Water distribution in brine salted cod (Gadus morhua) and salmon (Salmo salar): a low-field 1H NMR study

Low-field (LF) (1)H NMR T 2 relaxation measurements were used to study changes in water distribution in lean (Atlantic cod) and fatty (Atlantic salmon) fish during salting in 15% NaCl and 25% NaCl brines. The NMR data were treated by PCA, continuous distribution analysis, and biexponential fitting and compared with physicochemical data. Two main water pools were observed in unsalted fish, T 21, with relaxation times in the range 20-100 ms, and T 22, with relaxation times in the range 100-300 ms. Pronounced changes in T 2 relaxation data were observed during salting, revealing changes in the water properties. Salting in 15% brine lead to a shift toward longer relaxation times, reflecting increased water mobility, whereas, salting in saturated brines had the opposite effect. Water mobility changes were observed earlier in the salting process for cod compared to salmon. Good linear correlations ( F 相似文献   

Proteome analysis elucidating post-mortem changes in cod (Gadus morhua) muscle proteins

Proteome analysis was successfully applied to study the alterations in fish muscle proteins during ice storage. The processes occurring during post-mortem metabolism are known to lead to characteristic changes in the texture and taste of fish muscle. Endogenous proteases are anticipated to play the major role in these processes, although the exact mechanisms during fish meat tenderization have yet to be depicted. Protein changes in cod (Gadus morhua) muscle were followed during 8 days of storage. Within the partial proteome (pI 3.5-8.0, MW 13-35 kDa) significant changes were found in 11 protein spots. In nine protein spots the intensity increased, and for eight of these the increases were significant (p < 0.05) within the first 2 h post-mortem. In contrast, two protein spots decreasing in intensity showed significant (p < 0.03) changes after 8 days, thereby indicating that in the fish muscle different biochemical processes are involved in the protein changes observed post-mortem.     

Characterization of volatile compounds in chilled cod (Gadus morhua) fillets by gas chromatography and detection of quality indicators by an electronic nose

Volatile compounds in cod fillets packed in Styrofoam boxes were analyzed during chilled storage (0.5 degrees C) by gas chromatography (GC)-mass spectrometry and GC-olfactometry to screen potential quality indicators present in concentrations high enough for detection by an electronic nose. Photobacterium phosphoreum dominated the spoilage bacteria on day 12 when the fillets were rejected by sensory analysis. Ketones, mainly 3-hydroxy-2-butanone, were detected in the highest level (33%) at sensory rejection, followed by amines (TMA) (29%), alcohols (15%), acids (4%), aldehydes (3%), and a low level of esters (<1%). The electronic nose's CO sensor showed an increasing response with storage time coinciding with the production of ethanol and 2-methyl-1-propanol that were produced early in the storage, followed by the production of 3-methyl-1-butanol, 3-methyl-butanal, 2,3-butandiol, and ethyl acetate. Lipid-derived aldehydes, like hexanal and decanal, were detected in similar levels throughout the storage time and contributed to the overall sweet odors of cod fillets in combination with other carbonyls (3-hydroxy-2-butanone, acetaldehyde, 2-butanone, 3-pentanone, and 6-methyl-5-heptene-2-one).     

Effect of low pH on the susceptibility of isolated cod (Gadus morhua) microsomes to lipid oxidation

During the extraction of muscle to produce protein isolates by acid or alkali solubilization, membranes are exposed to abnormally low or high pH. Low but not high pH treatment induces rapid oxidation of membrane phospholipids in the presence of hemoglobin. The goal of this research work was to study the oxidative stability of microsomes under the conditions met during acid solubilization. Isolated microsomes from cod muscle were used as a model system. At pH 5.3 or lower, 99% of isolated cod membranes sedimented at low centrifugation speeds. Isolated membranes that were exposed to pH 3.0 were less susceptible to hemoglobin-mediated lipid oxidation. Cod hemoglobin exposed to pH 3 was rendered less pro-oxidative than the untreated cod hemoglobin. However, when microsomes and hemoglobin were together exposed to low pH, oxidation was promoted. Citric acid and calcium chloride, as well as press juice isolated from cod muscle, were able to inhibit lipid oxidation of microsomal suspensions.     

pH-induced shift in hemoglobin spectra: a spectrophotometeric comparison of atlantic cod ( Gadus morhua ) and mammalian hemoglobin

Due to a pH-sensitive effect in many fish hemoglobins (Hb), analytical errors may occur when mammalian Hb is used as a standard in quantitative spectrophotometric multicomponent analysis of fish blood. The aim of this work was to examine differences in the optical spectra of mammalian (human) and fish (farmed Atlantic cod) Hb subjected to pH 7.4 and 6.5. The absorption spectra of the common derivatives, deoxy- (HHb), oxy- (OHb), carboxy- (COHb), and methemoglobin (metHb), were determined in the spectral range of 450-700 nm. The metHb spectra of fish differed considerably from the corresponding human Hb spectra, whereas only minor differences in OHb, HHb, and COHb were found. Cod Hb was significantly (P < 0.05) influenced by a drop in pH compared to mammalian Hb. This resulted in deoxygenation of the Hb and increased autoxidation. For human Hb, a pH-independent isosbestic point in the spectra of OHb, HHb, and metHb at 523 nm was found. This isosbestic point was not found in the absorption spectra of cod Hb. In conclusion, spectra of cod metHb and human metHb behave differently. This must thus be taken into account in spectrophotometric multicomponent analysis. Ideally, Hb in muscle or blood should be determined by comparison to a standard made from the same species.     

Effect of chitosan and chitin on the separation of membranes from proteins solubilized by pH shifts using cod (Gadus morhua)

Studies with isolated membranes and isolated membranes suspended in muscle proteins solubilized at pH 3 showed that mixing chitosan and membranes at this low pH followed by a pH adjustment to 10.5 could sediment membranes effectively at 4000 g. In the solubilized muscle homogenate, the effectiveness of membrane removal by chitosan at 4000 g for 15 min was molecular weight dependent. About 80% of the phospholipids and 28% of proteins were sedimented from solubilized muscle homogenate by mixing muscle homogenate (10 g of muscle tissue homogenized with 90 mL of distilled water) with 10 mL of MW 310-375 k chitosan (10 mg/mL in 0.1 N HCl) before solubilizing it at pH 10.5, whereas 55% of the phospholipids and 12% of proteins were sedimented by mixing muscle homogenate with the MW 310-375 k chitosan before solubilizing the homogenate at pH 3. Low molecular weight chitosans (at MW 1k or 33k) showed little effect on membrane sedimentation under the same conditions. Chitin was not useful for removing membranes at either pH 3 or 10.5, whether added before or after pH adjustment.     

Effect of antioxidants, citrate, and cryoprotectants on protein denaturation and texture of frozen cod (Gadus morhua)

To investigate the role of antioxidants and cryoprotectants in minimizing protein denaturation in frozen lean fish, cod fillets were treated with either antioxidants (vitamin C (500 mg kg(-1)) or vitamin C (250 mg kg(-1)) + vitamin E (250 mg kg(-1))), antioxidants (vitamins C + E 250 mg kg(-1)each) with citrate (100 mg kg(-1)), cryoprotectants (4% (w/w) sucrose + 4% (w/w) sorbitol), or a mixture of antioxidants (vitamins C + E 250 mg kg(1)), citrate (100 mg kg(-1)), and cryoprotectants (sucrose 40 g kg(-1) + sorbitol 40 g kg(-1)). Untreated and treated fish samples were stored at -10 degrees C; cod fillets stored at -30 degrees C were used as a control. Stored frozen samples were analyzed at intervals for up to 210 days for changes in protein extractability, thermodynamic parameters (transition temperature T(m) and enthalpy DeltaH), structure by FT-Raman spectroscopy, and rheological properties by large and small deformation tests. Results indicated that protein denaturation and texture changes were minimized in the presence of cryoprotectants, as well as in the presence of antioxidants with citrate, antioxidants alone, or the mixture of antioxidants, citrate, and cryoprotectants. In the presence of increased formaldehyde levels in fish treated with vitamin C, toughening was still lower compared to that of the -10 degrees C control due to the antioxidant property of vitamin C. Thus, ice crystal formation and lipid oxidation products are the major factors that cause protein denaturation in lean frozen fish, and antioxidants in addition to cryoprotectants can be used to minimize toughness.     

Hemoglobin-mediated lipid oxidation and compositional characteristics of washed fish mince model systems made from cod (Gadus morhua), herring (Clupea harengus), and salmon (Salmo salar) muscle

The use of washed cod light muscle minces in mechanistic studies of hemoglobin (Hb)-mediated fish lipid oxidation has largely increased in the past 5 years. Although cod light muscle has a low level of intrinsic lipid oxidation catalysts, a prerequisite for a good oxidation model system, we believe it cannot fully mimic the oxidation kinetics taking place in other fish species being more susceptible to lipid oxidation. The aim of this study was to systematically investigate whether washed mince model systems useful in Hb-mediated oxidation studies could be prepared also from herring (Clupea harengus) and salmon (Salmo salar) light muscles. The kinetics of oxidation in the washed models was measured during ice storage (+/-Hb), and the results were related to compositional differences. Minces from cod, herring, and salmon light muscles were washed 3 times with 3 volumes of water and buffer. A 20 microM portion of Hb and 200 ppm streptomycin was then added, followed by adjustment of pH and moisture to 6.3 and 86%, respectively. Samples with or without Hb were then stored on ice, and oxidation was followed as peroxide value (PV), rancid odor, redness (a*) loss and yellowness (b*). Prior to storage, all minces and models were also analyzed for total lipids, fatty acids, alpha-tocopherol, proteins, Hb, Fe, Cu, and Zn. Hb-mediated lipid oxidation appeared within 2 days on ice in all models. Small differences in the oxidation rates ranked the models as herring > cod > salmon. These differences were ascribed to more preformed peroxides and trace elements in the herring model, and more antioxidants in the salmon model. Controls, without Hb, stayed stable in all cases except herring, where a very slight oxidation appeared, especially if the herring raw material had been prefrozen. In conclusion, fattier fish like dark muscle species and salmonoids are useful for making washed mince model systems and would be a better choice than cod if there is an interest in the oxidation kinetics of such species.     

Incorporation and stabilization of omega-3 fatty acids in surimi made from cod, Gadus morhua

Surimi containing omega-3 fatty acids from algal oil was prepared by the addition of oil-in-water emulsions or bulk oil. Emulsion and bulk oil were added separately to surimi to provide approximately 500 mg of omega-3 fatty acids per serving of surimi (85 g). Addition of the emulsion had no effect on surimi gel strength, whereas bulk oil decreased gel strength an average of 31%. All surimi treatments containing algal oil increased in Hunter b values due to the presence of carotenoids in the oil. Among cryoprotectants, sodium tripolyphosphate was the major surimi additive responsible for retarding the formation of lipid hydroperoxides and thiobarbituric acid reactive substances (TBARS). Lipid hydroperoxide and TBARS formation was lower in surimi containing bulk oil compared to surimi with emulsified oil. Both EDTA and lipid soluble antioxidants were able to decrease lipid oxidation in surimi fortified with omega-3 fatty acids. This suggests that surimi containing nutritionally beneficial omega-3 fatty acids could be developed with good oxidative stability and gel strength.     

Production of cod (Gadus morhua) muscle hydrolysates. Influence of combinations of commercial enzyme preparations on hydrolysate peptide size range

The complement of enzyme activities of a selection of commercial protease preparations were determined using fluorogenic substrates. Alcalase was used in combination with other commercial enzyme preparations to produce cod muscle (Gadus morhua) hydrolysates. Each muscle hydrolysate was characterized with respect to the percentage degree of hydrolysis (DH %), peptide molecular weight range, and free amino acid content. The enzyme preparations containing predominantly protease or endopeptidase activities achieved high DH % and produced significant amounts of peptides below a molecular weight of 3000. Alcalase combined with exopeptidase-rich preparations produced hydrolysates rich in low-molecular-weight peptides. Selecting combinations of enzyme preparations with complementary activity profiles could be used to manipulate the peptide molecular weight profile of hydrolysates.     

Effects of fish meal replacement with full-fat soy meal on growth and tissue fatty acid composition in Atlantic cod (Gadus morhua)

Atlantic cod of initial mean weight approximately 220 g were fed a control diet and three diets in which fish meal (FM) was replaced with increasing levels of full-fat soybean meal (FFS) supplied at 12, 24, and 36% of dry diet, for 12 weeks. There were no significant differences in final weights, but the specific growth rate (SGR) was significantly higher in fish fed the control (FFS0) diet compared to fish fed the FFS12 and FFS36 diets, and the feed conversion ratio (FCR) was significantly lower in fish fed the FFS0 diet compared to the other three treatments. The fatty acid (FA) compositions of the cod muscle and liver were highly affected by dietary treatment, and linear relationships between dietary and tissue FA concentrations were shown for some of these. Moreover, selective utilization or accumulation in the tissues of specific FA was suggested by the results.     

Lipid fractions with aggregatory and antiaggregatory activity toward platelets in fresh and fried cod (Gadus morhua): correlation with platelet-activating factor and atherogenesis

Cod (Gadus morhua) is a popular part of the diet in many countries on both sides of the North Atlantic; in most cases it is consumed fried. In this study, total lipids of cod muscle were separated into neutral and polar lipids, which were further fractionated by HPLC. The lipid fractions were tested in vitro, against washed rabbit platelets, for the probable existence of lipid compounds that either exhibit an action similar to that of platelet-activating factor (PAF) or inhibit the action of PAF. The platelet bioassay was used to evaluate total lipids, total polar lipids, and total neutral lipids, before any further separation. Detection of these compounds in fresh and fried cod could be used to evaluate the nutritional value of this important fish. The in vitro biological study of lipids showed that in fresh cod lipid fractions, ranges of PAF-like and anti-PAF-like activities were present, whereas in fried cod lipid fractions, both neutral and polar, anti-PAF activities were mainly observed. Because it has already been reported that PAF is involved in atheromatosis generation, the existence of PAF inhibitors in cod may contribute to the possible protective role of fish, in this case cod, against atherosclerosis.     

Effects of oxidized dietary oil and vitamin E supplementation on lipid profile and oxidation of muscle and liver of juvenile atlantic cod (Gadus morhua)

The effects of oxidized dietary lipid and the role of vitamin E on lipid profile, retained tocopherol levels, and lipid oxidation of juvenile Atlantic cod (Gadus morhua) were evaluated following a 9-week feeding trial. Four isonitrogenous experimental diets containing fresh or oxidized (peroxide value of 94 mequiv/kg) fish oil with or without added vitamin E (alpha-tocopherol or mixed tocopherols) were fed to juvenile cod in duplicate tanks. There was no significant (P > 0.05) influence on major lipid classes of cod liver and muscle by diet with the exception of sterols. Sterols content was increased in liver but decreased in muscle by oxidized dietary oil in the absence of vitamin E. Dietary vitamin E supplementation decreased the sterols level in cod liver but with no significant (P > 0.05) effect on their level in the muscle. Fatty acid composition varied between lipid fractions in muscle tissue and was affected by the diet. Oxidized oil significantly (P < 0.05) decreased the deposition of alpha-tocopherol in liver but not in muscle. gamma- and delta-Tocopherols from dietary tocopherol mixtures were retained at very low levels in liver, but higher retention was observed in muscle tissue. The oxidative state of both liver and muscle, as measured by the 2-thiobarbituric acid reactive substances (TBARS) and headspace propanal, negatively correlated with tissue vitamin E levels. It is suggested that oxidized oil affected juvenile Atlantic cod by causing vitamin E deficiency in certain tissues and that these effects could be alleviated by supplementation of a sufficient amount of dietary vitamin E. The results also indicate that mixed tocopherols were good antioxidants for Atlantic cod, although less effective than alpha-tocopherol alone in many tissues with the exception of muscle, where gamma- and delta-tocopherols were deposited at relatively high levels.     

Bioactive compounds in cod (Gadus morhua) products and suitability of 1H NMR metabolite profiling for classification of the products using multivariate data analyses

This work investigates the suitability of (1)H NMR spectroscopy to identify the fate of some bioactive compounds in seafood submitted to several processing conditions and examines the possibility of using (1)H NMR spectroscopy profiling to classify such products. Perchloric acid extracts of cod white muscle from newly killed and (i) unprocessed, (ii) boiled, and (iii) fried fillets and from (iv) frozen fillets, (v) the frozen fillets after thawing, and (vi) their drip loss and from (vii) rehydrated cod klippfish (n = 5) were analyzed by 500 MHz (1)H NMR spectroscopy. It was possible to identify taurine, betaine, anserine, creatine, and trimethylamine oxide (TMAO) in all extracts examined, and frozen fish was recognizable by the presence of dimethylamine (DMA). None of the heating procedures seemed to induce the loss of bioactive compounds from the fillet, but freezing and thawing did: the compounds were lost in what is known as drip loss. About 80% of the samples were correctly classified using a probabilistic neural network procedure having as inputs the scores of the first 20 principal components of the principal component analysis of a selected region of the NMR spectra.     

Ultrastructure of the myofibrillar component in cod (Gadus morhua L.) and hake (Merluccius merluccius L.) stored at -20 degrees C as a function of time.

Transmission electron microscopy and image analysis techniques were used to study the ultrastructure of the myofibrillar component in cod and hake muscle stored at -20 degrees C for varying periods of time. Cod muscle showed a deformation of the hexagonal array of thick filaments with the storage time, reflected in an increase in the eccentricity value, a parameter defined to measure changes in the ratio of maximum to minimum hexagon diameter, and an increase in the cross-linkings between the filaments. Degradation of cod thick filaments leading to detachment was also visible upon prolonged storage. In hake muscle significant changes were not found in the arrangement and morphology of thick filaments during frozen storage, suggesting a high incidence of intrafilament aggregation. The ultrastructural differences in the array of thick filaments between species were accompanied by a difference in the textural measurements.     

茯苓采后不同预处理方式对其品质及干燥特性的影响

为进一步优化茯苓加工工艺,降低茯苓品质劣变风险,该文以传统"发汗"、水蒸气蒸制、鲜茯苓直接切制（无预处理）处理的茯苓为研究对象,对不同预处理方式下的茯苓品质、干燥动力学展开了系统研究。结果表明：1）预处理方式是影响茯苓品质的重要因素。①传统"发汗"处理茯苓的水溶性多糖质量分数是鲜茯苓直接切制的1.5倍、水蒸气蒸制的1.7倍,水蒸气蒸制处理茯苓的水溶性多糖质量分数显著低于鲜茯苓直接切制。②传统"发汗"处理茯苓的三萜质量分数显著低于鲜茯苓直接切制及水蒸气蒸制,水蒸气蒸制与鲜茯苓直接切制间无显著差异;通过适当控制"发汗"时间、"发汗"温度,可保持茯苓三萜含量不发生显著降低。③受传统"发汗"过程中物质迁移积累现象的影响,传统"发汗"处理茯苓的成品显著变白,色泽改善;水蒸气蒸制处理茯苓的成品显著变黄、变红,色泽变差。2）预处理方式是影响茯苓干燥特性的重要因素。与鲜茯苓直接切制相比,茯苓经传统"发汗"、水蒸气蒸制处理后,物料组织状态（硬度、孔隙率等）、化学成分（含量等）发生改变,从而使得毕渥数Bi显著增大（表明干燥过程中物料内部导热热阻的作用增大）,形状参数β在0.3～1的区间内显著减小（表明干燥过程始终为内部水分扩散控制）,有效水分扩散系数与传质系数显著增加,最终表现为干燥速率升高,干燥时间缩短。水蒸气蒸制处理在提升干燥速率方面的效果更优。研究结果可为进一步优化茯苓加工工艺,降低品质劣变风险,研究不同预处理方式对茯苓品质形成及干燥动力学变化的作用机理,研究中药材发汗的机理与作用机制,促进中药材产地初加工的规范化提供试验参考与依据。     

Flavor characterization of ripened cod roe by gas chromatography, sensory analysis, and electronic nose

Characterization of the flavors of ripened roe products is of importance to establish a basis for a standardized product. Flavor profiles of commercially processed ripened roe from Iceland and Norway were studied by sensory analysis, gas chromatography-olfactometry (GC-O), gas chromatography-mass spectrometry (GC-MS), and an electronic nose to characterize the headspace of ripened roe. Sensory analysis showed that ripened roe odor and flavor in combination with caviar flavor and whey/caramel-like odor give the overall positive effect of the complex characteristic roe flavor. Analysis of volatiles by GC-MS and electronic nose confirmed the presence of aroma compounds contributing to the typical ripening and spoilage flavors detected by the sensory analysis. Methional, 1-octen-3-ol, and 2,6-nonadienal were the most important compounds contributing to ripened roe odor. Spoilage flavors were partly contributed by 3-methyl-1-butanol and 3-methylbutanal, which can be measured by the electronic nose and are suggested as quality indicators for objectively assessing the ripening of roe. Principal component analysis of the overall data showed that GC-O correlated well with sensory evaluation and the electronic nose measurements.     

不同预处理对铁皮石斛热风干燥特性及品质的影响

为了优化铁皮石斛干燥工艺,降低其品质劣变风险,对热风干燥前的铁皮石斛鲜条进行直接剪切、烫漂和冻融预处理。研究不同预处理条件的铁皮石斛干燥特性和品质变化;利用低场核磁共振技术分析预处理对铁皮石斛干燥过程中水分迁移的影响。结果表明,预处理是影响铁皮石斛热风干燥过程的重要因素。与直接剪切相比,烫漂和冻融预处理提高了水分有效扩散系数,缩短了干燥时间,降低了能耗,尤以冻融预处理最为显著,干燥时间缩短了44.4%,能耗降低了42.76%（P<0.05）。微观结构观察表明,烫漂和冻融预处理使铁皮石斛组织间隙变大,细胞壁受到破坏,减弱了铁皮石斛组织对水分的束缚并增强了水分流动性,引起水分的重新分布,有利于水分迁移。低场核磁共振技术分析显示,干燥过程中去除的主要是自由水,烫漂和冻融预处理均降低了自由水的脱除时间,冻融预处理去除自由水的时间最少,为120 min。与直接剪切相比,冻融预处理提高了铁皮石斛干品中多糖和多酚的含量,分别提高了10.66%和12.32%,而烫漂预处理降低了铁皮石斛多糖和多酚的含量,分别降低了11.73%和14.73%,3种预处理铁皮石斛生物碱含量差异不显著（P>0.05）。总之,冻融预处理方法可以降低铁皮石斛干燥品质劣变风险,研究结果为石斛加工规范化生产提供参考。     

Adsorption of deoxyribonucleic acid (DNA) by willow wood biochars produced at different pyrolysis temperatures

Adsorption of DNA by biochars was investigated in the present study. Biochars were produced from air-dried willow wood chips at 300, 400, 500, and 600 °C under limited oxygen supply. The resulting products, referred to as BC300, BC400, BC500, and BC600, respectively, were characterized for their elemental composition, cation exchange capacity (CEC), specific surface areas (SSA), and microporosity. According to a Langmuir isotherm, maximum DNA adsorption capacity of biochars was ranked as BC500?>?BC600?>?BC400?>?BC300. Increasing solution pH (from 4.0 to 9.0) faintly decreased DNA adsorption onto biochars. The addition of Na⁺, Mg²⁺, and Ca²⁺ slightly increased the adsorption of DNA, and the effect decreased by increasing the pyrolysis temperature of biochars, indicating that electrostatic interaction was not the main driving force for DNA adsorption onto those biochars. Correlation analysis showed that SSA and micropore surface area were the main factors influencing DNA adsorption on biochars.     

苜蓿不同部位干燥和质量特性研究

研究了几种干燥条件（干燥温度：100～200℃,表现速度：0.15～0.45m/s）对苜蓿各部位的干燥特性和品质指标的影响规律。收割后的苜蓿被分成茎秆、压扁茎秆、带叶的压扁茎秆和叶片。苜蓿的品质指标包括茎叶水分差异、粗蛋白质和粗纤维。随着干燥温度和表现速度的增加,苜蓿的干燥速度也增加,其中叶片干燥速度最高,未压扁的茎秆速度最低,并且叶片和茎秆的水分差异也增大。当干燥温度低于160℃时,苜蓿叶片中的蛋白质没有显著变化,同时绿度(同时表现速度不大于0.3 m/s)增加。在本研究中,干燥温度为160℃和表现速度0.3 m/s的干燥条件可以同时保证干燥速度和干燥后的苜蓿品质。