低盐和高盐条件下L-组氨酸对肌原纤维蛋白结构及体外消化特性的影响

研究低盐（0.2 mol/L NaCl）及高盐（0.6 mol/L NaCl）条件下L-组氨酸（L-histidine，His）添加量（0、0.2、0.4 g/100 mL）对猪肉肌原纤维蛋白（myofibrillar protein，MP）结构及体外消化特性的影响。结果表明：在低盐和高盐条件下，His的添加均引起MP发生解折叠，使其分子构象发生转变，α-螺旋结构含量降低，并伴随其他二级结构（β-折叠、β-转角、无规则卷曲）含量的增加；同时暴露出埋藏在蛋白分子内部的疏水基团，表面疏水性增加；随着His添加量的升高，MP的α-螺旋结构含量显著下降（P＜0.05），表面疏水性显著升高（P＜0.05）；体外消化结果表明，His的添加使得MP体外消化率显著提高（P＜0.05），酶解产物粒径显著降低（P＜0.05）。因此，在低盐或高盐条件下，His的添加可引起MP结构发生解折叠，暴露出更多酶切位点，进而促进胃蛋白酶和胰蛋白酶对MP的酶解作用，从而提高MP消化率。     

三种中国传统干腌火腿中粗多肽的抗氧化与抑菌活性的比较

提取宣威火腿、金华火腿、如皋火腿中粗多肽并比较其体外抗氧化活性与抑菌活性。分别以三种干腌火腿为材料提取粗多肽,测定火腿中股二头肌部分的盐含量及火腿中粗多肽的肽含量。测定粗肽液清除DPPH自由基能力、铁离子还原能力、清除ABTS+自由基能力和氧自由基吸收能力并分析肽中氨基酸成分,比较三种火腿中粗多肽生物活性的差异。结果表明,宣威火腿盐含量显著低于其他两种火腿(p<0.05),粗多肽的肽含量显著高于如皋火腿(p<0.05);三种火腿粗多肽中都富含Glu和Asp,宣威火腿粗多肽中Val和Pro等疏水性氨基酸的含量显著高于其他两种火腿(p<0.05)。在质量浓度1.0、5.0 mg/mL时,宣威火腿粗肽液清除DPPH自由基能力最强;宣威火腿粗肽液铁离子还原能力和氧自由基吸收能力显著高于金华火腿及如皋火腿粗肽液(p<0.05);三种干腌火腿都具有较强的抑制大肠杆菌的能力,在质量浓度大于0.5 mg·mL-1时,宣威火腿与如皋火腿粗肽液抑制大肠杆菌能力显著大于金华火腿(p<0.05),抑菌率接近50%。与其它两种火腿粗多肽比较,宣威火腿粗肽中含有较高的肽含量和较多的疏水性氨基酸,宣威火腿粗肽液具有更高的抗氧化能力与抑菌能力。     

3种干腌火腿中细菌群落结构和风味的差异及相关性分析

为比较不同产地干腌火腿微生物多样性对风味的影响,对3种火腿（金华、宣威和如皋火腿）中的游离氨基酸、挥发性风味物质及微生物群落结构进行比较分析。结果表明,金华火腿中鲜味和甜味氨基酸含量显著高于宣威火腿（P＜0.05）,风味物质中壬醛和苯甲醛的含量高于宣威火腿,己醛含量低于宣威火腿;金华火腿中优势微生物为葡萄球菌属和四联球菌属,如皋火腿中科贝特氏菌属和宣威火腿中盐单胞菌属相对丰度高于金华火腿。葡萄球菌属与谷氨酸、蛋氨酸等游离氨基酸的产生呈显著正相关（P＜0.05）、且葡萄球菌属和四联球菌属有利于壬醛和苯甲醛等风味物质的产生,盐单胞菌属与己醛含量的变化呈正相关。该研究阐明了3种火腿中微生物菌群结构差异以及与风味相关的主要微生物,为后续筛选功能微生物与提升火腿品质提供理论基础。     

超声波对草鱼肌肉肌原纤维蛋白溶液理化特性的影响

采用超声波技术对草鱼肌原纤维蛋白进行处理,通过分析处理前后肌原纤维蛋白粒度、表面疏水性、巯基含量及分子质量等结构信息的变化,研究超声波对草鱼肌肉肌原纤维蛋白溶液理化特性的影响。结果表明：超声波处理可使草鱼肌原纤维蛋白颗粒分布更加均匀,肌原纤维蛋白颗粒粒径、热聚集程度、内源荧光强度及巯基含量降低,且随着处理时间的增加,降低的幅度增加,肌原纤维蛋白颗粒平均粒径最小可达270.3 nm。处理后的肌原纤维蛋白表面疏水性增加,分子质量无明显变化。这说明超声波可诱导草鱼肌原纤维蛋白分子展开,使疏水基团等暴露,高级结构受到破坏,蛋白颗粒发生解聚集,但对肌原纤维蛋白一级结构无影响。     

热处理和蛋白浓度对肌原纤维蛋白乳液的稳定性和流变特性的影响

为了获得稳定的肌原纤维蛋白乳液,本文以冷冻白鲢鱼糜为原料提取肌原纤维蛋白,研究热处理（85 ℃ 10 min）和蛋白浓度（5、10、15、20、25 mg/mL）对肌原纤维蛋白溶液聚集比例、粒径、电位和微观结构等及对大豆油-肌原纤维蛋白乳液结构、表观粘度和色度的影响。结果表明:热处理使肌原纤维蛋白溶液中的蛋白发生聚集,使乳液粒径增大,表观粘度减小,乳液的L*和b*增加,疏水性减弱。随蛋白浓度的增加,未热处理组和热处理组的肌原纤维蛋白溶液的表观粘度逐渐增大,电位值波动上升,且分别在蛋白浓度为10和25 mg/mL时平均粒径最小。随蛋白浓度增加,肌原纤维蛋白乳液中参与乳化的油滴数量增多,油滴粒径减小,聚结程度减小。因此,在油相比为0.6,蛋白浓度为10~20 mg/mL时,热处理组的肌原纤维蛋白乳液液滴小而分散,表观粘度低,乳液稳定性高。本研究对开发稳定的肌原纤维蛋白乳液具有重要意义。     

氯化钠对鸡肉冷藏过程中肌原纤维蛋白氧化的影响

为探究氯化钠对鸡肉腌制冷藏过程中肌原纤维蛋白氧化的影响,采用不同添加量（0.0%、1.5%、3.0%、4.5%、6.0%、7.5%）的氯化钠处理鸡胸肉,冷藏不同时间（0、2、4 d）后提取肌原纤维蛋白,通过测定其表面疏水性、粒径、羰基、巯基含量等判断肌原纤维蛋白氧化程度。结果表明：随着氯化钠添加量的增加及贮藏时间的延长,鸡肉肌原纤维蛋白羰基含量逐渐增加,巯基含量则显著减少（P＜0.05）;肌原纤维蛋白产生一定的聚集交联现象,平均粒径呈增大趋势;肌原纤维蛋白中α-螺旋相对含量随着氯化钠添加量的增加而降低,而色氨酸荧光强度随氯化钠添加量的增加先升高后降低。综上所述,氯化钠对鸡肉腌制冷藏过程中的肌原纤维蛋白氧化有一定促进作用,其中氯化钠添加量4.5%时对鸡肉肌原纤维蛋白的氧化效果最为明显。     

宣威火腿与金华火腿中游离脂肪酸组成比较分析

以两年宣威火腿和金华火腿为对象,采用气相色谱-质谱联用法(GC-MS)分别对宣威火腿和金华火腿的皮下和肌内脂肪中游离脂肪酸的组成进行分析。结果表明:宣威火腿和金华火腿的肌内脂肪和皮下脂肪中均检测出22种游离脂肪酸,含量较高的脂肪酸为棕榈酸(C16:0)、硬脂酸(C18:0)、油酸(C18:1n9c)与亚油酸(C18:2n6c),且不同火腿及不同部位间的脂肪酸组成含量存在明显差异;金华火腿肌内及皮下脂肪中总游离脂肪酸含量分别为29.24、102.68 μg/mg,分别比宣威火腿高34.58%(p<0.05)、29.09%(p>0.05);宣威火腿和金华火腿肌内脂肪中饱和脂肪酸含量高于不饱和脂肪酸含量,皮下脂肪中不饱和脂肪酸含量高于饱和脂肪酸含量。金华火腿肌内、皮下游离脂肪酸含量均高于宣威火腿相应部位游离脂肪酸含量。     

不同盐对鲤鱼肌原纤维蛋白结构和凝胶特性的影响

肌原纤维蛋白是鱼肉中的主要蛋白质,对鱼糜类制品的质量起到关键的作用。文中研究了NaCl、CaCl2和Na4P2O73种盐类及其浓度对鲤鱼肌原纤维蛋白结构特性(表面疏水性、蛋白聚合程度)和凝胶特性(质构、微观结构、蛋白浊度)的影响。结果表明:鲤鱼肌原纤维蛋白的等电点为5.5;3种盐加入肌原纤维蛋白后会引起肌原纤维蛋白发生一定程度的聚集,表面疏水性降低;随着盐浓度的增大,肌原纤维蛋白凝胶硬度、弹性、浊度降低;添加CaCl2比其它盐类更明显降低鱼糜的凝胶硬度、弹性和浊度,且差异性显著(P<0.05);NaCl和Na4P2O7使鱼糜凝胶微观结构更致密、CaCl2使鱼糜凝胶微观结构变得松散。因此,在鲤鱼肌原纤维蛋白中添加NaCl、CaCl和NaPO对鱼糜肌原纤维蛋白结构和凝胶特性均有不同程度的影响。     

糖基化大豆分离蛋白对鲤鱼鱼糜凝胶和乳化特性的影响

选择天然大豆分离蛋白和糖基化大豆分离蛋白(蛋白与葡萄糖质量比1:1,添加量为10%、20%、30%、40%和50%)与鲤鱼肌原纤维蛋白进行混合,测定不同混合蛋白的质构特性、乳化性能、表面疏水性、白度值,探讨糖基化大豆分离蛋白对鲤鱼肌原纤维蛋白功能性质的影响。结果表明:糖基化大豆分离蛋白与肌原纤维蛋白混合凝胶的硬度、弹性和黏结性比天然大豆分离蛋白混合凝胶显著提高(P0.05),乳化性和表面疏水性较之也有显著提升(P0.05),且比纯肌原纤维蛋白凝胶均显著升高(P0.05);混合凝胶的白度值比纯肌原纤维蛋白凝胶有所下降,在添加量较小时,差异不显著(P0.05)。     

米糠酸败对米糠蛋白体外胃蛋白酶消化产物结构特征的影响

将新鲜米糠贮藏不同时间后进行稳定化和脱脂制备米糠蛋白,研究米糠酸败对米糠蛋白体外胃蛋白酶消化产物结构特征的影响。结果表明：随着米糠酸败程度增加,米糠清蛋白亚基、谷蛋白酸性亚基和球蛋白亚基完全被胃蛋白酶消化降解的时间先提前后延迟,而米糠谷蛋白碱性亚基和醇溶蛋白亚基表现为更难被胃蛋白酶消化;分子质量分布和粒径分布结果表明,米糠酸败过程中形成的米糠蛋白氧化聚集体会抑制米糠蛋白体外胃蛋白酶消化;此外,随着米糠酸败程度的增加,米糠蛋白体外胃蛋白酶消化产物内源荧光峰位的红移幅度先增大后减小,表面疏水性则逐渐下降。总之,米糠酸败导致的米糠蛋白氧化对米糠蛋白消化产物的共价交联状态、聚集行为和表面疏水性等结构特征产生了重要影响。     

Evaluating the profile of myofibrillar proteins and its relationship with tenderness among five styles of dry-cured hams

In order to investigate the relationship between profile of myofibrillar proteins and tenderness among 2 kinds of Chinese hams (Jinhua and Xuanwei) and 3 kinds of European hams (Iberian, Serrano and Parma), shear force, myofibril fragmentation index (MFI), SDS-PAGE, carbonyls content and Raman spectroscopy were investigated. The shear force and salt content of Chinese hams were significantly higher than that of European hams, while moisture content was lower than that of European hams (p < 0.05). MFI values and SDS-PAGE profile revealed that the degradation of myofibrillar proteins in Chinese hams was lower than in European hams. In addition, Chinese hams showed significantly higher carbonyls content and β-sheet content compared with European hams, indicated that proteins aggregation intensively inhibited the degradation of myofibrillar proteins in Chinese hams. These results indicated that the higher shear force in Chinese style hams could be attributed to the lower moisture content and limited proteolysis.     

Proteolysis in biceps femoris during Jinhua ham processing

Sixty experimental Jinhua hams were processed by a traditional method. The nitrogen fractions and free amino acids in biceps femoris were analyzed. Intense proteolysis was found in ham muscle and totally more than 10% of muscle proteins were degraded during the course of Jinhua ham processing. The proteolytic index of Jinhua ham was between 14 and 20. Both insoluble and soluble proteins were degraded to some degree and the later showed more intense degradation. In the soluble fraction, the percentage of non-protein nitrogen (NPN) increased gradually whereas that of protein nitrogen decreased during processing (P<0.05). However, very small amount of peptides larger than 1kDa was accumulated during the whole course of processing, which proved that intense degradation reactions were also happened to them, especially at the post ripening stage when dramatic decrease of nitrogen fraction from all the peptides larger than 1kDa was found. As a result, more than 90% of the NPN products from muscle proteolysis were free amino acids and peptides of MW less than 1kDa that might make important contribution to Jinhua ham taste and provide precursors for the generation of volatile flavor compounds in ham muscle. The pattern of muscle proteolysis coincided with the reported changes of muscle proteolytic enzymes during processing, seemingly indicating that the enzymes could have played important roles in ham muscle proteolysis.     

Effect of intensifying high‐temperature ripening on proteolysis,lipolysis and flavor of Jinhua ham

BACKGROUND: The flavor quality of dry‐cured ham comes from proteolysis, lipolysis and lipid oxidation, Maillard reaction and Strecker amino acid degradation. Intense proteolysis, lipolysis and lipid oxidation make major contributions to flavor development of dry‐cured ham. Increasing the temperature in fermenting and ripening could promote these reactions and accelerate flavor development in dry‐cured hams. The specific aroma flavor of Jinhua ham is developed only during long‐time high‐temperature ripening in July and August. Our objective was to effectively shorten the process time by intense high‐temperature ripening based on the flavor and quality features of traditional Jinhua ham. RESULTS: Muscle dehydration rate of 80‐day ripened hams (29.43 ± 1.16%) was higher than that of the traditional process (P < 0.05). The total free fatty acids in ripened hams of 45–80 days were all higher than that of traditional hams (P < 0.05) and the level of TBARS was significantly lower (P < 0.01). The flavor profile of modern‐processed hams was different from that of the traditional Jinhua ham. The contents of carboxylic acids and aldehydes were obviously higher than those of the traditional products (P < 0.05). The results of organoleptic evaluation for flavor and quality showed that 80‐day ripened hams reached the first‐grade level of traditional Jinhua ham. CONCLUSION: Long‐time (25–30 days) intensifying high‐temperature ripening (35–37 °C) could accelerate the proteolysis, lipolysis, lipids oxidation, flavor development and effectively shorten the process time based on the traditional flavor and quality features of dry‐cured ham. Copyright © 2009 Society of Chemical Industry     

Effect of dry-cured ham maturation time on simulated gastrointestinal digestion: Characterization of the released peptide fraction

This study deals with the identification of the peptides released after in vitro simulated gastrointestinal digestion of dry-cured Parma hams, using a physiological digestion model in terms of number of steps and composition of digestive juices. The obtained peptide mixture was analysed by ultra-high performance liquid chromatography with single quadrupole mass spectrometer detector and liquid chromatography hyphenated with triple quadrupole mass spectrometry and LTQ-orbitrap. This approach allowed for the identification of up to 81 different peptide sequences, mainly originating not only from myofibrillar proteins but also from sarcoplasmic proteins: the MW range spans between 200 and 1700 Da, with a high number of very short sequences (21 dipeptides and 12 tripeptides). Several identified released peptides are precursors of potentially bioactive sequences. The effect of the maturation time of the ham on the peptide profile obtained upon digestion was assessed: Principal Component Analysis allows for differentiating between 18 months and 24 months aged hams, underlying the importance of maturation on the digestibility of meat proteins and on the eventual release of bioactive sequences.     

Proteomic analysis of water soluble and myofibrillar protein changes occurring in dry-cured hams

The myofibrillar fraction of raw ham muscles and dry-cured hams with different ripening times was extracted in denaturing and reducing conditions and subjected to two-dimensional gel electrophoresis. The two-dimensional maps gave overall pictures of the already noted progressive disappearance of actin, tropomyosin and myosin light chains during ripening. In addition, two fragments from Myosin Heavy Chain proteolysis, marked as myosin chain fragments MCF1 and MCF2, were identified by immunodetection and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). Furthermore, a new form of actin on two-dimensional gel was identified by MALDI-TOF peptide mapping. In 12-month-old dry-cured ham, most myofibrillar proteins were completely hydrolyzed. At this stage of ripening, in fact, in some Parma and S. Daniele dry-cured ham samples, myosin heavy chain fragments and other unidentified neo-formed spots were found. Some of the sarcoplasmic proteins in water extracts from pork meat markedly decreased in amount or disappeared totally, during ripening. Surprisingly, two-dimensional gel electrophoresis maps of the water soluble protein fraction from dry-cured ham showed the presence of two spots identified as tropomyosin α- and β-chain. This result suggests that some of the saline soluble myofibrillar proteins can disappear from this fraction because of salt solubilization and not due to complete enzyme action. Two-dimensional gel electrophoresis (2-DGE) has proved a powerful tool to evaluate the enzymatic susceptibility of meat proteins and the evolution of protein map fragmentation throughout ripening process as well as a means of obtaining a standard fingerprinting map characterizing the final product.     

Changes of alanyl aminopeptidase activity and free amino acid contents in biceps femoris during processing of Jinhua ham

Sixty experimental Jinhua hams were processed by a traditional method. The potential alanyl aminopeptidase (AAP) activity in biceps femoris was determined. The effects of temperature, salt content, sodium nitrate content and pH on muscle AAP were evaluated using response surface methodology. Porcine muscle was found to possess very strong potential AAP activity that decreased gradually during processing from 201,635 U g⁻¹ before salting to 6147 U g⁻¹ after aging. Temperature, pH and salt content had significant exponential effects on AAP activity (P < 0.001). Both temperature and salt content interacted with pH in their effects on AAP activity (P < 0.01). However, 0–50 mg L⁻¹ sodium nitrate had no detectable effect on AAP activity (P > 0.05). The regression model showed muscle AAP maintaining its activity all through Jinhua ham processing, indicating that muscle AAP may generate free amino acids during the processing and storage of Jinhua ham. The concentrations of free amino acids increased significantly (P < 0.05) during Jinhua ham processing, except for arginine and cystine. The concentrations of most free amino acids were 5–20 times higher in the final product than in hams before salting. Final concentrations exceeded thresholds for sensory detection, thus implicating an important role of free amino acids in the determination of Jinhua ham flavor.     

肌肉非蛋白氮和游离氨基酸在金华火腿加工过程中的变化

以60只浙江兰溪当地杂交猪后腿为原料,按传统工艺加工金华火腿,分析了股二头肌中非蛋白氮(Non-proteinnitrogen,NPN)和游离氨基酸(Freeaminoacids,FAA)浓度随加工时间而变化的规律。结果表明,肌肉中的NPN和FAA含量都随金华火腿加工进程逐渐升高;NPN在后熟期和晒腿期间升高速度最快,而FAA在成熟过程中升高最快,成品火腿的蛋白质降解指数在14～20之间;成品火腿中的FAA占NPN的70%以上,其中以Arg、Glu、Leu、Lys、Ala和Val等含量较高。FAA总含量比腌制前提高13.8倍,火腿中大部分FAA浓度为腌制前的10～20倍,其中增加比例较大的FAA有Lys、Asp、Ser、Tyr和Ile等。火腿中大部分游离氨基酸的浓度多倍于其感觉阈值,因此可能对火腿风味的形成有重要贡献。     

Biochemical changes during processing of traditional Jinhua ham

Jinhua ham is the most famous traditional meat product of China and one of the most famed dry-cured hams in the world. Its processing consists of six stages: green ham preparation, salting, washing and sun-drying and shaping, ripening, and post-ripening. Intense proteolysis and lipolysis occur during processing period. As a result, the content of free amino acids in final ham products is 14-16 times that of green ham, and 191 volatile compounds have been identified during processing, which make a major contribution to the flavor of Jinhua ham.     

Oxidation of sarcoplasmic proteins during processing of Cantonese sausage in relation to their aggregation behaviour and in vitro digestibility

The physicochemical changes of sarcoplasmic proteins, especially oxidation behaviour, were measured to determine their mechanism of action on in vitro protein digestibility during Cantonese sausage processing. The results indicated that carbonyl level increased (p<0.05) during the process. The fluorescence loss of tryptophan residues was a direct consequence of the oxidative degradation. All the parameters of protein aggregation were highly (p<0.05) correlated with carbonyl level and protein surface hydrophobicity (H(0)), indicating that protein oxidation and thermal denaturation could induce protein aggregation, leading to secondary structural changes. The analysis of in vitro digestibility showed no correlation between pepsin activity and protein oxidation, due to the biphasic response of sarcoplasmic proteins toward proteolysis. However, a highly significant (p<0.05) correlation was observed with trypsin and α-chymotrypsin activity, indicating that protein oxidation induced the changes in H(0), protein aggregation and secondary structure, which further influenced in vitro digestibility.