Casein glycomacropeptide pH-driven self-assembly and gelation upon heating

Casein glycomacropeptide (CMP) found in cheese whey is a C-terminal hydrophilic glycopeptide released from κ-casein by the action of chymosin during cheese making. In a previous work a self-assembly model for CMP at room temperature was proposed, involving a first step of hydrophobic assembly followed by a second step of electrostatic interactions which occurs below pH 4.5. The objective of the present work was to study, by dynamic light scattering (DLS), the effect of heating (35–85 °C) on the pH-driven CMP self-assembly and its impact on the dynamics of CMP gelation. The concentration of CMP was 3% w/w for DLS and 12% w/w for rheological measurements. The solutions at pH 4.5 and 6.5 did not show any change in the particle size distributions upon heating. In contrast the solutions at pH lower than 4.5 that showed electrostatic self-assembly at room temperature were affected by heating. The mean diameter of assembled CMP increased by decreasing pH. For all solutions with pH lower than 4.5, the particle size did not change on cooling, suggesting that the assembled CMP forms formed during heating were stable. The gel point determined as G′–G″ crossover, occurred in all systems at 70 °C, but at different times. The rate of self-assembly determined by DLS as well as the rate of gelation increased with increasing temperature and decreasing pH from 4 to 2. Increasing temperature and decreasing pH, the first step of CMP self-assembly by hydrophobic interactions is speed out. All the self-assembled structures and the gels formed at different temperatures were pH-reversible but did not revert to the initial size (monomer) but to associated forms that correspond mainly to CMP dimers.     

超滤法分离纯化酪蛋白糖巨肽的研究

酪蛋白糖巨肽(Casein glycoma cropeptide,简称CGMP)是蛋白酶酶解κ-酪蛋白得到的C末端亲水性糖肽,具有多种生理功能。研究了超滤法分离纯化CGMP的条件,得到超滤的最佳条件是在室温下,压差为0.02MPa,浓缩比为8。通过此方得到了比较纯的CGMP,蛋白回收率为1.77%,糖基化程度(唾液酸/蛋白质)为70.1μg/mg,并且此方法适用于工业化生产。     

Casein gelation under simultaneous action of transglutaminase and glucono-delta-lactone

Casein solutions (5% w/v) were treated with microbial transglutaminase (MTG) and glucono-delta-lactone (GDL) under varying conditions in order to obtain gels. Storage modulus (G') and gelation time of the gels were measured by oscillation rheometry, while protein cross-linking was determined by gel permeation chromatography. The addition of only GDL to milk resulted in very weak gels, while MTG on its own was not able to create gel networks. Simultaneous action of both ingredients led to gels, the firmness of which was linearly related to the added amount of MTG, but passed through a maximum with rising GDL concentrations. Using chromatographical analysis, increasing G' values were interrelated with the formation of MTG-induced oligomers. The gelation time was directly proportional to the GDL concentration but not influenced by the addition of MTG within the studied range of concentration.     

Dynamics of gelation,textural and microstructural properties of gelatin gels in the presence of casein glycomacropeptide

The aim of this work was to study the interaction between gelatin and casein glycomacropeptide (CMP) in the dynamic of gelation and the textural and microstructural properties of the mixed gels. Size particle, dynamic of gelation and textural and microstructural properties of CMP, gelatin and CMP-gelatin systems at pH 3.5 and pH 6.5 were determined. Size particle of gelatin increased by decreasing temperature from 35 °C to 5 °C, while no differences were observed in the size particle of CMP. At pH 6.5 the critical gelling concentration of gelatin was 1.5% and CMP did not gel, but the behavior of mixed systems was similar to gelatin. The more relevant result was observed at pH 3.5 since at concentrations in which CMP and gelatin did not gel on its own, the mixed systems gelled suggesting a synergistic effect.     

Structure-forming processes in Ca-induced whey protein isolate cold gelation

The structure-forming process of Ca²⁺-induced whey protein isolate (WPI) gels was studied, at 24°C, in the presence of 10 and 120 m CaCl₂. Pre-heating WPI suspensions (10% protein) at 90°C dramatically increased specific viscosity, but did not change the number of accessible sulfhydryl groups, compared to pre-heating at 70°C. The most important factor governing the process appeared to be CaCl₂ concentration, rather than the reactive sulfhydryl groups. At 10 m CaCl₂, the increase in aggregate size and network connectivity over time was achieved by clustering of adjacent aggregates. At 120 m CaCl₂, the increase in aggregate size and connectivity was by enlargement of the aggregates which formed connected paths and filled up interstitial spaces.     

The dynamics of heat gelation of casein glycomacropeptide – β-lactoglobulin mixtures as affected by interactions in the aqueous phase

The dynamics of heat gelation of casein glycomacropeptide (CMP) and β-lactoglobulin (β-lg) mixtures as affected by their interactions in the aqueous phase were studied at pH 3.5 and 7.0. At pH 7.0, whereas CMP did not gel, all the mixed systems gelled, but strong synergism was observed for 25:75 CMP:β-lg ratio. In comparison, at pH 3.5 where both components gelled on their own, a strong antagonism was observed, mainly at 75:25 CMP:β-lg ratio. The behaviour of mixed gels is ascribed to the formation of electrostatically driven assembled CMP:β-lg structures, modulated by pH, which were observed by dynamic light scattering and DSC measurements.     

Immunogenicity of kappa-casein and glycomacropeptide

Glycomacropeptide (GMP), arising from the cleavage of κ-casein by chymosin or pepsin, has been correlated with a wide variety of biological activities including immunosuppression capacity, inhibition of pathogen invasion, and induction of satiety. Due to the interest in exploiting such potential of GMP, we aimed at characterizing the immunogenic properties of GMP as an indication of its potential allergenicity. Immunogenicity of κ-casein and GMP were investigated using 2 animal models based on different routes of immunization: 1) mice immunized intraperitoneally or subcutaneously with either κ-casein, polymerized GMP, GMP coupled to the immunogenic carrier ovalbumin, or GMP alone; 2) mice coadministered κ-casein or GMP and cholera toxin. The specific antibody response to GMP was evaluated as well as the antigen-specific T-cell response. The results demonstrated that immunization or feeding with κ-casein induced GMP-specific antibodies, whereas GMP per se lacked immunogenicity independently of the mode of presentation. The size of the presented form of GMP did not influence its immunogenicity. Because the results showed that GMP did not induce a specific T-cell response, we postulate that GMP lacks the ability to stimulate antigen-specific T cells.     

Casein gelation under simultaneous action of transglutaminase and glucono‐δ‐lactone

Casein solutions (5% w/v) were treated with microbial transglutaminase (MTG) and glucono‐δ‐lactone (GDL) under varying conditions in order to obtain gels. Storage modulus (G ′) and gelation time of the gels were measured by oscillation rheometry, while protein cross‐linking was determined by gel permeation chromatography. The addition of only GDL to milk resulted in very weak gels, while MTG on its own was not able to create gel networks. Simultaneous action of both ingredients led to gels, the firmness of which was linearly related to the added amount of MTG, but passed through a maximum with rising GDL concentrations. Using chromatographical analysis, increasing G ′ values were interrelated with the formation of MTG‐induced oligomers. The gelation time was directly proportional to the GDL concentration but not influenced by the addition of MTG within the studied range of concentration.     

酪蛋白糖巨肽的生物活性及其分离技术

本文对酪蛋白糖巨肽的来源及结构作了简要概括,对酪蛋白糖巨肽的生物活性及其营养功能作了一个比较详细的介绍,并对其现有的分离技术进行了分析和比较.     

Influence of sucrose on cold gelation of heat‐denatured whey protein isolate

A solution of heat‐denatured whey proteins was prepared by heating 100 g kg⁻¹ whey protein isolate (WPI) at pH 7.0 to 75 °C for 15 min in the absence of salt. Heat treatment caused the globular protein molecules to unfold, but electrostatic repulsion opposed strong protein–protein aggregation and so prevented gel formation. When the heat‐denatured whey protein solution was cooled to room temperature and mixed with 15 mM CaCl₂, it formed a gel. We investigated the influence of the presence of sucrose in the protein solutions prior to CaCl₂ addition on the gelation rate. At relatively low concentrations (0–100 g kg⁻¹), sucrose decreased the gelation rate, presumably because sucrose increased the aqueous phase viscosity. At higher concentrations (100–300 g kg⁻¹), sucrose decreased the gelation rate, probably because sugar competes for the water of hydration and therefore increases the attraction between proteins. These data have important implications for the application of cold‐setting WPI ingredients in sweetened food products such as desserts. © 2000 Society of Chemical Industry     

Evaluation of some physico-chemical properties of restructured trout and hake mince during cold gelation and chilled storage

Cold gelation was carried out on trout (Oncorhynchus mykiss) or on hake (Merluccius merluccius) mince with or without addition of fish oil and using microbial transglutaminase (MTGase). Products were stored at 4 °C for 6 days and lipid oxidation, protein oxidation, texture, water binding capacity, and colour were followed. Results indicated that MTGase was able to generate gels with good properties for both trout and hake. Gels prepared with trout were oxidised whilst gels prepared with hake were stable toward oxidation even in the presence of 5% fish oil. However, in the presence of oil, as an alternative for generating omega-3 enriched products, the activity of MTGase was impaired, as the gels took longer to reach maximum hardness. Furthermore, in all samples containing MTGase, protein oxidation was high.     

不同因素对CaCl2透析诱导大豆分离蛋白冷凝胶特性的影响

以大豆分离蛋白为原料,通过对CaCl2透析诱导形成的冷凝胶的质构特性和持水能力进行测定,考察了温度、蛋白质浓度、加热时间、pH及盐离子浓度对冷凝胶特性的影响。研究结果表明,室温下CaCl2透析诱导形成冷凝胶的方法大大增强了大豆分离蛋白的凝胶性。通过响应面分析分析得出其形成凝胶的最佳条件为:蛋白浓度10%、加热温度85℃、加热时间45 min、CaCl2浓度40 mmol/L、pH8.0左右。     

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.     

Effect of soy protein substitution for sodium caseinate on the transglutaminate-induced cold and thermal gelation of myofibrillar protein

The influence of soy protein isolate (SPI) substitution for sodium caseinate (SC) on the properties of cold-set (4 °C) and heat-induced gels of pork myofibrillar protein (MP) incubated with microbial transglutaminase (TG) was investigated. The strength of cold-set MP–SC gels (formed in 0.45 M, NaCl, 50 mM phosphate buffer, pH 6.25) increased with time of TG incubation, but those gels with more than 66% SPI substituted for SC had a >26% reduced strength (P < 0.05). Upon cooking, both incubated and non-incubated protein sols were quickly transformed into highly elastic gels, showing up to 6000 Pa in storage modulus (G′) at the final temperature (72 °C). However, no differences (P < 0.05) in G′ were observed between heated samples with SPI and SC. Myosin heavy chain, casein and soy proteins gradually disappeared with TG incubation, contributing to MP gel network formation. Both cold-set and heat-induced gels had a compact protein matrix, attributable to protein cross-linking by TG.     

Effects of Iron Source on Iron Availability from Casein and Casein Phosphopeptides

ABSTRACT: :
Iron availability from FeSO₄ in samples containing sodium caseinate (SC), casein phosphopeptides (CPP) or whey protein concentrate (WPC), and from ferric citrate (Fe-CA) in samples containing SC or CPP was measured using an in vitro digestion/Caco-2 cell culture model. In FeSO₄ spiked samples, relative availability was CPP > SC, CPP = WPC, and CPP = FeSO₄ alone. In samples containing Fe-CA, a soluble iron chelate, relative availability was CPP = SC and CPP < Fe-CA alone. These results suggest that CPP enhances iron availability from foods with low availability but does not improve and may inhibit availability from soluble iron species.     

辣木凝乳酶水解酪蛋白位点及其酪蛋白磷酸肽、酪蛋白糖巨肽

基于十二烷基硫酸钠-聚丙烯酰胺凝胶电泳,液相色谱-串联质谱法研究辣木凝乳酶对酪蛋白的酶切位点和水解特性,并分析该凝乳酶水解产生的酪蛋白糖巨肽和酪蛋白磷酸肽.结果表明,辣木凝乳酶酶切κ-酪蛋白的Arg 93-His 94位点导致凝乳,区别于其他已报道的凝乳酶,具有明显特异性.酶作用下κ-酪蛋白的米氏常数Km=0.49 m...     

凝固剂及凝固条件对大豆蛋白胶凝性质的影响

以大豆蛋白的凝胶强度、持水性、凝固速率这3个胶凝特性为主要指标,测定了包括蛋白浓度、热处理温度和时间、凝固剂种类和添加量、pH值、离子强度在内的这些因素对上述胶凝性质的影响,并确定了最优凝固工艺条件:质量浓度60g/L的SPI溶液经95℃热处理15min后,分别以质量分数0.4%熟石膏(CaSO4·1/2H2O)和质量分数0.28%葡萄糖酸内酯(GDL)作为凝固剂,保温30min后,冷却至室温;最佳离子强度为0.01mol/L(NaCl)。     

Influence of inulin/oligofructose on the acid‐induced cold aggregation and gelation of preheated soy proteins

BACKGROUND: In recent years inulin‐type prebiotics have attracted much attention due to consumers' awareness of the health benefits of functional foods. Currently no information is available about the possible texture‐modifying effect of these non‐ionizable polar carbohydrates in different soy‐based food systems. In this study, the effect of inulin/oligofructose on the cold aggregation and gelation of preheated soy protein isolate (SPI) and its fractions (7S, 11S, and their mixture), induced by glucono‐δ‐lactone (GDL), were evaluated by turbidity (A₆₀₀) and dynamic rheological measurements. RESULTS: Oligofructose significantly delayed the aggregation of all protein samples and decreased the end‐point optical density of 11S fraction and SPI. Inulin, a long‐chain fructan, only delayed the aggregation of 7S globulin and reduced the capacity of aggregation (A₆₀₀) of SPI. While oligofructose showed no significant effect, the addition of 5% (w/v) inulin enhanced the gelation of SPI and the 7S/11S mixture, which was demonstrated by the increase in gel storage modulus up to 13.6% and 10.1% (P < 0.05), respectively. CONCLUSION: Inulin was found to enhance the viscoelastic properties of GDL‐induced cold‐set soy protein gels. It is expected that ‘functional’ cold‐set gel products with improved texture can be prepared from preheated soy proteins and inulin. Copyright © 2009 Society of Chemical Industry