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In this study, gelatin was extracted from bighead carp (Hypophthalmichthys nobilis) scales by water bath (WB) and ultrasound bath (UB) at 60°C for 1 h, 3 h and 5 h, named WB1, WB3, WB5, UB1, UB3 and UB5, respectively. The physicochemical properties of gelatin were investigated. The result indicated that gelatin extracted from bighead carp scales had a high protein content (84.15~91.85 %) with moisture (7.111 3.65 %), low ash content (0.31~0.97 %). All extracted gelatin contained α-and β-chains as the predominant components. Gelatin extracted by UB obtained much higher yield (30.94-46.67 %) than that of WB (19.15-36.39 %). More voids and less sheets of gelatin structure were observed, when the gelatin was extracted by UB for longer time. Gelatin of UB-assisted extraction normally exhibited lower gel strength and melting points than that of WB, which may be resulted from the protein degradation reflected by the FTIR spectra and higher free amino group content. However, there was no significant difference between WB1 and UB1. Therefore, the ultrasound assisted extraction in a short time was a promising method to enhance the yield and obtain gelatin with high quality.

The glycation extent of bovine serum albumin (BSA) before and after ultrasonication was evaluated by MALDI-TOF and Orbitrap mass spectrometry. Ultrasonic pretreatment significantly improved the incorporation of galactose to BSA. Prior to ultrasonic pretreatment, only 12 sites (11 lysines and 1 arginine) were glycated, whereas the number of glycation sites was increased to 42, including 39 lysines and 3 arginines, after treatment. Average degree of substitution per peptide molecule of BSA (DSP) was used to evaluate the glycation level for each glycation site. The ultrasonic pretreatment significantly improved the DSP value of all glycation sites. The prevalently promoted glycation by ultrasonic pretreatment suggests that ultrasonication improves glycation through altering the structure of BSA throughout all three domains. An ultrahigh-resolution linear ion trap Orbitrap mass spectrometer facilitates unambiguous localization of glycation sites, allowing an in-depth analysis of the nature and extent of protein glycation at the molecular level. High-intensity ultrasonication can greatly improve protein glycation and, therefore, opens new routes to modify the functionality of proteins in a positive way.

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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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