Guang-xian Liu

Comparison of glycation in conventionally and microwave-heated ovalbumin by high resolution mass spectrometry

The glycation extent of ovalbumin under two heating conditions, conventional and microwave heating was monitored by high resolution mass spectrometry, following pepsin digestion. The sequence coverage of the unglycated and glycated ovalbumin was 100% and 95%, respectively. About 35.2% of the lysines after microwave heating and 40.8% of the lysines after conventional heating were modified by d-glucose. The glycation content increased quickly when ovalbumin-glucose mixture was incubated for 15min, under both processing conditions. These modifications were slowed down after 30min of heating and no obvious advanced stage products were observed. The glycated peptides exhibited varying degrees of glycation, under both conventional and microwave heating, suggesting that glycation is strongly relevant to the protein structure. The fact that some peptides showed a lower level of glycation when heated by microwave indicated that microwave radiation might be a non-thermal process. In addition, the lack of browning after microwave heating emphasised the difference between microwave and conventional heating.

High-quality photonic crystal heterostructures fabricated by a modified self-assembly method

High-quality three-dimensional photonic crystal (PC) heterostructures were fabricated using the modified self-assembly method, and their structural and optical properties were analyzed. Results suggest that the optical quality of heterostructures formed by depositing bigger particles on small ones is superior to that of heterostructures formed by stacking smaller particles on big ones, due to the rough interface effects in the latter structure. The roughness of the interface in the latter structure can be largely improved by introducing a thin two-dimensional planar defect layer into the PCs, and significant progress in the quality of the heterostructures is achieved. The important role of the thin planar defect layer in the quality of the heterostructures was also verified by numerical simulations.

Monitoring of the functional properties and unfolding change of Ovalbumin after DHPM treatment by HDX and FTICR MS: Functionality and unfolding of Oval after DHPM by HDX and FTICR MS

Dynamic high-pressure microfluidizaiton (DHPM) induced unfolding of proteins and enzymes could enhance the functional properties and hydrolytic ability of the molecules. In this study, the effect of DHPM on the surface activities of Ovalbumin (Oval), namely foaming and emulsifying properties, was investigated at 0, 40, 80, 120 and 160MPa. Improvement in the foaming and emulsifying properties was observed at 120 and 80MPa, respectively. Hydrogen/deuterium exchange (HDX) coupled with Fourier transform infrared spectroscopy-mass spectrometry (FTICR MS) was performed to investigate the exact unfolded region of Oval and analyze the mechanism promoting the foaming and emulsifying properties after 120 and 80MPa, respectively, compared with those at 0MPa. Prevalent unfolding of Oval after 80 and 120MPa treatment was revealed by HDX-MS, indicating a more flexible conformation induced by DHPM. However, lower deuterium incorporation was observed for the large six-stranded β-sheet. Therefore, the combined forces could enhance the flexibility and surface activities of Oval, which increased its foaming and emulsifying properties.

Identification and quantification of the phosphorylated ovalbumin by high resolution mass spectrometry under dry-heating treatment.

The specific phosphorylation sites and degree of phosphorylation (DP) at each site are directly related to proteins structure and functional properties. Thus, characterizing the introduced phosphate groups is of great importance. This study was to monitor the phosphorylation sites, DP and the number of phosphorylation sites in P-Oval achieved by dry heating in the presence of pyrophosphate for 1, 2 and 5days by using Fourier transform ion cyclotron mass spectrometry (FTICR MS). Two phosphorylation sites were found in natural ovalbumin, but the number of phosphorylation sites increased to 8, 8 and 10 after dry-heating phosphorylation for 1, 2 and 5days, respectively. In addition, dual-phosphorylated peptides were detected for samples without extensive heating. The phosphorylation sites were found to be mainly on Ser residues, which could be the preferred phosphorylation site for dry heating in the presence of pyrophosphate.

Simulation and measurement of spontaneous emission characteristics from quantum dots in proximity to photonic crystals

A hybrid structure with a finite three-dimensional photonic crystal (PC) self-assembled on top of an SU8 organic film was proposed. Spontaneous emission (SE) from CdSe/ZnS core–shell quantum dots embedded in the organic film in such a structure was studied theoretically and experimentally as a function of the film thickness. The results reveal that the SE spectrum presents a damped periodic oscillatory dependence on the film thickness due to the synergy of the surface modes and the interference between the direct SE field and the reflected field; shoulder peaks appearing in the photoluminescence (PL) spectrum of the hybrid originate from the redistribution of the photon density of states at the band edges of the gap of PCs.

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.

Ultrasonic Pretreatment Combined with Dry-State Glycation Reduced the Immunoglobulin E/Immunoglobulin G-Binding Ability of α-Lactalbumin Revealed by High-Resolution Mass Spectrometry

Bovine α-lactalbumin (α-LA) is one of major food allergens in cows milk. The present work sought to research the effects of ultrasonic pretreatment combined with dry heating-induced glycation between α-LA and galactose on the immunoglobulin E (IgE)/immunoglobulin G (IgG)-binding ability and glycation extent of α-LA, determined by inhibition enzyme-linked immunosorbent assay and high-resolution mass spectrometry, respectively. The IgE/IgG-binding ability of glycated α-LA was significantly decreased as a result of ultrasonic pretreatment, while the average molecular weight, incorporation ratio (IR) value, location and number of glycation sites, and degree of substitution per peptide (DSP) value were elevated. When the mixtures of α-LA and galactose were pretreated by ultrasonication at 150 W/cm2, glycated α-LA possesses seven glycation sites, the highest IR and DSP values, and the lowest IgE/IgG-binding ability. Therefore, the decrease in the IgE/IgG-binding ability of α-LA depends upon not only the shielding effect of the linear epitope found to be caused by the glycation of K13, K16, K58, K93, and K98 sites but also the intensified glycation extent, which reflected in the increase of the IR value, the number of glycation sites, and the DSP value. Moreover, allergenic proteins and monosaccharides pretreated by ultrasonication and then followed by dry-state glycation were revealed as a promising way of achieving lower allergenicity of proteins in food processing.

Investigation into allergenicity reduction and glycation sites of glycated β-lactoglobulin with ultrasound pretreatment by high-resolution mass spectrometry

Ultrasound treatment could change the conformation of β-lactoglobulin (β-Lg) and improve the glycation reaction in aqueous solution under neutral condition. However, the effect of ultrasound pretreatment on glycation of β-Lg with pentose at dry-state remains ambiguous, and the relationship between glycation and allergenicity of β-Lg with ultrasound pretreatment is unclear. This study aimed to evaluate the effect of ultrasound pretreatment on glycation and allergenicity of β-Lg. Markedly decreased allergenicity of β-Lg was observed after glycation with ribose before and after ultrasound pretreatment with the minimum found at 400 W. Orbitrap LC-MS/MS showed that the glycation degree of some peptides in glycated β-Lg with and without ultrasound pretreatment were different although the content of free amino group and molecular mass were insignificantly different. Therefore, ultrasound pretreatment promoted the reduction in allergenicity by improving the glycation extent of some glycation sites although it hardly enhanced the whole glycation degree of β-Lg.

LC-Orbitrap MS analysis of the glycation modification effects of ovalbumin during freeze-drying with three reducing sugar additives

In general, the reducing sugars were extensively utilized as additives to prevent denaturation and inactivation during the freeze-drying process. However, different additives have unequal protective effects on the protein conformation. To evaluate the mechanism of protection the protein structure using different additives in the freeze-drying process, the glycated sites and degree of substitution per peptide (DSP) of each site were investigated by LC-Orbitrap MS. We found that the ovalbumin that was supplemented with ribose and then lyophilized (R-oval) have the highest extent of glycation modification. K227 was the most reactive glycated site in R-Oval, with a DSP of 0.83. The ovalbumin that was supplemented with lactose and then lyophilized (L-Oval) have the lowest degree of glycation, and K227 did not undergo the glycation reaction. It was hypothesized that the order impact of different additives on protection of the protein conformation were lactose > galactose > ribose during the freeze-drying process.

Improved Antioxidant Activity and Glycation of α-Lactalbumin after Ultrasonic Pretreatment Revealed by High-Resolution Mass Spectrometry

High-resolution mass spectrometry was performed to investigate the relationship between bovine α-lactalbumin (α-LA) subjected to ultrasonication and glycation treatment with respect to antioxidant activity. After α-LA was pretreated by ultrasonication combined with glycation, the treated α-LA showed low intrinsic fluorescence emission and high antioxidant activity at increased ultrasonic power levels. Prior to ultrasonic pretreatment, three glycated sites were identified, whereas the number of glycation sites was increased to four, four, five, and six after ultrasonic power at 60, 90, 120, and 150 W/cm2, respectively, for 15 min. Thus, no obvious difference was found among the glycation sites at the ultrasonic power of 60 and 90 W/cm2. The average degree of substitution per peptide molecule of α-LA was used to evaluate the glycation level per glycation site. All the samples pretreated by ultrasonication exhibited a higher glycation level compared with the untreated samples. Ultrasonic power at 150 W/cm2 showed the most highly enhanced glycation extent and antioxidant activity. Therefore, the intensified glycation extent and the conformational changes of protein were responsible for the increase of antioxidant activity of α-LA. Moreover, high-resolution mass spectrometry is an efficient technique to understand the mechanism of the improved antioxidant activity.