龙头鱼中内源性甲醛产生的酶促机理初探

对比了龙头鱼不同内脏对肌肉甲醛含量的影响,其中肾脏活性最强;从龙头鱼肾脏中获得了提取物,在体外模拟体系中,该提取物能够将氧化三甲胺分解为甲醛和二甲胺,通过响应面分析,发现该提取物反应最适条件为50℃,pH=7,能够被三氯乙酸灭活而丧失分解氧化三甲胺的能力,该提取物在不同的温度和pH条件下呈现酶的特性,且分解产物甲醛和二甲胺的含量比例关系稳定,保持在1.6～1.8之间。在一定程度上解释了龙头鱼中甲醛的产生原因,表明龙头鱼中的甲醛可以自身产生。     

高效液相色谱法测定水产品中β-阿朴-8′-胡萝卜素醛的含量

建立了水产品中β-阿朴-8′-胡萝卜素醛的高效液相色谱检测方法.样品采用抗氧化剂焦性没食子酸保护,酸化乙腈提取,二氯甲烷萃取,旋转蒸干后乙腈定容,高效液相色谱-紫外检测器检测,外标法定量.流动相乙腈+0.1％甲酸溶液=97+3,检测波长457 nm,色谱柱ZORBAX Eclipse XDB-C 18柱(4.6mm×150 mm,粒度5 μm).实验结果表明β-阿朴-8′-胡萝卜素醛在0.02～10.0 μg/mL范围内线性良好(r=0.999 95);检出限0.01 mg/kg,平均回收率62％～107％之间,平行样品的标准偏差≤6.1％.     

不同诱食剂对暗纹东方鲀鱼种诱食效果的比较

以体长20～25 cm暗纹东方鲀为试验对象,通过不同配比诱食剂在基础饲料中1.0％的添加量进行诱食效果比较.结果表明:在饲料中添加氧化三甲胺(TMAO),甜菜碱+丙氨酸+甘氨酸对暗纹东方鲀鱼种摄食率分别为(89.2±6.9)％和(87.2±2.4)％,均具有极显著的诱食作用(P＜0.01).     

离子对反相高效液相色谱法同时检测水产品中6种ATP关联化合物

建立了水产品中6种ATP关联化合物的离子对反相高效液相色谱(IP-RPLC)检测方法,确定了缓冲液的最佳pH、流速和浓度,并对方法的准确度、精确度和检测限进行了测定.采用10％的高氯酸分离提取样品,用KOH溶液中和后进行HPLC分析.采用Waters 2695色谱系统,Thermo ODS-2 Hypersil(250 mm ×4.6 mm,5μm)色谱柱,柱温为25℃;以10％甲醇,90％ 0.05 mol/L磷酸盐溶液为流动相,磷酸盐溶液含9 mmol/L四丁基氢氧化氨(TBA),并用1 mol/L的磷酸调pH至6.5,采用等度洗脱,流速为0.9 mL/min;检测波长为254 nm.结果表明:6种ATP关联化合物在13 min内完全分离;在2～400 μg/mL范围内线性关系良好,相关系数在0.9994～1.0000之间;方法最低检测限(信噪比S/N =3)在0.1～0.4 μg/mL之间;加标平均回收率为82.2％ ～110.0％,相对标准偏差为4.2％ ～9.5％.本方法可用于水产品中ATP、ADP、AMP、IMP、Hx和HxR等6种ATP关联化合物的同时测定和分析.     

基于高温非酶途径的秘鲁鱿鱼内源性甲醛的控制

以甲醛(FA)为指标筛选确定了秘鲁鱿鱼抑制剂种类,分析了抑制剂作用特性,采用单因素和正交试验设计优化了FA抑制剂组合和作用浓度。结果表明,柠檬酸(CA)、CaCl2、MgCl2、茶多酚(TP)、桑叶黄酮(MF)能有效抑制秘鲁鱿鱼肌肉和上清液高温FA形成,Na2SO3、Fe2++Asc、Fe2++Cys促进鱿鱼FA的生成。低浓度CA、CaCl2和TP能减少鱿鱼上清90%以上的FA,最佳抑制浓度分别为10mmol/L、10mmol/L和0.1%。抑制剂CA、CaCl2、MgCl2能显著减少鱿鱼高温氧化三甲胺(TMAO)分解生成FA、二甲胺(DMA)和三甲胺(TMA),而TP和MF能有效结合鱿鱼高温生成的FA。通过正交试验确定了最佳FA抑制剂组,即为0.04%TP、10mmol/CaCl2。该复合抑制剂能显著降低鱿鱼片中的FA和DMA含量,对蛋白含量无显著影响。结果表明,复合抑制剂对鱿鱼等水产品加工中FA控制具有一定的应用前景。     

水产品中挥发性盐基氮测定方法的改良

使用不同浓度的高氯酸溶液对罗非鱼(Tilapia niloticus)、蓝圆(Decapterus maruadsi)、南美白对虾(Litopenaeusvannamei)和近江牡蛎(Crassostrea rivularis)4种水产品的肌肉样品进行前处理,并采用蒸馏法测定样品提取液中挥发性盐基氮(TVBN)的含量,研究了高氯酸溶液浓度、浸提时间和蒸馏前样品的放置时间对测定的结果影响。结果表明,以0.6 mol.L-1高氯酸溶液均质样品2 min后测定4种水产品中TVBN,样品加标回收率在98.35%~100.80%,相对标准偏差在1.53%以下。这种方法所得结果与GB/T 5009.44蒸馏法相比,不存在显著性差异,且操作简便、快速。[中国水产科学,2006,13(1):146-150]     

高效液相色谱—串联质谱法同时测定水产品中19种磺胺类药物残留量

针对水产品中磺胺类药物的多残留问题,建立了用高效液相色谱—串联质谱( HPLC - MS/MS)法同时测定水产品中19种磺胺类药物残留的方法.样品经匀浆后以乙酸乙酯为提取剂,提取液经正己烷脱脂,净化、浓缩后,用高效液相色谱—串联质谱法测定,氘代内标法定量.该方法可通过梯发洗脱,将具有相同定性离子的磺胺良好分离,方便快速,适用于批量样品的检测,检出限为1.0～10 μg/kg,回收率为80％ ～105％,相对标准偏差(RSD)≤10％(n=5).     

超高效液相色谱法（UPLC）快速测定水产品中17种磺胺类抗生素残留

采用超高效液相色谱(UPLC)—二极管阵列检测器(PDA),建立了水产品中17种磺胺类(SAs)抗生素残留的快速同时检测技术。样品经乙酸乙酯提取,HLB固相萃取柱净化,ACQUITY UPLCTM BEHC18色谱柱(2.1mm×100mm,1.7μm)分离,以甲醇-0.1%乙酸为流动相,二极管阵列检测器(PDA)检测。17种磺胺在8min内实现同时分离测定,磺胺类抗生素在0.01～5μg/ml(磺胺醋酰、磺胺嘧啶和磺胺二甲异嘧啶为0.01～2μg/ml)范围内线性关系良好(r≥0.9998)。方法的检出限(S/N=3)为2.0～5.0μg/kg,17种磺胺在添加水平分别为10、40μg/kg时,平均回收率为70.4%～91.4%和73.3%～92.5%,相对标准偏差(RSD)小于10%。结果表明,该方法快速、灵敏、高效,适用于水产品中多种磺胺类抗生素的同时测定。     

二硝基苯肼衍生-高效液相色谱法测定水产品中甲醛含量的研究

通过水蒸汽蒸馏法分离提取水产品中的甲醛,采用二硝基苯肼衍生一高效液相法测定甲醛含量,确定了有关测定的方法参数。该方法样品蒸馏液检出限为7．20μg／L,样品中的检出限为0．20mg／kg,回收率为90．00％～104．48％。方法灵敏度高,专一性强,重复性好,可为水产品甲醛含量监测提供灵敏、准确的分析方法。     

柱前衍生化-气相色谱法测定水产品中的游离甲醛

应用柱前衍生化-气相色谱(GC)法检测水产品中游离甲醛含量。野生鲤、鳙、鲢、草鱼、鲫和乌苏里白鲑等样品经超声萃取、衍生化、正己烷提取,用HP-5毛细管色谱柱分离,电子捕获检测器进行检测,外标法定量。结果表明,使用优化改进后的方法测定的游离甲醛含量在0.1~50μg/L范围内,标准曲线线性拟合度r~2=0.999,线性良好;在2.0、5.0、10.0μg/kg 3个水平下加标回收率为83.80%~103.15%,相对标准偏差小于5.0%。方法检出限为0.38μg/kg,定量限为0.50μg/kg。本研究调查了查干湖和黑龙江中的野生鱼类中游离甲醛的本底含量为1.67~7.66 mg/kg,地区与种间差异不显著(P0.05)。优化后的方法操作简便,分析灵敏度高,稳定性好,可满足水产品中微量游离甲醛的检测需要,对开展水产品中甲醛本底含量及安全限量的研究具有重要的现实意义。     

Comparative Variations of Extractive Nitrogenous Components and Quality in Fresh Muscle and Dried Product of Rabbitfish (Siganus fuscescens) in Taiwan

ABSTRACT

Variations in the level of quality and extractive nitrogenous components were investigated in the fresh muscle and commercial dried products of rabbitfish Siganus fuscescens collected from Penghu, Taiwan. The respective freshness quality for fresh muscle is as follows: trimethylamine oxide (TMAO), 29.50 mg N/100 g; trimethylamine (TMA), 2.30 mg N/100 g; NH₃, 6.61 mg/100 g; total volatile basic nitrogen (TVBN), 13.32 mg/100 g; aerobic plate count, 1.53 log CFU/g; and K-value, 28.80%. The respective freshness quality for dried products is as follows: TMAO, 43.44 mg N/100 g; TMA, 25.56 mg N/100 g wet wt.; NH₃, 52.00 mg/100 g wet wt.; TVBN, 149.98 mg/100 g; aerobic plate count, 4.16 log CFU/g; and K-value, 89.73%. The major fatty acids in the fresh muscle and dried products are C16:0, C18:1 n-9, C18:0, C16:1 C22:6 n-3, and C22:5 n-3. The major nucleotide compound is inosine 5?-monophosphate (IMP) in the fresh muscle (68%) and hypoxanthine (Hx) in the dried products (79%). The level of total free amino acids in the dried products shows significant variation depending on the processing method of the plants.     

Changes in trimethylamine oxide and trimethylamine in muscle of wild and farmed cod (Gadus morhua) during iced storage

Trimethylamine oxide (TMAO) is found at high levels in wild Atlantic cod. Trimethylamine oxide is reduced to trimethylamine (TMA) during iced storage. In this study, the levels of TMAO and TMA in wild and farmed cod and the impact of storage, gender and season on these levels were investigated. Wild cod had higher levels of TMAO than farmed cod. Wild cod also had higher levels of TMA after 15 days of iced storage. Farmed cod were found to have levels of TMA‐N <5 mg/100 g after 15 days of iced storage, which is below the maximum permitted level for fresh fish. Therefore, TMA appears to be an unsuitable measure of freshness in farmed cod. Female farmed cod had higher levels of TMAO than male farmed cod; no such difference between genders was found in wild cod. Female and male farmed cod had similar levels of TMA after post‐mortem iced storage. The hepatosomatic index (HSI) of female farmed cod was higher than that seen in male cod and this may be the underlying reason for the differences in muscle TMAO. Levels of TMAO in male farmed cod were higher during the autumn and were correlated with a larger HSI during the same period.     

Quality Changes and Browning Developments During Storage of Dried-Seasoned Squid (Dosidicus gigas and Ommastrephes bartrami)

ABSTRACT

The physicochemical changes—moisture, water activity, crude protein, total volatile basic nitrogen (TVB-N), trimethylamine oxide (TMAO), dimethylamine (DMA) and formaldehyde, reducing sugar and amino acid; microbiological changes—aerobic plate count (APC) and coliforms; and browning development (browning intensity and color) in dried-seasoned squids (Dosidicus gigas and Ommastrephes bartrami) during storage at 25°C were investigated. After the storage, the moisture and water activity decreased significantly. The content of crude protein decreased, accompanied by progressive accumulation of TVB-N and slow increase of APC. The high level of TMAO in dried-seasoned squid gradually decreased, whereas DMA and formaldehyde increased significantly during the whole period of storage. The browning intensity and b* value significantly increased, which revealed the occurrence of browning in two squid products. The dominant reducing sugar, lactose, and glucose, and the total amino acid including lysine and proline, decreased remarkably, which were well-correlated with the browning development. The quality deterioration in jumbo squid was more rapid than in neon flying squid partially due to the high level of reducing sugar in the former product. To improve quality and resist browning reaction of dried squid product during storage, the addition of extrinsic reducing sugar became a control factor.     

Effect of urea and low temperature on the expression and activity of flavin-containing monooxygenase in the liver and gill of rainbow trout (Oncorhynchus mykiss)

Little is known about the physiological role of flavin containing monooxygenases (FMOs) in teleost fish. Recent studies have indicated induction during saltwater adaptation in several telost species including rainbow trout. A physiological product of FMOs, trimethylamine N-oxide (TMAO) and urea have also been shown to increase in rainbow trout muscle during saltwater adapatation. TMAO counteracts the denaturing effects of urea. In order to evaluate urea as a possible inducer of FMO expression and activity, adult rainbow trout were infused for 48 h with urea/saline solutions at a loading rate of 8 mmol urea/kg/day. To determine whether low temperature had any effect on FMO expression and activity, one group of animals was infused with urea and exposed to low temperature (2–3 °C) for 48 h. Gill FMO-catalyzed thiourea oxygenase activity was significantly induced by low temperature, with twice the activity observed at low temperature (1.116±0.356 nmol/min/mg) compared to urea infusion at 10 °C (0.585±0.282 nmol/min/mg). Low temperature without urea treatment caused a 50% increase in gill FMO activity. In the liver, urea infusion caused an increase in liver FMO activity (from 0.144±0.053 nmol/min/mg to 0.464±0.237 nmol/min/mg), but was unaffected by co-exposure to low temperature (0.523±219 nmol/min/mg). FMO expression and activity correlated with elevated tissue urea levels, but TMAO concentrations were not related. The interactions between urea, temperature and the tissue-specific induction of FMOs indicate FMOs may contribute to other physiological and cellular processes besides osmoregulation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of surimi processing on dimethylamine formation in fish meat during frozen storage

Trimethylamine-N-oxide (TMAO) degrades to dimethylamine (DMA) and formaldehyde, which cause a decline in fish quality. Suppression of DMA formation in frozen surimi was investigated using croaker, lizardfish, and walleye pollock. The leaching process in surimi processing was shown to reduce not only the TMAO, iron, and taurine content, but also to reduce unidentified factors that accelerate DMA formation in lizardfish muscle; in contrast, unidentified factors that suppress DMA formation were reduced in croaker and pollock muscle. Sucrose, used as a cryoprotectant, was shown to decrease DMA formation in vitro, likely due to the reduction in freezing-induced concentration of solutes. The effects of pH on DMA formation were different in minced frozen meat among the three species. DMA formation was not observed in croaker when the pH varied between 6 and 8. On the other hand, DMA was elevated in lizardfish under acidic conditions, and DMA formation in pollock was maximal when the pH of the meat was neutral. Thus, the suppression of TMAO degradation by surimi processing results from the removal of TMAO, iron, and reductants from fish meat; sucrose also reduces DMA formation. Furthermore, unidentified factors in croaker, lizardfish, and pollock meat substantially affect DMA formation.     

TMAOase, trimethylamine-N-oxide demethylase, isa thermostable and active enzyme at 80°C

ABSTRACT:   Purified trimethylamine- N -oxide demethylase (TMAOase)from walleye pollack muscle is a thermostable protein that was notinactivated after heating at 80°C for 30 min.The heated enzyme was electrophoresed in the same manner as fornative enzyme. Circular dichroism (CD) spectra for purified enzymechanged reversibly in the temperature range of 10–80°C.As the enzyme was still active at 80°C, the CD spectralchange did not directly relate to enzyme activity. TMAOase activity inthe myofibrillar fraction decreased sharply above 30°C,but was extracted and recovered from the heated myofibrillar fraction,suggesting that the activity seemed to be interrupted and apparently inactivateddue to the thermal alteration of myofibrillar proteins or some unknownfactors. The complicated profile found in dimethylamine (DMA) formationfrom trimethylamine- N -oxide (TMAO) in walleye pollack muscleduring heating consisted of both enzymic and non-enzymic processes.Most DMA was produced enzymatically below 40°C and interruptedabove 40°C. Therefore, DMA and trimethylamine was formednon-enzymatically at high temperatures regardless of the presenceof native enzyme. A new, simple and easy purification method wasproposed based on the thermostable nature of the enzyme.     

Urea and trimethylamine oxide in diets for seawater farmed rainbow trout: effect on fat belching,skin vesicle,winter ulcer and quality grading

Three experiments were conducted in order to evaluate the effects of urea and trimethylamine oxide (TMAO) supplementation in diets for seawater‐farmed rainbow trout Oncorhynchus mykiss. In all experiments, commercial extruded feed was used as basal control diet, whereas experimental diets were the basal diet supplemented with either 10 g kg^–1 TMAO, 10 g kg^–1 urea or 10 g kg^–1 TMAO and 10 g kg^–1 urea. The experiments were conducted both in research units and in a commercial fish farm. Quality was evaluated in three different commercial slaughterhouses, sorting the rainbow trout into superior, ordinary or processing grade. Significantly more TMAO was observed in muscle of rainbow trout given dietary supplementation of TMAO. However, the levels were low compared with levels in marine fish in general. Trimethylamine (TMA) was not found. No increase in muscle urea content was observed in trout fed urea in the diet. Significantly reduced fat belching, seen as reduced number of fat droplets surfacing in the net pen, was observed in groups given TMAO‐supplemented feeds. At least twice as many rainbow trout with skin vesicles were observed in the control group as in the group fed urea‐supplemented diet. In addition, skin vesicles developed into open sores in the winter only in rainbow trout fed control diet. In a large‐scale trial, quality grading of almost 200 000 market‐sized rainbow trout showed significantly more (88 vs. 83%) trout of superior grade in the group fed dietary urea compared with fish fed control diet. The main reason for downgrading from superior to ordinary and processing grade was skin lesions, supporting the observations made in the experimental units.     

Nitrogen-Containing Taste Components of Oyster Wash Water and Changes in Quantities During Heat Concentration

Oyster wash water contained 115 mg/100g of nitrogen-containing taste components including free amino acids, small peptides, nucleotide compounds and quaternary ammonium bases. Major constituents of these taste compounds were found to be glycine betaine, taurine, alanine, glutamic acid, glycine, homarine and inosine. A steam-jacketed kettle was used to concentrate these taste components. The levels of all these compounds increased with the increase of total solids except trigonelline and trimethylamine oxide (TMAO). These compounds, however, were sensitive to heat and thus exhibited quantitative loss. The levels of trigonelline, TMAO, lysine, arginine, aspartic acid, serine and histidine decreased more than those of other compounds.     

Effects of High Pressure Treatment on Physicochemical Quality of Pre- and Post-Rigor Palm Ruff (Seriolella Violacea) Fillets

Fish and fish products are characterized for having a short shelf life. Nonthermal processing techniques such as high hydrostatic pressure (HHP) have increasingly been employed to extend shelf life of food products. The aim of this study was to evaluate changes on flesh physicochemical spoilage parameters (pH, total volatile bases (TVB-N), trimethylamine (TMA), thiobarbituric acid (TBA), and color) of palm ruff (Seriolella violacea) fillets in pre- and post-rigor conditions, subjected to two different HHP conditions: 450 MPa and 550 MPa, for 3 and 4 min each. Unpressurized and pressurized fillets were kept in chilled storage (4 ± 1°C) for 26 days to assess the effect of HHP on shelf life. pH and TBA values increased after HHP treatment and with storage time for both unpressurized and pressurized samples. This is attributable to pressure-induced lipid oxidation. Lightness (L*) values increased with pressure, where fish fillets had a cooked appearance. TMA and TVB-N values decreased after HHP treatment compared to the unpressurized samples, showing that HHP treatment is an efficient method to maintain the quality of palm ruff fillets. There was no clear difference between pre- and post-rigor in the parameters evaluated.     

大菱鲆0、25℃贮藏的鲜度变化和货架期

以感官、化学和微生物为指标,对大菱鲆在冰藏(0℃)、室温(25℃)贮藏过程中的鲜度变化和货架期进行了研究,并探讨了菌落总数(TVC)、挥发性盐基氮(TVBN)、三甲胺氮(TMA)与感官评价的一致性程度。结果表明,0℃和25℃贮藏大菱鲆,高品质期分别为526 h和26 h,货架期分别为763 h和49 h;TVC在高品质期终点分别为6.88、6.38 lg(cfu/g),在货架期终点分别为7.67、7.90 lg(cfu/g);TVBN在高品质期终点分别为15.97、16.46 mg/100g,在货架期终点分别为33.1、28.58 mg/100 g;TMA在高品质期终点分别为1.29、0.74 mg/100 g,在货架期终点分别为12.89、11.37 mg/100g。各指标间均无显著性差异(P>0.05),表明TVC、TVBN值、TMA值作为大菱鲆贮藏中的品质指标保持较好的一致性。大菱鲆0℃和25℃贮藏的主要腐败菌均为假单胞菌属(Pseudomonas spp.),其次为腐败希瓦氏菌(Shewanella putrefaciens)。