Changes of proximate and fatty acid compositions of the dorsal and ventral ordinary muscles of the full-cycle cultured Pacific bluefin tuna Thunnus orientalis with the growth

Using the full-cycle cultured (FC) Pacific bluefin tuna, Thunnus orientalis [body weights: 13.1 ± 4.5 (FC1; April in 2004), 20.2 ± 1.8 (FC2; July in 2004), 28.5 ± 6.3 (FC3; November in 2004), 27.0 ± 3.3 (FC4; February in 2005) and 33.5 ± 4.7 kg (FC5; May in 2005), n = 3, respectively] and wild bluefin tuna [33.3 ± 1.5kg (June in 2005), n = 3], proximate and fatty acid compositions of the cephalal (Ce-) and caudal (Ca-) parts of the dorsal (D) and ventral (V) ordinary muscles (OMs) were investigated. Lipid contents of the Ce-DOM and VOMs of FC1-5 increased with growth. In particular, lipid content of the Ce-DOM (23.0%) and VOMs (55.1%) of FC5 was higher (P < 0.05) than those of wild tuna [D-(2.0%) and VOMs (16.2%)]. However, lipid contents of the Ca-DOM and VOMs of FC1-5 did not change with growth. On the other hand, the fatty acid compositions of the Ce-DOM and VOMs of FC2-5 resembled each other. However, there was no specific tendency of the changes of each fatty acid composition of the Ce-DOM of FC tuna with growth. On the other hand, total monounsaturated fatty acid content (30.1%) of the Ce-DOM of FC5 was higher (P < 0.05) than that (25.5%) of wild tuna. The ratio of n–3: n–6 (9.4%) of the Ce-VOM of FC5 was lower (P < 0.05) than that (14.0%) of wild tuna. However, the fatty acid compositions of the Ce-DOM and VOMs of FC tuna were not reflected by those of feed (whole fish bodies of sesame mackerel).     

绿原酸对蓝鳍金枪鱼肌肉品质及肌红蛋白构象的影响

以蓝鳍金枪鱼为对象,研究低温贮藏过程中不同质量浓度的绿原酸(200 mg/kg样品,400 mg/kg样品)对金枪鱼肉色泽、蛋白及脂肪氧化、新鲜度、水分分布及肌肉微观结构等品质特性的影响。通过拉曼光谱及荧光光谱等技术探究绿原酸对肌红蛋白结构及微环境的影响。结果表明,加入绿原酸能够有效延缓金枪鱼肉的褐变情况,抑制蛋白氧化及脂肪氧化的发生,维持样品的新鲜度。与处理组相比,对照组样品的肌纤维束收缩、间隙变大,产生不同程度的断裂。综合来看,低浓度的绿原酸的效果优于高浓度处理组。多光谱结果显示绿原酸对肌红蛋白有荧光猝灭效果。而对照组、绿原酸处理组样品的α-螺旋比例的下降率分别为39.2%,28.0%,说明绿原酸能够较好地稳定肌红蛋白的二级结构。     

没食子酸对蓝鳍金枪鱼肌肉品质及肌红蛋白构象的影响

为了研究低温贮藏过程中没食子酸对蓝鳍金枪鱼肌肉品质及肌红蛋白构象的影响,使用不同质量浓度的没食子酸(200、400 mg/kg)处理鱼肉,分析鱼肉品质特性变化;通过多光谱技术进一步探究没食子酸对金枪鱼肌红蛋白结构及微环境的影响,并通过分子对接模拟确定肌红蛋白和没食子酸的结合位点.结果表明,在4 ℃贮藏期间,金枪鱼肉的品质出现不同程度的下降,肉色发生褐变、红度值降低.与没食子酸处理组相比,对照组的脂肪氧化程度及高铁肌红蛋白相对含量、总挥发性盐基氮含量和菌落总数呈明显上升趋势;结合水含量降低,水分发生迁移;肌肉的肌纤维束也产生不同程度的断裂.低质量浓度(200 mg/kg)的没食子酸对延缓金枪鱼肉品质劣变有较好的效果.多光谱结果显示,低质量浓度的没食子酸能够较好地稳定肌红蛋白的二级结构,而且对肌红蛋白具有荧光猝灭的作用.分子对接结果表明,肌红蛋白与没食子酸之间通过Leu 42、Pro 44和His 42形成了氢键.研究旨在为改善解冻蓝鳍金枪鱼品质提供理论依据.     

Risk-benefit analysis of fish consumption: Fatty acid and mercury composition of farmed southern bluefin tuna, Thunnus maccoyii

The docosahexanoic acid (DHA) and eicosapentaenoic acid (EPA) contents and total mercury concentration were measured in whole tissue composites of all edible tissues of wild caught and farmed southern bluefin tuna (Thunnus maccoyii, SBT) and each of the marketed tissue cuts (akami, chu-toro and o-toro) of these fish. Rapid lipid accumulation during culture resulted in a net reduction in mercury concentration of SBT composite tissues and an increase in the concentration of the dietary essential fatty acids. Moreover, the increased affinity of lipid for certain tissue cuts (o-toro) over that of others (e.g. akami), resulted in cross carcass variation in the mercury concentration of fish muscular tissue. Results highlight the potential for farming to be used as a tool to improve the flesh quality of fish species which could otherwise provide limited dietary essential fatty acids to consumers and potentially contain elevated contaminant levels.     

多重实时聚合酶链式反应熔解曲线法同步鉴别蓝鳍金枪鱼、裸盖鱼、异鳞蛇鲭

为实现鱼类及其制品掺假的快速鉴别,以蓝鳍金枪鱼（Thunnus thynnus）线粒体DNA的D-loop区、裸盖鱼（Anoplopoma fimbria）线粒体DNA的16S rRNA基因及异鳞蛇鲭（Lepidocybium flavobrunneum）线粒体DNA的ND4L基因为靶位点,设计扩增产物熔解温度（Tm）具有显著性差异的特异性引物,建立一种快速鉴别鱼类及其制品中蓝鳍金枪鱼、裸盖鱼、异鳞蛇鲭源性成分的3 重实时聚合酶链式反应熔解曲线分析法,通过引物特异性、灵敏度及市售样品的检测,对该方法进行检验和评价。结果表明：构建优化的方法具有良好的特异性及灵敏度,单物种DNA检出限为0.001 ng,多物种混合DNA检出限均为0.1 ng,蓝鳍金枪鱼、裸盖鱼、异鳞蛇鲭源性成分的相对检出限分别为0.5%、1%、0.5%,通过对市售样品的检测表明,该方法可用于实际样品掺假的快速鉴别。     

海水和淡水养殖锯缘青蟹的营养成分分析

利用常规的营养测试方法对海水与淡水养殖锯缘青蟹的肌肉营养成分进行初步研究。结果显示：海水养殖锯缘青蟹水分、粗灰分、粗蛋白和粗脂肪含量分别为70.26%、4.59%、15.57% 和1.09%;淡水养殖锯缘青蟹则分别为78.36%、4.35%、17.42% 和0.75%,表明不同养殖环境中的锯缘青蟹的肌肉水分含量差异较大。共检测出17 种氨基酸,海水与淡水养殖锯缘青蟹肌肉中的必需氨基酸占总氨基酸的比例分别为34.39% 和31.20%,构成比例均符合联合国粮农组织/ 世界卫生组织的评价标准。海水养殖锯缘青蟹肌肉必需氨基酸指数(EAAI)为85.20,而淡水养殖锯缘青蟹则为68.35。海水与淡水养殖锯缘青蟹肌肉的第一限制性氨基酸均为缬氨酸。海水和淡水养殖锯缘青蟹肌肉脂肪酸中,前者的饱和脂肪酸含量要显著高于后者(P ＜ 0.05),EPA+DHA 含量分别为11.18%和9.27%,差异不显著(P ＞ 0.05)。综合数据表明,海水养殖锯缘青蟹肌肉的营养价值稍优于淡水养殖锯缘青蟹,而风味稍差于淡水养殖锯缘青蟹。     

不同解冻方式对金枪鱼色泽的影响研究

金枪鱼肉质柔嫩鲜美,营养丰富,多以生鱼片方式食用,其肉质的品质尤其是色泽与解冻方式有着密切关系。通过对几种不同解冻方式的研究比较,测定色差值、高铁肌红蛋白含量、细菌总数3项理化指标,结合鱼肉色泽的感官评价,获得较适合的解冻方法。结果显示,温度梯度解冻-55℃→-25℃下解冻1h后进行加工色泽最好,但不适宜于生产。相比之下,带包装的10℃下的水浴解冻更适于工厂生产需要,且各项指标变化情况也满足金枪鱼生鱼片的加工要求。     

乐清湾北部及嵊泗区域养殖贝类肌肉中镉含量调查及健康风险评估

目的 进行乐清湾北部及嵊泗区域养殖贝类肌肉中镉含量调查并探讨通过摄食途径可能导致的健康风险。方法 测定2016～2018年间采自乐清湾北部缢蛏、青蛤及嵊泗区域紫贻贝等三种养殖贝类肌肉中镉含量水平,与国家限量标准进行比对,并运用单因子污染指数(Pi)评估样品中镉污染程度,并以目标危害系数(THQ)和目标致癌风险(TR)为考量指标,评估通过摄食途径可能导致的健康风险。结果 三种肌肉样品中镉检出率为100%,但超标率为0。含量平均值总体比较：紫贻贝﹥缢蛏﹥青蛤。结论 本研究中所有样品Cd 单项污染指数的Pi 值均远低于1.0 ,绝大部分为正常背景水平,少量呈轻度污染水平。健康风险评估结果显示,所有样品THQ 值均小于安全基准值1.0,数据表明暴露人群没有明显的非致癌健康风险。TR的评价结果均在美国环保署推荐的可接受风险值(10_^-6～10_^-4)范围内,但也有部分样品超过了国际辐射防护委员会(ICRP)推荐的最大可接受风险值(5.0×10_^-5),需引起关注。     

野生与池养刀鲚肌肉品质特性及抗氧化性的比较分析

比较研究了野生和池养刀鲚（Coilia nasus）肌肉营养成分组成、质构特性和抗氧化特性。结果显示,野生刀鲚肌肉中水分、羟脯氨酸、胶原蛋白含量以及胶原蛋白/总蛋白比值均显著低于池养型,而脂肪含量则显著提高;两者的蛋白质含量、pH均无显著性差异;池养刀鲚肌肉弹性、硬度、咀嚼度、胶着性相较于野生型呈上升趋势,但无统计学差异。野生刀鲚肌肉中SOD、CAT、T-AOC、MDA、GSH-PX、iNOS、GSH/GSSG均显著高于池养型。表明野生和池养刀鲚营养品质存在差异,建议在人工养殖刀鲚中应该注意饵料的种类和丰度,其养殖模式有待进一步改善。     

Physicochemical Changes in Pacific Whiting Muscle Proteins during Iced Storage

No changes in actomyosin Ca²⁺-, Mg²⁺-, or Mg²⁺-Ca²⁺-ATPase activities were observed during iced storage of Pacific whiting fillets, but Mg²⁺-EGTA-ATPase increased with a loss of Ca²⁺-sensitivity. Surface hydrophobicity of actomyosin increased substantially within 2 days, but not total sulfhydryl (SH) content. During longer storage, the SH content decreased gradually, but surface hydrophobicity remained constant. Autolytic degradation products increased in fish muscle with storage time. Myosin heavy chain (MHC) was degraded by 45% within 8 days, but no noticeable difference was observed in actin. Results indicated that autolysis may be the main cause of physicochemical changes in Pacific whiting muscle proteins during iced storage.     

Angiotensin I‐converting enzyme inhibitory and Ca‐binding activities of peptides prepared from tuna cooking juice and spleen proteases

Tuna cooking juice is a by‐product from the tuna canning industry. In this study, tuna cooking juice was hydrolysed by proteases extracted from the spleen. Tuna cooking juice showed the highest ACE inhibitory and Ca‐binding activities after hydrolysis for 270 and 180 min, respectively. The hydrolysate was further fractionated by ultrafiltration. The permeate exhibited highest ACE inhibitory and Ca‐binding activities when passed through 1 and 5 kDa cut‐off membranes, respectively. Gel filtration chromatography was used to determine the MW of bioactive peptides that exhibited highest ACE inhibitory and Ca‐binding activities. Those peptides that exhibited highest ACE inhibitory and Ca‐binding activities were the MW range of 238–829 Da and 1355–1880 Da, respectively. These results suggest that the tuna cooking juice and the spleen protease extract are a potential source of bioactive peptides that can be utilised as bioactive ingredients in functional food and nutraceuticals.