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.     

木材高压萃取木质素的热机械分析

木质素的热流体性似乎对其在工业领域的各种应用都是必需的，如木质素转化为薄膜，纤维及其它塑料。本研究采用热机械分析（TMA）对兴安落叶松（Larix gmelinii Rupr.)木材近临界高压乙醇－水萃取的木质素的热行为进行了考察，结果表明，高压萃取木质素的热性能明显优于硫酸盐木质素的，前者的玻璃转化温度较低，并具有部分熔融特性，因此，高压萃取木质素可不必像硫酸盐木质素那样经化学修饰才有可能转化为可溶材料。     

三甲胺/氧化三甲胺摩尔比值法在美国红鱼鲜度评价中的应用

以美国红鱼(Sciaenops ocellatus)为研究对象,对不同温度贮藏过程中三甲胺(TMA)、氧化三甲胺(TMAO)、挥发性盐基氮(TVB-N)、菌落总数(TVC)进行检测,并进行感官评定。建立以三甲胺/氧化三甲胺摩尔比值为指标的鱼产品鲜度评价方法,并通过与传统的感官评定、挥发性盐基氮、菌落总数对比,检验新方法的可行性。结果表明,该比值与传统方法有着极显著的相关性,三甲胺/氧化三甲胺摩尔比值法比传统方法更能直接有效反映鱼产品的新鲜度,操作也更简便。     

鱼腥味鸡蛋的形成:从营养到遗传

鸡蛋的鱼腥味问题从首次提出到目前为止已接近一个世纪.鱼腥味影响鸡蛋的品质和风味,降低消费者的购买欲望,给蛋鸡养殖带来经济损失.文章概括了鱼腥味鸡蛋的形成机制,阐述了影响鱼腥味鸡蛋形成的因素,总结目前研究存在的问题,展望未来研究方向,以期为相关研究提供参考.     

Measurement of trimethylamine concentration and evaluation of pig meat natural quality by a spectrophotometric method

Pig meat off-flavor is attributed to trimethylamine (TMA) concentration, and it is considered as the precursor of the fishy off-flavor problems. In this study, TMA concentrations in pig meat were determined, and the interactions with breed and gender effects were discussed. In addition, the TMA threshold for meat off-flavor and pig meat natural quality was measured in relation to meat storage and movement, and the influential factors including the pig breed and storage time were discussed. The results indicated positive effects on the precursor of the fishy off-flavor and the TMA threshold. Native breeds were found to have lower TMA concentrations than European breeds (P<0.01), and females and castrated males had significantly lower TMA concentration than males (P<0.01), The threshold concentration of TMA when meat was classed as off-flavored was 25 μg·g^-1, and this occurred after 35–38 h of storage. The natural qualities, such as appearance, flavor, color and overall acceptable scores declined significantly after 4 days in storage (P<0.01). It is concluded that pig meat off-flavor, breed and gender were essential factors affecting flavor for meat breeding programs, and storage time is important for pig meat natural quality.     

鱼腥昧鸡蛋形成机制及其影响因素的研究进展

鱼腥味是一种难闻的令人不悦的刺激性气味,严重影响鸡蛋的品质和风味,给蛋鸡生产者带来了一定的困扰.本文总结了鱼腥味鸡蛋的形成机制及其影响因素,以期为其相关研究提供一定的参考.     

三聚氰胺—尿素—甲醛树脂固化初期胶层粘度变化的热机械分析研究

用热机械分析（ＴＭＡ）方法研究了三聚氰胺－尿素－甲醛树脂固化初期胶层粘度的变化。将少量胶粘剂涂于两个直径为１０ｍｍ的木片表面，使涂胶面相对组合成一个胶层粘度测量模型，胶层厚度０．１５～０．２５ｍｍ。测量时，将模型加热使温度随时间线性升高（１０℃／ｍｉｎ），同时在模型上施以恒定的压力。根据胶层厚度的变化，可以计算出胶层的粘度。试验结果表明，在常温下陈化，由于水分和小分子树脂渗入木材内部以及水分的蒸发，胶层粘度急剧升高，３０ｍｉｎ后达到１０４Ｐａ·ｓ以上。在加热过程中，胶层粘度随温度和时间的变化可用二重指数方程描述。随着温度的升高，胶层粘度先降低达到一个最小值，此后由于固化反应速度加快，粘度急剧增加并迅速达到∞。固化剂用量对胶层的流变性能有重要影响，加入０．５、１．５和３％的氯化铵，胶层粘度由下降变为上升的转折点温度分别为８７、７６和７１℃。加入２０％的填料（淀粉），可以增加胶层的初始粘度，提高粘度转折点温度     

不同储藏温度对鲢鱼鲜度品质的影响

对储藏于10℃、-1℃和-20℃条件下的鲢鱼进行感官评定,并测定挥发性盐基氮(T-VBN)、三甲胺(TMA)和K值等,从而分析不同储藏条件下鲢鱼鲜度品质的变化情况.感官评定结果表明:10℃条件下鲢鱼块的储藏期不超过3 d;-1℃条件下不超过9 d.十二烷基硫酸钠-聚丙烯酰胺凝胶电泳(SDS-PAGE)图谱显示:在10℃条件下储藏至第3天,肌球蛋白重链明显发生降解;在-1℃和-20℃条件下储存至第9天,出现肌球蛋白重链的降解务带;但随着冻藏时间的延长,肌球蛋白重链进一步降解的趋势并不明显.在3种储存条件下,T-VBN、TMA和K值均随着储藏时间的延长而不断上升,且储藏温度越高,上升趋势越快,与感官检测结果一致;因此,蛋白质降解、ATP降解及三甲胺的形成是评价鲜度损失的理想指标,而且充分地解释了鱼体鲜度降低的规律.此外,低温冻藏有效地减缓了淡水鲢鱼储藏过程中鲜度的降低速率.     

脲醛树脂固化过程的热机械性能分析

为了进一步了解脲醛树脂的固化过程,用热机械性能分析（TMA）,同时辅以差式扫描量热法（DSC）分析和胶合性能测试,分析了TMA图谱信息构成,评估了固化剂种类和固化剂用量对脲醛树脂固化的影响。结果表明:①TMA图谱可以提供脲醛树脂固化反应起始温度、固化反应速率、固化后树脂机械性能以及固化后树脂热稳定性能等信息,这些信息与DSC和胶合性能测试的结果互相印证。②不同固化剂种类对脲醛树脂固化起始温度和固化速率影响各不相同。在该研究范围内,增加固化剂用量对脲醛树脂固化起始温度、固化速率等没有显著影响,但过量使用固化剂将导致树脂热解,从而降低树脂机械性能。③较高甲醛/尿素摩尔比的脲醛树脂对固化剂用量改变的反应更为敏感。      

组织芯片及其应用的研究进展

组织芯片(tissue microarray,TMA)是用于同步分析基因在多个组织样本中表达的高通量技术。作者综述了组织芯片的原理特点、发展历史及制作方法,概括了其应用领域,提出了目前存在的一些问题及其发展前景。