Hx Content Research Articles

Two dimensional iron metal-organic framework nanosheet with peroxidase-mimicking activity for colorimetric detection of hypoxanthine related to shrimp freshness

Two dimensional iron metal-organic framework nanosheet (2D Fe MOF) was facilely synthesized at room temperature by simple stirring of iron salts and terephthalic acid ligand in a mixed solution containing triethylamine. Its morphology and structure were fully characterized by TEM, AFM, XPS and TEM element mapping. Then, its peroxidase-mimicking activity was studied by using H2O2 and 3, 3′, 5, 5′- tetramethylbenzidine as substrate. Km and Vmax of 2D Fe MOF towards H2O2 were 0.02 mM and 2.08 × 10−8 M s−1, respectively. Through the formation of cascade reaction between xanthine oxidase and 2D Fe MOF, a visual method for hypoxanthine (Hx) detection was constructed to evaluate aquatic products freshness. After effective validation, this method presented wide linear range (5.0–500.0 μM), low limit of detection (3.29 μM), satisfied accuracy (recovery of 94.78–99.85%), and good selectivity. By using this method, Hx content in shrimp samples at different storage time were determined.

Co(OH)2/MXene-Ti3C2 nanocomposites with triple-enzyme mimic activities as hydrogel sensing platform for on-site detection of hypoxanthine.

Novel Co(OH)2/MXene-Ti3C2 nanocomposites with oxidase (OXD)-mimic, peroxidase (POD)-mimic, and catalase (CAT)-mimic activities were prepared by asimple two-step method. The Co(OH)2/MXene-Ti3C2 nanocomposites with triple-enzyme mimic activities were embedded into sodium alginate (SA) gels for the first time to fabricate a target-responsive hydrogel-assisted assay. The catalytic mechanism and steady-state kinetics of Co(OH)2/MXene-Ti3C2 nanocomposites were investigated. Subsequently, hypoxanthine (Hx) was catalyzed by xanthine oxidase (XOD) to form H2O2, which reacts with 3,3',5,5'-tetramethyl-benzidine (TMB) in the presence of Co(OH)2/MXene-Ti3C2 nanocomposites to form a blue oxide (ox-TMB) in the hydrogel. The visible color change of the hydrogel with the increase of Hx concentration can be recognized through a smartphone App to transfer the red (R), green (G), and blue (B) values for the quantitative determination of Hx, with adetection range from 5 to 250μM, and detection limit of0.2μM. Themethod was applied to the determination of Hx content in different aquatic products. The spiked recoveries of the aquatic products were from 94.1 to 106.4%, and the relative standard deviations (RSD) were less than 5.4%. Our results show that the Co(OH)2/MXene-Ti3C2 nanocomposites hydrogel-assisted colorimetric biosensor is cost-effective, sensitive, and selective andhas excellent application prospects forin-the-field determinationof Hx.

Fluorescent Copper Nanoclusters for Highly Sensitive Monitoring of Hypoxanthine in Fish

Hypoxanthine (Hx) is an important freshness indicator reflecting the initial freshness of aquatic products. In this work, a novel fluorescence method was established based on cysteine functionalized copper nanoclusters (Cys-CuNCs) for monitoring Hx in fish. The as-synthesized Cys-CuNCs exhibit favorable fluorescent property. Importantly, the fluorescence can be quenched significantly when the solution contained a small amount of hydrogen peroxide (H2O2), which was due to both the oxidation of H2O2 towards Cys-CuNCs and the resulting Cu(II). Owing to that Hx can generate H2O2 under dissolved oxygen and xanthine oxidase (XOD), a fluorescent method for Hx was established. Under the optimal conditions, the Hx concentration in the range of 8–400 μmol/L has a good linear relationship with the fluorescence quenching efficiency, and the detection limit is 0.7 μmol/L. Finally, the as-established sensor was applied to determine Hx content in carp. By comparing to the total volatile basic nitrogen (TVB-N) results, the proposed method was feasible in the evaluation of carp freshness.

A fluorescent biosensor based on catalytic activity of platinum nanoparticles for freshness evaluation of aquatic products

In this study, a fluorescence biosensor based on the peroxidase mimicking activity of platinum nanoparticles (Pt NPs) was fabricated for rapid detection of hypoxanthine (Hx), which is a sensitive indicator of the freshness of aquatic products. The fluorescence intensity of the sensing system had a linear relationship with the concentration of Hx in the range of 8–2500 μM, and the limit of detection was as low as 2.88 μM (S/N = 3). Moreover, benefiting from the excellent selectivity of the biosensor, Hx content in fish, shrimp and squid samples could be quickly detected with good recovery rates (103.94–109.00%). And the Pt NPs used in the biosensor was reusable, which was proved by the recovery rate was only slightly decreased to 91% after three cycles. In addition to the advantages of facile preparation and low cost, the proposed biosensor will be a promising candidate for rapid and convenient freshness evaluation of aquatic products.

Effect of long-term moderate exercise on muscle cellularity and texture, antioxidant activities, tissue composition, freshness indicators and flavor characteristics in largemouth bass (Micropterus salmoides)

Fish fillet is heavily influenced by swimming exercise and other factors leading to a great change in fish physiology. During the present study, muscle cellularity, texture and composition, antioxidant activities and flavor characteristics were assessed and compared between non-exercised (N-EXF) and long-term exercised Largemouth bass. Exercised fish (EXF) showed improve in muscle cellularity and texture with high protein, hydroxyproline, collagen and low crude lipid compared to N-EXF. In addition, EXF showed Higher INOS, T-AOC, CAT and lower MDA, indicating high antioxidant activities in EXF compared to N-EXF. Furthermore, EXF showed lower hydrocarbons and alcohols content but higher in carboxylic acid, esters and aromatic compounds content compared N-EXF. EXF also showed lower TMAO, TMA, HX and high IMP content, indicating better freshness. Generally, EXF largemouth bass should be preferred depends on its high nutrition value, better flesh and freshness quality; and pleasant flavor.

The impact of gas mixtures of Argon and Nitrous oxide (N2O) on quality parameters of sardine (Sardina pilchardus) fillets during refrigerated storage

The effect of modified atmosphere packaging (MAP) with unconventional gas mixtures on the main qualitative parameters of sardine fillets during refrigerated storage was investigated. Four different atmospheres conditions were tested: air; 30% CO2 + 70% N2; 30% CO2 + 70% N2O and 30% CO2 + 70% Ar. All samples were packaged in polypropylene trays sealed with a high barrier film and stored at 2–4 °C for 12 days. The quality and the freshness of sardine fillets packed in MAP were evaluated by microbiological, physical and chemical analyses after 0, 1, 2, 5, 6, 8 and 12 days of the storage period. The 2-thiobarbituric acid-reactive substances (TBARS) values for MAP samples were lower compared to air samples, reaching a final value of 1.09 mg malonaldehyde (MA)/kg and 3.39 mg MA/kg, respectively. The samples packed in Ar reached the fixed threshold for total mesophilic and psychrotrophic bacteria after 12 days of storage, resulting the best MAP condition adopted, able to increase the sardine shelf-life of 3 days with respect to the other tested conditions. Air packed samples showed significantly higher (p < 0.05) Hx content (50 mg/kg) compared to the rest of the MAP samples (20 mg/kg). At the end of the storage period, the sample packed in Ar showed a significantly lower value (p < 0.05) (around 40 mg/kg), than the other MAP conditions.

Chemical Parameters for Traceability of Raw Material Freshness of Tropical Surimi

ABSTRACTChanges in chemical parameters of tropical fish used for surimi production—namely, threadfin bream (TB; Nemipterus spp.), lizardfish (LZ; Saurida spp.), and goatfish (GF; Upeneus spp.)—during ice storage and their respective washed mince were investigated. Total volatile basic nitrogen (TVB-N), trimethylamine (TMA), hypoxanthine (Hx), and total biogenic amine (BA) content of mince increased with storage time. Crude protein of fish and their respective washed mince reduced as storage time of fish was prolonged. Principal component analysis (PCA) revealed that washed mince produced from fish stored in ice for 7–12 days showed chemical characteristics that were distinct from those of washed mince prepared from spoiled fish. The TMA, TVB-N, and Hx content of washed mince appeared to be sufficient raw material freshness indicators in these three species.

Effect of Freeze-Chilled Treatment on Flavor of Grass Carp (Ctenopharyngodon idellus) Fillets and Soups During Short-Term Storage

ABSTRACTIn order to evaluate the effect of chilled (T1), frozen (T2), and freeze-chilled (T3) treatment on the flavor of grass carp fillets and soups, adenosine triphosphate (ATP)-related compounds, umami-taste amino acids (UTAA), thiobarbituric acid (TBA), peroxide value (PV), and soup sensory score were analyzed. Results showed that the sum of ATP, ADP, and AMP contents in T2 fillets were significantly higher (p < 0.05) than others, but the sum of hypoxanthine riboside (HxR) and hypoxanthine (Hx) contents for T2 fillets and soups were significantly lower (p < 0.05) than others during storage. The T3 fillets and soups had lower inosine 5-monophosphate (IMP) contents than T1 after Day 2, but higher UTAA contents than T1 during storage. The T3 fillets had the highest TBA and PV values among the three groups during storage. According to the total aerobic counts, K value, and sensory score, all the fillets and soups kept good quality during storage. Therefore, freeze-chilled treatment not only can extend fish shelf life but also retain excellent fish flavor.

Acute-Phase Protein Hemopexin Is a Negative Regulator of Th17 Response and Experimental Autoimmune Encephalomyelitis Development

Hemopexin (Hx) is an acute-phase protein synthesized by hepatocytes in response to the proinflammatory cytokines IL-6, IL-1β, and TNF-α. Hx is the plasma protein with the highest binding affinity to heme and controls heme-iron availability in tissues and also in T lymphocytes, where it modulates their responsiveness to IFN-γ. Recent data have questioned regarding an anti-inflammatory role of Hx, a role that may be both heme-binding dependent and independent. The aim of this study was to investigate the role of Hx in the development of a T cell-mediated inflammatory autoimmune response. During experimental autoimmune encephalomyelitis (EAE), the mouse model of multiple sclerosis, Hx content in serum increased and remained high. When EAE was induced in Hx knockout (Hx(-/-)) mice, they developed a clinically earlier and exacerbated EAE compared with wild-type mice, associated to a higher amount of CD4(+)-infiltrating T cells. The severe EAE developed by Hx(-/-) mice could be ascribed to an enhanced expansion of Th17 cells accounting for both a higher disposition of naive T cells to differentiate toward the Th17 lineage and a higher production of Th17 differentiating cytokines IL-6 and IL-23 by APCs. When purified human Hx was injected in Hx(-/-) mice before EAE induction, Th17 expansion, as well as disease severity, were comparable with those of wild-type mice. Taken together, these data indicate that Hx has a negative regulatory role in Th17-mediated inflammation and prospect its pharmacological use to limit the expansion of this cell subset in inflammatory and autoimmune disease.

Simple method for simultaneous detection of uric acid, xanthine and hypoxanthine in fish samples using a glassy carbon electrode modified with as commercially received multiwalled carbon nanotubes

A simple electrochemical sensor was designed, based on a glassy carbon electrode modified with “as commercially received” multiwalled carbon nanotubes (GCE/MWCNT), for the simultaneous detection of three purine bases: uric acid (UA), xanthine (X) and hypoxanthine (Hx) by differential pulse voltammetry (DPV). Comparison amongst various carbon nanotubesviz.; as commercially received-MWCNT, functionalized-MWCNT, purified-MWCNT and single walled carbon nanotubes for modified electrode preparation, and in turn for the simultaneous electrochemical detection of the purines by DPV, the “as received MWCNT” modified GCE showed the best performance in terms of well-separated peaks and higher peak current values. Scan rate experiments on discreet oxidations of UA, X and Hx suggested that the electron-transfer mechanism for both UA and X follows a mixed diffusion–adsorption controlled pathway, while in the case of Hx, a diffusion controlled route is followed. Calibration responses for the simultaneous detection of UA, X and Hx were linear up to 700, 200 and 150 μM respectively. Corresponding detection limit values were 141 nM, 134 nM and 2.87 μM. Finally analysis of UA, X and Hx content in three different fresh dead fish samples was successfully demonstrated with recoveries of around 100%.

Hypoxanthine-based enzymatic sensor for determination of pork meat freshness

An enzyme sensor employing xanthine oxidase (XO), soluble or immobilised, in combination of an oxygen electrode has been developed and optimised to determinate the hypoxanthine (Hx) content in pork meat at different post-mortem times as measure of meat freshness. The amperometric signal obtained due to the oxygen depletion during the Hx oxidation was related with the consumed oxygen at 190 s in the soluble enzyme sensor or enzymatic rate at 10 s in the immobilised enzyme sensor. In both cases a linear relationship between the signal and the Hx concentration in the range 8.68–26.05 μM ( R 2 = 0.999) and 15.63–127 μM. ( R 2 = 0.995), respectively, was found. Both enzyme sensors exhibited very good working conditions and storage stability. A study of Hx oxidation was carried out in order to compare the Hx content measured by both sensors and those measured by high performance liquid chromatography (HPLC) obtaining a good agreement between both techniques. Therefore, the easy preparation and operation of both enzyme sensors suggests a reliable, rapid and an economical alternative for simple or multiple Hx measurements constituting a useful tool as quality control of meat freshness.

Relevance of season and nucleotide catabolism on changes in fillet quality during chilled storage of raw Atlantic salmon ( Salmo salar L.)

Farmed 5–6 kg Atlantic salmon were pre-rigor filleted, vacuum packed and subsequently analysed after 1, 9 and 13 days of storage at 4 °C. The study was repeated in February, April, August and October. The conversion of hypoxanthine (Hx) showed the highest seasonal variation among the nucleotide metabolites, with an inverse relationship with sea temperature at harvesting ( R 2 = 0.95–0.96). The Hx content was inversely related to fresh odour and flavour ( R 2 = 0.81–0.83), but positively to tenderness ( R 2 = 0.87). Hence, these results suggest that salmon reared in seawater of 11–15 °C (August–October) maintain a superior sensory quality for a longer period post-mortem than salmon reared at 6–8 °C (February–April). The colour intensity increased from days 1 to 9 post-mortem, probably due to rigor contraction. The highest increase in drip loss was observed in October and the lowest in April. It is proposed that seawater temperature significantly influences the storage life of raw salmon, and that Hx is a valuable biomarker for sensory quality.

Nucleotide degradation in sardine (Sardina pilchardus) stored in different storage condition at 4°C

Degradation products of nucleotide in sardine stored up to 15 days in stored in boxes without ice, vacuum package (VP) and modified atmosphere package (MAP) at 4oC were investigated using a rapid HPLC method. Nucleotide degradation was more rapid in sardine stored in air than those stored in MAP and VP. The lowest value from production of ATP derivatives were observed in sardine held in MAP, followed by VP. ATP content was not detected under the three conditions. AMP and ADP levels were less than 0.2 μmol/g on day 0 in all cases. The shelf-life of fish stored in MAP was 12 days according to sensory assessment, at which the content of IMP, Hx and Ino were approximately 0.2, 0.7 and 0.6 μmoles/g, respectively. Although IMP and Ino showed fluctuations under all of storage conditions, Hx content increased linearly with storage time. Thus, it might be used as a freshness indicator for sardine stored under MAP and VP. The maximum levels of Hx compound were 0.79 μmoles/g for MAP and 0.75 μmoles/g for VP at day 15, respectively.

NUCLEOTIDE CATABOLISM IN COLD STORED ADDUCTOR MUSCLE OF SCALLOP (ZYGOCHLAMYS PATAGONICA)

The postmortem catabolism of adenosine triphosphate (ATP) in cold stored scallop adductor muscles was examined. The change In the pH of stored muscles was also investigated. The ATP content increased for a short time after death and afterwards decreased up to 24 h of storage. Thereafter, the nucleotide level remained unchanged up to 120 h of storage. The ADP content slightly decreased up to 48 h and after that remained unchanged. The AMP slowly accumulated to around 15% of the total nucleotide concentration when the ATP decreased. Small amounts of IMP were detected in all samples. Conversely, adenosine (Ado) was not detected. Inosine (HxR) slightly increased after 48 h of storage and hypoxanthine (Hx.) significantly increased after 24 h. The 260/250-absorbance ratio of muscle extracts and the pH of stored muscles fell sharply up to 24 h and then decreased slowly. The Hx contents were positively correlated (P < 0.01) with both the Hx/AMP ratios and the K values.

Multianalyte sensor for the simultaneous determination of hypoxanthine, xanthine and uric acid based on a preanodized nontronite-coated screen-printed electrode

Simultaneous determinations of purine bases of hypoxanthine (Hx), xanthine (X), and uric acid (UA) were demonstrated on preanodized nontronite-coated screen-printed carbon electrodes (NSPEs ∗). Good enhancement in the electrochemical sensitivity was noticed upon preanodization at 2.0 V versus Ag/AgCl. The measured interaction parameter “ r” reveals a strong attractive force of the purine bases to the NSPE ∗. Cyclic voltammetric studies show different charge transfer behavior among the purine bases on the NSPE ∗. The experimental parameters were systematically optimized for each analyte of Hx, X, and UA. The calibration curves were all linear in the range of 4–30, 2–40, and 2–40 μM with detection limits ( S/ N=3) of 0.34, 0.07, and 0.42 μM for Hx, X, and UA, respectively. The analytical performance of the NSPE ∗ was demonstrated for the simultaneous determination of Hx, X, and UA in blood plasma and urine samples. The estimation of the fish freshness by monitoring the Hx content was also established with very good reproducibility.

Temporal variation of RAPD-PCR phenotype composition of the grain aphid Sitobion avenae (Hemiptera: Aphididae) on wheat: the role of hydroxamic acids.

Hydroxamic acids (Hx) contained in wheat are active mutagens which play an important role in the defence of the plant against aphids. Random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) dominant markers were used to assess genetic variability in the aphid Sitobion avenae (Fabricius) in relation to hydroxamic acid levels in their host-plants. Colonies of aphids belonging to a single RAPD-PCR profile were grown on different host-plants differing in their Hx content under greenhouse conditions. The RAPD-PCR phenotypic pattern showed the appearance of two new RAPD-PCR variants after four to five generations of exposure to wheat cv. Chagual (high Hx levels), one after exposure to wheat cv. Huayún (low Hx levels), and none after exposure to oat (lacking Hx). Differential appearance of new RAPD-PCR aphid phenotypes also occurred on field-grown wheat. While the overall phenotypic 'richness' diminished during the season, the number of RAPD-PCR phenotypes decreased on cv. Huayún and increased on cv. Chagual. The preferential appearance in the field and in the greenhouse of new RAPD-PCR phenotypes of S. avenae on cv. Chagual is discussed on the basis of mutagenesis induced by hydroxamic acids and by the products of their transformation within the aphid. Aphid abundance is interpreted in terms of antixenosis and antibiosis by hydroxamic acids. The appearance on cv. Chagual of phenotypes first detected on cv. Huayún was accounted for by intercrop migrations.

Postmortem Changes in the Adductor Muscle of Scallop (Chlamys tehuelchus) in Chilled and Frozen Storage

The effects of freezing and frozen storage on the biochemical properties of scallop adductor muscles stored at 2-4EC were investigated. Glycogen content fell 40% in the first 12 hr of chilled storage and decreased slowly thereafter. ATP content increased for a short time after death and then decreased slowly. Glycogen and ATP degradation was accompanied by a decrease in both pH and 260/250 absorbance ratio of scallop muscle extracts. A significant increase (p < 0.05) in the hypoxanthine (Hx) content was also observed in chilled stored adductor muscles. Adductor muscles showed a significant decrease (p < 0.05) in the 260/250 absorbance ratio of extracts and an increase in the Hx level after freezing. An increase in Hx content was observed during frozen storage of adductor muscles frozen immediately after processing. Expressible juice increased with freezing and frozen storage of the muscles. The results shown in this paper indicate a rapid loss of quality in scallop adductor muscles during storage at 2-4. Freezing and frozen storage enhanced the quality deterioration of the muscles.

Effects of Gamma Radiation on Sensory Qualities, Microbiological and Chemical Properties of Salted and Fermented Squid

The effects of gamma radiation on sensory quality, microbial population, and chemical properties of salted and fermented squid were investigated. Squid (Todarodes pacificus) was sliced, washed, and then salted with 5, 10, and 20% (wt/wt) sodium chloride. Salted squid was irradiated with dosages of 0, 2.5, 5.0, and 10 kGy of gamma radiation and fermented at 15°C for 50 days. Proximate composition, salinity, water activity, sensory evaluation, and total microbiological populations were examined. Chemical analyses providing information on degree of fermentation, such as amino nitrogen (AN), volatile basic nitrogen (VBN), trimethylamine (TMA), and hypoxanthine (Hx) were also conducted. Irradiated squid was not different in proximate composition, salinity, and water activity from nonirradiated squid. Sensory evaluation scores, total bacteria populations, and pH values were variable depending on salt concentration and irradiation dose. During fermentation, AN, VBN, TMA, and Hx contents increased rapidly as the salt concentration and irradiation dose decreased. Specifically, these chemical compounds of salted and fermented squid prepared with 10% salt and 10 kGy of gamma radiation maintained the appropriate level of fermentation. The present results showed that the combination of low salt concentration (10%) and gamma radiation was effective in processing salted and fermented squid and extending its shelf life compared to control (20% of salt) without adding any food additives.

Hydroxamic acids in cereal roots inhibit the growth of take-all

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) was the only hydroxamic acid (Hx) found in wheat ( Triticum aestivum) roots, whereas both DIMBOA and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) were present in the roots of triticale ( Triticosecale) and rye ( Secale cereale). The Hx content of wheat, triticale and rye roots was highest in the apices. Growth of two isolates of the fungus Gaeumannomyces graminis var. tritici ( Ggt), which causes the root disease take-all, was inhibited when extracts prepared from triticale and rye roots were incorporated into nutrient media. Similar extracts from two cultivars of wheat did not inhibit the growth of Ggt. When Hx were incorporated individually into nutrient media, DIBOA inhibited the growth of Ggt at concentrations as low as 0.5 mM, whereas 1 mM DIMBOA was required to inhibit fungal growth. The decomposition products of DIBOA and DIMBOA, 2(3)-benzoxazolinone (BOA) and 6-methoxybenzoxazolinone (MBOA), respectively, were less potent inhibitors of Ggt growth than the corresponding parent Hx. The effects of the Hx at concentrations up to 5 mM were only fungistatic, as growth of the colonies resumed when they were transferred to Hx-free media. The inhibition of Ggt growth by extracts of triticale and rye is attributed to the presence of DIBOA.

Effects of ammonia solution on the gastric mucosa in cirrhotic rats and therapeutic effects of geranylgeranylacetone.

We designed an animal model in order to clarify whether Helicobacter pylori infection causes the gastric mucosal lesion frequently seen in cirrhotic patients. Ammonia (NH3) solution was given to rats with carbon tetrachloride-induced cirrhosis. The gastric mucosal hexosamine (Hx) content and histopathological findings in the cirrhotic rats were analysed and compared with those of the intact liver rats. Moreover, the usefulness of geranylgeranylacetone (GGA) was investigated in both rat groups. Both rat groups were subdivided according to the treatment as follows: a control group, an NH3 (0.02% solution) group, and an NH3 + GGA (400 mg/kg per day) group; and fed for 4 weeks. The gastric mucosal Hx content of the control group of the cirrhotic rats (16.7 +/- 5.2 microg/mg) was significantly lower than that of the control group of the intact liver rats (26.6 +/- 4.5 microg/mg, P < 0.05). In the cirrhotic rats, the Hx content of both the NH3 (31.9 +/- 13.1 microg/mg) and the NH3 + GGA group (31.9 +/- 9.8 microg/mg) was significantly higher than the Hx content of the control group (P < 0.05). Microscopically, in the cirrhotic rats, while scattered mucosal erosions were recognized in three of five rats of the NH3 group, there were no erosions in any rats of the NH3 + GGA group. These data suggest that the gastric mucosal defence mechanism is defective in liver cirrhosis and that NH3 enhances this defensive mechanism by acting as mild irritant; however, in some cirrhotics this results in gastric erosion due to excessive irritation. Geranylgeranylacetone protects the gastric mucosa against NH3 irritation in cirrhotics without enhancing the Hx content. Thus, H. pylori infection may be a possible cause of the gastric mucosal lesion in patients with liver cirrhosis. The mechanism of the therapeutic effect of GGA is not due to an enhancement of the gastric mucosal Hx content.