Mingyong Zeng

A novel ACE inhibitory peptide isolated from Acaudina molpadioidea hydrolysate

Body wall protein from the sea cucumber (Acaudina molpadioidea) was hydrolyzed sequentially with bromelain and alcalase. The hydrolysate was fractionated into two ranges of molecular weight (PH-I, >2 kDa; PH-II, <2kDa) using an ultrafiltration membrane bioreactor system. The PH-II brought about a high angiotensin I-converting enzyme (ACE) inhibitory activity. An ACE inhibitory peptide was isolated from the PH-II, using the chromatographic methods including gel filtration, ion-exchange chromatography and reversed phase high-performance liquid chromatography. The purified ACE inhibitory peptide was a novel peptide, showing very low similarity to other ACE inhibitory peptide sequences, and was sequenced as MEGAQEAQGD. It was found that the inhibitory activity of the peptide was intensified by 3.5 times from IC(50) 15.9 to IC(50) 4.5 microM after incubation with gastrointestinal proteases. The ACE inhibitory peptide from A. molpadioidea showed a clear antihypertensive effect in spontaneously hypertensive rats (SHR), at a dosage of 3 microM/kg.

Reactive oxygen species-related activities of nano-iron metal and nano-iron oxides

Nano-iron metal and nano-iron oxides are among the most widely used engineered and naturally occurring nanostructures, and the increasing incidence of biological exposure to these nanostructures has raised concerns about their biotoxicity. Reactive oxygen species (ROS)-induced oxidative stress is one of the most accepted toxic mechanisms and, in the past decades, considerable efforts have been made to investigate the ROS-related activities of iron nanostructures. In this review, we summarize activities of nano-iron metal and nano-iron oxides in ROS-related redox processes, addressing in detail the known homogeneous and heterogeneous redox mechanisms involved in these processes, intrinsic ROS-related properties of iron nanostructures (chemical composition, particle size, and crystalline phase), and ROS-related bio-microenvironmental factors, including physiological pH and buffers, biogenic reducing agents, and other organic substances.

The involvement of bacterial quorum sensing in the spoilage of refrigerated Litopenaeus vannamei

Quorum-sensing signals in refrigerated shrimp (Litopenaeus vannamei) undergoing spoilage were examined using bioreporter assays, thin-layer chromatography and gas chromatography-mass spectrometry, and the results revealed the presence of three types of autoinducers including acetylated homoserine lactones (AHLs) (i.e., N-hexanoyl-homoserine lactone, N-oxohexanoyl-homoserine lactone and N-octanoyl-homoserine lactone), autoinducer-2, and cyclic dipeptides (i.e., cyclo-(L-Pro-L-Leu), cyclo-(L-Leu-L-Leu) and cyclo-(L-Pro-L-Phe)). Autoinducer-2, rather than any AHL, was detected in extracts from pure cultures of the specific spoilage organisms (SSO), i.e., Shewanella putrefaciens (SS01) and Shewanella baltica (SA02). As for the cyclic peptides, only SA02 was determined to produce cyclo-(L-Pro-L-Leu). According to the transcription levels of LuxR (the master quorum-sensing regulator) in the SSO in response to exogenous autoinducers, the SSO could sense AHLs and cyclo-(L-Leu-L-Leu), rather than autoinducer-2, cyclo-(L-Leu-L-Leu) and cyclo-(L-Pro-L-Phe). In accordance with the results of LuxR expression, the production of biofilm matrixes and extracellular proteases in the SSO was regulated by exogenous AHLs and cyclo-(L-Pro-L-Leu), rather than 4,5-dihydroxy-2,3-pentanedione (the autoinducer-2 precursor), cyclo-(L-Leu-L-Leu) and cyclo-(L-Pro-L-Phe). Exogenous N-hexanoyl-homoserine lactone and cyclo-(L-Pro-L-Leu) increased the growth rates and population percentages of the SSO in shrimp samples under refrigerated storage, and interestingly, exogenous 4,5-dihydroxy-2,3-pentanedione also increased the population percentages of the SSO in vivo by inhibiting the growth of the competing bacteria. However, according to the levels of TVB-N and the volatile organic components in the shrimp samples, exogenous 4,5-dihydroxy-2,3-pentanedione did not accelerate the shrimp spoilage process as N-hexanoyl-homoserine lactone and cyclo-(L-Pro-L-Leu) did. In summary, our results suggest that quorum sensing involves the spoilage of refrigerated Litopenaeus vannamei.

Optimization of Hydrolysis Conditions for the Production of the Angiotensin-I Converting Enzyme Inhibitory Peptides from Sea Cucumber Collagen Hydrolysates

The effects of different hydrolysis conditions on the angiotensin-I converting enzyme (ACE) inhibitory properties of giant red sea cucumber (Parastichopus californicus) collagen hydrolysates were investigated. Optimal conditions predicted by central composite rotatable design (CCDR) modeling for producing ACE inhibitory peptides were found to be 54.9°C, 1.76 h and an enzyme to substrate (E/S) ratio of 0.064. Compared with experiments performed under these optimal conditions, the predicted degree of hydrolysis (DH) and ACE inhibitory activities had error rates of 3 to 6%. Under optimum conditions, the molecular weights of collagen hydrolysates were less than 6.5 kDa. Lineweaver-Burk plots suggest that the collagen hydrolysates acted as competitive inhibitors with an inhibition constant (Ki) value of 0.706 mg/mL.

Formation of ferric oxyhydroxide nanoparticles mediated by peptides in anchovy (Engraulis japonicus) muscle protein hydrolysate.

Nanosized iron fortificants appear to be promising and can be synthesized in a greener way using peptides as biotemplates. Anchovy is a huge underdeveloped source of muscle protein that enhances human nonheme iron absorption. This paper shows that peptides in anchovy ( Engraulis japonicus ) muscle protein hydrolysate (AMPH) mediate the formation of monodispersed ferric oxyhydroxide nanoparticles (FeONPs) with diameters of 20-40 nm above pH 3.0. Peptides in AMPH nucleate iron through carboxyl groups and crystal growth then occur as a result of condensation of carboxylate-ligated hydroxide iron centers, yielding Fe-O-Fe cross-link bonds. Monomers of FeONPs are formed after steric obstruction of further crystal growth by peptide backbones with certain lengths and further stabilized by surface-adsorbed peptides. The iron-loading capacity of peptides in AMPH is up to 27.5 mg iron/g peptide. Overall, the present study provides a greener alternative route to the synthesis of FeONPs.

Characterization of N-acyl homoserine lactones (AHLs) producing bacteria isolated from vacuum-packaged refrigerated turbot (Scophthalmus maximus) and possible influence of exogenous AHLs on bacterial phenotype.

Quorum sensing (QS) is a cell-to-cell communication mechanism through which microbial cells communicate and regulate their wide variety of biological activities. N-acyl homoserine lactones (AHLs) are considered to be the most important QS signaling molecules produced by several Gram-negative bacteria. The present study aimed to screen the AHLs-producing bacteria from spoiled vacuum-packaged refrigerated turbot (Scophthalmus maximus) by biosensor assays, and the profiles of AHLs produced by these bacteria were determined using reversed-phase thin-layer chromatography (RP-TLC) and gas chromatography-mass spectrometry (GC-MS). Effects of exogenous AHLs and QS inhibitor (QSI) on the phenotypes (i.e., extracellular proteolytic activity and biofilm formation) of the AHLs-producing bacteria were also evaluated. Our results demonstrated that eight out of twenty-two isolates were found to produce AHLs. Three of the AHLs-producing isolates were identified as Serratia sp., and the other five were found to belong to the family of Aeromonas. Two isolates (i.e., S. liquefaciens A2 and A. sobria B1) with higher AHLs-producing activities were selected for further studies. Mainly, RP-TLC and GC-MS analysis revealed three AHLs, i.e., 3-oxo-C6-HSL, C8-HSL and C10-HSL were produced by S. liquefaciens A2, while five AHLs, i.e., C4-HSL, C6-HSL, C8-HSL, C10-HSL, and C12-HSL, were produced by A. sobria B1. Moreover, production of AHLs in both bacterial strains were found to be density-dependent, and the AHLs activity reached a maximum level in their middle logarithmic phase and decreased in the stationary phase. The addition of exogenous AHLs and QSI decreased the specific protease activity both of the Serratia A2 and Aeromonas B1. Exogenous AHLs inhibited the biofilm formation of Serratia A2 while it enhanced the biofilm formation in Aeromonas B1. QSI inhibited the specific protease activity and biofilm formation in both bacterial strains.

Antioxidant balance and accumulation of advanced glycation end products after the consumption of standard diets including Maillard reaction products from silver carp peptides

The aim of this research was to investigate the accumulation and excretion of AGEs including fluorescent compounds and N-ε-carboxymethyllysine (CML) in streptozotocin-induced diabetes C57BL/6J mice fed on a diet containing Maillard reaction products (MRPs) from a silver carp peptide-glucose model system at different heating temperatures for the first time, and analyze the relationship between their in vitro antioxidant activity based on DPPH and ORAC assays and in vivo oxidative stress. The in vitro antioxidant activity of MRPs positively correlated with their AGEs level and molecular weight distribution. However, the opposite results were found by malondialdehyde (MDA) and super oxide dismutase (SOD) assays that MRPs from a higher heating temperature could aggravate the oxidative stress of diabetic mice. CML accumulation in serum was aggravated, but changes of MRPs in diets hardly affected CML accumulation in the kidney and liver. Therefore, the high AGEs levels from a diet containing peptide MRPs have negative effects on the oxidative stress of diabetic mice.

Enhancement of non-heme iron absorption by anchovy (Engraulis japonicus) muscle protein hydrolysate involves a nanoparticle-mediated mechanism.

The mechanisms by which meat enhances human absorption of non-heme iron remain unknown. Recently, anchovy (Engraulis japonicus) muscle protein hydrolysate (AMPH) was found to mediate the formation of nanosized ferric hydrolysis products in vitro. The current paper evaluates the effects of AMPH on the bioavailability and the intestinal speciation of non-heme iron in rats, followed by an investigation of cellular uptake pathways of in vitro-formed AMPH-stabilized nanosized ferric hydrolysis products (ANPs) by polarized human intestinal epithelial (Caco-2) cells. The hemoglobin regeneration efficiencies in anemic rats followed the order ferric citrate (9.79 ± 2.02%) < commercial bare α-Fe2O3 nanoparticles (16.37 ± 6.65%) < mixture of ferric citrate and AMPH (40.33 ± 6.36%) ≈ ferrous sulfate (40.88 ± 7.67%) < ANPs (56.25 ± 11.35%). Percentage contents of intestinal low-molecular-weight iron in the groups of FC+AMPH, FeSO4, and ANPs were significantly lower than the corresponding hemoglobin regeneration efficiencies (P < 0.05), providing strong evidence for the involvement of nanosized iron in intestinal iron absorption from FC+AMPH, FeSO4, and ANPs. Calcein-fluorescence measurements of the labile iron pool of polarized Caco-2 cells revealed the involvement of both divalent transporter 1 and endocytosis in apical uptake of ANPs, with endocytosis dominating at acidic extracellular pH. Overall, AMPH enhancement of non-heme iron absorption involves a nanoparticle-mediated mechanism.

Assessing the Antioxidant Activity of the Ultrafiltration Fractions From Silver Carp Protein Hydrolysate by Different Antioxidant Methods

Silver carp protein hydrolysate (SH) was fractionated by 5- and 1-kDa cutoff ultrafiltration (UF) membrane, and three ultrafiltrates were obtained: SHI (>5 kDa), SHII (1–5 kDa), and SHIII (<1 kDa) which were screened for antioxidant activity by five in vitro assays. The SHIII showed higher 2, 2-azobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and oxygen radical absorbance capacity (ORAC) values, inhibiting effects for liposome oxidation induced by Fe3+/VC. The SHII showed higher ferric reducing power (FRAP) and inhibiting effects for liposome oxidation induced by 2, 2′-azobis (2-methylpropionamidine) dihydrochloride (AAPH). However, the SHI showed the highest 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radicals scavenging activity. Therefore, the antioxidant activity of silver carp protein hydrolysates was mainly associated with their molecular weight distribution, and the antioxidant assays used to test different samples gave comparable results.

Quorum Sensing Involved in the Spoilage Process of the Skin and Flesh of Vacuum-Packaged Farmed Turbot (Scophthalmus maximus) Stored at 4 °C

Fish skin has both positive and negative effects on the shelf-life of the fish. This study aimed to investigate the spoilage process of the skin and flesh of refrigerated farmed turbot (Scophthalmus maximus) with vacuum packaging. Microbial community changes were analyzed by combining culture-dependent and culture-independent methods. The results indicated that the shelf-life of vacuum-packaged refrigerated turbot was 16 d; skin mucus was the interference factor of turbot quality. The culture-dependent analysis demonstrated that the total viable counts and the population of H2 S-producing bacteria, Pseudomonas spp., Enterobacteriaceae spp., and lactic acid bacteria in skin had a range of 0.45 to 1.40 log (CFU/g) higher than the microbial numbers in flesh after 16 d in storage. 16S high throughout sequencing results demonstrated that the compositions of spoilage microbes were similar in skin and flesh. Shewanella spp., followed by Carnobacterium spp., was the dominant spoilage organism at day 16. Quorum sensing (QS) signaling activity increased during the storage. Exogenous N-butanoyl-L-homoserinelactone(C4-HSL) and N-hexanoyl-Lhomoserine lactone (C6-HSL) significantly accelerated the spoilage process of refrigerated turbot, while the addition of 4, 5-Dihydroxypentane-2, 3-dione (DPD) prolonged the lag phase duration. Therefore, QS may be involved in the spoilage process of refrigerated turbot.