籼米为基质的脂肪替代品的凝胶性质

利用AR1000流变仪和TA．XTZI质构仪研究了籼米为基质脂肪替代品的凝胶性质。随着脂肪替代品的DE值的下降，胶凝温度上升，这表明DE值越低，可在较高的温度下形成凝胶；不同DE值脂肪替代品的凝胶强度随DE值降低而增加，相同DE值产品的凝胶强度随样品制备时酶水解温度升高而增强；并用凝胶过滤色谱测定了不同DE值脂肪替代品的分子量分布，从而在分子水平上探讨胶凝机理。     

不同温度下亚麻籽胶对肌原纤维蛋白凝胶特性的影响及机制

本实验研究了不同加热温度下,添加亚麻籽胶对肌原纤维蛋白保水性、凝胶强度、流变特性、二级结构、微观结构的影响及其作用机制。结果表明,随着温度升高,肌原纤维蛋白凝胶保水性显著下降（P＜0.05）,凝胶强度显著上升（P＜0.05）,加热温度高于50 ℃时添加亚麻籽胶显著提高了肌原纤维蛋白凝胶保水性（P＜0.05）,同时显著降低了凝胶强度（P＜0.05）;拉曼光谱结果表明随着温度从30 ℃上升至80 ℃,凝胶α-螺旋含量显著下降,β-折叠含量显著上升;添加亚麻籽胶使得肌原纤维蛋白存在α-螺旋含量下降,β-折叠含量上升现象,影响凝胶的形成及性质。流变学特性结果显示高于50 ℃时添加亚麻籽胶后肌原纤维蛋白储能模量G’下降。从微观结构发现,添加亚麻籽胶后肌原纤维蛋白在50 ℃出现更多凝胶孔洞,且在70、80 ℃时形成的凝胶三维网络结构更为致密均一。     

Curdlan: Properties and Application to Foods

Gel formation of curdlan at 100–130°C and behaviors of curdlan gels under frozen state were investigated by measuring gel strength and syneresis. Even when aqueous suspensions of curdlan were heated to 100°C or higher, they formed a gel, and gel strength increased with temperature. Curdlan gel was also stable against freezing and thawing. The syneresis of a 4% curdlan gel after freezing and thawing was reduced from 20.6% to about 2.1% by addition of 5% waxy corn starch and to 8.9% by addition of 20% sucrose. Suggested by these findings, new applications to foods have been developed, especially those subject to retorting and/or freezing.     

Improvement of pea protein gelation at reduced temperature by atmospheric cold plasma and the gelling mechanism study

Pea protein as an alternative of soy protein has attracted growing interest in food industries. However, high temperature (> 95 °C) is required to enable heat-induced gelation and the formed gels are relatively weak. This research aimed to study the efficacy of atmospheric cold plasma (ACP) as a novel non-thermal technique to improve the gelling properties of pea protein. While native pea protein concentrate (PPC) (12 wt%) could not form gel under 90 °C, ACP-treated PPC showed good gelling properties when heated at 70–90 °C. The gels exhibited homogeneous three-dimensional network structure with interconnected macropores, and those prepared at 80 and 90 °C possessed good mechanical strength and viscoelasticity, as well as high water holding capacity. The gelling mechanism was studied by monitoring pea protein structural changes during ACP treatment and gel formation process via a transmission electron microscope, a Fourier transform infrared spectrometer, and a rheometer. These results revealed that ACP treatment contributed to the formation of protein fibrillar aggregates, and significantly reduced the PPC denaturation temperature, leading to protein unfolding at reduced temperature of 80–90 °C. ACP treatment also increased the protein surface hydrophobicity and exposed free sulfhydryl groups, which could facilitate the formation of hydrophobic interactions and disulfide bonds, leading to gels with improved mechanical properties. Moreover, hydrogen bonding could play an important role to stabilize the gel network during the gelling process. Owing to the short exposure time and energy efficiency, ACP is a promising technology to enable wide applications to pea protein as a gelling ingredient of plant protein-based food products, such as meat analogues and egg alternatives.     

Gelation properties of salt-extracted pea protein isolate induced by heat treatment: Effect of heating and cooling rate

Gel network formation of a salt-extracted pea protein isolate was studied using dynamic rheological measurements. The gelling point was dependent on heating rate and was unaffected by cooling rate. When both the heating and cooling rates were increased (from 0.5 to 4 °C/min) final G′ value decreased, indicative of decreased gel strength. During the heating phase, the storage modulus and loss modulus fluctuated below 1 Pa at almost constant values with the storage modulus smaller than the loss modulus until the gelling point was reached. The rate of cooling has a greater impact on the development of storage modulus than that of heating. Compared to the gel strength of commercial pea protein isolate (PPIc) and soy protein isolate (SPIc) at the same protein concentration, salt-extracted pea protein isolate (PPIs) was much stronger than PPIc but weaker than SPIc. Careful control of the heating and cooling rates enable maximum gel strength for heat-induced pea protein gel, thus enhancing utilisation of pea protein as an additive in meat food industry.     

Slow lowering of pH induces gel formation of myosin

It has been found that solutions of myosin (10 mg/ml) form gels at 5°C if the pH is decreased slowly, by dialysis, to a value in the region of 2.5 to 5.5. Gel strength displays strong dependence on final pH, having a maximum at about pH 4.5. Salt (KCl) concentration was found to affect gel strength positively and linearly. Differential scanning calorimetry revealed that the myosin of pH-induced gels absorbed no thermal energy when heated, implicating acid-induced denaturation as the basis of gel formation. By comparison with heat-induced gelation of myosin and from the fact that low pH is conducive to filament formation, it is suggested that filaments may also be involved in the gelation process.     

谷氨酰胺转氨酶对山杏仁蛋白凝胶特性的影响

为提高山杏仁蛋白的凝胶特性,采用谷氨酰胺转氨酶(TG酶)作为交联剂,通过单因素实验研究了TG酶添加量、pH、交联温度、交联时间对蛋白凝胶硬度、弹性、内聚力的影响,并以凝胶强度为指标,利用响应面法对山杏蛋白形成条件进行优化。优化的TG酶交联山杏仁蛋白形成凝胶的条件如下:TG酶添加量17 U/g,交联温度43℃,pH为7.2,交联时间2.5 h时,此时凝胶硬度达到(135±7.14) g。结果表明利用TG酶交联山杏仁蛋白形成凝胶具有可行性,为提高山杏仁蛋白的功能性质和应用价值提供参考。     

低DE值麦芽糊精组成与凝胶性质研究

通过凝胶过滤色谱研究了不同DE值麦芽糊精分子量分布情况和分支化度,并在此基础上通过流变仪和质构仪测定凝胶温度和凝胶强度,研究了麦芽糊精的组成对其凝胶性质的影响.结果表明;随着DE值的增大,样品中高分子量聚合物的含量降低.使得样品的凝胶温度和凝胶强度呈现下降的趋势.同时也表明DE值在5左右的麦芽糊精由于其在常温下具有较好的凝胶性质,可以作为脂肪替代品应用于低脂食品中.     

SMALL AMPLITUDE OSCILLATORY TESTING (SAOT). APPLICATION TO PECTIN GELATION

The setting characteristics of pectin gels during cooling from 105°C to 25°C and reheating to above 100°C have been determined using a versatile food rheometer capable of small amplitude oscillatory testing. Gel strength development during cooling was linearly correlated to temperature and on reheating the gel softened initially then hardened again as the temperature exceeded about 70°C. The linear parameters (slope, intercept) describing the gel development on cooling were related to pectin concentration up to 0.85% but 1% pectin could not be distinguished from 0.85%. On cooling, 75–85% of the gel strength attainable on standing overnight was developed within 30 min. The quick set up on cooling provides the possibility of developing a rapid test method for determining pectin gel properties.     

Studies on fish and pork paste gelation by dynamic rheology and circular dichroism

ABSTRACT:  The muscle paste of fish, pork, and their mixtures were prepared to study the gelling characteristics by dynamic rheological measurement. The gelation mechanisms of muscle paste were also investigated by circular dichroism. Gel formation of fish paste occurred in 2 steps of 5 to 35 and 51 to 90 °C respectively, while pork paste mainly in 1 step of 49 to 72 °C. Gel formation was relative to the α-helix unfolding of myosin, which responded the melting temperatures of 40 and 50 °C for fish myosin and 50 and 60 °C for pork myosin, respectively. Alpha-helix unfolding of myosin was beneficial for gel formation. During gel formation, G ' of muscle paste was linearly related to α-helical content of myosin. The interactions of fish and pork proteins at high temperature (>35 °C) could change the gel forming characteristics of muscle paste. Mixed paste exhibited a similar gelation pattern to individual fish paste with 2 visible increases in G '. Addition of pork could suppress the breakdown of fish gel structure at approximately 50 °C. Mixing pork and silver carp in a certain ratio could improve the gel properties of silver carp products.     

Roles of components of rice-based fat substitute in gelation

The roles of maltodextrin, protein and fat in the gelation of the rice-based fat substitute were investigated. Rheological properties and gel strength of samples were measured. Results showed that the rising rates of both G′ and G″ of rice starch-based fat substitute were higher than those of rice-based fat substitute when temperature was lower than 35 °C. G′ was equal to G″ at 60 °C for 25% rice-based fat substitute whilst it was at 35 °C for rice starch-based fat substitute. The presence of rice protein and fat increased G′ and G″. Gel strength of rice-based fat substitute was lower than that of starch-based fat substitute at 25% solid content. However, gel strength of a fat substitute increased in the presence of protein. SEM showed that protein particles aggregated to gel. Therefore, protein in rice-based fat substitute gelled firstly, followed by maltodextrin which formed the main matrix of the rice-based fat substitute gel. Fat benefited for gel formation.     

Gel formation by β-conglycinin and glycinin and their mixtures

Gel formation and gel properties of β-conglycinin, glycinin and their mixtures were studied as a function of pH using small and large deformation rheology and differential scanning calorimetry. We conclude that heat denaturation is a prerequisite for gel formation. Gelation temperatures of β-conglycinin were lower than those of glycinin and more dependent on protein concentration. At pH 7.6, protein solutions gelled at a higher temperature than at pH 3.8.Glycinin gels were stiffer than β-conglycinin gels at the same pH and protein concentration, and fractured at a higher strain and stress. At pH 7.6, G′ is lower than at pH 3.8 for both proteins and the gels could be deformed to a larger extent. Based on the appearance of the gels (turbid at pH 7.6, white at pH 3.8) and the fracture properties, we conclude that different network structures are formed as a function of pH. The reason why glycinin gives a better gel than β-conglycinin is believed to be due to a difference in network structure as well as in strength of interaction between the protein molecules.Mixing of both soy proteins resulted in improved gelling properties at pH 3.8. The elastic modulus of the mixture was larger than the weighed sum of the separate contributions. Furthermore, mixing reduced the protein dispersability at pH 7.6. This strongly indicates the presence of an interaction between the proteins. Gels of the 1:1 mixture (pH 3.8) had a fracture stress and strain in between those of the gels of the separate proteins.     

魔芋葡甘聚糖复合凝胶网络结构的研究进展

凝胶是一种性质介于固体和液体之间的特殊分散体系,魔芋葡甘聚糖(KGM)凝胶稳定性差、强度低,物理共混能方便、快捷地改善其凝胶性质.主要综述KGM复合凝胶的网络结构变化,并介绍不同复合凝胶在食品、医药、材料工程等领域的应用.分析表明,KGM复合凝胶网络能通过氢键、席夫碱反应、形成多重网络结构和填充的方式改善其凝胶特性.     

TG酶对高温杀菌鱼糜凝胶特性影响

高温杀菌处理会造成淡水鱼糜凝胶品质劣化。以白鲢鱼糜为原料,通过测定质构特性、凝胶强度、持水性、白度和流变特性,研究谷氨酰胺转氨酶(TG酶)对高温杀菌鱼糜凝胶特性的影响。结果表明,添加TG酶所制得鱼糜凝胶经121℃,10 min高温杀菌后,硬度、弹性、持水性、白度及流变特性均有较好的改善。与对照组相比,添加0.5%TG酶的鱼糜凝胶强度增加48.7%。红外光谱测定结果表明,TG酶的加入有利于蛋白质α-螺旋结构的维持,减少蛋白主要二级结构破坏,使鱼糜制品维持良好凝胶结构。     

Variable effects on egg yolks and yolk lipoprotein fractions of feeding methyl sterculate to hens: Periodic changes in lipid composition and gelation temperature

As part of a study of the reasons for the large effects of a small dietary supplement of methyl sterculate on the physical properties and lipid composition of hen's egg yolk, individual yolks from sterculate-fed hens have been examined. These yolks set to a firm gel on cooling in the range 20-0 °C, but there were large variations in eggs from different hens that were accompanied by variations in the proportion of saturated fatty acid residues in the yolk lipids. Gel formation was reversible on immediate rewarming but prolonged storage at low temperature caused irreversible alterations. Diluted yolk showed analogous changes in viscosity on cooling and provided a convenient model system for examining the effect of pH, ionic strength, and the action of trypsin. From these results it is concluded that the protein of the high-lipid low-density lipoprotein of yolk is directly involved in the gelation of the yolk. A series of eggs laid by one sterculatefed hen over 30 days showed large and possibly periodic variations in the lipid composition and gelation temperature of the yolks. These results and some data from other hens suggested that large variations in yolk properties accompany a high response to sterculate feeding.     

Modification of pork-skin jelly by enzymatic cross-linking: melting resistance and quality improvement

Improvements of melting resistance and quality by modification of pork-skin jelly through enzymatic cross-linking were studied, and the mechanism of quality improvement was discussed in this work. Gel strength, springiness and chewiness of modified gel increased significantly (P < 0.05). Transglutaminase (TGase) also improved the viscoelasticity, stability and melting resistance of gel system, as proved by rheological analysis. Sensory evaluation showed that increase in texture need to be moderate and the utilisation of 0.6% TGase was the most appropriate for pork-skin jelly. Significant effects of TGase on inducing protein cross-link and aggregation were confirmed by determining rheology during enzyme treatment and cross-linking extent of pork-skin soup. Correlation analysis showed TGase could improve melting temperature and texture by facilitating cross-linking. Covalent interaction based on ε-(γ-glutamyl)-lysine induced by TGase could play the main role in these improvements. This study suggested that TGase could be applied to design gelatin-based food for tailored quality properties through enzymatic cross-linking.     

Heat-induced gelation of actomyosin

Rheological properties of actomyosin gels were markedly affected by protein concentration, pH and heating temperature. Gel strength increased with increasing protein concentration (30-60 mg ml(-1)) and heating temperature (55-75°C), but decreased with increasing pH (5·5-9·0). Low heating temperatures (50-55°C) favoured the formation of more cohesive actomyosin gels than the higher heating temperatures (60-75°C). Gels formed at low pH (5·5 and 6·0) were less cohesive than those formed at high pH (7·5-9·0). Addition of ATP and pyrophosphate (10 mm) prior to heating decreased gel strength and cohesiveness, whereas EDTA (1-5 mM) reduced gel strength but did not affect gel cohesiveness.     

Factors Influencing Gel Formation by Myofibrillar Proteins in Muscle Foods

Abstract: Considerable research has been done to better understand the basis for gel formation by myofibrillar proteins (MPs) in effort to manufacture acceptable processed meats with lower cost and more desirable nutritional characteristics. Results from research available indicate that there is no substitute for the myofibrillar protein myosin in gel formation by proteins from a wide variety of animal and fish species. This report consolidates information on determinants of protein gel formation, examining types of muscles and fibers, the species influence, and interactions of the MPs actin and myosin with each other and with fat, gelatin, starch, hydrocolloids, some protein soy, whey, and nonprotein additives such as phosphates and acidifiers, and the influences of pH, ionic strength, rates of heating, and its absence, protein oxidation, as well as the use of transglutaminase and high hydrostatic pressure. It is of interest that myosin alone will form acceptable gels. Gel formation by MPs is optimized at pH 6, an ionic strength of 0.6 M, and at 60 to 70 °C. The observations that collagen‐derived gelatin can reduce the rubbery texture of low‐fat products and that solubilization of MPs is not always essential for gel formation, and the observation that good gels can be formed in the absence of salt, are exciting developments that should be considered as pressure mounts to continue to reduce fat and salt in the diet.     

Gelation behaviour of gelatin and alginate mixtures

Mixtures of alginate and gelatin were studied by rheology as a function of different parameters, such as temperature, biopolymer concentrations, calcium concentration and ionic strength. In particular conditions, the formation of a mixed gel of alginate and gelatin is obtained. A slow release of calcium ions leads first to an irreversible alginate gel and cooling results in a reversible gelatin gel. Depending on experimental conditions, non-linear behaviours upon gelation of alginate occur and a collapse of alginate gel is directly observable by rheology. These trends are favoured between 35 and 45 °C, by a high total biopolymer concentration or a high calcium concentration and ionic strength. Different mechanisms could be responsible for this collapse, such as a competition between alginate gelation and phase separation in the biopolymer mixture or an over-association of alginate chains at high Ca²⁺ concentration, favoured by the presence of gelatin.     

超声波处理对大豆分离蛋白凝胶流变性和凝胶形成的影响

为探讨超声波处理对大豆分离蛋白(Soybean protein isolate,SPI)凝胶特性的影响,以商用SPI为试验原料在不同功率(100、200、400、600、800 W)下进行超声处理,利用TA流变仪的小振幅振荡剪切模式,分析对其流变特性和凝胶形成的影响。结果表明,超声波降低了SPI分散液的储能模量(Storage modulus,G')、损耗模量(Loss modulus,G″)以及表观黏度,改变了其起始黏弹性。模拟SPI热凝胶过程试验结果表明,超声处理能够改变SPI胶凝能力。低功率减弱SPI凝胶形成能力;高功率则延迟凝胶的形成;中功率(200~600 W)超声可以显著改善SPI凝胶性能,加速凝胶形成。中功率超声波处理明显提高了SPI凝胶黏弹性能,且400 W超声组的效果最佳,其形成的凝胶具有最大的G'、G″和最小的损耗因子(Loss tangent,tanδ)。因此适当功率的超声波可以增强商用SPI的凝胶性能。