食品中蛋白质―多糖混合体系研究进展

蛋白质与多糖是食品中共存两类重要大分子物质,该文介绍食品中蛋白质―多糖混合体系凝胶特性、表面特性等研究概况及电解质、蔗糖、pH值等外部因素对蛋白质―多糖混合体系影响。     

多糖/蛋白质复合体系相转变及其在食品中的应用

多糖/蛋白质体系相行为的调节和控制一直被认为是食品领域的重要课题,同时也是重大挑战。因为它在很大程度上决定了食品的结构、稳定性、口感等重要性质。然而大多数蛋白质/多糖复合体系对于外界环境的干预均表现出很强的敏感性,相转变较易发生且较难控制。综述了影响多糖/蛋白体复合系相行为转变的因素、热动力学及与食品微结构之间的关系,并对其相转变在食品中的应用进行了阐述,最后对从蛋白质/多糖复合体系的相行为调控食品结构和构建新型食品进行了展望。     

多糖-蛋白质复合水凝胶研究进展

多糖和蛋白质是食品中最重要的2种功能大分子,可以通过相互作用形成复合水凝胶。与单一组分相比,多糖和蛋白质形成的复合水凝胶不仅具有优异的物理结构和化学性质,而且具有提高复合体系机械性能的潜在优势。该文对部分多糖-蛋白质复合水凝胶的研究进展进行总结,综述了形成复合水凝胶的多糖及蛋白质的类型和条件、二者主要相互作用及影响二者相互作用的内部和外部因素,阐述了多糖对其与蛋白质形成复合水凝胶机械性能的影响,并概述了多糖-蛋白质复合水凝胶在食品工业及生物医药等领域的应用现状。该文将为多糖-蛋白质基创新凝胶的设计、开发及应用提供理论参考依据。     

大豆蛋白/葡聚糖混合体系相行为及流变性质的研究

研究了室温下,pH 7.0时不同尺寸大小的大豆蛋白热聚集体和不同分子质量的葡聚糖混合体系的相分离行为,并以天然大豆蛋白和葡聚糖混合体系作为对照体系。通过离心、化学分析和目测建立了相图,结果表明两种大分子的相分离是由于葡聚糖分子链的排空相互作用,使得蛋白质富集部分间产生了交联;蛋白质聚集体的尺寸和葡聚糖的分子质量大小同时影响了混合体系的相行为,随着蛋白质粒子增大或多糖分子质量增加,相边界发生了位移,混合体系的均相区域变窄,凝胶区域增大。流变研究进一步证明蛋白质聚集体的尺寸和葡聚糖的分子质量大小同时影响了相分离体系的微观结构。     

蛋白质/多糖自组装及其应用

蛋白质和多糖,作为食品体系中最为重要的两种大分子,其自组装行为不仅影响食品品质,还在营养、药物递体系及软材料构建等方面有着广泛的应用。介绍蛋白质/多糖主要的自组装形式,包括复合物、纳米凝胶等,并简介蛋白质/多糖自组装在食品及其它领域的应用。     

天然生物大分子及其复合物在食品微凝胶传递体系中的应用研究进展

微凝胶是一种内部交联的纳米或微米级粒子,能形成三维网络结构,可作为食品功能因子的递送载体。本文综述了适用于制作微凝胶的两大类天然生物大分子：蛋白质和多糖。介绍了常见的几种不同来源蛋白质和多糖的组成结构及胶凝特性,综述了天然生物大分子在食品传递体系中应用的最新进展,探讨其在食品微凝胶制备中的潜在价值及未来研究热点。     

蛋白-多糖复合凝胶性质及微观结构研究进展

蛋白质和多糖是食品中重要的组成成分,蛋白-多糖复合凝胶性质对食品品质有重要影响,因而其营养功能品质受到广泛的关注。本文综述蛋白-多糖复合凝胶体系构建技术、流变学性质以及复合凝胶形成过程中微观结构变化及应用,提出目前存在的问题并展望未来,旨在为富含多糖蛋白食品的精准开发与品质调控提供依据。     

蛋白质-多糖相分离性质及其研究进展

食品中两种主要成分蛋白质和多糖相分离行为对食品体系结构和质构具有重要作用。该文介绍蛋白质和多糖相分离性质原理及研究现状和意义,可通过控制体系的相分离行为而得到想要食品结构。     

蛋白质和多糖在界面处的相互作用研究进展

蛋白质和多糖两种生物大分子在界面处的相互作用对于乳状液和泡沫体系有显著影响。蛋白质和多糖混合后的协同效应可构建新的、功能性的纳、微或宏观结构,改变食品的力学和流动特性,对改良食品,降低生产成本具有重要意义。本文对近年来蛋白质的界面行为,多糖的界面行为以及蛋白质-多糖复合物的界面行为所做的一些研究进行综述。     

大豆蛋白组分与κ-卡拉胶混合凝胶的流变学研究

对κ-卡拉胶与大豆蛋白组分glycinin (11S)混合体系的凝胶流变学性质进行了研究.结果表明:κ-卡拉胶与glycinin形成的蛋白质多糖混合凝胶相对单一浓度的κ-卡拉胶或单一浓度的glycinin凝胶而言具有较高的弹性模量;随着体系中卡拉胶浓度增加,蛋白质多糖混合凝胶的弹性模量逐渐增加;不同钠离子强度对体系的凝胶强度影响不同.TPA测定结果表明,蛋白质多糖混合凝胶的硬度和弹性值随变性的glycinin浓度增加而增大.     

Microstructural features of composite whey protein/polysaccharide gels characterized at different length scales

Mixed biopolymer gels are often used to model semi-solid food products. Understanding of their functional properties requires knowledge about structural elements composing these systems at various length scales. This study has been focused on investigating the structural features of mixed cold-set gels consisting of whey protein isolate and different polysaccharides at different length scales by using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). Whey protein cold-set gels were prepared at different concentrations to emulate stiffness of various semi-solid foods. Mixed gels contained different concentrations of gellan gum, high methyl pectin or locust bean gum. Results obtained with CLSM, at the micrometer length scale, indicated the homogeneous nature of the investigated gels. Results obtained with SEM, at the sub-micron length scale, indicated the presence of spherical protein aggregates. During the gel preparation (acidification), the presence of polysaccharides in the whey protein gels led to on initially segragative phase separation into a gelled protein phase and a polysaccharide/serum phase at a micrometer length scale. At the final pH of the gels (pH 4.8, i.e. below the pI of whey proteins), the negatively charged polysaccharides interacted with the protein phase and their spatial distribution was effected by charge density. Polysaccharides with a higher charge density were more homogeneously distributed within the protein phase. Neutral polysaccharide, locust bean gum, did not interact with the protein aggregates but was present in the serum phase. Using SEM, a new type of microstructure formed in the whey protein/polysaccharide gels was characterized. It composed of a protein continuous, porous network at the length scale of 100 μm, coexisting next to the pools of serum which contained spherical protein-rich domains. Heterogeneity of the structure strongly related to the macroscopic behavior of the gels under large deformation. Upon uniaxial compression these heterogeneous gels releases a large amount of serum. Combination of the results of two microscopic techniques, CLSM and SEM, appeared to offer unique possibilities to characterize the structural elements of whey protein/polysaccharide cold-set gels over a wide range of length scales.     

Effects of enzymatic modification of soybean protein on the pasting and rheological profile of starch–protein systems

Reformulation of traditional food systems to introduce new ingredients may change their structure and perceived texture. Interactions between proteins and starch during processing can markedly influence starch gel network structure and rheological profile. The present work aimed to study the effects of soybean protein and the products of enzymatic modification on the pasting and rheological profile of corn and cassava starch. The behavior of those protein‐enriched gels during storage was also assessed. Soybean protein isolate (SPI) was incubated with endopeptidase (AL) or food grade microbial transglutaminase (TG). Pasting and rheological behavior, water retention capacity, and structure of protein– and hydrolyzed protein–starch gels were analyzed. Protein incorporation increased the viscosity of starch suspension during and after heating. SPI‐modified proteins increased peak viscosity. Only the structural modifications brought by TG on SPI increased the final viscosity during starch pasting and the storage modulus (G′). This modulus (G′) of the gelled systems decreased with the addition of AL‐treated protein isolate. Light and fluorescence microscopy showed that SPI formed a continuous phase, like a network, in the gelled system. Different network structures and rheological properties can be obtained when SPI are modified by protease and TG enzymes, which may be very useful for designing new food products.     

Combining protein micro-phase separation and protein–polysaccharide segregative phase separation to produce gel structures

The ability of protein micro-phase separation and protein–polysaccharide segregative phase separation to generate a range of gel structures and textures was evaluated. Whey protein isolate/κ-carrageenan mixed gels were prepared with 13% (w/v) whey protein isolate, 0–0.6% (w/w) κ-carrageenan and 50, 100 or 250 mM NaCl. The microstructure of gels, determined by confocal laser scanning microscopy, varied from homogenous to protein continuous, bicontinuous, coarse stranded or κ-carrageenan continuous, depending on the κ-carrageenan concentration. Microstructure also varied from stranded to particulate (micro-phase separated) depending on the salt concentration. The rheological behavior of mixed gels corresponded to the shift in the continuous phase from protein to κ-carrageenan. At small concentrations of κ-carrageenan, where carrageenan-rich droplets were dispersed in a continuous protein-rich matrix, gel strength (fracture stress) and firmness (G′) increased due to increased local concentration of proteins caused by phase separation. At higher κ-carrageenan concentrations, gels were substantially less firm, weaker and less deformable (fracture strain). The change in the continuous phase from protein continuous to carrageenan continuous explained the major change in mechanical properties and water-holding properties. The shift in microstructure occurred at lower concentrations of κ-carrageenan when whey proteins were under micro-phase separation conditions. The results demonstrated how the combined mechanisms of ion-induced micro-phase separation of proteins and protein–polysaccharide phase separation and inversion can be used to alter gel structure and texture.     

Improvement and modification of whey protein gel texture using polysaccharides

Whey proteins (WP) and polysaccharides are two gelling biopolymers used in the food industry for their wide range of rheological and textural properties. Mixed gels containing more than one gelling agent are usually classified into three types: interpenetrating, coupled, and phase-separated networks. Large deformation behavior of whey protein gels mixed with polysaccharides is presented. pH, and the concentration and nature of the cations added in the system, affect both protein and polysaccharide gels. These factors will also modify the mixing behavior of protein-polysaccharide solutions. The effect of cations and pH are respectively explained using WP/κ-carrageenan and WP/pectin systems. Under the conditions studied, two types of mixed systems were obtained: one with two gelling biopolymers (WP/κ-carrageenan), and the other where protein is the only gelling biopolymer (WP/pectin). Conditions favoring incompatibility can lead to spherical inclusions of whey protein.     

THE RHEOLOGY OF GELS

The following aspects of the rheological behavior of polysaccharide and protein gels are discussed with particular emphasis on recent investigations: (1) Viscoelasticity of gels; (2) Validity of rubber elasticity theory; (3) Rupture strength of gels; and (4) Single-point measurements of gel strength.
It is concluded that in contrast to most food materials gels show linear viscoelastic behavior up to strains of the order of 0.1. Results obtained from creep and stress relaxation experiments would suggest that noncovalent crosslinks in gels move or break when the gel is stressed. Activation energies associated with crosslink breakage have been estimated from the temperature dependence of viscoelastic parameters. For gelatin and polysaccharide gels energies ranging from 5–65 Kcals/mole have been reported.
The stiff and extended nature of polysaccharide chains make it unlikely that polysaccharide gels obey rubber elasticity theory, though it is possible that this theory holds for gelatin gels and also for ovalbumin gels in 6 M urea.
It is emphasized that the rupture strength of a gel is not necessarily related to its elastic modulus and therefore 'single point' measurements of 'gel strength' based on rupture tests will not always rank a series of gels in the same order as tests which involve small deformations without rupture. One of the reasons for this is that the elastic modulus and rupture strength depend in different ways on the primary molecular weight of the polymer from which the gel is formed.     

Evaluation of the effect of Gleditsia amorphoides gum on the properties of rennet-induced milk protein gels

The study and characterisation of food gels obtained from phase-separated systems has gained interest since a wide variety of gel structures and textures can be developed. In this study, the phase and rheological behaviour of milk protein/espina corona gum (MP/ECG) mixtures were evaluated. These mixtures presented a segregative phase separation and a rheological behaviour proportional to the ECG concentration. Microstructural analysis, textural parameters and water-holding capacity of gels obtained from MP/ECG mixed systems using rennet as gelling agent were determined. At high ECG concentrations (≥0.05%, w/v), the gel microstructure changed from a coarse strand to a bicontinous microstructure. Such microstructural changes affected the textural parameters, firmness and break point, and the water-holding capacity of the gels. The results obtained in this work could be explained by the interplay between the segregative interaction of the biopolymers and the rennet-induced gelation rate.     

Mixed gels of fine-stranded and particulate networks of gelatin and whey proteins

Mixed gels of gelatin and whey protein concentrate were investigated, as well as their pure systems, by tensile tests and by dynamic oscillatory measurements. The systems were studied for homogeneous particulate whey protein gels at pH 5.4 and for inhomogeneous particulate whey protein gels at pH 4.6. The influence on the systems of the Bloom number of the gelatin component has also been investigated. Results of the fracture properties, such as stress and strain at fracture, indicate a transition in rheological properties. Results of the elastic modulus, obtained by tensile measurements, as well as the storage modulus, obtained by dynamic oscillatory measurements, both agree with predictions for phase inversions from the Takayanagi models as modified by Clark, which are in agreement with the fracture properties. The transition points are different for the different mixed gel series but take place between 1 and 3 wt% gelatin and 8 wt% whey protein concentrate, depending on factors such as the microstructure of the whey protein concentrate. Dynamic oscillatory measurements showed that gel formation of whey protein concentrate is unaffected by the presence of gelatin, which is in agreement with light microscopy results. Light microscopy revealed that the mixed gel systems were bicontinuous and that the whey protein network structure was unaffected by the presence of gelatin. It is postulated that the predicted phase inversions of the mixed gels are due to a shift in rheological properties without any phase inversions in the microstructure.     

Impact of phase separation of whey proteins/hydroxypropylmethylcellulose mixtures on gelation dynamics and gels properties

This work constitutes a study of the impact of phase separation behaviour on the gels properties of a low viscosity hydroxypropylmethylcellulose and whey protein concentrate (WPC) mixed system. The phase separation was characterized by drawing the limit of thermodynamic compatibility, i.e. binodal curve, at pH 6.5 and room temperature (25 °C). Gelling properties were studied under thermodynamic compatibility (WPC 12% (w/w)/E50LV 0.25% (w/w) mixed system) and incompatibility conditions (WPC 12% (w/w)/E50LV 4% (w/w) and WPC 20% (w/w)/E50LV 4% (w/w) mixed systems)Under thermodynamic compatibility the WPC/E50LV mixed system shows gelling parameters similar to WPC. Confocal scanning laser microscopy (CSLM) micrographs showed a regular pattern of microdomains of proteins imbibed into E50LV matrix.Confocal microscopy of WPC/E50LV mixture under thermodynamic incompatibility offered details about the constitution of continuous and non-continuous phase and characteristics of non-continuous phase domains. Related to gelling parameters, the solid character upon heating was reinforced in mixed systems since they reflected the concentrating effect arising from phase separation. On the other hand, the solid character of gels upon cooling correlated with the component constituting the continuous phase, and the gelation temperature was similar to polysaccharide-rich phase predicted gelation temperature.Regarding to textural properties, the presence of the polysaccharide diminished the hardness of the mixed gels inducing less resistance to small and large deformation. WPC 20% (w/w)/E50LV 4% (w/w) mixed gel presented an interesting particulated macrostructure. This result would find application in food design and technology if the E50LV concentration is chosen to finely control the rate and extent of WPC aggregation-gelation-particulation. These results could be used in microparticulation or microencapsulation application of whey proteins.     

Improved thermal gelation of oat protein with the formation of controlled phase-separated networks using dextrin and carrageenan polysaccharides

The thermal gelation of oat protein (OP) was investigated in the presence of polysaccharides at different pHs. The compressive stress dramatically increased in these phase-separated protein–polysaccharides gels due to an apparent increase in protein concentration. The polysaccharide structure significantly affected the degree of phase-separation and gel mechanical properties. The observed two-fold increase in gel compressive stress can be attributed to strong repulsive forces caused by carrageenan molecules. These resulted in a greater degree of phase-separation with the formation of carrageenan rich domains embedded in the protein phase, and a highly ordered protein network, stabilized by hydrogen and hydrophobic interactions. In the case of OP-dextrin gels, the rate of phase separation was slower than the rate of protein aggregation, thus the dextrin particles were uniformly distributed within the protein network. This research contributes to the basic understanding required for designing textures for novel plant-based protein products.