-Lg treated after different DHPM methods and pressures yielded a significant discrepancy in IgE-binding capacity. When β-Lg was pretreated by DHPM, the IgE-binding capacity of β-Lg-galactose conjugates decreased with increasing pressure; however, the conjugates showed higher IgE-binding capacity at 120MPa than that at 80 and 160MPa when the β-Lg-galactose mixture was treated by DHPM. Results of thermal properties, intrinsic fluorescence spectroscopy, surface hydrophobicity, and circular dichroism (CD) spectra indicated the occurrence of protein unfolding, as well as the tertiary and secondary structural changes of β-Lg. The results suggested pretreatment by DHPM and glycation with galactose was a promising approach for eliminating the IgE-binding capacity of β-Lg.

Characterisation of bovine serum albumin-fucoidan conjugates prepared via the Maillard reaction

Bovine serum albumin (BSA)-fucoidan conjugates were prepared by the Maillard reaction (60 °C and 79% relative humidity for 96 h), and were then identified by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and size-exclusion chromatography (SEC). Molecular characteristics of the BSA-fucoidan conjugates were investigated, using atomic force microscopy (AFM), dynamic light scattering (DLS), fluorescence spectroscopy, and circular dichroism spectroscopy. SDS-PAGE patterns provided evidence for the covalent bonding between BSA and fucoidan. SEC profiles showed that about 1.5-2.0 mol of fucoidan were covalently linked to 1 mol of BSA, resulting in high-molecular-weight compositions (conjugates). AFM images and DLS results indicated that most particles in the conjugates were nano-structured and more spherical than those of a regular BSA-fucoidan mixture. The fluorescence intensity and maximum emission wavelength of the conjugates together revealed that the BSA molecules had converted from an ordered conformation into a partially folded molten globule state.

Improved glycation after ultrasonic pretreatment revealed by high-performance liquid chromatography-linear ion trap/Orbitrap high-resolution mass spectrometry

The glycation extent of bovine serum albumin (BSA) before and after ultrasonication was evaluated by MALDI-TOF and Orbitrap mass spectrometry. Ultrasonic pretreatment significantly improved the incorporation of galactose to BSA. Prior to ultrasonic pretreatment, only 12 sites (11 lysines and 1 arginine) were glycated, whereas the number of glycation sites was increased to 42, including 39 lysines and 3 arginines, after treatment. Average degree of substitution per peptide molecule of BSA (DSP) was used to evaluate the glycation level for each glycation site. The ultrasonic pretreatment significantly improved the DSP value of all glycation sites. The prevalently promoted glycation by ultrasonic pretreatment suggests that ultrasonication improves glycation through altering the structure of BSA throughout all three domains. An ultrahigh-resolution linear ion trap Orbitrap mass spectrometer facilitates unambiguous localization of glycation sites, allowing an in-depth analysis of the nature and extent of protein glycation at the molecular level. High-intensity ultrasonication can greatly improve protein glycation and, therefore, opens new routes to modify the functionality of proteins in a positive way.

Microwave heating enhances antioxidant and emulsifying activities of ovalbumin glycated with glucose in solid-state

The aim of this study was to characterize the properties of ovalbumin (OVA) after glycated with glucose under microwave heating. For this purpose, microwave at 480 and 640 W power levels were used for heating the OVA-glucose system in solid-state for 0, 5, 10, 15, 20 and 25 min, respectively. The results indicated that the protein molecular weight was increased after glycated with glucose under microwave treatment, the pH of the system was decreased with the increase of microwave treatment power and time, while the UV absorbance, browning intensity, antioxidant activities as well as the emulsifying activity and emulsion stability of the Maillard reaction products (MRPs) were increased in according with the raise of microwave treatment power and time. The reaction time of microwave treatment is much shorter than those using traditional methods, suggesting that microwave irradiation is a novel and efficient approach to promote Maillard reaction (MR) in dry state and improve protein antioxidant and functional properties.