To elucidate the differences in the antioxidant and antidiabetic activities of different phenolic fractions from Rubus chingii Hu, aqueous-soluble, alcohol-soluble, free and bound polyphenols from the fruits of R. chingii Hu were extracted using different solvents and methods. The difference in the contents of total phenolic compounds, total flavonoids, and hydrolyzable tannins in the different extracts were compared, and the radical scavenging, α-glucosidase inhibitory and antiglycation activity of the extracts were determined. The major chemical components in the extract with the highest activity were determined using mass spectrometry (MS). The results indicated that the alcohol-soluble polyphenol-rich extract had the highest contents of total phenols and hydrolysable tannins (414.95 μg/mg and 182.47 μg/mg (expressed as gallic acid equivalent in per milligram of extract), respectively). Meanwhile, it also presented the strongest ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonate) (ABTS) cation radical and to inhibit α-glucosidase activity with half maximal inhibitory concentration (IC₅₀) values of 40.68, 23.90 μg/mL and 1.65 μg/mL, respectively. But the highest total flavonoid content and antiglycation activity were observed in the bound polyphenol-rich extract. Totally, 31 compounds were tentatively identified from the bound polyphenol-rich extract, and tannins and flavonoids were the major bioactive constituents. Therefore, the R. chingii Hu residues left after the extraction of free polyphenols and aqueous-soluble constituents can be further utilized to develop bioactive constituents with high antioxidant and antidiabetic activities.

In order to investigate the influence of the refining process on the quality and sensory properties of snakehead fish oil, the physicochemical properties, fatty acid composition and volatile flavor composition during the refining process of crude fish oil extracted from snakehead viscera were evaluated. The results showed that the physicochemical properties of snakehead fish oil were significantly improved; the acid value, peroxide value, moisture content, volatile content, anisidine value and unsaponifiable matter content were significantly reduced, and the iodine value was increased. In total, 27 fatty acids were detected in snakehead fish oil, the major ones being oleic acid, linoleic acid, and palmitic acid. During the refining process, the number of fatty acids was almost unchanged, the contents of monounsaturated and polyunsaturated fatty acids increased, while a reverse trend was observed for the content of saturated fatty acids. Additionally, a total of 99 volatile compounds were detected during the refining process of snakehead fish oil, among which 14 compounds including 1-octen-3-ol, hexanal, nonanal, 2-heptenal, (E,Z)-2,6-nonadienal, 2,4-decadienal, and trans-2,4-decadienal were the key flavor substances of snakehead fish oil. These findings provide a theoretical basis and technical support for the deep processing and high-value utilization of snakehead fish visceral oil.

In this study, the effect of quercetin-3-O-β-D-glucuronide (Q3G) on the formation of fructosamine and 5-hydroxymethylfurfural (5-HMF), the amount of free amino groups and browning degree in a non-enzymatic glycosylation model consisting of bovine α-lactalbumin (α-La) and fructose were evaluated. In addition, the inhibitory mechanism of Q3G against non-enzymatic glycosylation was explored by molecular docking and mass spectrometry (MS). The results indicated that Q3G could significantly reduce the browning degree, increase the free amino groups, inhibit the formation of fructosamine and 5-HMF, and delay the process of glycosylation reaction. The effect was most pronounced at 2 mmol/L Q3G. Molecular docking analysis indicated that Q3G could bind with the active amino acid residues of α-La through hydrogen bonds, van der Waals force and hydrophobic interactions, delaying the process of glycosylation reaction. Meanwhile, by ultra-high performance liquid chromatography-quadrupole-orbitrap tandem mass spectrometry (UPLC-Q-Orbitrap MS/MS) analysis, it was found that Q3G shielded the potential glycosylation sites Lys93 and Lys108, and the activity of the glycosylation site Lys98 was weak, indicating inhibited non-enzymatic glycosylation reaction. This study can provide a theoretical basis for the development of Q3G as a potential anti-glycosylation agent.

Gut microbiota plays an important role in food allergy. The immunoglobulin G (IgG)/immunoglobulin E (IgE) binding capacity and human gut microbiota changes of digestion products derived from glycated ovalbumin (OVA) were investigated. Gastrointestinal digestion effectively destroyed the primary structure of glycated OVA, resulting in a significantly higher digestibility than gastric digestion, and more abundant peptides < 3 kDa. Moreover, gastric and gastrointestinal digestion products have different fluorescence quenching and red shift of fluorescence peaks, and possess different conformational structures. These changes resulted in a decrease in 28.7% of the IgE binding capacity of gastrointestinal digestion products beyond that of pepsin. Moreover, gastrointestinal digestion products of glycated OVA increased significantly the proportion of Subdoligranulum, Collinsella, and Bifidobacterium. Therefore, gastrointestinal digestion products of glycated OVA altered human intestinal microbiota, reducing the risk of potential allergy.

Bovine α-lactalbumin (BLA) induced severe cow's milk allergy. In this study, a novel strategy combining ultrasonication, performed before glycation, and phosphorylation was proposed to reduce BLA allergenicity. Result showed that IgE- and IgG-binding capacities and the release rates of histamine and interleukin-6 from RBL-2H3 were reduced. Moreover, intrinsic fluorescence intensity and surface hydrophobicity were decreased, whereas glycated sites (R10, N44, K79, K108, N102 and K114) and phosphorylated sites (Y36 and S112) of BLA were increased. Minimum allergenicity was detected during BLA treatment after ultrasonic prior to glycation and subsequent phosphorylation because of considerable increase in glycated and phosphorylated sites. Therefore, the decrease in allergenicity of BLA, the effect correlated well with the shielding effect of glycated sites combined with phosphorylated sites and the conformational changes. This study provides important theoretical foundations for improving and using the ultrasonic technology combined with protein modification in allergenic protein processing.