肉桂醛复合保鲜剂对南美白对虾贮藏品质的影响

为延长南美白对虾贮藏期,对8种天然化合物的抑菌和南美白对虾多酚氧化酶( PPO)抑制活性进行了对比试验,发现肉桂醛同时兼具抑菌和抑制多酚氧化酶活性的双重效果.经酶反应动力学分析,证明肉桂醛是多酚氧化酶的非竞争性抑制剂.采用正交试验,对肉桂醛、植酸和海藻酸钠进行复配比较,确定复合保鲜剂的最佳组分为:肉桂醛质量分数0.10％、植酸质量分数0.05％、海藻酸钠质量分数0.50％.复合保鲜剂处理可有效抑制虾体菌落总数的增加和挥发性盐基氮的积累;同时还可抑制贮藏过程中的脂肪氧化,对感观品质具有良好的保持作用,在(4±1)℃条件下贮藏期可达8 ～10d,明显提高了南美白对虾贮藏过程中的品质和货架期.     

Blood vessel melanosis: a physiological detoxification mechanism in Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>)

Melanin deposits in white muscle represent a potentially serious quality problem for farmed cod. Black lines of deposited melanin are associated with blood vessels and consist of layers of melanin-filled cells. Despite numerous anecdotal reports of melanosis in farmed cod no detailed investigations into the underlying mechanisms have been undertaken. In this study we have confirmed that melanosis is present in both farmed and wild cod. However, the incidence of melanosis in wild fish is much lower than that in farmed fish. In addition, we have demonstrated that tyrosinase, a copper-dependent metalloenzyme that is the primary enzyme of melanin synthesis, is present in cod tissues. Copper levels are significantly different in the white muscle of farmed (0.5 ± 0.03 mg/kg wet weight) and wild (0.34 ± 0.01 mg/kg wet weight) cod (P < 0.05) and in the blood vessels of farmed (2.23 ± 0.37 mg/kg wet weight) and wild (0.32 ± 0.02 mg/kg wet weight) cod (P < 0.05). Similarly, differences in the levels of tyrosinase activity were observed in both muscle and blood vessels. Melanised tissues contain higher copper concentrations than tissue containing little or no melanin. Furthermore, we have shown that the addition of copper to protein extracts from fish muscle causes an increase in tyrosinase activity in vitro. Our results suggest that overabundance of copper in commercial feeds leads to increased melanin synthesis via increased tyrosinase activity. We propose that melanin is deposited at sites of high copper exposure and subsequently sequesters copper as a means of reducing the overload stress on other homeostatic mechanisms.     

冷藏温度下凡纳滨对虾组织黑变与内源多酚氧化酶活性相关性研究

[目的]探索凡纳滨对虾在冷藏过程中多酚氧化酶(PPO)活性变化程度与对虾黑变之间的相关性,明确关键控制点。[方法]通过感官鉴定、光电色差和分光光度测定凡纳滨对虾冷藏过程中的黑变规律,据此研究PPO活性变化与凡纳滨对虾黑变之间的相关性。[结果]试验表明,同一时间内凡纳滨对虾不同组织部位的PPO活性有明显差异,头部最高,腹部次之,最后是尾部。相关性分析表明,在冷藏过程中凡纳滨对虾黑变度与PPO活性变化均趋于上升,黑变度的变化规律与PPO的活性变化趋势呈显著正相关,头部、腹部、尾部的相关系数分别达到0.987 3、0.971 6、0.973 2,定量证明PPO活性变化是引起凡纳滨对虾黑变的主要因素。[结论]研究可为凡纳滨对虾冷藏期间的黑变控制提供理论依据。     

南极磷虾与鹰爪糙对虾酚氧化酶生化性质对比分析

黑变是南极磷虾(Euphausia superba)贮运流通过程中的突出问题，为探究南极磷虾与普通海捕虾在黑变进程方面的异同，选取南极磷虾和海捕鹰爪糙对虾(Trachypenaeus curvirostris)作为研究对象，对2种虾在(2±1)℃贮藏过程中的黑变进程进行了感官评价，提取其酚氧化酶(PO)并进行了纯化，对2种虾PO的生化性质进行了对比分析。结果显示，冷藏条件下，24 h时南极磷虾的黑变已非常严重，黑变部位主要集中在头胸部、腹部甲壳以及尾节部分。72 h时鹰爪糙对虾的头胸部和尾节部分开始有轻微的黑变，之后逐渐扩散到躯干。南极磷虾和鹰爪糙对虾PO粗酶液经硫酸铵沉淀、Sephadex G-100凝胶过滤后，酶的纯化倍数分别达到17.22和19.67。2种虾PO的最适温度分别为30℃和40℃，南极磷虾PO在低温下仍具有较高的活力。二者的最适pH均为6.0~7.0之间。焦亚硫酸钠、亚硫酸氢钠、4-己基间苯二酚、L-半胱氨酸和抗坏血酸均可较好地抑制2种虾PO活力，其中，4-己基间苯二酚抑制效果最好。研究结果为南极磷虾冷链物流过程中的品质控制提供了依据，同时，为虾死后如何有效抑制其黑变提供了参考。