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In the present study, Diplodusproteins were hydrolyzed using one of two proteases alcalase and savinase, then, the hydrolysates were characterized by their chemical composition, functional properties and peptide content. Protein hydrolysates of Diplodus annulariswith different degrees of hydrolysis (DH of 8.14% and 15.42%) were prepared using the enzymes alcalase® and savinase®. The protein hydrolysates obtained by treatment with savinase® had a higher protein content than that produced with alcalase®. Both hydrolysates showed great heterogeneity in their peptide composition. In comparison with the alcalase generated hydrolysate, savinase hydrolysate is richer in hydrophobic peptides as shown by RP-HPLC results. Also, the RP-HPLC-MS/MS, according to database survey, allowed the identification of 906 peptides in this hydrolysate against only 536 peptides in the alcalase hydrolysate. Regarding the functional properties, the maximum solubility values, the best foaming properties and the greatest oil and water retention capacities were obtained with the hydrolysate produced by savinase action. The emulsifying property and emulsion stability showed higher values for the alcalase generated hydrolysate with a lower degree of hydrolysis. As a consequence of increasing hydrolysate concentrations, the emulsifying activity index decreased. Conversely, the foaming abilities increased as the hydrolysate concentrations increased. The results of the present study suggest that alcalase and savinase can be used for the conversion of Diplodus annularisproteins into numerous peptides with promising functional properties.

•Food and marine proteins as source to produce bioactive peptides.•There is a high biodiversity of bioactive peptides from animal or plant sources.•Bioactive peptides play an important role in energy homeostasis.•Peptidome identification is needed to understand the bioactivity.•Controlled bioprocesses are needed for the separation of bioactive peptides.

Human inter-α-inhibitor (IαI) is a plasma serine-proteinase inhibitor. It consists of three polypeptide chains covalently linked by a glycosaminoglycan chain: a light chain named bikunin carrying the anti-proteinase activity and two heavy chains, H1 and H2, which exhibit specific properties, e.g. they interact with hyaluronan thus stabilizing the extracellular matrix. In this study, using matrix-assisted laser desorption ionization–time-of-flight MS and amino acid sequencing of tryptic peptides, we provide a detailed analysis of the glycosylation pattern of both heavy chains. H1 carries two complex-type N-glycans of predominantly biantennary structure linked to asparagine residues at positions 256 and 559 respectively. In contrast, the oligosaccharides attached to H2 are a complex-type N-glycan in the N-terminal region of the protein (Asn64) and three to four type-1 core-structure O-glycans mono- or di-sialylated, clustered in the C-terminal region. We propose that these O-glycans might function as a recognition signal for the H2 heavy chain. The biological implications of this hypothesis, notably for the biosynthetic pathway of IαI, are discussed.

Congenital and acquired modifications of glycosylation in diseases are a rapidly growing field that demonstrates the importance of glycosylation in human biology. Unfortunately, in clinical biochemistry, very few tests are available to explore oligosaccharide metabolism on a large scale. Such an assay needs to be of high throughput, rapid, and preferentially noninvasive. In the present study, we describe a method to analyze qualitative variations of N-glycosylation of human serum proteins. The method is based on direct release of N‐linked oligosaccharides from patient serum samples, a single-step purification, and a matrix-assisted laser desorption ionization time of flight mass spectrometric analysis. A complementary structural study of the released oligosaccharides was achieved by enzymatic digestions, linkage analysis, and electrospray ionization ion trap mass spectrometry (ESI-IT-MS) of the permethylated N-glycome. A total of 26 oligosaccharide structures were individualized, their presence in human serum being the result of the combination of the biosynthesis and catabolic pathways. Application of the protocol to the serum of patients with cirrhosis demonstrates the ability of this assay to identify acquired modifications of glycosylation. Furthermore, we have analyzed the N-glycans and showed the increase in bisecting N-acetylglucosamine residue, core fucosylation, and the presence of an important population of neutral oligosaccharides. The study of total serum N-glycome modifications is a preliminary for the discovery of new noninvasive diagnostic or prognostic biomarkers resulting from the variations of the N-glycan metabolism during diseases.