High Hydrostatic Pressure Treatment of Oysters (Crassostrea gigas)-Impact on Physicochemical Properties, Texture Parameters, and Volatile Flavor Compounds.

High hydrostatic pressure (HHP) treatment is a non-thermal processing technology, which is widely used in the food processing field at present. In this study, the effects of HHP treatment (100~500 MPa for 5 min) on the physicochemical properties, texture parameters, and volatile flavor compounds of oysters were investigated. The results showed that HHP treatment increased the water content while reducing the crude protein and ash content of the oyster. Texture parameters showed that HHP treatment improved the hardness, springiness, chewiness, and cohesiveness of oysters, compared with the control group. In addition, the saturated fatty acid (SFA) content was slightly increased after HHP treatment, while the difference in monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) content was not significant. Furthermore, HHP increased hexenoic aldehyde, 2,4-heptadienal, 1-octene-3-ol, and 2-octen-1-ol and decreased the contents of 3. 6-nadien-1-ol, 3-octanone, and 2-undecanone, suggesting that HHP might inhibit the fishiness of oyster and showed a positive effect on its flavor. Based on the above results, HHP improved the edible qualities such as texture properties and volatile flavor of oysters. This meets the requirements of consumers on the edible quality of seafood and provides new ideas for the development of seafood.

Siderophore (from Synechococcus sp. PCC 7002)-Chelated Iron Promotes Iron Uptake in Caco-2 Cells and Ameliorates Iron Deficiency in Rats.

Siderophores are iron chelators with low molecular weight secreted by microorganisms. Siderophores have the potential to become natural iron fortifiers. To explore the feasibility of the application of Synechococcus sp. PCC7002-derived siderophores as iron fortifiers, Synechococcus sp. PCC7002, as a carrier, was fermented to produce siderophores. The absorption mechanism and anemia intervention effect of siderophores-chelated iron (SCI) were studied through the polarized Caco-2 Cell monolayers and the rat model of iron-deficiency anemia, respectively. The results indicated that siderophores (from Synechococcus sp. PCC7002) had an enhancing effect on iron absorption in polarized Caco-2 cell monolayers. The main absorption site of SCI was duodenum with pH 5.5, and the absorption methods included endocytosis and DMT1, with endocytosis being dominant. The effect of sodium phytate on SCI was less than that of ferrous sulfate. Therefore, SCI could resist inhibitory iron absorption factors in polarized Caco-2 cell monolayers. SCI showed significantly higher relative bioavailability (133.58 ± 15.42%) than ferrous sulfate (100 ± 14.84%) and ferric citrate (66.34 ± 8.715%) in the rat model. Food intake, hemoglobin concentration, and hematocrit and serum iron concentration of rats improved significantly after Fe-repletion. Overall, this study indicated that siderophores derived from Synechococcus sp. PCC7002 could be an effective and feasible iron nutritive fortifier.

Effects of High Pressure Modification on Conformation and Digestibility Properties of Oyster Protein.

To expand the utilization of oyster protein (OP), the effects of high pressure (100 to 500 MPa) on chemical forces, structure, microstructure, and digestibility properties were investigated. High pressure (HP) treatment enhanced the electrostatic repulsion (from -13.3Control to -27.8HP200 mV) between protein molecules and avoided or retarded the formation of protein aggregates. In addition, the HP treated samples showed uniform distribution and small particle size. The changes in electrostatic interaction and particle size contributed to the improvement of solubility (from 10.53%Control to 19.92%HP500 at pH 7). The stretching and unfolding of protein were modified by HP treatment, and some internal hydrophobic groups and -SH groups were exposed. HP treatment modified the secondary structure of OP. The treated samples contained less α-helix and ß-sheet structures, whereas the proportions of ß-sheet and random coil structures were increased. The treated samples have high digestibility in the stomach (from 26.3%Control to 39.5%HP500) and in the total digestive process (from 62.1%Control to 83.7%HP500). In addition, the total digestive production showed higher percentages of small peptides (<1 kDa) after HP treatment. The protein solubility and digestibility were increased after HP treatment, and high solubility and high digestibility might increase the chance that OP become a kind of protein supplement.

Oyster polysaccharides relieve DSS-induced colitis via anti-inflammatory and maintaining the physiological hypoxia.

Oyster polysaccharides (OPS) possess potent anti-inflammatory properties and mediate gut microbiome. The research aimed to investigate the beneficial effect of OPS on attenuating colitis. OPS administration decreased the disease activity index and suppressed the increase in colon length. Hematoxylin and eosin staining results displayed that OPS restored the DSS-induced histopathological damage. After oral administration of OPS, myeloperoxidase activity and pro-inflammatory cytokines (TNF-α) in colitis mice were inhibited, while IL-10 was elevated. Western blotting results revealed that OPS improved the expression of tight junction proteins (ZO-1, Claudin-4, and Occludin). Additionally, OPS stabilized the expression of hypoxia-inducible factor-1α (HIF-1α) and prevented the levels of bacterial endotoxin (lipopolysaccharides). OPS activated barrier-protective genes (intestinal trefoil factor) via mediating HIF-1α. These results indicated that OPS alleviated DSS-induced colitis by inhibiting inflammation and regulating HIF-1α. OPS would be a potential candidate to alleviate DSS-induced colitis.

Effect of chitosan coating on the properties of nanoliposomes loaded with oyster protein hydrolysates: Stability during spray-drying and freeze-drying.

Oyster protein hydrolysate (OPH) has high bioactivity and excellent performance, but its application in food formulation is still limited due to poor flavor and instability. In the present study, OPH was prepared by enzymatic hydrolysis and loaded into nanoliposomes. Then, the effects of chitosan coating (0, 0.25, 0.5, and 1.0%) on the physical properties, stability, and antioxidant activity were evaluated. The results showed that 1% chitosan-coated nanoliposomes had high encapsulation efficiency (EE) and physical stability. Additionally, chitosan coating slowed the release rate of nanoliposomes and increased the retention rate of antioxidant activity of OPH. The stability of the uncoated/coated nanoliposomes in a maltodextrin matrix by spray/freeze drying was evaluated. FTIR spectrum showed that hydrogen bonds, hydrophobic, and electrostatic interactions had been formed between chitosan-coated nanoliposomes and maltodextrin. Chitosan coating significantly improved the physical stability and antioxidant activity retention of nanoliposomes during powder reconstitution.

Effect of κ-carrageenan on the gelation properties of oyster protein.

Proteins and polysaccharides commonly coexist in the food system, forming complexes and coacervates to make tailor-made food. In this study, the effects of κ-carrageenan on the rheological behavior, network structure, textures, and molecular force of oyster protein (OP treated with high-pressure homogenization were investigated. Rheological results showed that κ-carrageenan improved the storage modulus of OP, and the higher concentration of κ-carrageenan accelerated the gelation of OP. The second derivative of infrared spectroscopy revealed that κ-carrageenan contributed to the formation of ß-sheet in OP. Molecular force and texture analysis showed that κ-carrageenan might promote the increase of hydrophobic bonds and disulfide bonds, which was helpful to enhance gel strength. The microstructure showed that the OP gel with 1.5% κ-carrageenan had a compact network structure with abundant minor mesh and sheet edge. This study reveals the gelation mechanism of OP/κ-carrageenan and provides the theoretical basis for developing innovative oyster products.

Oyster (Crassostrea gigas) polysaccharide ameliorates obesity in association with modulation of lipid metabolism and gut microbiota in high-fat diet fed mice.

Oyster is nutritious shellfish, wildly consumed throughout the world. Its polysaccharide (OPS) has various bioactivity. In the present study, the anti-obesity effect of OPS was evaluated in obese mice induced by a high-fat diet (HFD). The results showed that OPS significantly alleviated weight gain, dyslipidemia, and metabolic endotoxemia of obese mice, and accelerated the production of short-chain fatty acids. OPS also regulated lipid metabolism of adipose and liver by activating the expression of p-AMPKα to further down-regulate the expression of SREBP-1c, PPARγ, and p-ACC-1. 16S rRNA results indicated that OPS corrected HFD-induced gut microbiota dysbiosis by enriching beneficial bacteria (Bifidobacterium, Lactobacillus, Dobosiella, and Faecalibaculum) and decreasing harmful bacteria (Erysipelatoclostridium, Helicobacter, and Mucispirillum). In summary, these results revealed that OPS could serve as a potential prebiotic to improve obesity.

Shell water-soluble matrix protein from oyster shells promoted proliferation, differentiation and mineralization of osteoblasts in vitro and vivo.

Matrix protein is secreted by the membrane of bivalve shellfish to and used to regulate shell biomineralization. In this study, we extracted water-soluble matrix protein (WSMP) from oyster shells to investigate its effects on osteogenic differentiation and mineralization of MC3T3-E1 cells and osteoporosis rats. Our results suggested that WSMP was an acidic glycoprotein by amino acid analysis and secondary structure analysis. In vitro, WSMP could promote osteoblastic proliferation. Moreover, alkaline phosphatase (ALP) and osteocalcin (OCN) were increased, mineralized nodules were increased, and BMP-2 expression was up-regulated. Additionally, in vivo, tartrate-resistant acid phosphatase (TRAP) and Bone alkaline phosphatase (BALP) expressions in the medium-dose and high-dose groups were significantly decreased compared with the model group, while OCN expression was significantly increased. Bone mineral density (BMD) and bone mineral content (BMC) of bone recovered significantly. In summary, WSMP can promote the proliferation, differentiation and mineralization of osteoblasts in vitro and in vivo.

In vitro simulated digestion and fermentation characteristics of polysaccharide from oyster (Crassostrea gigas), and its effects on the gut microbiota.

Oyster is a kind of nutritious shellfish widely consumed globally, and its polysaccharide (OPS) has been verified to have strong functional activity. However, it is still unclear about the specific digestion and prebiotic properties of OPS. In the present study, the digestion and fermentation properties of OPS and its effect on gut microbiota were evaluated using simulated digestion (saliva, stomach, and small intestine) and fermentation models in vitro. The results showed that the molecular weight (Mw) of OPS decreased from 5.73 × 106 to 4.35 × 106 Da, and the reducing sugar content increased from 0.043 to 0.096 mg/mL, indicating that OPS was partially degraded during the saliva-gastrointestinal digestion. During fermentation, the Mw and carbohydrate residue of indigestible OPS (OPSI) decreased, and free monosaccharides were released, suggesting that OPSI could be further degraded and utilized by gut microbiota. Notably, OPSI could regulate the composition and diversity of the microbial community, especially increase the abundance of beneficial bacteria such as Bacteroides, Prevotella, and Faecalibacterium. Additionally, after fermentation for 24 h, OPSI promoted the production of short-chain fatty acids (SCFAs), and acetic acid, propionic acid, and n-butyric acid were the main metabolites. These results provided a reference for the digestive characteristics of OPS and revealed that OPS might be a potential prebiotic to prevent diseases by improving intestinal health.

Encapsulation of oyster protein hydrolysates in nanoliposomes: Vesicle characteristics, storage stability, in vitro release, and gastrointestinal digestion.

In this study, oyster protein hydrolysates (OPH) were obtained from oyster meat by hydrolysis using animal complex proteases and then encapsulated in nanoliposomes. The physicochemical properties, stability, and digestive characteristics of OPH-loaded nanoliposomes were evaluated. The average size and zeta potential ranged from 95.64 to 102.39 nm and from -47.36 to -36.43 mV, respectively. Liposomes containing 4 mg/mL OPH had the highest encapsulation efficiency (74.53%). Fourier transform infrared spectroscopy analysis showed that effective ionic complexation and hydrogen bonding existed between phospholipid and peptides. The liposomes exhibited the highest stability when stored at 4 °C. Liposomal encapsulation may protect the antioxidant peptides in OPH during storage and simulated digestion. The nanoliposomes were not hydrolyzed and the structural integrity was maintained in gastric digestion, but exhibited lower stability in the intestinal phase. A prolonged release of OPH from nanoliposomes was also observed as compared with free OPH. Liposome containing protein hydrolysates may be used as a formula in functional foods. PRACTICAL APPLICATION: This study provides some useful information on the application of oyster protein hydrolysates or peptides in functional foods. The incorporation into liposomes may protect the hydrolysates against harsh conditions during storage and digestion, and also prolong the release time.

Mediation of the microbiome-gut axis by oyster (Crassostrea gigas) polysaccharides: A possible protective role in alcoholic liver injury.

The objective of this study was to evaluate the molecular mechanism by which polysaccharides from Crassostrea gigas (RPS) prevent alcoholic liver injury and to uncover whether the steaming process affects the bioactivities of RPS. Oral administration of RPS or polysaccharides from steamed oyster (SPS) (282 mg/kg b.w.) significantly attenuated alcoholic liver injury in mice. RPS and SPS treatments protected gut functions by significantly enhancing the expression of tight-junction proteins and suppressing inflammatory responses. RPS and SPS treatments also significantly increased Lactobacillus reuteri and Roseburia spp. and decreased the level of Escherichia. Microbial metabolites, especially propionate and butyrate, were also increased in RPS- and SPS-treated mice. Correlation analysis revealed that the beneficial effects of RPS and SPS were strongly correlated with the microbiota composition and SCFAs. These results indicated that oyster polysaccharides alleviated alcoholic liver injury by mediating the gut-liver-metabolite axis, and the steaming process had little influence on the bioactivity.

Extraction and characterization of matrix protein from pacific oyster (Crassostrea gigs) shell and its anti-osteoporosis properties in vitro and in vivo.

Matrix protein is a kind of secretory protein that regulates the biomineralization of the bivalve shell. In this study, a water-soluble matrix protein (WSMP) from Pacific oysters (Crassostrea gigs) shell was isolated, and its structure was analyzed in detail, in addition to its anti-osteoporosis activity in vitro and in vivo. Results showed that WSMP was an acidic protein with an apparent molecular mass of 47 and 79 kDa and contained a glycoprotein structure. In vitro, the reduction of Tartrate-resistant acid phosphatase (TRAP) and deoxypyridinoline (DPD) indicated that osteoclast activity was inhibited compared with the model group. Moreover, the increased osteocalcin (OCN) and BMD levels suggested that the high osteoblast activity and bone mineralization was improved. SEM analysis of the femur showed that there were fewer bone pits in experimental groups, which was consistent with the above results. In vivo, WSMP promoted the expression of alkaline phosphatase (ALP) and osteogenic differentiation factor BMP-2 in osteoblasts. In addition, the activity of osteoclasts was inhibited by regulating the process of osteoclast differentiation induced by RANKL. Both in vitro and in vivo studies showed that WSMP could promote osteogenesis and inhibit osteoclast absorption, thus demonstrating their potential applications in osteoporosis.

Effect of different cooking methods on sensory quality assessment and in vitro digestibility of sturgeon steak.

Sous vide can keep the nutritional properties and improve taste of food compared with other conventional methods. In addition, this method may reduce the risk of recontamination after cooking and during storage. The purpose of this paper was to study the effects of four cooking methods (steaming, microwaving, baking, and frying) on the sensory and digestibility on sturgeon steak pretreated by sous vide during the cold storage (0-25 days). The results showed that the digestibility of steaming and microwaving groups (range from 80.34% to 90.12%) significantly higher than that of the other treatment groups (p < .05); however, the overall acceptability of the two groups was lower. What more, the frying group has the highest acceptability and the lowest digestibility (range from 65.12% to 70.89%). The springiness (4.12-6.56 mm) and chewiness (1.75-3.12 mm) of the frying group were significantly higher than those of the other treatment groups, which was consistent with the results of scanning electron microscopy (SEM) that frying treatment group has a denser structure and smaller pores. With the prolonged refrigeration time, especially between 15 and 25 days, the volatile flavor components (nitrogen oxide, methane, and alcohol) and stagnant water (T21) were significantly decreased. Principal component analysis showed that the moisture content was the main factor affecting the overall acceptability and best consumption time of the sturgeon was within 15 days. Simulating the effects of home cooking conditions and refrigeration storage time on the quality of sturgeon steak provided a reference for consumers using similar products.

Synthesis and characterization of hydroxyapatite nano-rods from oyster shell with exogenous surfactants.

The Hydroxyapatite (HA, Ca10(PO4)6(OH)2) has attracted widely research interests in many aspects, especially in repairing and replacing human hard tissues due to its brilliant biocompatibility, biological activity and so on. In the present article, HA nano-rods were rapidly developed via hydrothermal reaction synthesized with two representative surfactants (hexadecyltrimethylammonium bromide and sodium dodecyl sulfate) taken oyster shells as raw materials. The scanning electron microscopy (SEM) observations demonstrated that the micromorphology of synthesized HA was constructed of relatively regular nano-rods. From the zeta potential (ZP) analysis, the zeta potential of the developed HA was affected by different surfactants, which demonstrated the opposite potential value. The Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) results showed the HA phase was successfully and rapidly developed on the surface of oyster shell with the help of surfactants. The bio-safety of HA nano-rods was confirmed by MTT cytotoxicity assay using pre-osteoblasts cells. A possible hard-template transformation mechanism from the calcite and aragonite phases into the HA phase was proposed.

Characterization of Maillard reaction products micro/nano-particles present in fermented soybean sauce and vinegar.

The endogenous micro/nano-particles in daily food have drawn much attention due to specific properties potential biological impact. The aim of this study was to investigate the nanoparticles in traditional fermented soybean sauces and vinegars in order to study the safety problems of nanoparticles in daily food. The transmission electron microscope results showed that all samples exhibited diverse nanostructures with diameters ranging from 10 to 400 nm. The concentration of nanoparticles in these foods was determined to be around 1.15 × 107-3.43 × 109 particles/mL. Furthermore, the absorbance at 420 nm was found in all the fermented foods, which was ascribed to Maillard reaction products. The 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyl-tetrazolium bromide (MTT) results showed that nanoparticles in traditional fermented foods did not decrease cell viability in the concentration range tested (<200 µg/mL), which were equivalent to 20 L~200 L of selected soybean sauces and vinegars. However, further studies need to be performed to find out the interaction of nanoparticle with cell (food with body) after ingestion.

Nano-complexation of ε-poly-l-lysine with DNA: Improvement of antimicrobial activity under high phosphate conditions.

ε-Poly-l-lysine (PL) has high antimicrobial activity and a wide antimicrobial spectrum and is applied broadly in the food industry. However, PL may lose part of its activity in phosphate systems, which are typically used in seafood processing. To enhance antimicrobial activity under high phosphate conditions, DNA/PL nanoparticles were fabricated via the nanoprecipitation method. The DNA/PL nanoparticle size was smallest when the ethanol to water ratio was 7:1, and the mean diameter was 101 nm. UV-vis showed hypochromism and a redshift of the DNA in the presence of PL, indicating an intercalative interaction between DNA and PL. FTIR spectroscopy revealed that strong hydrogen bonds and hydrophobic interactions were involved in DNA/PL nanoparticle formation. Compared with that of PL, the antimicrobial activity of the nanoparticles against S. aureus, B. subtilis, and E. coli was enhanced. Additionally, the DNA/PL nanoparticles still retained higher antimicrobial activity in the phosphate system than free PL. The antimicrobial mechanistic analysis provided evidence that the DNA/PL nanoparticles showed high bioactivity due to cell membrane damage. This work provides a potential method to enhance the antimicrobial activity of PL under adverse conditions, which can promote the application of PL in seafood containing phosphate compounds.

In vitro inhibition of pancreatic α-amylase by spherical and polygonal starch nanoparticles.

Nanoparticles are novel and fascinating materials for tuning the activities of enzymes. In this study, we investigated the influence of spherical and polygonal starch nanoparticles (SNPs) on α-amylase activity and revealed the reaction mechanisms by ultraviolet-visible spectrophotometry, fluorescence spectroscopy, and circular dichroism (CD) spectroscopy. We discovered that both spherical and polygonal SNPs could inhibit the α-amylase activity, with half-inhibitory concentration values of 0.304 and 0.019 mg mL-1, respectively. Furthermore, spherical and polygonal SNPs followed competitive and mixed competitive inhibition mechanisms, respectively. The fluorescence data indicated that static quenching was dominant in the interaction between SNPs and α-amylase. The CD results demonstrated that the inhibition of α-amylase by SNPs was accompanied by the decreased intensity of the CD spectra of α-amylase. Our findings provide a novel strategy to inhibit α-amylase to reduce the digestion of starch, thus managing blood glucose levels.

Enhanced antibacterial activity of lysozyme immobilized on chitin nanowhiskers.

In this paper, the contribution of chitin nanowhiskers (CHNW) to the enzymatic activity and antimicrobial activity of lysozyme adsorbed on CHNW was investigated. An activity assay showed that the lysozyme-CHNW system exhibited significant promotion potency on lysozyme activity, which was approximately 1.5-fold greater than that of free lysozyme. The molecular promotion mechanism of lysozyme immobilized by adsorption onto CHNW was investigated by ultraviolet-visible spectrophotometry, fluorescence spectroscopy, and circular dichroism spectroscopy. The results indicated that changes in the secondary structure of lysozyme adsorption onto CHNW resulted in superior enzymatic activity. Furthermore, the antimicrobial assays indicated that the antimicrobial activity of the lysozyme-CHNW system was greater than that of free lysozyme, whereas its antimicrobial effect on a gram-negative bacterium was better than that on gram-positive bacteria. This research provides a facile and promising approach for increasing the application of chitin-derived and enhancing the antibacterial efficiency on preservation.

Functional Properties of Glutinous Rice Flour by Dry-Heat Treatment.

Glutinous rice flour (GRF) and glutinous rice starch (GRS) were modified by dry-heat treatment and their rheological, thermal properties and freeze-thaw stability were evaluated. Compared with the native GRF and GRS, the water-holding ability of modified GRF and GRS were enhanced. Both the onset and peak temperatures of the modified samples increased while the endothermic enthalpy change decreased significantly (p < 0.05). Meanwhile, dry heating remarkably increased the apparent viscosities of both GRF and GRS. Importantly, compared with GRS samples, the storage modulus (G') and loss modulus (G") values of modified GRF increased more greatly and the tanδ values decreased more remarkably, indicating that the dry-heat treatment showed more impact on the GRF and a higher viscoelasticity compared with GRS. Our results suggest the dry-heat treatment of GRF is a more effective method than that of GRS, which omits the complex and tedious process for purifying GRS, and thereby has more practical applications in the food industry.

Preparation and Characterization of Octenyl Succinic Anhydride Modified Taro Starch Nanoparticles.

The polar surface and hydrophilicity of starch nanoparticles (SNPs) result in their poor dispersibility in nonpolar solvent and poor compatibility with hydrophobic polymers, which limited the application in hydrophobic system. To improve their hydrophobicity, SNPs prepared through self-assembly of short chain amylose debranched from cooked taro starch, were modified by octenyl succinic anhydride (OSA). Size via dynamic light scattering of OSA-SNPs increased compared with SNPs. Fourier transform infrared spectroscopy data indicated the OSA-SNPs had a new absorption peak at 1727 cm-1, which was the characteristic peak of carbonyl, indicating the formation of the ester bond. The dispersibility of the modified SNPs in the mixture of water with nonpolar solvent increased with increasing of degree of substitution (DS). OSA-SNPs appear to be a potential agent to stabilize the oil-water systems.