Enzymolysis Reaction Kinetics and Liquid Chromatography High-Resolution Mass Spectrometry Analysis of Ovalbumin Glycated with Microwave Radiation

Mechanism studies of gliadin-glucose glycation reaction and products formation by heat treatment with different conduction modes

Heat treatments induce protein-reducing sugar glycation reactions easily, leading to protein structural transformations and advanced glycation end products generation. In this study, effects of four heat conduction modes (air, contact, vapour and liquid-conduction) on the spatial conformation and glycation products of gliadin-glucose system were evaluated. The results showed that gliadin tertiary structure expanded and exposed more hydrophobic sites in vapour-conduction, resulting in more glycation sites. Conversely, air-conduction promoted the protein folded, causing a lighter glycation degree and lower glyoxal, methylglyoxal, acrylamide, 5-hydroxymethylfurfural and carboxymethyl lysine contents (following vapour-conduction > contact-conduction > liquid-conduction > air-conduction). The above phenomena were attributed to the different water content in the different conduction modes. Furthermore, the glycation sites identified in vapour-conduction and contact-conduction were approximately two-fold of that in air-conduction. Conclusively, gliadin-glucose systems subjected to air-conduction showed less glycated intensity and hazardous products.

Comparison of ovalbumin glycation induced by high-temperature steaming and high-temperature baking: A study combining conventional spectroscopy with high-resolution mass spectrometry

High-temperature steaming (HTS) and high-temperature baking (HTB)-induced ovalbumin (OVA)-glucose glycation (140 °C, 1-3 min) were compared, and the different mechanisms were evaluated by changes in protein conformation, glycation sites and average degree of substitution per peptide molecule (DSP) values as well as the antioxidant activity of glycated OVA. Conventional spectroscopic results suggested that in comparison with HTB, HTS promoted protein expansion, increased β-sheet content and made OVA structure more orderly. Liquid chromatography-high resolution mass spectrometry (LC-HRMS) analysis showed that 10 glycation sites were found under HTB, while 4 new glycation sites R111, R200, R219 and K323 appeared under HTS, and 2 of them (R219 and K323) were located in internal β-sheet chains. The antioxidant activities of glycated OVA increased with increasing treatment time, and HTS showed stronger enhancement effect than HTB. Furthermore, the DSP values were generally higher under HTS than HTB. Compared with HTB, HTS with high penetrability could enhance the change of OVA primary structure and spatial conformation, making the protein structure more unfolded and stable, leading to more protein-sugar collisions occurred in inner OVA molecular and significantly promoted glycation. In conclusion, HTS is a promising method for high-temperature short-time glycation reaction, with drastically increasing the protein antioxidant activities.

Enhancing nonspecific enzymatic hydrolysis of chitin to oligosaccharides pretreated by acid and green solvents under simultaneous microwave-radiation

It is hard to degrade untreated highly crystalline chitin. In this study, two solvents pretreatment chitin (acid swollen chitin (AC), super fine chitin (FC)) and microwave-heating method were used to enhance nonspecific enzymatic hydrolysis (lysozyme and pepsin), which obviously improved the enzymolysis rates by at least 1.31 times. Characterizations of chitin substrates (M_v, SEM, XRD) showed that calcium solvent pretreatment (obtained FC) was milder but effective than phosphoric acid pretreatment (obtained AC). The highest yield of chitin oligosaccharides (37.58 mg/g) were obtained after hydrolyzing AC under five-hour simultaneous microwave radiation by pepsin, among them, the content of N-acetylglucosamine was 13.76 mg/g. While, more chitin oligosaccharides with DP (degree of polymerization) 3-4 and lower DA (degree of acetylation) were obtained when using lysozyme than pepsin. Significantly, the conversion rate of chitin to oligosaccharides went best only when microwave and enzymes acting together (simultaneous strategy), which were at least 35.59% higher than separately pretreatment enzymes and substrates by microwave. The damages of microwave radiation on lysozyme and chitin substrates were revealed, and the operating principle of the whole enzyme reaction system heated by microwave was preliminatively explored.

Mechanism of Reduction in Allergenicity and Altered Human Intestinal Microbiota of Digested β-Lactoglobulin Modified by Ultrasonic Pretreatment Combined with Glycation

The effects of ultrasound combined with glycation (UCG) on the allergenicity and human microbial community of β-Lg during in vitro digestion were studied by ELISA, cell experiments, and 16S rRNA high-throughput sequencing. UCG modification and subsequent digestion significantly reduced allergenicity. The decrease in the allergenicity of β-Lg depended not only on the low digestibility of glycated β-Lg, which led to the decrease of some peptides with complete immunogenicity, but also the masking effect of glycation on allergen epitopes of β-Lg. Meanwhile, UCG modification and subsequent digestion could alter the structures of intestinal microbiota and the community abundance at phylum, family, and genus levels, such as Bacteroidota, Fusobacteriota, Enterobacteriaceae, Bacteroidaceae, Ruminococcaceae, Bacteroides, and Faecalibacterium. These results show that simulated in vitro digestion of modified β-Lg reduces allergenicity and alters human intestinal microbiota, which could provide a theoretical basis for studying the relationship between intestinal dysbiosis and cow's milk allergy.

Mechanism of the Reduced IgG/IgE Binding Abilities of Glycated β-Lactoglobulin and Its Digests through High-Resolution Mass Spectrometry

Glycation between proteins and reducing sugars is the common chemical modification in food protein, and many studies have focused on the allergenicity of the glycated protein. However, a systemic study on the allergenicity change of its digests is lacking. In this work, we explored the change rule of the digestibility and allergenicity of glycated β-Lg during in vitro gastrointestinal digestion and interpreted the mechanism using high-resolution mass spectrometry. Glycation with arabinose increased the resistance of β-Lg to digestive enzyme, with a low hydrolysis value. Indirect competitive ELISA showed that the IgG/IgE binding rates of β-Lg were reduced after glycation and further reduced after digestion, in comparison with the digests of unglycated β-Lg. There are two reasons for this phenomenon. On the one hand, 11 glycated sites were determined in the lowest allergenicity arabinose-β-Lg conjugation (Ara-β-Lg), which was distributed in the IgG and IgE linear allergic epitopes of β-Lg. On the other hand, glycation masking linear allergenic epitopes had a more significant effect on reducing allergenicity in comparison to digestive enzyme hydrolysis. These results indicated that the allergenicity of Ara-β-Lg in the human body might be lower than that of unglycated β-Lg.