Structural stability of myosin rod from silver carp as affected by season

Chymotrypsin digestion and Circular dichroism (CD) spectroscopy were used to study the structural stability of myosin rods prepared from silver carp in summer and winter. Differences in the thermal stability were clearly demonstrated by the chymotryptic digestion patterns and CD data obtained at pH 7.5 in 0.5 M KCl for myosin rods in both seasons, indicating the structural properties differed seasonally. In winter, the myosin rods were more susceptible to be cleaved into short (40 kDa) subfragments when digested at high temperature (30 °C). The major peaks in unfolding profiles showed that transition temperatures for the rods were 35 °C in winter, and 36 and 41 °C in summer. Rod subfragments (S-2 and LMM) were isolated and further analyzed by CD. In both winter and summer, the LMM fragments showed an unfolding transition at around 35.5 °C, but the S-2 fragments showed large seasonal difference; in winter, they showed a major unfolding peak around 35 °C and a minor peak at 40.5 °C, while in summer, they unfolded mostly at 44.5 °C, which was 8 °C higher than that for the LMM fragments. Short (40 kDa) S-2 subfragments isolated from winter rods gave a single unfolding transition at 41 °C. These results suggest that differences in the thermal stability of myosin rods between winter and summer were due to differences in the stability of S-2 region. PRACTICAL APPLICATION: The aim of this study was to detect the differences in the structure thermal stability of myosin rods between summer and winter, which is a very important portion for gel formation. The information will be very useful for producing surimi from freshwater fish species in different seasons.     

Seasonal Expression of 2 Types of Myosin with Different Thermostability in Silver Carp Muscle (Hypophthalmichthys molitrix)

Myofibrils were prepared from dorsal muscle of silver carp monthly from Jul 2003 to Jun 2004. Myofibrils of silver carp in the summer season were much more stable than those in the winter season as measured by (Ca‐ATPase) thermal inactivation rate (k_D) at 0.1 M KCl. The k_D of myofibrils measured at 2 M KCl was referred as 1 for myosin without protection by F‐actin. It was proved that myosin itself in summer season fish (summer‐type) was very stable compared with that in winter season fish (winter‐type). Winter‐type myosin easily denatured upon storage in ice. Analysis of the thermal inactivation profiles of myosin monthly prepared demonstrated that myosins in December, January, February, and March were winter‐type, and ones in June, July, August, and September were summer‐type. It was also demonstrated that both winter‐type and summer‐type myosin at different ratios coexisted in the transit season (April, May, October, November), showing the breaking point in the inactivation profile. It was concluded that silver carp expresses 2 types of myosin with different k_D seasonally and that the exchange of the expression completed in 2 mo.     

Comparison of Gel-forming Properties of Silver Carp (Hypophthalmichthys molitrix) Surimi Prepared in Different Seasons

ABSTRACT: The gel-forming properties of silver carp surimi made in different seasons were compared. Surimi prepared in winter and spring formed gel at 30°C, while autumn and summer surimi required a higher temperature of 40°C for gel formation. All surimi showed marked disintegration when incubated at 60°C. Ca²⁺-ATPase inactivation rate of myofibrils prepared from 4 surimi samples showed that myofibrils in autumn and summer surimi were much more stable than those in winter and spring surimi by about 10°C. These results demonstrated a close relationship between the gel-forming temperature of surimi and the thermal stability of myofibrils in surimi, namely that autumn and summer surimi containing stable myofibrils required higher temperature than winter and spring surimi for the gel formation.     

TGase抑制剂对鲢鱼糜热诱导凝胶形成的影响

本实验通过研究三种转谷胺酰胺酶(Tgase)抑制剂对白鲢鱼糜凝胶的凝胶特性、溶解率、催化肌球蛋白重链(MHC)带强度及微观结构的影响,探讨TGase抑制剂对鲢鱼糜热诱导凝胶形成的影响及其抑制效果。结果表明:鲢鱼糜中存在内源TGase;三种TGase抑制剂均抑制鲢鱼糜凝胶的形成,显著提高鱼糜凝胶的溶解率、增强MHC带强度;随抑制剂浓度的增加,鱼糜凝胶特性显著降低,溶解率显著升高,MHC带强度显著增加;酰基转移反应抑制剂氯化铵的抑制效果最好,其次是巯基阻断剂N-甲基顺丁烯亚胺(NEM),EDTA的抑制效果最小。     

3种鱼糜蛋白质特性及油炸特性比较

目的：探究3种鱼糜的蛋白质特性及其油炸特性。方法：以草鱼、鲢鱼和巴沙鱼为原料,通过测定孔隙率、硬度和吸水性等指标表征鱼糜的油炸特性,测定鱼糜的动态流变学性质、泡沫稳定性和SDS-PAGE探究其影响机制。结果：相较于草鱼鱼丸和鲢鱼鱼丸,巴沙鱼鱼丸组织疏松,孔洞大,孔隙率最高,且硬度最低,吸水率最高。巴沙鱼鱼糜的凝胶强度远大于鲢鱼鱼糜和草鱼鱼糜,且草鱼、鲢鱼和巴沙鱼鱼糜的泡沫稳定性分别为63.0%,27.7%,82.0%。SDS-PAGE凝胶电泳结果表明巴沙鱼鱼糜的肌动蛋白和肌球蛋白含量较高。结论：巴沙鱼鱼糜含有较高的肌动蛋白和肌球蛋白,是提高鱼糜凝胶强度和泡沫稳定性的关键因素之一,最终影响鱼糜的油炸特性。     

鸡蛋清蛋白对微生物转谷氨酰胺酶诱导鲢鱼鱼糜凝胶形成的影响

通过对鲢鱼鱼糜凝胶特性和溶解率的测定及SDS-PAGE检测研究鸡蛋清蛋白改善鱼糜凝胶特性的机理及其对微生物转谷氨酰胺酶(MTGase)诱导鱼糜凝胶形成的影响。结果表明：鸡蛋清蛋白(EA)和MTGase均能显著提高鱼糜凝胶特性。EA会降低MTGase诱导鱼糜凝胶的形成,显著降低MTGase诱导鱼糜凝胶的凝胶强度和破断强度,但不阻碍MTGase对肌球蛋白重链(MHC)的交联。     

淡水鱼肉蛋白质组成及其在鱼糜制品加工中的变化

本文通过鱼肉蛋白质组成、鱼糜凝胶特性的测定及SDS-PAGE凝胶电泳,研究了鲢、鳙、草、鲫四种淡水鱼鱼糜凝胶特性及其凝胶形成过程中蛋白质组成的变化。四种淡水鱼肉粗蛋白质含量基本相同,但凝胶特性存在明显差异,其原因是四种淡水鱼肉的盐溶性蛋白含量不同。在鱼糜制品加工过程中,盐溶性蛋白质、水溶性蛋白的比例逐渐下降,而不溶性蛋白比例逐渐上升。弹性凝胶体的形成始于盐擂阶段,主要形成于低温凝胶化阶段。SDS-PAGE凝胶电泳图谱显示,肌球蛋白重链的量在鱼糜凝胶形成过程中明显减少,而肌球蛋白轻链和肌动蛋白的量几乎未发生变化。肌球蛋白重链在内源转谷氨酰胺酶作用下,发生分子间或分子内的ε-(γ-Glu)-Lys共价交联,形成了网络状的不溶性蛋白。     

采用圆二色谱法研究冬夏鲢鱼鳞胶原蛋白的稳定性

采用圆二色谱法,研究比较了冬夏季鲢鱼鳞胶原蛋白的热稳定性。结果表明,对胶原蛋白溶液于30℃,33℃加热时,冬季鱼鳞胶原蛋白发生解螺旋现象,而夏季鱼鳞胶原仍保持完整的三螺旋结构;变性温度曲线显示,夏季样品的变性温度为36℃,而冬季样品出现2个峰值,分别为30℃和34℃。结果表明,夏季鲢鱼鳞胶原蛋白的热稳定性高于冬季胶原蛋白,这种不同可能与冬夏季鲢鱼生长环境温度的差异有关。     

酸碱法提取鲢鱼肌肉蛋白的胶凝特性

采用酸碱法(pH-shifting)提取鲢鱼肌肉蛋白,并研究不同工艺提取的鱼糜蛋白的胶凝特性。结果表明：与水洗鱼糜相比,酸提蛋白的肌球蛋白重链明显降解,肌动蛋白含量减少;碱提蛋白的肌动蛋白含量最高,加热胶凝造成碱提蛋白的肌球蛋白重链部分降解;酸碱提取蛋白胶凝温度和储能模量(G＇)降低;酸提蛋白胶凝热损失显著高于水洗鱼糜凝胶和碱提蛋白,但水洗鱼糜凝胶和碱提蛋白胶凝热损失之间没有显著差异(P＜0.05);酸提蛋白和碱提蛋白凝胶的保水性显著低于水洗鱼糜凝胶(P＜0.05);酸提蛋白凝胶的凝胶强度最低(46.81N×mm),但碱提蛋白凝胶(60.59N×mm)和水洗鱼糜凝胶(63.57N×mm)的强度之间没有显著差异(P＜0.05)。碱法是提取鲢鱼肌肉蛋白的合适方法。     

鲢鱼与金线鱼混合鱼糜的凝胶特性

为研究鲢鱼与金线鱼混合鱼糜的凝胶特性,本实验对混合鱼糜凝胶的凝胶强度、持水性、蒸煮损失、白度值、横向弛豫时间、微观结构和肌原纤维蛋白进行分析。结果表明：混合鱼糜的白度值较纯金线鱼鱼糜显著提高（P＜0.05）,且鲢鱼鱼糜与金线鱼鱼糜质量比5∶1混合后的凝胶白度值高于纯鲢鱼鱼糜;此配比下的混合鱼糜凝胶性能最好,其中凝胶破断力、凹陷距离、凝胶强度和持水性较鲢鱼鱼糜分别提高了18.33%、27.29%、51.01%和5.65%,较金线鱼鱼糜分别提高了5.84%、19.50%、26.49%和3.45%;该配比下的混合鱼糜凝胶的蒸煮损失较鲢鱼鱼糜和金线鱼鱼糜分别降低了15.88%和7.48%。低场核磁共振分析显示鲢鱼鱼糜与金线鱼鱼糜质量比5∶1混合后的鱼糜凝胶的横向弛豫时间T22比鲢鱼鱼糜凝胶T22缩短了10.34 ms。通过扫描电镜观察发现鲢鱼鱼糜与金线鱼鱼糜质量比5∶1混合时可形成高度均匀、致密的空间凝胶网络结构。肌原纤维蛋白凝胶电泳图显示该配比下肌球蛋白重链（myosin heavy china,MHC）发生交联,大分子聚集体形成,进入凝胶中MHC更少,条带更细窄。     

大豆分离蛋白对微生物转谷氨胺酶诱导鲢鱼糜凝胶形成的影响

本实验通过对鲢鱼糜凝胶特性和溶解率的测定及SDS-PAGE、扫描电镜观察,研究大豆分离蛋白(SPI)对微生物转谷氨酰胺酶(MTGase)诱导鱼糜凝胶形成的影响及作用机理。结果表明：SPI 和MTGase 均能显著提高鱼糜凝胶特性,但SPI 的添加会阻碍MTGase 对肌球蛋白重链(MHC)的交联,降低鱼糜凝胶特性,增加溶解率。SPI改善鲢鱼糜凝胶特性的机理是自身的凝胶作用和抑制蛋白酶活性。     

The effect of the subunit composition on the thermostability of collagens from the scales of freshwater fish

Collagens were isolated from the scales of carp and silver carp caught both in winter and summer. The denaturation temperatures measured by circular dichroism indicated that the thermostability of summer collagens was higher than that of the winter equivalents. The subunits of scale collagens were studied by column chromatography, which showed that the winter collagens had lower contents of α1 chain, but higher percentages of α2 and α3 chain, than the summer equivalents. It was suggested when season changes from summer to winter, the subunit compositions of scale collagens change accordingly; the content of α1 chain decreased, while contents of α2 and α3 chain increased. Therefore, the seasonal difference in the thermostability of scale collagens from the fish may be attributed to the subunit changes of collagens. This change may substantially affect tissue formation and construction, thus, have dramatic physiological consequences.     

Effect of season on contractile and metabolic properties of desert camel muscle (Camelus dromedarius)

Thirty fattened one humped desert camels were used to examine the effect of season on contractile and metabolic properties of Longissimus thoracis (LT) muscle. Ten camels were slaughtered according to seasons of the year (winter, summer and autumn). Season significantly influenced muscle chemical composition, ultimate pH (pHu) and color. Activities of metabolic enzymes were higher during autumn season compared to summer and winter for phosphofructokinase (+ 64% compared to both seasons) and for isocitrate dehydrogenase (+ 35% and + 145% in autumn vs. summer and winter, respectively). Quantification of muscle myosin heavy chain isoforms by SDS-PAGE electrophoresis showed only presence of type I and type IIa MyHC in camel muscle and indicated high proportion in winter for type I and in autumn for type IIa with respect to other seasons. Several correlations between different MyHC proportions and enzyme activities were reported. These findings indicated that muscle characteristics in camels are influenced by season.     

鲢鱼新鲜度对鱼糜凝胶品质的影响

通过对4 ℃条件下鲢鱼死后10 h感官特性、pH值和僵直指数的变化过程以及鲢鱼死后不同时间鱼肉的挥发性盐基氮（total volatile basic nitrogen,TVB-N）值和Ca2＋-ATP酶活性变化的检测,研究鲢鱼肉新鲜度对鱼糜凝胶品质的影响。结果表明：鲢鱼在死后2～3 h开始进入僵直期,鱼体僵直指数升高,pH值下降;随着鲢鱼死后时间的延长,鱼肉的TVB-N值显著升高,Ca2＋-ATP酶活性显著降低。采用死后不同时间的鲢鱼肉制作的鱼糜凝胶,其凝胶强度、保水性和白度均有显著差异,其中以新鲜鲢鱼为原料制作的鱼糜凝胶的凝胶强度最高,而鱼糜凝胶的保水性和白度在鱼肉的僵直期最差。     

加热方式对鱼糜凝胶特性的影响

以鲢鱼糜为原料,研究蒸制、煮制及微波加热对鱼糜凝胶品质的影响,采用分形分析鱼糜凝胶微观结构,并初步探讨鱼糜微观结构与鱼糜凝胶特性的相关性。结果表明：加热方式显著影响鱼糜凝胶的硬度、咀嚼性、凝胶强度、破断强度和微观结构参数(P≤0.05),对内聚性、凹陷深度、持水性有一定影响。相关性分析表明：分形维数较大和平均当量直径较小时,鱼糜凝胶的硬度、咀嚼性、凝胶强度、破断强度、凹陷深度和持水性都较大。     

Comparison of Gel Properties of Surimi from Alaska Pollock and Three Freshwater Fish Species: Effects of Thermal Processing and Protein Concentration

ABSTRACT The gel strength of surimi made from Alaska pollock, common carp, grass carp, and silver carp was determined and compared for different incubation temperatures and periods. Gel strength and setting of the 3 freshwater fish species were inferior to that of Alaska pollock. Effects of the protein concentration, heating temperature and heating period on the gel strength were evaluated and compared utilizing the response surface methodology. Models for the breaking force and breaking distance of the surimi of the 4 species were established. Protein concentration was the major factor affecting the gel strength. Effects of heating temperature and heating period had differed somewhat among the surimi of the 4 species.     

Comparison of functional properties and SDS-PAGE patterns between fish protein isolate and surimi produced from silver carp

The purpose of this study was to investigate and compare the physicochemical properties of fish protein isolate (FPI) produced from silver carp (Hypophthalmichthys molitrix), which is a relatively cheap fish with low consumption in Fars (a state of Iran). In this research, proteins were isolated using pH shifts method. Results showed that in terms of production efficiency, protein recovery, lipid reduction and functional properties such as water-holding capacity, emulsifying capacity, foaming capacity and water absorption, FPI was better than conventional surimi. The treated samples at pH?=?2.5 represented better functional properties relative to other samples. The electrophoretic patterns demonstrated that acidic pH led to vanish high molecular weight protein bands because these proteins were converted to low molecular weight proteins, whereas basic pH caused the formation of high molecular weight proteins relative to myosin heavy chain. It seems that in basic pH, the proteins were linked together after denaturation and then aggregated. Overall, the results showed that physicochemical qualitative properties of FPI were better than those of conventional surimi.     

基于物种特异性PCR技术检测鱼糜中白鲢成分

目的建立一种基于物种特异性引物PCR测定混合鱼糜中白鲢鱼糜成分的快速检测方法。方法根据NCBI数据库中白鲢小清蛋白特异性较强的DNA序列位置设计引物进行PCR实验,通过测序得到了白鲢小清蛋白DNA的一段内含子序列,在此基础上设计了白鲢的特异性引物。提取样品DNA后进行PCR实验,产物经2%琼脂糖电泳分析进行引物特异性验证。结果在白鲢小清蛋白内含子位置设计的白鲢特异性引物,对巴沙鱼、铜盆鱼等8种鱼具有很强的物种特异性,可以实现对这9种鱼的混合鱼糜中白鲢成分的定性检测,且方法灵敏度为1%。结论本方法无需测序,能够快速、准确检测鱼糜中白鲢成分。     

纳米鱼骨对鲢鱼肌球蛋白凝胶性能的影响

本实验以鲢鱼骨为原料制成纳米鱼骨(nano-scaled fish bone,NFB)、微米鱼骨(micro-scaled fish bone,MFB),并以CaCl2为对照,将其加入至鲢鱼肌球蛋白中,通过静态流变学、动态流变学、表面疏水性分析以及活性巯基浓度和溶解度的测定,比较不同钙源对肌球蛋白凝胶性能的影响.结果表...     

Cathepsin Degradation of Pacific Whiting Surimi Proteins

Cathepsin B was the most active cysteine protease in Pacific whiting fish fillets; cathepsin L was predominant in surimi. Cathepsin L showed highest activity at 55°C in both fish fillets and surimi, indicating its function in myosin degradation during conventional heating of fillets and surimi, gels. Washing during surimi processing removed cathepsin B and H but not cathepsin L. Myosin heavy chain was the primary substrate during autolysis of surimi paste and actin and myosin light chain showed limited hydrolysis during 2 hr incubation. Purified Pacific whiting cathepsin L hydrolyzed myofibrils, myosin and native and heat-denatured collagen. The degradation pattern of myofibrils by the protease was the same as the autolytic pattern of surimi.