冷藏和微冻条件下鲤鱼品质变化的研究

为了了解淡水养殖鲤鱼在冷藏和微冻贮藏条件下的品质变化情况,本研究将经前处理后的鲜活鲤鱼分别贮藏于4℃和-3℃冰箱中,测定了菌落总数(TVC)、挥发性盐基氮(TVB-N)、硫代巴比妥酸值(TBA)以及K值等指标的变化。结果显示:冷藏第12天鲤鱼的菌落总数为5.67 logcfu/g,微冻第40天为5.72 logcfu/g;冷藏第8天时TVB-N值为10.55 mg/100 g,微冻第30天TVB-N值为18.85 mg/100 g;冷藏条件下TBA值在贮藏的第14天为0.52 mg/kg,微冻第40天为1.06 mg/kg,均未超过2.00 mg/kg;冷藏第8天K值为55.96%,微冻第30天K值为53.99%。综合各指标变化,4℃和-3℃贮藏鲤鱼的贮藏期分别为8 d和30d,-3℃的微冻贮藏较4℃贮藏鲤鱼贮藏期延长了2.75倍。     

罗非鱼在微冻和冰藏条件下鲜度变化的研究

鱼类的低温贮藏方法主要有冰藏和冻藏二种。冰藏法的贮藏温度为0℃左右,其设备简单,温度易控制,但贮期较短,一般在7—10天;冻藏法的贮藏温度为-18℃,贮藏期较长,可达6个月以上,但需要一定的制冷及贮藏设备,耗能较大,而且冻品使用时必须经过解冻,难免产生汁液流失等现象,营养成分及风味都受到一定损失。近年来提倡的微冻保鲜法,是在略低于食品冻结点的温度条件下,使食品中的部分水份结冰,抑制酶和微生物的生长,达到保鲜目的的一种方法。微冻法在水产品保鲜中常用的温度     

冰藏过程中罗非鱼鱼片肌肉蛋白质变化

为研究冰藏过程中罗非鱼( Oreochromis niloticus) 肌肉蛋白质的变化, 提取了冰藏罗非鱼鱼片肌肉中的不同溶解性蛋白质与不同结构蛋白质, 并分析其在贮藏期间含量的变化, 对总可溶性、水溶性、高盐溶性和低盐溶性蛋白质分别进行十二烷基硫酸钠-聚丙烯酰胺凝胶电泳( SDS-PAGE) , 考察蛋白质的降解情况。结果表明, 冰藏期间高盐溶性蛋白质质量分数由84.99 mgg-1 下降至49.47 mgg-1 , 降低了41.79% ; 水溶性蛋白质质量分数由72.27 mgg-1下降至18.7 mgg-1 , 降低了74.58% ; 低盐溶性蛋白质质量分数分数由11.15 mgg-1 下降至 3. 39 mgg-1 , 降低了69.60% 。3 种不同结构蛋白质中, 肌原纤维蛋白质量分数下降最为明显( 由122. 10 mgg-1 下降至48. 65 mgg- 1 , P 0.05) , 肌浆蛋白质量分数也持续降低( 由37.79 mgg-1 下降至26. 57 mgg-1 , P 0.05) , 肌基质蛋白质量分数无明显变化( P 0.05) 。SDS-PAGE 图谱显示, 肌球蛋白重链、肌动蛋白、原肌球蛋白及其他一些蛋白质条带逐渐减弱, 在贮藏末期还出现了一些新的条带。     

凡纳滨对虾在不同冷藏条件下的品质变化研究

通过感官评估、生化分析及蛋白质指纹图谱比较研究了4 ℃和0 ℃冷藏条件下凡纳滨对虾的品质变化,并对评价指标的有效性进行了分析.试验结果表明,0 ℃冷藏能延缓虾的腐败,比4 ℃更有利于凡纳滨对虾的保藏.虾肌肉的挥发性盐基氮(TVB-N)含量随贮藏时间的延长而增加,但在0 ℃条件下无法准确反映虾的品质变化.K值也随贮藏时间的延长而增加,且与感官评价之间存在良好的相关性,能反映凡纳滨对虾在冷藏初期的品质变化.而肌浆蛋白和肌纤蛋白的指纹图谱则能标记冷藏后期凡纳滨对虾肌肉蛋白发生的降解.     

冷藏和微冻条件下长丰鲢鱼片品质变化规律的研究

通过测定长丰鲢（ Changfeng silver carp ）鱼片在冷藏（4℃）和微冻（-3℃）条件下的感官品质、菌落总数（ TAC）、汁液流失率、 pH、电导率（ EC）、挥发性盐基氮（ TVB-N）以及K值等指标的变化,评价两种贮藏条件对长丰鲢鱼片品质的影响。结果表明：长丰鲢鱼片分别在4℃贮藏至第8天和-3℃贮藏至第25天时失去感官食用价值。4℃贮藏第6天菌落总数为6.75 lg cfu/g,-3℃贮藏第20天为5.89 lg cfu/g。 TVB-N值在4℃贮藏至第8天为29.1 mg/100 g,-3℃贮藏至第25天为21.1 mg/100 g。与冷藏相比,微冻贮藏下长丰鲢有较高的汁液流失率。综合各项指标变化,冷藏和微冻贮藏条件下长丰鲢鱼片的货架期分别为6 d和20 d,微冻贮藏较冷藏长丰鲢鱼片贮藏期延长了2.3倍。     

食盐浓度对腌制鳙鱼片冷藏过程中品质变化的影响

为了详细了解不同食盐浓度腌制处理对冷藏在(4±1)℃条件下鳙鱼(Aristichthys nobilis)品质的影响,测定了感官分值、挥发性盐基氮(TVB-N)、菌落总数(TAC)、硫代巴比妥酸值(TBA)、腺苷三磷酸(ATP)关联物等指标。结果显示,感官分值随贮藏时间的延长逐渐降低,且对照组、T1组(1.5%盐腌)和T2组(4.0%盐腌)的感官品质分别在4 d、4 d后和8 d后不可接受。此外,TVB-N、TAC、次黄嘌呤(Hx)和K值在贮藏期间呈增长趋势,T2组在这些指标中显著低于对照组和T1组(P0.05)。TBA值也呈增长趋势,但T2组的TBA值显著高于其他两组(P0.05);这表明T2组脂肪氧化程度更严重。研究表明,1.5%的盐腌处理对冷藏过程中鳙鱼片的品质劣变有一定的延迟作用,但效果并不明显;4.0%的盐腌处理能显著减缓冷藏过程中的品质变化,延长货架期,但会促进脂肪的氧化。     

鳙在冷藏和微冻贮藏下品质变化规律的研究

文章研究了鳙（Aristichthys nobilis）在不同贮藏温度下的品质变化规律。将经过前处理的鳙分别贮藏在4℃和-3℃中,通过测定其感官和理化指标,即总挥发性盐基氮（TVB—N）、硫代巴比妥酸（TBA）、鲜度K值、pH、汁液流失率和蒸煮损失率,评价不同温度对鳙品质的影响。结果显示,鳙分别在4℃贮藏至第10天和-3℃贮藏至第30天时失去感官食用品质。但K值在4℃贮藏至第6天和-3℃贮藏至第20天超过临界值。4℃下鳙的TVB—N显著高于-3℃。在整个贮藏过程中TBA均未超过2．00mg·kg-1。的限量值,说明TBA不适合单独用于评价鳙的品质变化。pH分别在4℃贮藏至第4天和-3℃贮藏至第10天达到最低值,分别为6．81和6．76。与4℃相比,-3℃下鳙的汁液流失率和蒸煮损失率较高,这可能与-3℃微冻条件下鳙肉组织冰晶生成导致持水力下降有关。综合K值和感官指标的变化,4℃和-3℃下鳙的货架期分别为6d和20d,且-3℃贮藏能明显延长鳙的货架期。     

草鱼冷藏过程鱼肉品质与生物胺的变化及热处理对生物胺的影响

文章研究了草鱼（Ctenpharyngodon idellus）冷藏过程鱼肉品质与生物胺的变化及热处理对生物胺的影响.将经过前处理的草鱼鱼片于4℃条件下贮藏,对其感官品质、挥发性盐基氮（TVB-N）、菌落总数、汁液流失率以及生物胺等指标进行测定,另外经过85℃、15 min的热处理后对草鱼鱼片的生物胺进行测定,探求其变化规律及草鱼的生物胺与其品质指标的相关性.结果表明,随着贮藏时间的延长,草鱼的汁液流失率、TVB-N、菌落总数均呈现明显的上升趋势,与感官分值的变化趋势相符,草鱼的感官接受极限为9d.草鱼鱼片在冷藏加工过程中变化最显著的生物胺是腐胺和尸胺,第15天腐胺的质量分数达到（17.12±4.40） mg·kg^-1,尸胺的质量分数达到（237.47 ±3.96） mg·kg^-1,且腐胺和尸胺与其他评价指标有着较好的相关性.经热处理后,腐胺、尸胺、组胺、精胺的质量分数有所下降,但与未经热处理的鱼片没有显著性差异（P＞0.05）,故85℃、15 min的热处理对于草鱼中生物胺的破坏作用不明显,难以有效地去除生物胺.     

去除内脏对冰藏鲤感官、化学和微生物变化的影响

以感官、TVBN、菌落总数、假单胞菌为指标,探讨去除内脏对冰藏鲤(Cyprinus carpio)品质变化及货架期的影响。结果表明,去除内脏和未去除内脏冰藏鲤的高品质期分别为333h和330h,货架期分别为575h和654h;去除内脏鲤冰藏的货架期略短,但无显著性差异(P0.05)。在冰藏过程中二者假单胞菌数量占优势,高品质期终点,去除内脏和未去除内脏鲤的菌落总数(CFU/g)的对数值分别为6.33±0.02和6.07±0.03;假单胞菌数(CFU/g)的对数值分别为6.15±0.19和6.04±0.01;挥发性盐基氮值分别为(10.86±0.50)mg/(100g)和(10.15±0.01)mg/(100g)。货架期终点,二者细菌总数(CFU/g)的对数值分别为7.06±0.18和6.90±0.14;假单胞菌数(CFU/g)分别为6.89±0.13和6.31±0.05;挥发性盐基氮值分别为(19.03±0.90)mg/(100g)、(21.15±0.80)mg/(100g)。二者在高品质期终点和货架期终点的各指标均无显著性差异(P0.05)。与未去除内脏鲤相比,冰藏初期去除内脏鲤的挥发性盐基氮值略低,而其细菌增殖较快且直接进入对数增长期,这可能是由于去除内脏过程对鱼体造成破坏所致,而过了高品质期后,无论是挥发性盐基氮值还是感官评分都比未去除内脏的高,因此去除内脏鲤的货架期略短。     

冰藏过程中罗非鱼鱼片肌肉蛋白质变化

为研究微酸性电解水对新鲜罗非鱼片的杀菌效果,以杀菌对数值为指标,进行单因素和响应面实验,建立各因素与响应值之间的数学模型,确定最佳杀菌条件。结果表明,最佳杀菌条件为有效氯质量浓度35.00 mg·L^–1,浸泡时间22 min,料液质量体积比1∶6,在此处理条件下,杀菌对数值为(0.735±0.001) lg (CFU·g^–1),杀菌率为(81.59±0.04)%。

     

Identification of a novel gill-specific calpain from rainbow trout (Oncorhynchus mykiss)

Calpains are calcium-dependent neutral proteases responsible for many cellular functions. The two forms of calpain ubiquitously expressed in mammalian tissues are known as μ-calpain and m-calpain. We report here the identification of a novel calpain that is similar to but distinct from the μ- and m-calpains in rainbow trout. The cDNA of the novel gene is 2623 bp in length with a single open reading frame. The predicted protein (676 amino acids) contains the conserved calpain characteristic domains that include: domain I (pro peptide), II (cysteine catalytic site), III (electrostatic switch), and IV (calmodulin-like) with five Ca²⁺-binding EF hands. Northern blot and RT-PCR analyses demonstrated that the novel calpain gene is predominantly expressed in rainbow trout gills. Comparison of the novel protein with the ubiquitously expressed calpains and several mammalian tissue-specific calpains revealed that the novel calpain is an orthologue of the mammalian digestive tract specific calpain (calpain 9).     

Effect of different plant oils on growth performance,fatty acid composition and flesh quality of rainbow trout (Oncorhynchus mykiss)

This experiment intended to assess the effect of sesame (SO), sunflower (SFO) and linseed (LO) oils on growth performance, fatty acid composition of fillet and liver or flesh quality traits of rainbow trout. Fish fed different four iso‐nitrogenous and iso‐lipidic experimental feeds. The control feed contained only fish oil as the primary lipid source. The fillet eicosapentaenoic acid and docosahexaenoic acid levels were the highest in fish fed control feed. In contrast, the liver eicosapentaenoic acid level was the highest in fish fed LO feed. Fish fed SFO feed had the highest level of total n?6 fatty acids in fillet and liver. Fish fed SO feed had the highest level of 18:1 n?9 fatty acid in fillet and liver. During the 12 days refrigerated storage period at 1°C, thiobarbituric acid (TBA) and pH values gradually increased in all dietary groups. However, trimethylamin nitrogen (TMA‐N) values increased in all dietary groups between days 0 and 9 during the storage period. Generally, pH value in fillets of control group was slightly higher than the other fish groups during 12 days refrigerated storage. Nevertheless, the chemical indicators of spoilage, TBA, TMA‐N and pH values were in the limit of acceptability for human consumption. Results of growth performance and chemical tests in the present study showed that sesame, linseed and sunflower oils could be used in feeds for rainbow trout. Moreover, we concluded that further researches should be carried out on the partial replacement of fish oil by sesame oil in rainbow trout nutrition.     

Metabolism of exogenous histamine in rainbow trout (Oncorhynchus mykiss)

Information on the metabolism of exogenous histamine in fish is of much concern regarding the effect of dietary histamine on fish. Histamine catabolic enzymes, diamine oxidase and histamine N-methyl transferase were measured in the tissues of rainbow trout. Diamine oxidase was detected in the stomach, pylorus caeca and intestine. Histamine N-methyl transferase was detected only in the liver.A change in the contents of histamine and its metabolites was observed in the tissues of rainbow trout after oral administration of histamine. A large amount of imidazole acetic acid was observed in the serum, kidney, liver and muscle. On the other hand, 1-methyl histamine was detected only in the liver. Histamine and its metabolites, imidazole acetic acid and 1-methyl histamine were metabolized and diminished within 48 hr in all tissues.These results showed that histamine was metabolized by two metabolic routes in rainbow trout. One is the main pathway producing imidazole acetic acid by intestinal diamine oxidase and the other is the complementary pathway producing 1-methyl histamine by liver N-methyl-transferase.     

Insulin stimulates hepatic lipogenesis in rainbow trout,Oncorhynchus mykiss

The effects of the pancreatic hormones, insulin and glucagon, on rates of lipid biosynthesis in liver removed from rainbow trout, Oncorhynchus mykiss, were evaluated in vitro. Livers were removed from animals fasted for 30–36h, cut into ca. 1 mm³ pieces, and incubated in the presence of various concentrations of salmon insulin (sINS), bovine insulin (bINS), or a combination of BINS and bovine/porcine glucagon (GLU). Lipid synthesis was evaluated by total lipid concentration, ³H₂O incorporation into total lipid, and by fatty acid synthetase activity. Both mammalian and sINS tended to increase tissue total lipid concentration in hepatic tissue incubated for 5h. Insulin also stimulated ³H₂O incorporation into total lipid in a dose-dependent manner. Bovine INS (2 × 10^?6 M) stimulated de novo synthesis nearly 6-fold over control rates; sINS (2 × 10^?6 M) stimulated label incorporation more than 7-fold over control rates. Glucagon inhibited INS-stimulated ³H₂O incorporation; whereas, GLU alone had no effect on lipid synthesis in liver pieces incubated 5h. Lipid class analysis indicated that bINS significantly stimulated ³H₂O incorporation into phospholipids, fatty acids, and triacylglycerols. The greatest accumulation of label was in the triacylglycerol fraction, where incorporation was stimulated 17-fold over control levels. Hepatic enzymatic analysis indicated that bINS also significantly stimulated lipogenic enzyme activity 9-fold above control levels. These results indicate that INS is an important regulator of lipid synthesis in the liver of trout.     

Cholesterolaemia and triacylglycerolaemia in farmed rainbow trout,Oncorhynchus mykiss

Physiological (reference) value intervals determined by the lower 2.5% and upper 97.5% quantiles were calculated for blood plasma cholesterol (CHOL) and triacylglycerol (TGL) in farmed rainbow trout, Oncorhynchus mykiss, in raceway culture. The fish were given dry pelleted diets that contained 37–47% crude protein and 7–14% crude fat and were kept at a stocking density of 50 kg m^?3 in tanks provided with running freshwater at an ambient temperature of 3–16°C and dissolved oxygen, 8.4–11.5 mg L^?1. Blood was sampled between September and November at a photoperiod of 9:00–13:00 hours: 11:00–15:00 hours (light:dark). Cholesterol levels were significantly (P = 0.0001) greater in males (4.7–12.1 mmol L^?1, n = 34, mean weight 406 ± 138 g) than immature females (3.2–9.7 mmol L^?1, n = 386, mean weight 416 ± 147 g). Physiological range for TGL in immature females and males was 2.4–14.4 mmol L^?1 (n = 249, mean weight 418 ± 149 g). The distribution and density of the quantiles in the tested reference group were made possible by the use of histograms, which showed normal distributions for CHOL in males and in females, but not for TGL, in which a sinistral asymmetry was found. Correlation and regression analyses indicated significant (P = 0.0000) dependence between the CHOL and total protein (r² = 76.2%), CHOL and Fulton's condition factor (r² = 43.3%) and CHOL and absolute weight of liver (r² = 45.5%). Fluctuation in cholesterolaemia and triacylglycerolaemia, depending on nutrition and the aquaculture method is discussed below.     

Nutritional regulation of somatostatin expression in rainbow trout, Oncorhynchus mykiss

Previously we characterized three DNAs from the endocrine pancreas (Brockmann body) of rainbow trout (Oncorhynchus mykiss) that encode for distinct preprosomatostatin (PPSS) molecules: one containing somatostatin-14 and its C-terminus (PPSS I) and two containing [Tyr⁷, Gly¹⁰]-somatostatin-14 at their C-termini (PPSS II′ and PPSS II″). In the present study, the regulation of PPSS expression was studied in rainbow trout placed on varying nutritional regimes (fed continuously, fasted, fasted then refed). Fish that were fasted for one week displayed reduced growth compared to their fed counterparts, but no alteration in pancreatic PPSS expression was noted between the two groups. Fish fasted for 4 and 6 weeks also were growth retarded and displayed increased levels of PPSS I mRNA and PPSS II″ mRNA compared to fed animals; PPSS II′ mRNA levels were not affected by food deprivation. Refeeding fish for two weeks following 4 weeks of food deprivation restored growth and reduced PPSS I and PPSS II″ mRNA expression to levels similar to those displayed by continuously fed fish. Changes in PPSS expression were correlated with increases in plasma SS. These results indicate that nutritional state modulates differential expression of PPSSs. This revised version was published online in July 2006 with corrections to the Cover Date.     

Use of probiotics to control furunculosis in rainbow trout, Oncorhynchus mykiss (Walbaum)

Aerobic heterotrophic bacteria were isolated from the intestinal contents of Atlantic salmon, Salmo salar , rainbow trout, Oncorhynchus mykiss , and turbot, Scophthalmus maximus , on tryptone soya agar and De Man Rogosa and Sharpe agar, of which 11 of 177 (6% of the total) of the isolates were antagonistic to Aeromonas salmonicida . Four of these cultures, which were identified tentatively as A. hydrophila , Vibrio fluvialis , Carnobacterium sp. and an unidentified Gram-positive coccus, were beneficial to fish when fed singly or as an equi-mixture. Feed supplemented with the putative probiotics indicated survival of the organisms in the gastrointestinal tract for 7 days. Feeding with the probiotics for 7 and 14 days led to better survival following challenge with A. salmonicida . There was no indication of serum or mucus antibodies to A. salmonicida , but there was an increased number of erythrocytes, macrophages, lymphocytes and leucocytes, and enhanced lysozyme activity in the fish.