Marine glycoproteins: a mine of their structures, functions and potential applications.

Many bioactive compounds are reported from marine organisms, which are significantly different from those found in terrestrial organisms regarding their chemical structures and pharmacological activities. Marine glycoproteins (MGs) have aroused increasing attention as a good nutrient source owing to their potential applications in medicine, cosmetics and food. However, there is a lack of a comprehensive study on MGs to help readers understand the current state of research on marine-derived glycoproteins. The current review compiles the recent progress made on the structures and functions of MGs with future perspectives to maximize their value and applications via bibliometric analysis methods for the first time. The current research on MGs appears mostly limited to the laboratory, with no large-scale production of marine glycoproteins developed. The sugar chains are bound to proteins through covalent bonds that can readily be cleaved leading to difficultly in their separation and purification. Health effects attributed to MGs include treatment of inflammatory diseases, as well as anti-oxidant, immune modulation, anti-tumor, hypolipidemic, hypoglycemic, anti-bacterial and anti-freeze activities. This review can not only deepen the understanding of the functions of MGs, but also lay an important foundation for the further development and utilization of marine resources.

Overview on isolation, structural and functional properties of marine glycoproteins (MGs) via bibliometric analysis methods for the first time.Marine glycoproteins (MGs) have various biological activities and potential health applications.glycoproteins from marine organisms (MGs) significantly enhanced anti-oxidant and anti-inflammatory activities.

Steam Explosion Pretreatment of Polysaccharide from Hypsizygus marmoreus: Structure and Antioxidant Activity.

This paper investigated the effects of steam explosion (SE) pretreatment on the structural characteristics and antioxidant activity of Hypsizygus marmoreus polysaccharides (HPS). Hypsizygus marmoreus samples were pretreated at different SE temperatures (120-200 °C) and polysaccharides were extracted using the water extraction and alcohol precipitation method. The results showed that SE pretreatment improved the extraction rate of HPS. Under the conditions of SE treatment time of 60 s and temperature of 160 °C, the extraction rate of HPS was the highest (8.78 ± 0.24%). After SE pretreatment, the structural changes of HPS tended to enhance the antioxidant activity, which showed that the content of Gal and Man in the monosaccharide composition increased and the molecular weight decreased. When testing antioxidant activity in vitro, the ability of SE-pretreated HPS to scavenge DPPH radicals, hydroxyl radicals, and superoxide anion radicals was better than that of HPS without SE pretreatment. Our findings shed light on SE pretreatment as an efficient method for extracting active polysaccharides, providing a new way to improve their extraction rate and biological activity.

Porphyra haitanensis glycoprotein regulates glucose homeostasis: targeting the liver.

In this study, we investigated the effects of glycoprotein (PG)-mediated regulation of Porphyra haitanensis on liver glucose metabolism in hyperglycemic mouse models, and sought to establish the underlying mechanism, as determined by the changes in liver gene expression and metabolic profiles. The results showed that 30-300 mg kg-1 PG upregulated the expression of the liver genes Ins1, Ins2, Insr, Gys2, Gpi1, Gck, and downregulated the expression of G6pc, G6pc2, and G6pc3, in a concentration-dependent manner. 300 mg kg-1 PG downregulated the concentrations of glucose-related metabolites in the liver, but upregulated lactic acid, 2-aminoacetic acid, and glucose-1-phosphate concentrations. It was assumed that PG regulated liver glucose metabolism by enriching insulin secretion, glycolysis/gluconeogenesis, and the AMPK signaling pathway, and promoting insulin secretion, glycogen synthesis, and glycolysis. Our findings supported the development of P. haitanensis and its glycoproteins as novel natural antidiabetic compounds that regulated blood glucose homeostasis.

Dietary fiber-rich Lentinula edodes stems influence the structure and in vitro digestibility of low-moisture extruded maize starches.

Low-moisture extrusion (LME) can be used to improve the utilization of dietary fiber-rich Lentinula edodes stems (LES). The incorporation of dietary fiber can affect heat-induced interactions of starch molecules, which are critical for modifying starch characteristics via LME. In this work, a blend of LES and maize starch was extruded into a product at low moisture (30 %, w/v). The structure, physicochemical properties, and in vitro digestibility of extruded maize starches were investigated at different LES levels. The results showed that low levels (<7 %) of LES increased the crystallinity of LME-produced starch, while high levels (>7 %) did not. Because of the LES's soluble to insoluble dietary fiber ratios, the increased crystallinity of LES-added starch led to greater molecular ordering and the formation of an elastic gel after LME. At a suitable LES level (~3 %), highly crystallized starches were resistant to enzymolysis and had a high proportion of resistant starch. The obtained findings would contribute to a better understanding of how dietary fiber-rich LES affects starch extrusion and provide an alternative use for boosting the value of LES by-products.

Gut microbiome-serum metabolic profiles: insight into the hypoglycemic effect of Porphyra haitanensis glycoprotein on hyperglycemic mice.

The hypoglycemic activity of natural algal glycoproteins has attracted interest, but studies of their mechanism of regulating glucose metabolism are lacking. This study investigated the hypoglycemic activity of Porphyra haitanensis glycoprotein (PG) in a mouse hyperglycemia model. The underlying mechanism was elucidated by monitoring changes in the gut microbiome and untargeted serum metabolomics. The results indicated that 30-300 mg kg-1 PG regulated blood glucose levels by increasing insulin secretion, reducing glycated hemoglobin, and improving streptozotocin-induced hyperglycemia in a concentration-dependent manner. In particular, 300 mg kg-1 PG decreased fasting blood glucose by 63.11% and glycosylated hemoglobin by 24.50% and increased insulin secretion by 163.97%. The mechanism of the improvement of hyperglycemia by PG may involve regulating beneficial intestinal bacteria (e.g., norank_f__Muribaculaceae and Lachnospiraceae) and altering the serum metabolic profile (e.g., upregulation of hypotaurine, 3-hydroxy-2-naphthoic acid, and L-glycine), to regulate taurine and hypotaurine, the TCA cycle, AMPK, and pyruvate metabolism. Our findings supported the development of Porphyra haitanensis and its glycoprotein as novel natural antidiabetic compounds to regulate the glycemic balance.

Structure and Antidiabetic Activity of a Glycoprotein from Porphyra haitanensis.

A novel antidiabetic glycoprotein (PG) was isolated and purified from Porphyra haitanensis, and its structure and inhibiting activity on α-amylase and α-glucosidase were analyzed. The purity of the PG was 95.29 ± 0.21%, and its molecular weight was 163.024 ± 5.55 kDa. The PG had a tetramer structure with α- and ß-subunits, and it contained 54.12 ± 0.86% protein (with highly hydrophobic amino acids) and 41.19% ± 0.64% carbohydrate (composed of galactose). The PG was linked via an O-glycosidic bond, exhibiting an α-helical structure and high stability. In addition, the PG inhibited the activities of α-amylase and α-glucosidase, by changing the enzyme's structure toward the PG's structure in a noncompetitive inhibition mode. Molecular docking results showed that the PG inhibited α-amylase activity by hydrophobic interaction, whereas it inhibited α-glucosidase activity by hydrogen bonds and hydrophobic interaction. Overall, the PG was linked to polysaccharides via O-glycosidic bonds, showing an α-helical configuration and a hydrophobic effect, which altered the configuration of α-amylase and α-glucosidase and exerted hypoglycemic activity. This study provides insights into analyzing the structure and antidiabetic activity of glycoproteins.

The Anti-Fatigue Effect of Glycoprotein from Hairtail Fish (Trichiurus lepturus) on BALB/c Mice.

Fatigue is related to a variety of chronic diseases and has become a hot research topic in recent years. Various bioactive components have been extracted from hairtail fish (Trichiurus lepturus); however, none of these studies involved the anti-fatigue activity of hairtail fish glycoprotein (HGP). Thus, antioxidant experiments were conducted in vitro, and the anti-fatigue activity of HGP was further evaluated in BALB/c mice. The effects of HGP on the behavior of BALB/c mice were verified by classical behavioral experiments, and the indicators related to anti-fatigue activity were detected. The results showed that the antioxidant capacity in vitro of HGP increased gradually in the concentration range of 10 to 100 mg/mL. HGP improved the exercise ability of the mice. HGP was also found to significantly (p < 0.05) reduce the serum levels of lactate dehydrogenase (LDH), blood lactic acid (BLA), blood urea nitrogen (BUN), and creatine kinase (CK). The contents of liver glycogen (LG) and muscle glycogen (MG) were also significantly (p < 0.05) increased by HGP. Malondialdehyde (MDA) content in the serum and brains of the mice was significantly (p < 0.05) reduced and catalase (CAT), glutathione peroxidase (GPX), and superoxide dismutase (SOD) were significantly (p < 0.05) increased by HGP, especially in the middle- and high-dose groups. These results enhance our understanding of the anti-fatigue function of HGP and lay an important foundation for the further development and utilization of hairtail fish resources.

Structure-digestibility relationships in the effect of fucoidan on A- and B-wheat starch.

Fucoidans (FC) have a variety of biological activities, and it can also affect the functionality and nutritional characteristics of starch-based food products. However, there are few studies on the structural and digestive properties of starch - fucoidans blends. The effect of FC at different concentrations (0, 0.6 %, 0.8 %, 1.0 %, w/v) on the structural properties and digestibility properties of A-type wheat starch (AS) and B-type wheat starch (BS) subjected to autoclave treatment were investigated. The results show that compared with native wheat starch, AS with FC displayed higher crystallinity as well as the structural ordering, but the crystallinity and degree of order of BS with FC decreased, which was proposed due to AS interact with FC in crystalline region but BS reacts with FC in the amorphous region. With the interaction of FC with AS and BS, granules compactness of AS and BS were enhanced. The addition of FC delayed digestion in vitro of AS and BS, the rapidly digestible starch content was obviously lower than native one, and the proportion of slowly digestible starch raise markedly. This study might broaden the recognition of wheat starch with different proportion of AS and BS, and provide a theoretical basis for the potential utilization of FC in carbohydrate based food industry.

Insights into the formation and digestive properties of lotus seed starch-glycerin monostearate complexes formed by freeze-thaw pretreatment and microfluidization.

The objective of this paper was to investigate the formation and digestive properties of lotus seed starch-glycerin monostearate complexes (LSG) formed by freeze-thaw pretreatment and microfluidization. The results showed that the preparation of LSG with six freeze-thaw cycles at 60 MPa had the highest complex index (69.92%). The formation of LSG led to the conversion of the crystalline pattern of lotus seed starch from C-type to V-type and increased the proportion of the microcrystalline region. In addition, the digestive results indicated that LSG had a high resistance to digestive enzymes, which was conducive to increasing the content of resistant starch. Based on the above investigation, the formation and digestive properties showed that the appropriate number of freeze-thaw cycles of pretreatment could facilitate the complexation of starch and lipid under low-pressure microfluidization, which made for the directional regulation of helical conformation and anti-digestion.

Effect of chlorogenic acid on the structural properties and digestibility of lotus seed starch during microwave gelatinization.

The structural evolution of lotus starch (LS)-chlorogenic acid (CA) complexes was investigated after microwave-heating treatment, to reveal the relationship between the interactions of lotus starch and chlorogenic acid molecules, and the digestive properties of the starch, after microwave gelatinization. During the early stage of microwave gelatinization (65, 70 °C), CA was mainly participating in the rearrangement of starch molecules in a weakly-bound form, and at that stage, the LS-CA complex acted as an inhibitor of digestion, under small intestine conditions, mainly through the release of CA, which inhibited amylase. However, during the late stage of microwave gelatinization (85 °C), many chlorogenic acid molecules entered the hydrophobic helical cavity of the starch, promoting formation of the V-type starch helical structure in the LS-CA complex, which made a major contribution to inhibiting digestion under oral digestion conditions.

The impact of various exogenous type starch on the structural properties and dispersion stability of autoclaved lotus seed starch.

In order to investigate the effects of exogenous V-type starch on the structural properties and dispersion stability of lotus seed starch after autoclave treatment, the crystal structure, molecular structure, and dispersion stability were analyzed and discussed, as well as compared with exogenous A-type and B-type starches. Analysis of structural properties indicated that the addition of different crystal nuclei led the crystallization of disordered helices to a specific direction. The B- and V-type starch addition increased the crystallinities of starch and enhanced the ordered arrangement of disordered helices, whereas A-type starch had no significant positive influence on the stability of starch system. The microstructure observation showed that A- and B-type starch addition led to a rough and porous morphology of starch particles; the presence of V-type starch retarded the agglomeration and retrogradation of starch after autoclaving. Analysis of contact angle and dispersion stability revealed that the addition of various exogenous starch increased the contact angle of starch particles in different extent, suggesting the enhancement of hydrophobicity. But B-type starch addition resulted in the poor dispersion stability compared to A-type starch, instead V-type starch addition improved the dispersion stability of starch in aqueous solution, allowing the particles to stay dispersed for 141.12 ± 6.52 min. These results provided a theoretical basis for the effects of exogenous type starch on original starch properties, and revealed the potential of V-type starch as dispersion stabilizer.

Effects of freeze-thaw treatment and pullulanase debranching on the structural properties and digestibility of lotus seed starch-glycerin monostearin complexes.

The effects of multiple cycles of freeze-thaw treatment, combined with pullulanase debranching, on the structural properties and digestibility of lotus seed starch-glycerin monostearin complexes were investigated. The formation and melting of ice crystals during freeze-thaw treatment disrupted the crystalline structure of the starch granules, creating pores which facilitated access of pullulanase to the interior of the granules. Pullulanase debranching increased the free amylose content of the starch, which promoted the formation of starch-lipid complexes, which, in turn, increased the proportion of resistant starch and the overall resistance of the starch to digestive enzyme action. These effects increased with the number of freeze-thaw cycles, because more cycles increased both the disruption of the granule structure and the extent of pullulanase debranching. These findings provide a basis for the preparation of functional foods with low glycemic indices, which have strong potential for management of type II diabetes.

Physicochemical properties and in vitro digestibility of lotus seed starch-lecithin complexes prepared by dynamic high pressure homogenization.

The objective of this study was to investigate the physicochemical properties and in vitro digestibility of lotus seed starch-lecithin inclusion complexes (ICs), prepared by dynamic high pressure homogenization. Raman spectrometry indicated that the IC formed between starch and lecithin, compared with the control mixture, could modify the helix rearrangement between different amylose conformations, to promote the formation of an ordered and stable V-type conformation. The content of amylose single helix appeared to be an important factor in the formation of starch-lipid complexes. Dispersion stability and solubility determinations indicated that the effect of mixing lecithin with starch mainly focused on the dispersion stability and not the solubility of starch emulsions. ICs with a V-type conformation, formed by homogenization of lecithin and amylose, achieved the same, or better emulsion stability as mixed lecithin, and the formation of ICs reduced the affinity of starch chains for water molecules, lowering their solubility. Digestion analysis suggested that the higher proportion of microcrystalline region in V6I complexes, resulted in a lower digestion rate and a higher resistant starch (RS) content.

Effects of exogenous V-type complexes on the structural properties and digestibility of autoclaved lotus seed starch after retrogradation.

The effects of exogenous V-type complexes on the structural properties and digestibility of autoclaved lotus seed starch after retrogradation were investigated. The structural properties indicated that the addition of V-type complexes significantly retarded the initial recrystallization of amylose double helices and improved the disordered starch system to an ordered direction. However, the effects decreased with the increase in retrogradation time and the rearrangement completion of amylose chains, as reflected in the enhancement of starch retrogradation phenomenon in micro-morphology. On the other hand, exogenous V-type complexes added to the starch system enhanced the enzymatic resistance of the starch system and increased the proportion of resistant starch because of the highly indigestible microchip layer. These results provided a theoretical basis for the interaction between V-type complexes and autoclaved starch for functional application, and they revealed its potential as an anti-gel additive.

Effects of pullulanase pretreatment on the structural properties and digestibility of lotus seed starch-glycerin monostearin complexes.

The effects of pullulanase pretreatment, combined with ultrasound-microwave synergistic processing, on the structural properties and digestibility of lotus seed starch-glycerin monostearin complexes was investigated. The pullulanase pretreatment improved the complex index of the inclusion complexes. The structural properties analysis indicated the debranching of starch by pullulanase facilitated an increase in microcrystalline regions and ordering of starch. However, extensive debranching resulted in a blend of B- and V-type crystalline structures and a high degree of freedom of amylose chains. The microstructural morphology revealed that pullulanase debranching inhibited the gelatinization of starch by promotion of V-complex formation, while excessive enzymolysis did not. The stability of starch complex structure determined its digestibility, and the digestion analysis revealed that 100 min of pullulanase debranching contributed to the high content of V-type resistant starch. After that, starch helix conformations was more inclined to imperfect amylose double helices, reflecting an increase in slowly digestible starch content.