Thermal transition of collagen in ovine connective tissues

The thermal transition temperature (T(m)) of collagen in a range of muscle and non-muscle connective tissues from lambs, hoggets and mature sheep was measured by differential scanning calorimetry. The muscles selected were: semimembranosus (SM), semitendinosus (ST), biceps femoris (BF), Longissimus dorsi (LD) and psoas major (PM). Although the T(m) of intramuscular SM collagen from an aged ewe underwent no significant change with time post mortem, that of a 5-months-old lamb had dropped by 0·9°C after 2 days at 19°C. The epimysium of each muscle exhibited a higher T(m) than the corresponding intramuscular connective tissue. The LD and BF tendons each had a lower T(m) than corresponding intramuscular connective tissue but this was not true for the PM. Furthermore, the PM tendon generated an isometric tension more than five times that of the LD, BF or psoas minor tendons. This indicates that the PM tendon is richer in heatstable crosslinks than any of the other tendons investigated. In all tissues, except the liver capsule, there was an increase in T(m) with animal age. However, the rate of change T(m) varied from one tissue to another. For example, the SM intramuscular collagen matured at an earlier age than that of other muscles, the PM being slowest to mature. In keeping with the changes in T(m) values, the Warner-Bratzler peak force of ST muscles increased markedly in older sheep, but there was no significant difference in peak force of SM muscles between lambs, hoggets and mature sheep.     

Thermal stability of connective tissue from porcine muscles

Connective tissue of three porcine muscles (M. infraspinatus, IS; M. longissimus dorsi, LD; M. semimembranosus, SM) from 27 animals [populations A (n=13, reared in Ireland) and B (n=14, reared in Finland)] was studied by measuring the collagen content, collagen solubility and thermal shrinkage temperature of the connective tissue. Colour and pH were also determined. Collagen solubility was highest in IS (p<0.05) and lowest in SM (p<0.05) although no difference between LD and SM was found in population B. The onset and peak temperatures of thermal shrinkage (T(o) and T(p)) were highest in IS (p<0.05). The lowest T(o) and T(p) were found in SM from population B whereas no differences were seen between LD and SM muscles in population A. It was concluded that the thermal stability of the connective tissue in the three porcine muscles differ. IS, as a dark muscle has high thermal shrinkage temperatures and high collagen solubilities in comparison to the lighter LD and SM muscles which have lower thermal shrinkage temperatures and collagen solubilities. Collagen contents were highest in IS and lowest in LD.     

5 种淡水鱼肌肉热特性比较研究

为研究不同品种名优淡水鱼冷藏保鲜及热加工的特性,采用差示扫描量热法研究武昌鱼、草鱼、黄颡鱼、鲈鱼和鳜鱼5 种新鲜淡水鱼鱼肉的水分含量、冰点、变性温度、变性热焓和比热容并进行品种间的比较。结果发现：5 种淡水鱼冰点分布在－0.57～－0.1 ℃之间;50 ℃附近热吸收峰起始温度分布在37～41.57 ℃之间,终止温度分布在60.47～62.33 ℃之间;变性热焓在1.680 0～2.499 7 J/g之间;70 ℃附近热吸收峰的起始温度分布在66.33～71.13 ℃之间,终止温度分布在73.60～82.20 ℃之间,变性热焓在0.418 0～0.512 2 J/g之间;鱼肉的比热容在1.658 0～3.862 3 J/（g·K）之间。结果表明：在5 种新鲜淡水鱼中,武昌鱼水分含量和冰点相对较低;草鱼肌球蛋白和鳜鱼肌动蛋白变性温度和变性热焓相对较高,蛋白质稳定性更高;新鲜鱼肉的比热容高于冻结鱼肉,加工后鱼肉的比热容高于未加工鱼肉。     

纺织材料的热转变温度试验方法

用差示扫描量热仪(DSC)测定纺织材料的热转变温度,如熔融温度、结晶温度、玻璃化转变温度时发现：纺织材料的外推起始温度和熔融温度随升温速率增大向高温方向偏移;试样的形状影响转变温度;试样越多,峰顶温度向高温方向偏移,但外推起始温度不变;载气的流量越大,DSC曲线的斜移程度越严重。     

猪皮胶原蛋白的提取与应用浅析

胶原蛋白是动物体内结缔组织的重要结构蛋白,其中富含甘氨酸、脯氨酸和羟脯氨酸.现今,随着胶原提取技术的不断发展及对胶原蛋白功能性质认识的逐步提高,人们对胶原蛋白的应用给予了更多关注.本文在概述猪皮的基本纽分与提取工艺路线的基础上,对胶原蛋白的主要应用及今后的发展趋势进行了系统性阐述.     

罗非鱼皮胶原肽的制备及抗氧化活性研究

采用酶法从罗非鱼皮中制取胶原肽,选用动物蛋白水解酶,当酶的添加量为0.5%,61℃,pH 6.7下水解3 h时,蛋白质的回收率为92.97%,水解度为9.37%.水解产物90%以上相对分子质量低于10 kD的胶原肽.胶原肽对由Fe^2＋引发的卵磷脂脂质体过氧化有一定抑制作用,同时对·OH具备一定的清除作用.     

刺参体壁酶促溶性胶原蛋白的热变性

从刺参（Stichopus japonicus）体壁中提取酶促溶性胶原蛋白（pepsin-solubilized collagen,PSC）,并对其热处理过程中的降解规律及结构变化进行研究,发现PSC变性温度为35.3 ℃,当加热温度为40～70 ℃时,PSC三螺旋结构解缠绕,α-螺旋结构破坏严重,但在冷却后依靠分子间氢键和二硫键的相互作用仍可形成强凝胶体系;当加热温度超过70 ℃时,PSC的α-肽链开始逐渐降解成小分子多肽,冷却后分子间交联作用较差,不易形成凝胶体系。     

海蜇伞部酶促溶性胶原蛋白的热变性动力学

为阐明海蜇伞部酶促溶性胶原蛋白(pepsin-solubilized collagen,PSC)的热变性反应机理,以保持完整三螺旋结构的PSC为研究对象,通过微量热仪测定不同升温速率条件下PSC的变性温度,以及采用34、35、36、37、38、39℃加热不同时间后的PSC残存率,并进行热变性动力学分析。结果表明,海蜇伞部PSC对热变化敏感,随着加热温度升高,单位时间内提高的热量增加,使海蜇伞部PSC变性速率加快,完成变性时间缩短;随着升温速率的减慢,吸热峰逐渐向低温区移动,即变性温度随升温速率的减慢而降低,但升温速率的变化对反应热并无显著影响。反应级数为0.9的回归方程能够较好地描述PSC热变性过程,在恒温34、35、36、37、38℃及39℃的条件下,PSC变性的D90值(90%蛋白变性所需时间)分别为53.76、26.11、15.75、4.89、4.26、2.55 min,Z90值(D值降低90%的温度变化)为3.69℃,表观活化能为481.90 k J/mol。研究结果可为海蜇胶原蛋白的进一步开发利用提供理论参考。     

Distinctive characteristics of collagen and gelatin extracted from Dosidicus gigas skin

Squid skin, often discarded as processing by-product, is a good resource of collagen/gelatin. In this study, acid soluble collagen (ASC), pepsin soluble collagen (PSC) and water soluble gelatin (WSG) were extracted from squid (Dosidicus gigas) skin and physicochemically examined. The lowest yield of 33.5% was obtained for ASC extracted at 4 °C, and the addition of pepsin increased the collagen yield by around 35.0% (PSC). The highest yield of 81.9% (WSG) was achieved by thermal extraction at 60 °C. A low temperature can largely retain the native helix structures of ASC and PSC, contrariwise, thermal treatment converted collagen into gelatin with unordered and renatured structures. The proline and hydroxyproline contents of ASC, PSC and WSG were 183/1000 residues, 194/1000 residues and 175/1000 residues, respectively. In addition, WSG showed a denaturation temperature at 80.7 °C which was much higher than that of ASC (24.2 °C) and PSC (26.2 °C), while a significant lower resistance towards enzymatic digestion.     

Investigation of the peptides with calcium chelating capacity in hydrolysate derived from spent hen meat

Calcium peptide chelates are developed as efficient supplements for preventing calcium deficiency. Spent hen meat (SHM) contains a high percentage of proteins but is generally wasted due to the disadvantages such as hard texture. We chose the underutilized SHM to produce peptides to bind calcium by proteolysis and aimed to investigate chelation between calcium and peptides in hydrolysate for a sustainable purpose. The optimized proteolysis conditions calculated from the result of response surface methodology for two-step hydrolysis were 0.30% (w_enzyme/w_meat) for papain with a hydrolysis time of 3.5 h and 0.18% (w_enzyme/w_meat) for flavourzyme with a hydrolysis time of 2.8 h. The enzymatic hydrolysate (EH) showed a binding capacity of 63.8 ± 1.8 mg calcium/g protein. Ethanol separation for EH improved the capacity up to a higher value of 68.6 ± 0.6 mg calcium/g protein with a high association constant of 420 M⁻¹ (25°C) indicating high stability. The separated fraction with a higher amount of Glu, Asp, Lys, and Arg had higher calcium-binding capacity, which was related to the number of ─COOH and ─NH₂ groups in peptide side chains according to the result from amino acid analysis and Fourier transform infrared spectroscopy. Two-step enzymatic hydrolysis and ethanol separation were an efficient combination to produce peptide mixtures derived from SHM with high calcium-binding capacity. The high percentage of hydrophilic amino acids in the separated fraction was concluded to increase calcium-binding capacity. This work provides foundations for increasing spent hen utilization and developing calcium peptide chelates based on underutilized meat.     

Quality characteristics of imitation crab sticks made from Alaska Pollack and spent laying hen meat

Imitation crab stick (ICS) samples were divided into four treatments, a control (C) prepared with Alaska Pollack as a commercial ICS, T1, which consisted of Alaska Pollack with spent laying hen surimi collected by the pH adjust method, T2, which was composed of Alaska Pollack with spent laying hen surimi collected by the filter cake method, and T3, which consisted of Alaska Pollack with whole spent laying hen meat batter collected by the cutting method. The moisture content was significantly higher in T3 than in the other ICS samples; but, there was no significant difference in the crude protein, fat and ash content, regardless of the spent laying hen substitution methods. The lightness (L∗) and whiteness (W) was higher in the control than in the other ICS samples at 0 days of storage, whereas the yellowness (b∗) was significantly higher in T3 than in the other ICS samples. The level of polyunsaturated fatty acids was significantly higher in the control group than in the other ICS samples. Additionally, the pH increased with storage time in the spent laying hen substituted samples (T1, T2 and T3), with T1 showing a significantly higher pH during storage. The TBARS value increased with storage time in all ICS samples, with T2 showing a significantly lower TBARS value than the other ICS samples at the beginning and end of the storage periods. There was no significant difference in any sensory evaluation items among the ICS samples during storage. Thus, we assumed that T3 was better than other ICS samples, because T3 method (cutting) is much easier to collect spent laying hen surimi than T1 (pH adjust) and T2 (filter cake).     

Na~+、Ca~(2+)和pH值对鲸鲨皮胶原蛋白热变性温度的影响

通过差示扫描量热法(DSC)对不同浓度的Na+、Ca2+和pH值对鲸鲨皮I型胶原蛋白和鲸鲨皮Ⅱ型胶原蛋白热变性温度的影响进行系统研究。I型胶原蛋白的特征性紫外吸收波长位于233.05nm,Ⅱ胶原蛋白的特征性紫外吸收波长位于232.90nm和277.88nm。研究胶原蛋白的聚集动力学曲线,发现鲸鲨I型胶原蛋白和鲸鲨Ⅱ型胶原蛋白浊度随时间变化趋势均呈S型,其聚集过程均可分为初始阶段和生长阶段及趋于稳定阶段。通过高灵敏度差示量热扫描仪对鲸鲨I型胶原蛋白和鲸鲨Ⅱ型胶原蛋白的热稳定性进行表征。鲸鲨I型胶原蛋白的热变性温度为40℃,鲸鲨Ⅱ型胶原蛋白热变性温度为62℃。较低浓度的Na+、Ca2+使I型胶原蛋白和Ⅱ型胶原蛋白的热变性温度降低,这可能是由于金属离子的加入影响了胶原蛋白分子之间带电氨基酸残基的相互排斥作用,降低了胶原蛋白的热稳定性;较高浓度的Na+、Ca2+使I型胶原蛋白和Ⅱ型胶原蛋白的变性温度持续降低,这可能是由于金属离子与胶原蛋白分子竞争水分子,从而导致胶原蛋白的不稳定;继续增加Na+、Ca2+金属离子的浓度时,I型胶原蛋白和Ⅱ型胶原蛋白的变性温度由于发生盐析而增加。I型胶原蛋白在强酸强碱处理后,蛋白的吸热变...     

The measurement of the glass transition temperature of sucrose and maltose solutions with added NaCl

The effect of added NaCl on the glass transition temperatures of 200 and 300 g kg⁻¹ sucrose and maltose solutions was determined using DSC and capacitance measurements. Negative shifts of around 4 °C were seen upon the addition of 0.1 mol kg⁻¹ NaCl, consistent with the freezing point depression expected for the maximally freeze‐concentrated solutions. Changes in the capacitance were seen which matched both the onset of the devitrification event and the main heat capacity step seen in DSC scans. © 2000 Society of Chemical Industry     

Antimicrobial effects of selected plant essential oils on the growth of a Pseudomonas putida strain isolated from meat

Dielectric properties of beef biceps femoris muscle were recorded during heating (5-85°C) to assess their linkage to phase changes monitored by differential scanning calorimetry (DSC) and rheology. DSC indicated endotherms between 56 and 81°C corresponding to denaturation of actin, collagen and myosin. Matching changes in dielectric properties (dielectric constant (ε') and loss factor (ε″)) were noted at radio and/or microwave frequencies though the nature of the change differed depending upon frequency. The main observation in ε' was an increase above 65-66°C, most likely due to fluid release on collagen denaturation. This fluid plus liquid from myosin denaturation most likely solvated ions freed during myosin denaturation which manifested as an ε″ increase. However, it must be noted that meat structural protein denaturation is compounded with physical shrinkage which can also influence dielectric properties. Rheological parameters of beef muscle heated from 5 to 85°C also displayed marked changes relating to structural protein denaturation.     

曼式无针乌贼肌肉的低温相变区热特性及蛋白热稳定性研究

以曼式无针乌贼肌肉为原料,采用差式扫描量热仪（DSC）研究乌贼肌肉的热特性。本文一方面测定新鲜乌贼肌肉低温相变区（-40¹0℃）的热特性,另一方面比较4℃贮藏（冷藏）和4℃下冰块包埋贮藏（冰藏）乌贼肌肉在贮藏期间的热特性差异。结果分析表明:乌贼肌肉冰点是-3.3℃,冻结焓170.75 J/g,冻结温度-15.1℃,不可冻结含水率为22.98%;表观比热首先缓慢增加,然后快速增加达到峰值28.242 J/（g·℃）,随后迅速减小,并且表观比热和温度拟合良好,拟合度R²=0.9879;乌贼肉的热焓值在升温过程中明显增大;冰藏组（4℃冰块包埋）和冷藏组（4℃）对比,肌球蛋白和肌动蛋白贮藏稳定性更高。本实验研究曼式无针乌贼肌肉的热特性,为乌贼肉的加工提供理论依据。      

Determination of critical aggregation concentration and aggregation number of acid-soluble collagen from walleye pollock (Theragra chalcogramma) skin using the fluorescence probe pyrene

The aim of this paper was to investigate the critical aggregation concentration and aggregation number of acid-soluble collagen from walleye pollock (Theragra chalcogramma) skin using the fluorescence probe pyrene. Results showed that pyrene was fit for studying the aggregation behaviour of collagen in sodium phosphate buffer at pH 7.2. The plots of the pyrene I₁/I₃ ratio, as a function of the logarithm of total collagen concentration, revealed a typical sigmoidal decrease, the critical aggregation concentration (CAC) from which was determined to be at 0.48 mg/ml. The subsequent transient fluorescence decay study indicated that the aggregation number of collagen was not constant, but varied with different concentrations of collagen. The structure of the aggregates tended to be stable, when the collagen concentration exceeded 1.2 mg/ml.     

Stabilization of low denaturation temperature collagen from fish by physical cross-linking methods

Collagen matrices were prepared from atelo salmon collagen (SC). SC has a lower denaturation temperature (19 degrees C) than mammalian collagen. SC matrices were successfully stabilized by ultraviolet irradiation and dehydrothermal treatment, and their optimum conditions were determined. By sponging at 37 degrees C, partial denaturation of the collagen molecules resulted in shrinkage of the matrices.     

Thermal stability of myofibrillar protein from Indian major carps

The characteristics and stability of natural actomyosin (NAM) from rohu (Labeo rohita), catla (Catla catla) and mrigal (Cirrhinus mrigala) were investigated. The total extractable actomyosin (AM) was higher (7.60 mg ml^?1) in the case of rohu compared with that from catla and mrigal (5 mg ml^?1). Although the specific AM ATPase activity was similar (0.43–0.5 µmol P min^?1 mg P^?1) among the three species, the total ATPase activity was lower in mrigal (25 µmol g^?1 meat) compared with the other species (37 µmol g^?1 meat). The inactivation rate constants (k_d) of AM Ca ATPase activity showed differences in the stabilities of actomyosin among these fish, the actomyosin from catla being least stable. The NAM from these species was stable up to 20 °C at pH 7.0. Catla AM became unstable at 30 °C, while rohu and mrigal AM could withstand up to 45 °C. The thermal denaturation with respect to solubility, turbidity, ATPase activity, sulphhydryl group and surface hydrophobicity showed noticeable changes at around these temperatures. Copyright © 2004 Society of Chemical Industry