【作者】 刘海梅；

【导师】 谢笔钧； 熊善柏；

【作者基本信息】 华中农业大学 ， 水产品加工及贮藏工程， 2007， 博士

【摘要】 鲢是我国主要的淡水养殖鱼类，不仅资源丰富，而且价格低廉，是开发生产鱼糜制品的良好原料。但相对海水鱼糜的研究仍处在一般加工条件阶段，报道相对集中的是漂洗条件、加工工艺、外源添加剂对鱼糜凝胶特性的影响及冷冻变性等方面，对凝胶形成的机理则鲜见报道。因此，研究影响鲢鱼糜凝胶形成的因素及形成机理，对有效控制凝胶形成过程、开发高品质鲢鱼糜制品具有重要的理论和实验意义。本文旨在研究鲢鱼糜的凝胶化条件及相关基础问题，着重探讨肌球蛋白的聚集行为与构象对鲢鱼糜凝胶形成的影响及添加外源蛋白质（大豆分离蛋白、鸡蛋清蛋白）、MTGase和淀粉及其它亲水性胶体等多糖类物质改善鲢鱼糜凝胶的特性，为淡水鱼糜的研究与开发提供理论依据和实验基础，主要研究结果如下：1、鲢鱼糜的凝胶化作用基础研究在确定鲢鱼糜凝胶形成条件的基础上，对鲢鱼糜凝胶形成过程中的蛋白质组成的变化、TGase激活剂与抑制剂对鲢鱼糜凝胶形成的影响进行了研究。在鲢鱼糜凝胶形成过程中，从加盐擂溃开始，因转谷氨酰胺酶催化肌球蛋白重链交联形成更高分子质量蛋白质聚合物，而使盐溶性蛋白含量逐渐减少、不溶性蛋白含量逐渐增加。NEM、EDTA、AC三种转谷氨酰胺酶抑制剂均可显著降低鲢鱼糜的凝胶特性。转谷氨酰胺酶激活剂Ca²⁺在低浓度（20 mmol／kg）范围内通过激活内源转谷氨酰胺酶促进肌球蛋白重链交联，从而提高鲢鱼糜凝胶特性；而高浓度钙离子（80 mmol／kg）在抑制TGase催化作用的同时，与鱼糜蛋白形成较多的钙桥，引起鲢鱼糜凝胶硬度加大、弹性降低。转谷氨酰胺酶激活剂C²⁺对鲢鱼糜凝胶特性的影响存在两种不同作用机制。当在鲢鱼糜中添加20 mmol／kg Ca²⁺时，鲢鱼糜凝胶强度达到最大。鲢鱼糜的凝胶化温度和时间显著影响其凝胶特性在鲢鱼糜的适宜凝胶化温度和时间为40℃、60 min的条件下，鲢鱼糜凝胶的破断强度、凹陷深度和凝胶强度分别达到470.50 g、11.32 mm和5331.53 g×mm，分别为凝胶化30 min的1.29倍、1.09倍、1.35倍。但是凝胶化时间过长会导致鱼糜凝胶强度显著下降。鲢鱼糜的凝胶化时间的选择受转谷氨酰胺酶催化的酰基转移反应和蛋白酶对鱼糜蛋白的水解作用的双重制约。鲢鱼糜在凝胶形成过程中，维持蛋白质结构和稳定的各种化学作用力及相应的蛋白质结构均发生了不同变化，这与凝胶化过程和鱼糜凝胶特性密切相关。随着凝胶化进程，氢键、离子键显著减少，而二硫键、疏水相互作用显著增加，并形成非二硫共价键。研究表明，二硫键、非二硫共价键、疏水相互作用是维持鲢鱼糜凝胶网络结构的主要化学作用力。拉曼光谱分析可知，鲢鱼糜经40℃凝胶化60 min和90℃蒸煮30 min后，除了在1653 cm^-1处出现表征鱼糜蛋白α-螺旋结构的谱带外，还在1664 cm^-1处出现表征无规卷曲结构的谱带；在530 cm^-1、540 cm^-1处表征二硫键含量的谱带强度增加；表征酪氨酸残基谱带的I_850／830强度比由0.98分别增加到1.01、1.05，疏水相互作用增强，这与化学作用力变化结果一致。2、鲢肌球蛋白聚集行为、构象及凝胶形成机理采用浊度法、动态流变学、SEM等方法研究了环境因素对肌球蛋白浊度和溶解度的影响及肌球蛋白形成凝胶的条件温度、pH值及焦磷酸钠、三聚磷酸钠、六偏磷酸钠三种磷酸盐均影响肌球蛋白的溶解度。在30℃、40℃，pH6.0～8.0之间，肌球蛋白溶解性较好；0.25～1.0％浓度范围内的三种磷酸盐均可增加肌球蛋白的溶解性。肌球蛋白凝胶形成的条件为：临界蛋白质浓度为10 mg╱mL，凝胶的粘弹性随着肌球蛋白浓度的增加而增加；形成凝胶的最佳pH为7.0，由微观形貌观察可见，过高或过低的pH均导致肌球蛋白凝胶结构变得不致密、均匀；低浓度的Ca²⁺可以增加肌球蛋白的凝胶形成能力。采用CD、DSC和SEM等现代分析手段对鲢肌球蛋白变性、构象变化与鱼糜凝胶化关系进行了研究由CD分析可知，在40℃凝胶化过程中，鲢肌球蛋白的α-螺旋结构含量逐渐减少，由加热前的94.11％（5℃）减少到60 min的27.00％，α-螺旋解旋达67.11％，同时转角和无规卷曲结构含量分别增加至10.40％、62.60％，增加了10.40％、56.71％，α-螺旋结构大部分转变成了无规卷曲结构；再进一步进行90℃高温加热30 min并冷却至4℃处理后，肌球蛋白的α-螺旋、转角、无规卷曲结构含量分别为33.70％、12.40％、53.90％，以无规卷曲为主。在肌球蛋白凝胶形成过程中，肌球蛋白分子充分伸展、转变为有利于肌球蛋白重链交联的无规卷曲结构。同时，化学测试结果表明，在结构转变过程中，肌球蛋白头部的巯基氧化形成二硫键，二硫键含量由0.6 mol／10⁶g显著增加到1.7 mol／10⁶g；肌球蛋白的表面疏水性（S₀ANS）由8946.78增加到29152.33，增加了2.26倍。由SEM微观形貌观察可见，肌球蛋白经40℃、60 min和90℃、30 min加热后，变性聚集形成有序的聚集体。DSC分析表明，肌球蛋白存在两个相变温度（43.32℃和51.59℃），前者正好与鱼糜凝胶化温度相对应。鲢鱼糜的凝胶化温度实质上是肌球蛋白的第一个变性峰值温度。3、MTGase、非肌肉蛋白对鲢鱼糜凝胶形成的影响添加MTGase可显著提高鲢鱼糜制品凝胶强度、持水性能，改善凝胶白度，MTGase的适宜添加量为6-10U／g_鱼蛋白，当MTGase添加量为10 U／g_鱼蛋白时，破断强度、凹陷深度、凝胶强度分别为793.00g、14.21 mm、11867.20 g×mm，比对照样分别增加了1.12倍、0.21倍、1.7倍。但添加过量的MTGase则会降低鱼糜凝胶特性。鲢鱼糜中大豆分离蛋白和鸡蛋清蛋白的适宜添加量分别为3％、10％，均可改善鲢鱼糜的凝胶特性和持水性能。三种外源添加成分中以MTGase的改善效果最好。大豆分离蛋白或鸡蛋清蛋白均会降低MTGase诱导鲢鱼糜的凝胶特性，导致其凝胶特性低于仅添加MTGase。因此，在鱼糜制品的生产中应避免大豆分离蛋白或鸡蛋清蛋白与MTGase同时使用。4、淀粉及亲水性胶体对鲢鱼糜凝胶形成的影响为了改善鲢鱼糜凝胶特性和提高适用性，本文还研究了不同来源和不同方法改性的淀粉对鲢鱼糜凝胶形成的影响。结果表明，不同来源淀粉对鲢鱼糜凝胶的影响是不同的，马铃薯、木薯、玉米三种淀粉中，以马铃薯对鱼糜凝胶特性的增强效果最佳，凹陷深度、破断强度、凝胶强度分别比对照增加了0.22倍、0.54倍、0.45倍。在变性淀粉中，交联酯化、醋酸酯化、磷酸酯化、羟丙基化淀粉均可提高鱼糜凝胶特性，而氧化淀粉、微细化淀粉将降低鱼糜凝胶特性。其中羟丙基化淀粉和交联酯化淀粉较适宜鱼糜制品加工。研究还表明，变性淀粉的胶长度越短、溶解度越小、膨胀势越大，鱼糜凝胶特性则愈好。卡拉胶、黄原胶、魔芋胶和瓜尔胶等亲水性胶体对鲢鱼糜凝胶特性有不同影响。在鲢鱼糜中，添加0.5％的卡拉胶或0.1％瓜尔胶能明显增加鱼糜凝胶的硬度和凝胶强度，降低粘性和脆性，改善制品色泽。而在鱼糜自然pH下，添加黄原胶和魔芋胶会影响鲢鱼糜凝胶形成，降低其凝胶强度。更多还原

【Abstract】 In China, Silver carp, one of the main fresh-water fish species, abundant and cheap, is a good material to develop and process surimi-based product. Compared with briny surimi, researches of silver carp surimi focused on influences of washing conditions, processing technics and additives on surimi gel properties and frozen denaturation, but little on the gel-forming mechanism. Thus, studies on affecting factors of silver carp surimi gel forming and gel forming mechanism are very important to promote the formation of surimi gel and develop silver carp surimi-based products with high quality.Setting conditions and relative ground works of silver carp surimi, influences of aggregation behavior and confirmation of myosin on the formation of silver carp surimi gel, and effects of soy protein isolate, egg albumin, MTGase, starches and some hydrocolloids on gel properties of silver carp surimi were investigated. The results were as follows:1. Studies on the basis of silver carp surimi gelation Based on the gel-forming conditions, the change of silver carp protein composition during gel forming and effects of transglutaminase activator and inhibitors on the forming of silver carp surmi gel were investigated. During the forming of silver carp surimi gel, the content of salt-soluble protein decreased gradually, while the content of insoluble protein increased correspondingly starting from smashing due to myosin heavy chain cross-linking catalyzed by transglutaminase and forming high molecule weight polymer. Three kinds of tmnsglutaminase inhibitors, NEM, EDTA, and AC, decreased gel properties of silver carp surimi. Low Ca²⁺ concentration （20mmol/kg） activated transglutaminase activity and promoted myosin heavy chain cross-linking, leading to improving silver carp surimi gel properties. However, high Ca²⁺ concentration depressed myosin heavy chain cross-linking induced by transglutaminase, and conduced to the formation of Ca-bridge between Ca²⁺ and protein, and also the hardness increased and the elasticity decreased for silver carp surimi gel. Effect of transglutaminase activator Ca²⁺ on gel properties of silver carp surimi had two kinds of mechanism. Gel strength of silver carp surimi was highest when the Ca²⁺ adding dosage was 20 mmol/kg.The setting temperature and time affected gel properties of silver carp surimi significantly. The optimum setting temperature and time were 40℃and 60min, respectively. Breaking force, deformation, and gel strength of silver carp surimi gel were 470.50g, 11.32ram and 5331.53g×mm, which were 1.29, 1.09, 1.35 times of that setting for 30min, respectively. But the longer setting time leaded to the decreasing of surimi gel strength. Setting time was decided by acyl-transfer reaction induced by transglutaminase and hydrolysis of surimi protein by endogenous protease. The chemical interactions and protein structures in order to maintain surimi protein structure and stability changed during surimi gel forming, which were correlated closely to gel forming procedure and surimi gel properties, Hydrogen bonds and ion bonds decreased significantly, while disulfide bonds and hydrophobicity increased significantly with surimi gel forming. And non-disulfide covalent bonds were formed. The main chemical interactions to maintain silver carp surimi gel network structure were disulfide bonds, non-disulfide covalent bonds and hydrophobicity. Ramman spectra results of surimi after setting 60min and then cooking 30min also showed that the band at 1664 cm^-1 indicating random coil also occurred, besides the band at 1653 cm^-1 indicatingα-helix structure of raw surimi protein; the band density near 530 cm^-1 and 540 cm^-1 indicating disulfide bonds increased; I850/830 ratio increased from 0.98 to 1.01 and 1.05, respectively indicating the increasing of hydrophobicity. This result was consistent with the change of chemical interactions.2. The aggregation behavior, configure and gel-forming mechanism of myosin from silver carp Effects of environmental factors on turbidity and solubility of myosin and myosin gel-forming conditions were investigated by turbidity method, dynamic rheology, and scanning electron microscope. Temperature, pH value, sodium paraphosphate, sodium tripolyphosphate and sodium hexa-metaphosphate could affect myosin solubility. Myosin had good solubility at 30℃or 40℃, and pH from 6.0 to 8.0. Sodium paraphosphate, sodium tripolyphosphate, and sodium hexa-metaphosphate with the concentration from 0.25% to 1.0% could increase solubility of myosin. The forming conditions of myosin gel, the critical concentration and optimum pH were 10mg/mL and 7.0, respectively. Viscoelasticity of myosin gel increased with myosin concentration being up. Dense and uniform gel structure did not form at pH higher or lower than 7.0. Low Ca²⁺ concentration enhanced gel-forming ability of myosin.The correlation among myosin denaturation, conformation change and surimi setting was investigated by CD, DSC, SEM. During setting at 40℃, the ratio ofα-helix structure of myosin reduced gradually and finally decreasing by 67.11%, which was 27.00% when setting for 60min, compared with 94.11% before setting. Meanwhile, the ratio of turn and random coil increased by 10.40% and 56.71% to 10.40% and 62.60%, respectively. A majority ofα-helix structure changed into turn. Further heating at 90℃for 30min and cooling to 4℃, the ratios of a-helix, turn and random coil of myosin were 33.70%, 12.40% and 53.90%, respectively and the main secondary structure was random coil. During the forming of myosin gel, myosin molecules extended and changed into random coil contributed to myosin heavy chain cross-linking. At the same time, the results of chemical measurements showed that -SH in myosin head was oxidized into disulfide bond, the content of which increased from 0.6 mol/10⁶g to 1.7 mol/10⁶g. And surface hydrophobicity increased from 8946.78 to 29152.33, increased by 2.26 times. Myosin denatured and aggregated into ordered aggregation after heating at 40℃for 60min and 90℃for 30min. DSC analysis showed that myosin had two phase transition temperature 43.32℃and 51.59℃. The former was corresponding to setting temperature of silver carp surimi. Setting temperature of silver carp surimi was actually the first peak temperature of myosin denaturalization..3. Effects of MTGase, soy protein isolate, and egg albumin on the formation of silver carp surimi gel MTGase could improve gel strength, water-holding ability, and whiteness of surimi gel. The optimum adding dosage of MTGase was 6-10U/g fish protein. Breaking force, deformation, and gel strength were 793.00g, 14.21mm, 11867.20g×mm, increasing by 1.12, 0.21, 1.7 times, respectively. But higher dosage decreased gel properties. When adding dosage of soy protein isolate and egg albumin were 3% and 10%, respectively, silver carp surimi gel properties and water-holding ability could be improved. However their improving mechanisms were different. Soy protein isolate improved gel properties because it might inhibit protease activity and gel by itself, while egg albumin was due to inhibiting serine protease and promoting myosin heavy chain cross-liking. These two kinds of proteins depressed the formation of MTGase-induced gel, so that gel properties of silver carp surimi were lower than that with MTGase only. Thus, soy protein isolate or egg albumin and MTGase could not use at same time during surmi-based products manufacturing.4. Effects of starches and hydrocolloids on the formation of silver carp suimi gel Effects of starches with different sources and modified methods on the gel formation of silver carp surimi were also investigated. Starch of different sources had different influences on surimi gel. Potato starch had the best improving effective among potato starch, tapioca starch, and corn starch. Breaking force, deformation, and gel strength of silver carp surimi gel with potato starch increased by 0.22, 0.54 and 0.45 times than that of control, respectively. Surimi gel properties might be improved through adding cross-linked and esterified starch, acetylated starch, phosphate estered starch, and hydropropylated starch, but were decreased by oxidized starch and micronized starch. Hydropropylated starch and cross-linked and esterified starch were suitable for processing surimi-based products. Better surimi gel properties could be obtained by starch with shorter gel length, lower solubility and bigger swelling power.Carrageenan, xanthan gum, konjac flour, and guar gum had different influences on silver carp surimi gel properties. 0.5% carrageenan or 0.1% guar gum obviously increased hardness and gel strength of surimi gel, decreased gumminess and brittleness, and improved color. However, gel strength would decrease when adding xanthan gum and konjac flour to surimi in natural pH.更多还原