Evaluation of glycation reaction of ovalbumin with dextran: Glycation sites identification by capillary liquid chromatography coupled with tandem mass spectrometry.

An important relationship exists between the changes in glycation sites and structure of proteins. A combination of liquid chromatography and tandem mass spectrometry was used to identify the glycation information from ovalbumin (OVA) after dextran (Dex) conjugation under water heating (WH) or microwave heating (MH) conditions. After Dex conjugation, 12O-linked glycation sites were identified in the OVA-Dex-MH conjugates, whereas 6O-linked, 2N-linked glycation sites were detected in the OVA-Dex-WH conjugates. These findings indicate that the amino acids at different positions in OVA molecular structure have different glycation reactivity under MH or WH induction systems. In addition, ß-sheet and ß-turn structures showed high glycation reactivity. The increased surface hydrophobicity of OVA-Dex conjugates was possibly attributed to the glycation sites that were mainly found in hydrophilic amino acids. Our study provides useful information for the glycation mechanism research of OVA and Dex.

Effects of single-mode microwave heating and dextran conjugation on the structure and functionality of ovalbumin-dextran conjugates.

The proteins modified with carbohydrates through the glycation reaction are capable of changing and improving the functional properties of proteins. In this study, dextran was conjugated to ovalbumin (OVA) by traditional wet heating (WH) or single-mode microwave heating (MH) to improve the functional properties of OVA. Compared with traditional WH, MH for 15-60 min significantly increased the grafting degree (GD). The emulsifying activity and emulsion stability of the OVA-dextran conjugates improved under both traditional WH or MH (p < 0.05), especially under MH at 90 ℃ for 20 min. Correlation analysis showed that the emulsifying activity was positively correlated with surface hydrophobicity (p < 0.05), and emulsion stability was significantly positively correlated with surface hydrophobicity (p < 0.01) and positively correlated with the ß-sheet contents (p < 0.05). Moreover, traditional WH and single-mode MH treatment could decrease tan δ, especially MH at 90 °C for 20 min. High GD and long MH treatment (≥25 min) resulted in a significant decrease in ⍺-helix and an increase in ß-turn and γ-random coil. The secondary structure of OVA became loose, which was disadvantageous to the thermal stability of the OVA-dextran conjugates. In conclusion, compared with traditional WH, dextran conjugation with OVA via single-mode MH was an effective and safe way to improve the utilization value of OVA.

Sonochemical effects on the structure and antioxidant activity of egg white protein-tea polyphenol conjugates.

The antioxidant properties of proteins could be enhanced by forming covalent conjugates with polyphenols. In this study, the antioxidant activity of egg white protein (EWP) was improved by conjugating with tea polyphenols (TP) using traditional and ultrasound-assisted alkaline/free radical methods. In addition, the influences of TP conjugation on the antioxidant activities and structural and digestive properties of EWP were comprehensively studied. Compared with the traditional methods, the sonochemistry (40 kHz) approaches significantly increased the efficiency of TP grafting to the EWP (P < 0.05) from 24 h to 1 h. Amino acid analysis showed that in the ultrasound-assisted alkaline method, TP was successfully conjugated to the EWP through proline, glutamic acid, cysteine, and tryptophan residues, whereas proline, cysteine, and tryptophan were involved in the free radical method. However, the number of cross-linking sites was increased significantly after ultrasound-assisted treatments. Moreover, the antioxidant activities of the EWP were significantly improved after covalent conjugation with TP using traditional and ultrasound-assisted alkaline/free radical methods, particularly the ultrasound-assisted approaches. Furthermore, circular dichroism revealed that the ultrasound-assisted approaches had the greatest impact with regard to decreasing the α-helix content and increasing the random coil content, which loosened the protein structure, thereby improving its reactivity and digestibility. Therefore, ultrasound-assisted alkaline/free radical methods were efficient and safe means for the production of EWP-TP conjugates.

Functional Magnetic Nanoparticles for Highly Efficient Cholesterol Removal.

In this study, magnetic nanoparticles functionalized with carboxylated ß-cyclodextrin (CM-ß-CD; referred to Fe3 O4 @CM-ß-CD) were synthesized and used for the efficient removal of cholesterol from milk and egg yolk via host-guest interactions. The results of Fourier-transform infrared, X-ray photoelectron spectroscopy, and thermogravimetric analysis indicated that the CM-ß-CD was successfully conjugated to the surface of Fe3 O4 , and the amount of CM-ß-CD attached on Fe3 O4 @CM-ß-CD was determined to be 9.164%. The X-ray diffraction and transmission electron microscopy data revealed that the process of CM-ß-CD coating did not result in a phase change of the Fe3 O4 , and the Fe3 O4 @CM-ß-CD nanoparticles were determined to have an average size of about 15 nm. The results of isotherm adsorption and kinetic properties indicated that CM-ß-CD functionalization increased the cholesterol removal efficiency, and the characteristics of cholesterol adsorption on Fe3 O4 @CM-ß-CD were fitted well with the Langmuir adsorption model and Lagergren pseudo-1st-order kinetic models. Furthermore, compared with the Fe3 O4 nanoparticles, the functionalized Fe3 O4 @CM-ß-CD nanoparticles exhibited greater cholesterol removal efficiency, and saponification of the milk and egg yolk was found to be beneficial for the cholesterol removal; using the Fe3 O4 @CM-ß-CD nanoparticles, 98.8% and 94.6% of the cholesterol was extracted in 1 h from saponified milk and egg yolk, respectively, and the Fe3 O4 @CM-ß-CD nanoparticles still displayed efficient cholesterol removal after 6 reuses.