Bovine α-lactalbumin (α-LA) is one of major food allergens in cow's 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/cm, 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.

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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/cm, respectively, for 15 min. Thus, no obvious difference was found among the glycation sites at the ultrasonic power of 60 and 90 W/cm. 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/cm 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.

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