醇法大豆浓缩蛋白（SPC）挤压组织化机理（Ⅱ）──蛋白质变性热力学的差示扫描量热分析法

采用差示扫描量热法分析大豆蛋白的变性热力学性质。在热变性过程中，醇法大豆浓缩蛋白的结构刚性大、次级键断裂程度低。水对蛋白质的热变性具有一定的促进作用。随着蛋白质水分含量的提高，其热变性温度（Ｔｄｅ）降低。根据这些性质，经调整醇法大豆浓缩蛋白的ｐＨ值使其热变性焓差（ΔＨｄ）增大，可实现其挤压组织化。所得挤出物的物理性质及其流变特性均有明显改善。     

酱油熟料消化中蛋白质热变性的研究

综述了酱油生产过程中蛋白质热变性机理及蛋白质热变性的变性种类及相关观点，通过蒸煮压力、时间、加水量、对酱油熟料消化中蛋白质的消化率、二级蛋白衍生物等的影响进行检测，研究蛋白质热变性对酱油生产的影响。     

醇法大豆浓缩蛋白（SPC）挤压组织化机理（Ⅱ）：蛋白质变性热力学的差…

采用差示扫描量热法分析大豆蛋白的变性热力学性质。在热变性过程中，醇法大豆浓缩蛋白的结构刚性大、次级健断裂程度低。水对蛋白质的热变性具有一定的促进作用。随着蛋白质水分含量的提高，其热变性温度（Ｔｄｅ）降低。根据这些性质，经调整醇法大豆浓缩蛋白的ｐＨ值使其热变性焓差（△Ｈｄ）增大，可实现其挤压组织化。所得挤出物的物理性质及其流变特性均有明显改善。     

蛋白溶解性分析法研究大米焙炒过程中蛋白质热变性行为

考察了焙炒过程中大米蛋白质的热变性行为,通过大米蛋白在不同功能溶剂中的溶解度变化了解大米蛋白质在焙炒过程中次级结构的变化及热变性信息。发现热变性主要发生在焙炒的前期,热变性包括蛋白质次级结构的变化和更高能级的化学变化。与传统蒸煮方法相比,焙炒大米的蛋白质热变性程度较低。粳米和糯米中的蛋白质热变性行为基本相似,选用不同的加热介质对大米蛋白的热变性没有影响。     

油发干货原料蛋白质热变性三步曲

蛋白质的热变性作用,是蛋白质的通性,即蛋白质在热的作用下,结构发生改变,性质发生了变化,且不能再恢复为原来的蛋白质.     

食品中蛋白质力学性质的研究进展

蛋白质对食品的色、香、味及组织结构等具有重要意义。近年来,越来越多的研究发现蛋白质的力学性质有助于改善食品的营养、风味、口感、质地。本文综述了食品中蛋白质的力学性质及其影响因素,阐述了蛋白质结构、功能与作用力之间的关系,蛋白质分子内和分子间相互作用力的改变导致蛋白质三维结构发生变化,进而影响其功能。分析了由热诱导产生的蛋白质分子内的力学性质,包括蛋白质折叠热力学稳定性和蛋白质解折叠的动力学性质,以及由热剪切产生的蛋白质分子间的粘弹性和力学强度。总结了影响蛋白质力学性质的主要因素,包括蛋白质溶液系统的自由能、蛋白质的构象、溶剂与外界环境条件、机械力的拉伸等。提出了蛋白质的力学性质对食品品质的调控具有参考价值,并对食品中蛋白质的加工与新产品的开发前景作出展望。     

鱼肉蛋白的热变性研究进展

在鱼肉蛋白的加工过程中,加热处理是最常见的工序之一。热处理造成的蛋白热变性会对蛋白质的理化性质和功能特性产生很大的影响,且这种影响多难以复原。本文总结了近几年来国内外关于鱼肉蛋白在加热过程中蛋白组成成分、总巯基和羰基、溶解度、浊度、黏度、Ca2+-ATPase活性、凝胶、质构等特性指标的变化趋势的研究进展,结合蛋白质热变性的机理深入分析其变化原因,提出今后在鱼类加工方面对于鱼肉蛋白热变性的研发方向,旨在为鱼制品选择合理的热加工工艺的提供理论依据。     

蛋白质热聚集行为机理及其对蛋白质功能特性影响的研究进展

蛋白质热聚集行为是食品加工过程中较常发生的现象。热处理条件会使蛋白质结构发生变化,引起蛋白质的理化性质的改变,从而导致蛋白质发生热聚集。热聚集体的大小、形态、界面性等直接影响蛋白质凝胶特性、溶解性、起泡性、乳化性等功能特性,从而影响富含蛋白质食品的品质。本文介绍了蛋白质热聚集行为的机理、分类和表征手段,重点综述了蛋白质热聚集行为的影响因素,及蛋白质热聚集行为对蛋白质功能特性的影响,为研究复杂蛋白质体系热聚集行为及对食品品质的影响提供理论基础。     

预热变性程度对大豆蛋白凝胶性质的影响

以非还原SDS-PAGE表征大豆蛋白的预热变性程度,并采用质构分析、流变分析研究预热变性程度对大豆蛋白凝胶性质的影响。SDS-PAGE结果表明,随着加热温度的升高蛋白质变性速率逐渐增大,相同加热时间条件下,蛋白质变性程度随加热温度升高呈S型曲线上升。质构、流变分析结果表明:随着预热变性程度的增大,大豆蛋白凝胶硬度先增大后减小,变性程度为86.11%时凝胶硬度最大,是未经预热变性的大豆蛋白凝胶硬度的2.15倍;凝胶弹性则随预热变性程度的增大持续增大;变性程度在22.28%以上时大豆蛋白形成凝胶更快,但完全变性大豆蛋白在形成凝胶时的降温阶段不能形成很好的凝胶结构。粒径分析结果表明,预热变性程度对大豆蛋白凝胶性质的影响与蛋白质预热变性时形成的聚集体尺寸及形态有关。     

热处理对大豆11S球蛋白溶解性和二级结构的影响

采用差示扫描量热仪、Lowry法以及傅里叶变换红外光谱法分别对大豆11S球蛋白的热性质、溶解性和二级结构进行测定与分析,研究热处理对11S球蛋白溶解性和二级结构的影响。热处理能够使大豆11S球蛋白Td和ΔH降低,导致蛋白质发生部分或完全变性。80?℃热处理使大豆11S球蛋白的溶解性降低,这可能由于热处理改变了蛋白质的空间结构和表面电荷所致,此时蛋白质的α-螺旋结构逐渐转变为β-折叠和无规卷曲结构。而90?℃和100?℃热处理一定时间后,蛋白质溶解性又稍有升高,这可能是形成可溶性聚集体造成的。此时蛋白质的α-螺旋和β-折叠结构向β-转角和无规卷曲结构转变,表明β-转角和无规卷曲结构对热聚集体的形成具有重要作用。此外,蛋白质变性和氢键断裂是导致二级结构相互转变的重要因素。     

Analysis of the effects of thermal protein denaturation on the quality attributes of sous‐vide cooked tuna

Traditional (low temperature, long time) and novel (low temperature, short time) sous‐vide cooking of lean tuna were characterized by analyzing the effects of thermal protein denaturation (TPD) on quality attributes, such as color, appearance, shrinkage, drip loss, and texture. TPD was analyzed by differential scanning calorimetry and estimated for several thermal schedules by kinetic analysis, following the dynamic method. When heated at a rate of 10 °C/min, myosin began to denature at around 35 °C. Actin did not denature, even when the temperature rose to approximately 51 °C, until the denaturation of myosin was complete. However, actin began to denature at approximately 58 °C and was completely denatured at 76 °C. Actin denaturation had a stronger effect than myosin denaturation on texture changes, whereas myosin denaturation was responsible for changes in color and appearance. A better preservation of tuna quality was obtained by novel sous‐vide cooking over the traditional sous‐vide method.

Practical applications

The results of this study are useful to both the research community and industry because they provide quantitative characterization of the consequences of sous‐vide cooking method on food quality explained by estimating TPD. Moreover, the kinetic parameters of the denaturation rate collected for kinetic modeling of the TPD of tuna, not only have application to simulate denaturation of actin and myosin under different thermal schedules of sous‐vide cooking, but also they can be used for the analysis of additional thermal treatments.     

A morphological and biochemical examination of the hydrothermal denaturation of collagen

The morphological changes occurring during the hydrothermal denaturation of collagen obtained from the tendinous sheath of the longissimus dorsi muscle of mature sheep have been examined. To investigate the influence of the physical state of the collagen on its subsequent denaturation, collagen has been heated in the form of isolated fibrils, small pieces of unrestrained tissue and strips of tissue restrained from contracting fully during heating and cooling. The morphological changes occurring during denaturation and the thermal stability of the collagen to melting have been found to be dependent on the physical state of the collagen, the thermal stability of collagen being lowest in isolated fibrils, intermediate in unrestrained pieces, and highest in restrained samples. In conjunction with the morphological studies, the extent of dissolution of collagen by heat alone and the susceptibility of collagen to pronase digestion were measured and examined as possible biochemical criteria for assessing the extent of thermal denaturation of collagen.     

Thermal stability of beta-lactoglobulins A and B: effect of SDS, urea, cysteine and N-ethylmaleimide

Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were used to monitor changes in the secondary structure and thermal stability of beta-lactoglobulin A and B in the presence of sodium dodecyl sulphate (SDS), N-ethylmaleimide (NEM), urea and cysteine. An increase in the thermal stabilities of both proteins was noted in the presence of 10 mM-SDS. In the presence of 50 mM-SDS, there was extensive denaturation of both variants. In general, the beta-strand/beta-sheet regions in the secondary structure of both variants were very susceptible to denaturation by SDS and cysteine, suggesting that these regions may be held by hydrophobic and disulphide bonds. At ambient temperature and physiological pH, a notable difference was observed in the 1636 and 1627 cm(-1) regions of the FTIR spectra of the two beta-lg variants. The results suggest possible differences in the nature of the beta-sheet/beta-strand distribution/ content of the two proteins. Urea and NEM at a concentration of 50 mM, had little effect on the secondary structure and denaturation of both variants. New findings are presented which further indicate that although the beta-lg B variant showed greater thermal stability than the A variant in all the cases studied, its denaturation temperature and secondary structure were affected to a greater extent by the protein perturbants than beta-lg A.     

Suppression of thermal denaturation of myosin and salt-induced denaturation of actin by sodium citrate in carp (Cyprinus carpio)

The effect of sodium citrate (Na-citrate) on myosin and actin denaturation in myofibrils was investigated. Na-citrate significantly suppressed the thermal inactivation of Ca²⁺-ATPase of carp myosin in a concentration-dependent manner. The effect was greater than that of sorbitol. A similar effect was observed with myofibrils in which myosin is stabilized by F-actin binding. Na-citrate dissolved myofibrils at lower concentration than NaCl. Nevertheless, Na-citrate at 1 M failed to denature F-actin in myofibrils, while 1 M NaCl denatured F-actin almost completely. Na-citrate suppressed the NaCl-induced F-actin denaturation. Sorbitol did not show such protective effect on F-actin denaturation. Moreover, Na-citrate suppressed the freeze denaturation of myofibrils at lower concentration than sorbitol. Thus, Na-citrate was proved to be superior to sorbitol. It was suggested that Na-citrate alone could substitute sorbitol as cryoprotectant in surimi and NaCl as dissolving reagent of myofibril in thermal gel production.     

Effect of thermal treatment on the proteins of amaranth isolates

The effect of thermal treatment of proteins from Amaranthus hypochondriacus was studied. Two protein isolates were obtained from the defatted flour by water extraction at a pH of 9 (A9 isolate) and 11 (A11 isolate), followed by isoelectric precipitation at a pH of 5. Effect of thermal treatment (70 and 90 °C, during 3, 5, 10, 15 and 30 min) on A9 and A11 dispersions were analyzed by differential scanning calorimetry (DSC), polyacrylamide gel electrophoresis, UV spectrophotometry, superficial hydrophobicity and solubility in water. Thermal treatment induced the aggregate formation of high molecular mass stabilized by disulfide and non‐covalent bond. Thermal treatment at 70 °C produced a 30% denaturation in both, while at 90 °C A9 was more denatured than A11 (75% and 55% of denaturation, respectively). An increase in thermal stability was also detected by DSC in A9 treated at 90 °C. The denaturation process was accompanied at short heating times by an increase in UV absorbance and changes in superficial hydrophobicity. A decrease in water solubility (35–50%, depending on time–temperature conditions) was also observed for the A9 isolates. The results suggest that the A9 isolates, enriched in a globulin protein fraction, are more sensitive to thermal treatment than isolates A11 enriched in glutelin protein fraction. The changes shown by both isolates, indeed, could affect their functional properties and could definitely limit their use in food products. Copyright © 2007 Society of Chemical Industry     

NMR relaxometry and differential scanning calorimetry during meat cooking

By combining simultaneous nuclear magnetic resonance (NMR) T₂ relaxometry and differential scanning calorimetry (DSC) on pork samples heated to nine temperature levels between 25 and 75 °C, the present study investigates the relationship between thermal denaturation of meat proteins and heat-induced changes in water characteristics. Principal component analysis (PCA) on the distributed ¹H NMR T₂ relaxation data revealed that the major changes in water characteristics during heating occur between 40 and 50 °C. This is probably initiated by denaturation of myosin heads, which however, could not be detected in the DSC thermograms obtained directly on the meat. In contrast, the DSC thermograms revealed endothermic transitions at 54, 65 and 77 °C, probably reflecting the denaturation of myosin (rods and light chain), sarcoplasmic proteins together with collagen and actin, respectively. Simultaneous modelling of DSC and NMR data by partial least squares regression (PLSR) revealed a correlation between denaturation of myosin rods and light chains at 53–58 °C and heat-induced changes in myofibrillar water (T₂ relaxation time 10–60 ms) as well as between actin denaturation at 80–82 °C and expulsion of water from the meat. Accordingly, the present study demonstrates a direct relationship between thermal denaturation of specific proteins/protein structures and heat-induced changes in water mobility during heating of pork.     

羊血中超氧化物歧化酶提取工艺研究——热变温度、热变时间和热变方式对SOD提取的影响及最佳工艺条件选择

目的:重点研究热变温度、热变时间、热变方式对SOD分离提取的影响,确定最优工艺参数。方法:采用正交试验设计。由正交试验得出最优组合为A2B2C2,即热变温度55℃,热变时间15min,0.01mol/lCuCl2的添加量2%。结论:热变性是羊血SOD提取的关键,按此工艺热变性后的SOD活性在1000U/mg蛋白以上。     

Studies on the Effect of Ethanol on Thermal Denaturation of Soybean Globulins by Differential Scanning Microcalorimetry

Scanning microcalorimetry has been used to study the effect of ethanol on thermal denaturation of soybean globulin fraction (SBGF) at pH 6.7 in the range of protein and ethanol concentrations from 0.4 to 4% and from 0 to 3.2M, respectively. The denaturation temperatures of the SBGF components decreased linearly with the increase of ethanol concentration. The specific denaturation enthalpy of SBGF did not depend upon protein and ethanol concentrations. A direct correlation between the slope of the dependence of denaturation temperature on ethanol concentration and the ratio of the square of denaturation temperature and the specific denaturation enthalpy of these proteins was shown.     

Relationship Between Thermal Denaturation of Porcine Muscle Proteins and Water-holding Capacity

ABSTRACT: Differential scanning calorimetry was used to investigate denaturation characteristics of pork muscle proteins from carriers and noncarriers of the RN-gene. Pork from RN-carriers deviated from noncarriers in maximum denaturation temperatures and denaturation enthalpy, with proteins of RN-carriers being the most heat-labile. Correlation studies on the results showed that water-holding capacity was significantly correlated to changes in enthalpy of the population mainly representing myosin tails and sarcoplasmic proteins (p < 0.001). Finally, the influence of ultimate pH and preheating on thermal characteristics of porcine muscle proteins was studied. Myosin tails and sarcoplasmic proteins were most sensitive to pH changes, while myosin heads were most sensitive to preheating simulating stress-induced temperature increases.