Modified Structural and Functional Properties of Fish Gelatin by Glycosylation with Galacto-Oligosaccharides

This study aimed to investigate the effects of galacto-oligogalactose (GOS) glycosylation on the structural and functional properties of fish gelatin (FG). Results showed that with the increase of glycosylation time, grafting degree and browning increased, and new protein bands with increased molecular weight were observed by SDS-PAGE. Structural analysis showed that glycosylation reduced intrinsic fluorescence intensity and increased surface hydrophobicity of FG. FTIR analysis showed α-helix content decreased while random coil content increased in glycosylated FG. Emulsion activity index and emulsion stability index along with foam activity and foam stability were significantly elevated in GOS-4 and GOS-8, but FG glycosylated longer than 12 h exhibited less pronounced improvement. Glycosylated FG showed lower gel strength than control. The results indicate that moderate glycosylation could be applied to improve interfacial properties of FG.

Ultrasonic pretreatment enhanced the glycation of ovotransferrin and improved its antibacterial activity

This study aims to evaluate the effect of ultrasonic pretreatment combined with glycation on the structural characteristics and antibacterial activity of ovotransferrin (OVT). Firstly, OVT (purity >90%) was isolated from egg white with a simple and efficient method. After the treatment of ultrasound and glycation, the browning degree of OVT increased with the rising power of ultrasound, while the number of free amino groups obviously decreased to 25.4%. Various spectrum detection showed that the structures of OVT have changed significantly, indicating the tertiary structure became more flexible and looser. The minimal inhibitory concentration of ultrasound glycated OVT were 25.0 and 32.1 μmol/L for E. coli and S. aureus, respectively. In summary, ultrasound-assisted glycation is an effective technique to improve the biological activity of OVT.

Improved antitumor activity and IgE/IgG-binding ability of α-Lactalbumin/β-lactoglobulin induced by ultrasonication prior to binding with oleic acid

Bovine α-lactalbumin (α-La)/β-lactoglobulin (β-Lg) was pretreated through ultrasonic treatment and subsequently binding with oleic acid (OA) by heat treatment. And, the antitumor activity, IgE/IgG-binding ability, and structural modifications were investigated. After α-La/β-Lg were treated by ultrasonic prior to binding with OA, the treated α-La/β-Lg showed high antitumor activity and IgE/IgG-binding ability, and significantly affected the structural modifications, which reflected by the reduction in α-helix content, the increase of molecular weight, intrinsic fluorescence intensity, and surface hydrophobicity. Molecular docking studies indicated that OA bound to α-La/β-Lg by hydrogen bonds and hydrophobic interaction. Therefore, ultrasonic prior to binding with OA could improve antitumor activity and IgE/IgG-binding ability of α-La/β-Lg as a result of structural modifications. And, ultrasonic prior to binding with fatty acid processing of milk products alone may increase the antitumor activity, this change may enhance the risk of an allergenic reaction in milk allergy patients to some extent. PRACTICAL APPLICATIONS: Fatty acids, natural ligands associated with the bovine milk proteins, and milk protein-fatty acid complex has a variety of functional applications in the food industry. This study revealed that antitumor activity, IgE/IgG-binding ability, and structural modifications of α-La/β-Lg induced by ultrasonic prior to binding with oleic acid. It will be beneficial to understand the mechanism of the functional changes of protein. Ultrasonic prior to binding with oleic acid will be more likely to develop a practical technology to improve the functional characteristics of milk protein and design the optimal nutritional performance of milk food.

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.

Mitigation of isoquercitrin on β-lactoglobulin glycation: Insight into the mechanisms by mass spectrometry and interaction analysis

Formation of advanced glycation end products (AGEs) on foods imposes threats to human health after intaking. This research firstly evaluated the inhibition of isoquercitrin on β-lactoglobulin (β-Lg) glycation, the mechanisms were elucidated by fluorescence spectroscopy, Orbitrap MSⁿ and molecular docking. Fluorescence spectra indicated that isoquercitrin effectively alleviated the formation of AGEs, it could stabilize the conformation structure of glycated β-Lg (G-β-Lg), change the micro-environment in the vicinity of chromophores. SDS-PAGE analysis revealed the suppressed cross-linking of G-β-Lg induced by isoquercitrin. The number of glycation site detected on G-β-Lg was reduced from ten to eight after the addition of isoquercitrin, and the relative glycation degree of substitution of per site (RGDSP) of most glycation sites were also greatly decreased. As indicated by intermolecular interaction, isoquercitrin quenched the fluorescence of β-Lg via a static mechanism, and their combination is an endothermic processing mainly derived by hydrophobic interaction, hydrogen bonds, and van der Waals forces. Isoquercitrin interacted with β-Lg to form an equimolar complex, and one hydrogen bond was formed between isoquercitrin and Lys69 (4.96 Å). Above results proved that isoquercitrin can be a promising anti-glycation agent used in food system to prevent the formation of harmful glycation products.

Observation of the structural changes of α-lactalbumin induced by ultrasonic prior to glycated modification

Bovine α-lactalbumin (BLA) was treated by ultrasonic at 150 W/cm² for different times and subsequently glycated with mannose by dry-heating. Molecular weight, intrinsic fluorescence spectra, glycation sites and degree of modified BLA were observed. The proteinaceous high molecular weight components were formed after ultrasonic prior to glycated modification, while the conformational changes were obvious. Prior to ultrasonic pretreatment, K62, K114, and K122 of BLA were identified. After treated by ultrasound at 150 W/cm² for 5, 10, 15, and 20 min, the sites were increased to four, four, five, and five, respectively. All glycated sites of modified BLA exhibited a higher degree of substitution per peptide (DSP) values compared to native BLA. Ultrasonic at 150 W/cm² for 20 min revealed the most significant change in the BLA structure. Therefore, conformational changes, the intensified glycation site, and DSP value were responsible for the structural changes of BLA. Practical applications BLA is suitable as an ingredient for infant nutrition in food, and has immune-modulating, antioxidant, antibacterial, and antitumor activity etc. This study revealed that the structural changes of BLA induced by ultrasonic prior to glycated modification. It will be beneficial to understand the mechanism of the functional changes of modified BLA. Ultrasonic prior to glycated modification will be more likely to develop a practical technology to modify protein in the food industry, and improve the functional characteristics of food, such as produce hypo-allergenic cow's milk in future.

Insights into the Mechanism of Quercetin against BSA-Fructose Glycation by Spectroscopy and High-Resolution Mass Spectrometry: Effect on Physicochemical Properties

Quercetin has been reported to suppress protein glycation or the formation of advanced glycation end-products (AGEs), but the inhibition mechanism related to protein structure and glycation sites and the influence on physicochemical properties remain unclear. The aim of the current research was to investigate the mechanism of quercetin against glycation with BSA-fructose as model by spectroscopic and spectrometric techniques. Changes in physicochemical properties were evaluated by antioxidant activity and emulsifying properties. The results indicated that quercetin dose-dependently inhibited the glycation of BSA by attenuating the alteration of conformational structure and microenvironment induced by glycation. It could also suppress the cross-linking or aggregation of glycated BSA, which reflected in the decreased molecular weight determined by SDS-PAGE and MALDI-TOF. Nanoliquid chromatography coupled to Q-Exactive tandem mass spectrometry analysis revealed the mapping of 20, 23, 19, and 19 glycation sites in glycated BSA with 0, 0.5, 1.5, and 3.0 mM quercetin, respectively. Quercetin changed the glycation sites of BSA, but it could not reduce the number greatly. In addition, quercetin reduced the antioxidant ability and increased the emulsifying properties of BSA, while negligible efficiency was observed on the antioxidant activity and emulsifying activity index of glycated BSA.