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

Enhancing the Gelation Behavior of Transglutaminase-Induced Soy Protein Isolate(SPI) through Ultrasound-Assisted Extraction

Gelation, as an important functional property of soy protein isolate (SPI), can be improved by some green technologies in food manufacturing, including ultrasound, ultrahigh pressure and microwave treatments. This work investigated the effect of an alkaline solubilisation step in SPI extraction combined with sonication on protein properties. The TGase-induced gel of the modified SPI was prepared to explore the effect of ultrasound on gel properties, including structures, strength, water-holding capacity and rheological properties. Additionally, the differences between traditional ultrasound modification of SPI and current modification methods were analyzed. The results showed that the ultrasonication-assisted extraction method could result in a significant increase in extraction rate from 24.68% to 42.25%. Moreover, ultrasound-assisted modification of SPI gels induced with transglutaminase (TGase) exhibited significant improvement in mechanical properties, such as texture, water-holding capacity and rheological properties, In particular, SPI extracted at 400 W ultrasound intensity for 180 s showed the best overall performance in terms of gel properties. Our method efficiently uniformizes gel structure, enhancing mechanical properties compared to conventional ultrasound methods, which reduced energy consumption and costs. These findings provide insights into the production of high-gelation SPI in food manufacturing.

Molecular structure, IgE binding capacity and gut microbiota of ovalbumin conjugated to fructose and galactose:A comparative study

Ovalbumin (OVA) was modified by fructose (Fru) and galactose (Gal) to study the structure, IgG/IgE binding capacity and effects on human intestinal microbiota of the conjugated products. Compared with OVA-Fru, OVA-Gal has a lower IgG/IgE binding capacity. The reduction of OVA is not only associated with the glycation of R84, K92, K206, K263, K322 and R381 in the linear epitopes, but also with conformational epitope changes, manifested as secondary and tertiary structural changes caused by Gal glycation. In addition, OVA-Gal could alter the structure and abundance of gut microbiota at phylum, family, and genus levels and restore the abundance of bacteria associated with allergenicity, such as Barnesiella, Christensenellaceae_R-7_group, and Collinsela, thereby reducing allergic reactions. These results indicate that OVA-Gal glycation can reduce the IgE binding capacity of OVA and change the structure of human intestinal microbiota. Therefore, Gal glycation may be a potential method to reduce protein allergenicity.

Research advance of non-thermal processing technologies on ovalbumin properties: The gelation, foaming, emulsification, allergenicity, immunoregulation and its delivery system application

Ovalbumin (OVA) is the most abundant protein in egg white, with excellent functional properties (e.g., gelling, foaming, emulsifying properties). Nevertheless, OVA has strong allergenicity, which is usually mediated by specific IgE thus results in gut microbiota dysbiosis and causes atopic dermatitis, asthma, and other inflammation actions. Processing technologies and the interactions with other active ingredients can influence the functional properties and allergic epitopes of OVA. This review focuses on the non-thermal processing technologies effects on the functional properties and allergenicity of OVA. Moreover, the research advance about immunomodulatory mechanisms of OVA-mediated food allergy and the role of gut microbiota in OVA allergy was summarized. Finally, the interactions between OVA and active ingredients (such as polyphenols and polysaccharides) and OVA-based delivery systems construction are summarized. Compared with traditional thermal processing technologies, novel non-thermal processing techniques have less damage to OVA nutritional value, which also improve OVA properties. OVA can interact with various active ingredients by covalent and non-covalent interactions during processing, which can alter the structure or allergic epitopes to affect OVA/active components properties. The interactions can promote OVA-based delivery systems construction, such as emulsions, hydrogels, microencapsulation, nanoparticles to encapsulate bioactive components and monitor freshness for improving foods quality and safety.

A high-resolution Orbitrap Mass spectral library for trace volatile compounds in fruit wines

The overall aroma is an important factor of the sensory quality of fruit wines, which attributed to hundreds of volatile compounds. However, the qualitative determination of trace volatile compounds is considered to be very challenging work. GC-Orbitrap-MS with high resolution and high sensitivity provided more possibilities for the determination of volatile compounds, but without the high-resolution mass spectral library. For accuracy of qualitative determination in fruit wines by GC-Orbitrap-MS, a high-resolution mass spectral library, including 76 volatile compounds, was developed in this study. Not only the HRMS spectrum but also the exact ion fragment, relative abundance, retention indices (RI), CAS number, chemical structure diagram, aroma description and aroma threshold (ortho-nasally) were provided and were shown in a database website (Food Flavor Laboratory, http://foodflavorlab.cn/). HRMS library was used to successfully identify the volatile compounds mentioned above in 16 fruit wines (5 blueberry wines, 6 goji berry wines and 5 hawthorn wines). The library was developed as an important basis for further understanding of trace volatile compounds in fruit wines.

Measurement(s)	volatile compounds
Technology Type(s)	GC-Orbitrap-MS

Deciphering Changes in the Structure and IgE-Binding Ability of Ovalbumin Glycated by α-Dicarbonyl Compounds under Simulated Heating

As a complex reaction, biological consequences of the Maillard reaction (MR) on dietary proteins need to be deciphered. Despite previous studies on the structural and antigenic properties of ovalbumin (OVA) by MR, associated changes induced by specific MR intermediates and their downstream products are largely unknown. This study focused on the impacts of glycation by α-dicarbonyl compounds (α-DCs), intermediates of MR and precursors of advanced glycation end-products (AGEs), on the structural and IgE-binding properties of ovalbumin (OVA) under simulated heating. Methylglyoxal (MGO), glyoxal (GO), and butanedione (BU) were selected as typical α-DCs to generate glycated OVA with different AGE-modifications (AGE-Ms). The results showed that reactions between OVA and α-DCs generated OVA-AGE with various degrees of modification and conformational unfolding, and the reactivity of α-DCs followed the order GO > MGO > BU. Depending on the precursor type, the levels of 10 specific AGEs were verified, and the amounts of total AGEs increased with heating temperature and α-DC dosage. Compared to native OVA, glycated OVA showed reduced IgE-binding levels but with sRAGE-binding ligands, the extent of which was associated with the contents of total AGEs and Nε-carboxymethyllysine, and changes in certain protein conformational structures. High-resolution mass spectrometry further identified different AGE-Ms on the Lys and Arg residues of OVA, confirming variations in the glycation sites and their associations with the immunoreactive epitopes of OVA under different conditions.

Apoptosis of hepatocellular carcinoma HepG2 cells induced by seleno-ovalbumin (Se-OVA) via mitochondrial pathway

Seleno-ovalbumin (Se-OVA) was a selenium conjugating protein synthesized by the combination of ovalbumin (OVA) and inorganic selenium. In this paper, the structure of Se-OVA was characterized, and the anticancer effect of Se-OVA on hepatocellular carcinoma HepG2 cells was investigated. Through FT-IR, UV, endogenous fluorescence and XRD assays, it was found that the structural characterization of Se-OVA changed after seleno-modification. In addition, the cell assays showed that Se-OVA could induce apoptosis of HepG2 cells by arresting cell cycle in S phase, generating intracellular reactive oxygen species, reducing the mitochondrial transmembrane potential, and triggering the Bax- and Bcl-2-mediated mitochondria apoptosis pathway. These findings revealed that Se-OVA might serve as a novel anticancer drug for cancer adjuvant therapy.

Insight into the mechanism of d-allose in reducing the allergenicity and digestibility of ultrasound-pretreated α-lactalbumin by high-resolution mass spectrometry

The mechanism of d-allose in reducing the allergenicity and digestibility of ultrasound-pretreated α-lactalbumin (α-LA) was studied. The intensity reduction and peak red shift occurred in fluorescence spectra of glycated samples. Enzyme-linked immunosorbent assay and basophil degranulation analysis showed that d-allose significantly reduced the allergenicity of α-LA, and ultrasound-pretreated α-LA showed the lowest allergenicity after glycation. Compared with α-LA, the degree of hydrolysis decreased in glycated samples. Size-exclusion high-performance liquid chromatography showed that the glycated α-LA was resistant to digestive enzymes. The glycated sites and average degree of substitution per peptide molecule were determined using LC Orbitrap MS/MS. These results suggested that the masking of linear allergenic epitopes by glycation could reduce the allergenicity. Therefore, the combination of ultrasound pretreatment and glycation is a potential method to reduce protein allergenicity in food processing and provides a useful approach for the application of rare sugars in food processing.

Insight into the mechanism of urea inhibit ovalbumin-glucose glycation by conventional spectrometry and liquid chromatography-high resolution mass spectrometry

The inhibition effect of urea on ovalbumin (OVA) glycation was investigated, and the mechanism was evaluated through the changes in protein structure as well as glycation sites and average degree of substitution per peptide molecule (DSP) by conventional spectrometry and liquid chromatography-high resolution mass spectrometry (LC-HRMS). A urea concentration of 3 M was chosen as the optimum condition. Ultraviolet and fluorescence spectra suggested that both glycation and urea treatment could unfold the OVA, but urea inhibited the glycation-induced protein unfolding. Circular dichroism spectra showed that urea treatment could increase the β-sheet content and reduce the α-helix content of OVA. LC-HRMS indicated that the number of glycation sites was reduced from 15 to 3, and DSP values decreased with urea treatment. In conclusion, urea could significantly inhibit the OVA-glucose glycation, and the sites competition as well as structure unfolding inhibition resulted from urea could be the main factors.

Mechanism of Selenium Nanoparticles Inhibiting Advanced Glycation End Products

Selenium nanoparticles (SeNPs) have been applied in fields of nanobiosensors, environment, nanomedicine, etc. as a result of their excellent characteristics. Early studies had shown that SeNPs have certain inhibition ability against glycation, but the inhibition mechanism, especially for the influence of SeNPs on the reaction activity of glycation sites, remains unclear. The aim of the presented research was to reveal the effects of SeNPs on the β-lactoglobulin (β-Lg)/d-ribose glycation system at the molecular level and explore the possible inhibitory mechanism of SeNPs on the formation of advanced glycation end products (AGEs) by analyzing the glycation sites via high-performance liquid chromatography (HPLC)-Orbitrap-tandem mass spectrometry (MS/MS). Changes in contents of AGE formation and free amino acid contents had indicated that SeNPs could significantly slow the glycation process, thus attenuating the formation of AGEs. HPLC-Orbitrap-MS/MS analysis revealed that, at 6, 12, and 24 h, the number of glycation sites of glycated β-Lg decreased from 7, 7, and 9 to 5, 5, and 6 after the intervention of SeNPs, respectively. The glycation extent of each glycation site was controlled, and the dual-glycation ability of K8, K14, K47, K91, and K101 was changed. All of these results confirmed that SeNPs could indeed slow the process of protein glycation at the molecular level. This may be the reason for SeNPs reducing the formation of AGEs during glycation. Therefore, this study shed light on the insight of how SeNPs reduce the formation of AGEs.

Influence of Hydroxyl Substitution on the Suppression of Flavonol in Harmful Glycation Product Formation and the Inhibition Mechanism Revealed by Spectroscopy and Mass Spectrometry

Quercetin (Que), kaempferol (Kaem), isorhamnetin (Irh), and myricetin (Myri) are typical flavonols that are abundant in plant resources. This research investigated their ability in attenuating harmful glycation product formation and the effect of hydroxyl substitution. The inhibition mechanisms were elucidated by fluorescence spectroscopy and nano-liquid chromatography Orbitrap tandem mass spectrometry. The results indicated that the 3'-OH on the B-ring is critical in alleviating harmful glycation product formation, methylation reduced its inhibition, and the 5'-OH showed much less contribution than the 3'-OH. Que showed the strongest suppression on initial product, 5-hydroxymethylfurfural, and advanced glycation end product formation, with the corresponding percentage inhibitions at 36.58 μM of 81.1, 56.9, and 95.4%. Que and Myri also clearly inhibited fructosamine and acrylaminde production, while no suppression was observed by Irh and Kaem. The number of glycated sites was reduced from ten to seven, five, six, and nine, respectively, when 36.58 μM Que, Myri, Kaem, and Irh was added. Suppressing the conformational changes of ovalbumin induced by glycation, trapping dicarbonyl compounds, altering the microenvironment around tryptophan, and reducing the glycation activity of potential sites were the major inhibition mechanisms. These results suggest that Que and Myri may be promising natural agents for inhibiting harmful glycation and provide theoretical support for the effective screening of natural antiglycation reagents.

Insight into the Mechanism of Reduced IgG/IgE Binding Capacity in Ovalbumin as Induced by Glycation with Monose Epimers through Liquid Chromatography and High-Resolution Mass Spectrometry

Ovalbumin (OVA) is one of the major food allergens in hen eggs. In this work, it was demonstrated that glycation with d-glucose and its epimers, including d-mannose, d-allose, d-galactose, and l-idose, could effectively attenuate the IgG/IgE binding of OVA, which was attributed to the covalent masking by sugars and to its structural changes. The glycation sites were determined, and their average degree of substitution was found using liquid chromatography coupled with high-resolution mass spectrometry. Fluctuations in OVA conformation were monitored by conventional spectrometry. Compared to those of OVA-Man and OVA-Glu, OVA-All, OVA-Gal, and OVA-Ido showed a higher glycation extent, and the alterations on their steric layouts were more drastic, suggesting that the configuration of hydroxyl groups at positions C-3, C-4, and C-5 in sugars might be important for the glycation reactivity; as such, their capabilities in binding with IgG/IgE decreased more significantly. Attempts were made to provide valuable information for in-depth understanding of the differences in biochemical functionality among epimeric sugars. These insights would be helpful for designing sweetened food products with a desirable level of safety.

Rapid in situ analysis of l-histidine and α-lactose in dietary supplements by fingerprint peaks using terahertz frequency-domain spectroscopy

A simple, green and nondestructive method based on terahertz fingerprint peaks has been developed for rapid in situ analysis of l-histidine and α-lactose in dietary supplements. Fingerprint absorption peaks of l-histidine and α-lactose located at 0.77 and 0.53 THz could be directly used for identification and quantitation of these analytes in commercial dietary supplements. Compared with the partial least squares regression model (PLSR), the linear least squares regression (LLSR) method based on peak areas presented better performance, with the linear correlation coefficients of 0.9899 and 0.9910 for l-histidine and α-lactose, respectively. Furthermore, analysis time per sample can be shortened to less than 1 min due to the narrower spectral acquisition region. The accuracies were 94.8-110% and 98.9-110%, comparable to those of ion chromatography for l-histidine and high-performance liquid chromatography for α-lactose. The results presented great potential of the developed method for rapid in situ analysis of nutrients in dietary supplements.

Effect and Mechanism of Elaeagnus angustifolia Flower and Its Major Flavonoid Tiliroside on Inhibiting Non-enzymatic Glycosylation

This study aimed to evaluate the antiglycation ability of Elaeagnus angustifolia flower extract and to elucidate the mechanism with its major compound. The results indicated that E. angustifolia flower extract and its major compound tiliroside (24.2 mg/g of extract) exhibited excellent antiglycation ability with inhibition rates of 92.1 and 78.9% at 37.5 μg/mL, which are much higher than that of aminoguanidine (55.3% at 37.5 μg/mL). The stable tiliroside-ovalbumin (OVA) complexes were formed through a spontaneous exothermic progress in an equimolar manner, and hydrophobic interaction, hydrogen bond, and van der Waals forces were the major driving forces. Tiliroside could significantly ameliorate the conformation changes of OVA induced by the glycation reaction, quench its fluorescence by a static mechanism, and change the microenvironment adjacent to tryptophan and tyrosine. Molecular docking revealed that tiliroside inserted into the OVA hydrophobic pocket resulted in the formation of five hydrogen bonds. Orbitrap tandem mass spectrometry showed that tiliroside significantly suppressed the glycation of OVA, and the number of glycation sites was reduced from 9 to 5 after tiliroside was added. The above results indicated that E. angustifolia flowers and tiliroside have a good antiglycation effect and can be used as food additives to suppress the undesired glycation reaction during food processing.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.

Investigation of the Mechanism of Conformational Alteration in Ovalbumin as Induced by Glycation with Different Monoses through Conventional Spectrometry and Liquid Chromatography High-Resolution Mass Spectrometry

Glycation between ovalbumin (OVA) and different monoses under mild dry heating at 37 °C was studied. The content of free amino groups decreased dramatically, and the conformational changes based on fluorescence and circular dichroism spectra were evident in glycated OVA. The glycated sites and the average degree of substitution per peptide molecule per site were determined using liquid chromatography high-resolution mass spectrometry. Lysine and arginine were the predominant glyaction sites, in which Lys207 was a relatively reactive site for glycation in all of the conjugates. In general, the extent of glycation of aldose was higher, and its alterations on the steric layouts of protein were more drastic than those of ketose. The configuration of hydroxyl groups at C-4 in sugar epimers might be important for the glycation reactivity and conformational modification in the glycated proteins. These insights would have important implications for the creation of sweetened food products with desirable structures and excellent quality control.

The Mechanism of Decreased IgG/IgE-Binding of Ovalbumin by Preheating Treatment Combined with Glycation Identified by Liquid Chromatography and High-Resolution Mass Spectrometry

Ovalbumin is one of the most important sensitizing ingredients in allergens of egg albumin, which restricts the application of egg in the field of food processing. Previous research has indicated that glycation could cause the protein to partially expand, which may bring about the destruction of the structural IgG and IgE epitopes and induce the decline of the IgG- and IgE-binding ability of ovalbumin. In this research, the effect of a preheating treatment integrated with glycation on the IgG- and IgE-binding capability and the conformation changes of ovalbumin was studied by detecting the glycated sites and the values of degree of substitution per peptide (DSP) by liquid chromatography and high-resolution mass spectrometry (LC-HRMS). Interestingly, we found that a glycation site (K227) attached by two ribose molecules was detected in glycated ovalbumin with preheating treatment. In addition, a new glycation site (K323) appeared in G-60. The results displayed that preheating treament could strengthen the changes in the secondary and tertiary structure of ovalbumin by enhancing glycation and further reduce the IgG/IgE-binding ability by integrating with glycation because of the cover of IgG and IgE epitopes. Therefore, preheating treatment integrated with glycation may offer a way for ovalbumin to reduce sensitization.

Glucose Glycation of α-Lactalbumin and β-Lactoglobulin in Glycerol Solutions

The glucose glycation of α-lactalbumin and β-lactoglobulin at 50 °C in a glycerol-based liquid system was investigated to evaluate the effect of water activity on glycation and site-specificity in a glycerol matrix. Glycation extent during the reaction was determined using the o-phthalaldehyde (OPA) method as well as ultraperformance liquid chromatography combined with electro-spray ionization mass spectrum (UPLC-ESI-MS) analysis. Glycation sites were identified by data-independent acquisition LC-MS (LC-MS^E). The surface potential achieved by PyMOL and the tertiary structure determined by circular dichroism (CD) were used to assist the analysis of the glycation site-specificity in the glycerol matrix. The water activity of glycerol solutions was negatively correlated to the glycerol concentration. Results showed that the initial glycation rate in glycerol matrix was fitted to a linear equation in the first 48 h. Glycation accelerated with the increase of glycerol concentration, namely, the decrease of water activity, regardless of the native structure of the protein. The glycation sites were identical at a similar DSP although achieved at different water activities, with 4 and 7 sites detected in α-lactalbumin and β-lactoglobulin, respectively. However, compared with the glycation sites in a water-based matrix, the site-specificity of glycation was affected by the glycerol matrix, depending on the native structure of the proteins. Glycation was prone to occur at the reactive sites distributed on the surface of the proteins, particularly in the region with positive potential.