Mechanism of Reduction in IgG and IgE Binding of β-Lactoglobulin Induced by Ultrasound Pretreatment Combined with Dry-State Glycation: A Study Using Conventional Spectrometry and High-Resolution Mass Spectrometry.

Bovine β-lactoglobulin (β-Lg) is one of major allergens in cow's milk. Previous study showed that ultrasound treatment induced the conformational changes of β-Lg and promoted the glycation in aqueous solutions, which is, however, less efficient compared with dry-state. In this work, the effect of ultrasound pretreatment combined with dry-state glycation on the IgG and IgE binding of β-Lg was studied. Dry-state glycation with mannose after ultrasound pretreatment at 0-600 W significantly reduced the IgG and IgE binding of β-Lg, with the lowest values observed at 400 W. The decrease in the IgG and IgE binding of β-Lg was attributed to the increase in glycation extent and the changes of secondary and tertiary structure, which reflected in the increase of UV absorbance, α-helix and β-sheet contents, as well as the decrease of intrinsic fluorescence intensity, surface hydrophobicity, β-turn, and random coil contents. Moreover, ultrasound pretreatment promoted the reduction of IgG and IgE binding abilities by improving glycation, reflecting in the increase of the glycation sites and the degree of substitution per peptide (DSP) value determined by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Ultrasound pretreatment at 400 W showed the most significantly enhanced glycation extent. Besides, the results suggested FTICR-MS could provide insights into the glycation at molecular level, which was conducive to the understanding of the mechanism of the reduction in the IgG and IgE binding of β-Lg. Therefore, ultrasound pretreatment combined with dry-state glycation may be a promising method for β-Lg hyposensitization.