Thermodynamic compatibility of sodium caseinate with different pectins. Influence of the milieu conditions and pectin modifications

Combinations of pectins and caseins are ingredients of many food products. Therefore the thermodynamic compatibility of both components was examined to investigate the influences of environmental factors as well as of the structure of the pectin. High‐methoxyl pectin was demethoxylated and amidated, respectively, and tested for the compatibility with sodium caseinate under varying conditions of pH and ionic strength. The compatibility increased with increasing pH and decreasing ionic strength. Demethoxylated pectins were more and amidated pectins less compatible with the caseinate. Changes in the pectin hydrophilicity, solubility and molecular weight and possibly local interactions such as electrostatic attraction, hydrogen bonding and calcium bridges are involved in the compatibility of the components. The type and degree of the pectin modifications as well as the type, composition and properties of the protein were found to be of great importance for the thermodynamic compatibility.     

Production and stabilization of a flaxseed oil multi-layer emulsion containing sodium caseinate and pectin

The purpose of this research is the evaluation of a flaxseed oil-in-water emulsion, stabilized by a multi-layer structure consisting of sodium caseinate (Na-caseinate) and pectin to provide a basis for the combination of these materials for future studies. In the first step, the o/w emulsion (10 g oil, 90 g aqueous phase, and a pH 6.8) with varying concentration of Na-caseinate was investigated. Second, the pectin solution (0.05–1.5 g/100 g solution) was added to the primary emulsions and the pH was adjusted to 3.0. The emulsions were characterized by mean particle size (dynamic light scattering and static light scattering techniques), ζ-potential, turbidity value, creaming index, and the visualization of the microstructure. A clear separation of the oil phase at low protein contents and destabilizing by depletion flocculation at high protein content were observed. Extensive droplet flocculation and coalescence were determined until the pectin concentration reached 0.5 g/100 g solution for the secondary emulsion. After 7 days of storage, a 1.5 g/100 g solution pectin content had good stability with a relatively small size distribution, high turbidity value, and no cream phase separation.     

Effect of processing conditions and composition on sodium caseinate emulsions stability

Many food products such as ice cream, yoghurt, and mayonnaise are some examples of emulsion-based food. The physicochemical properties of emulsions play an important role in food systems as they directly contribute to texture, sensory and nutritional properties of food. One of the main properties is stability which refers to the ability of an emulsion to resist physical changes over time. The aim of the present work was to analyze the effect of processing conditions and composition on sodium caseinate (NaCas) emulsions stability. The main destabilization mechanisms were identified and quantified. The relationship between them and the factors that influence them were also investigated. Emulsions stabilized with NaCas were prepared using an ultrasound liquid processor or a high pressure homogenizer. Stability of emulsions was followed by a Turbiscan (TMA 2000) which allows the optical characterization of any type of dispersion. The physical evolution of this process is followed without disturbing the original system and with good accuracy and reproducibility. To further describe systems, droplet size distribution was analyzed with light scattering equipment. The main mechanism of destabilization in a given formulation depended on different factors such as NaCas concentration, droplet size or processing conditions. The rate of destabilization was markedly lower with addition of sugar or a hydrocolloid to the aqueous phase. Xanthan (XG) and locust bean (LBG) gums produced an increase in viscosity of the continuous phase and structural changes in emulsions such as gelation. Sugars interacted with the protein decreasing particle size and increasing emulsion stability. The stability of caseinate emulsions was strongly affected not only by the oil-to-protein ratio but also by processing conditions and composition of aqueous phase. The structure of the protein and the interactions protein–sugar or the presence of a hydrocolloid played a key role in creaming and flocculation processes of these emulsions.     

Influence of pectin properties and processing conditions on thermal pectin degradation

Texture degradation of fruits and vegetables during thermal processing is partly due to pectin depolymerization. In this contribution we investigate the influence of pectin properties (degree and pattern of methoxylation) and processing conditions (pH 2.0, 3.0, 5.0 and 7.0; temperatures of 80 up to 110 °C) on pectin degradation rate constants. Pectins with different degrees and patterns of methoxylation were prepared and heated, the extent of acid hydrolysis, β-elimination and demethoxylation was assayed as a function of treatment time. As the degree of methoxylation and pH decreased, β-elimination rate constants decreased while acid hydrolysis rate constants increased. Demethoxylation rate constants were minimal at pH 3.0 and increased both at lower and higher pH. Reaction rate constants were not considerably influenced by the pattern of methoxylation. All reaction rate constants increased with increasing temperature. As β-elimination rates are reduced by competing demethoxylation, both rate constants were compared. The ratio of these reaction rate constants showed no trend with pH. However, an increase in degree of methoxylation or temperature resulted in a more pronounced increase in β-elimination rate constants than in demethoxylation rate constants.     

Influence of the homogenization conditions and lipid self-association on properties of sodium caseinate based films containing oleic and stearic acids

The effect of the homogenization conditions of the film-forming emulsions and lipid self-association on the physical properties of sodium caseinate films containing oleic and stearic acids was studied. For this purpose, different film-forming emulsions were prepared by using different homogenization methods and were characterized as to particle size distribution and rheological properties. Likewise, mechanical, structural and optical properties and water vapour permeability (WVP) of the obtained films were also determined. While films containing stearic acid showed a laminar-like structure, oleic acid was more homogeneously dispersed in the film matrix. These differences in structure make the stearic acid films less flexible, showing more surface roughness and less gloss and transparency than films containing oleic acid. The film microstructure also affects the WVP. In this sense, for oleic acid films, water barrier efficiency increased when homogenization conditions were more intense, whereas for films containing stearic acid, the opposite effect was observed. This different behavior was attributed to the different kind of lipid self-association in the aqueous media, protein interactions and their impact on the final film microstructure.     

Influence of xanthan gum on the formation and stability of sodium caseinate oil-in-water emulsions

Studies have been made of the changes in droplet sizes, surface coverage and creaming stability of emulsions formed with 30% (w/w) soya oil, and aqueous solution containing 1 or 3% (w/w) sodium caseinate and varying concentrations of xanthan gum. Addition of xanthan prior to homogenization had no significant effect on average emulsion droplet size and surface protein concentration in all emulsions studied. However, addition of low levels of xanthan (≤0.2 wt%) caused flocculation of droplets that resulted in a large decrease in creaming stability and visual phase separation. At higher xanthan concentrations, the creaming stability improved, apparently due to the formation of network of flocculated droplets. It was found that emulsions formed with 3% sodium caseinate in the absence of xanthan showed extensive flocculation that resulted in very low creaming stability. The presence of xanthan in these emulsions increased the creaming stability, although the emulsion droplets were still flocculated. It appears that creaming stability of emulsions made with mixtures of sodium caseinate and xanthan was more closely related to the structure and rheology of the emulsion itself rather than to the rheology of the aqueous phase.     

Purification of pectin from apple pomace juice by using sodium caseinate and characterisation of their binding by isothermal titration calorimetry

The binding of sodium caseinate to pectin using Isothermal Titration Calorimetry (ITC) under different pH values (2, 3, 3.5), and comparison of two purification processes (sodium caseinate or ethanol), based on the physicochemical characteristics of purified pectin was evaluated. The results indicated that ITC titration confirmed the existence of interactions between caseinates and pectin at pH 3 and 3.5. The interaction depicts two interdependent steps, one attributed to an electrostatic interaction and another related to a co-acervation mechanism. The chemical characteristics of pectins are strongly dependent on the purification process. Under some extraction conditions, ethanol is not specific to the recovery of pectin since it causes the precipitation of other compounds together with this polysaccharide.     

Formation of electrostatic complexes using sodium caseinate with high‐methoxyl pectin and carboxymethyl cellulose and their application in stabilisation of curcumin

Despite many reported bioactivities of curcumin, its application is limited due to its low bioavailability, solubility and stability. Proteins have been reported to stabilise curcumin in aqueous media, and stabilisation of curcumin could be enhanced when proteins form an electrostatic complex with polysaccharides. In this study, electrostatic complexes of sodium caseinate (NaCas) were prepared using high‐methoxyl pectin (HMP and NaCas‐HMP) and carboxymethyl cellulose (CMC and NaCas‐CMC). NaCas to polysaccharide ratio of 1:2 resulted in the lowest turbidity and sedimentation. The electrostatic complexes were more stable than native NaCas against pH change and ionic strength. Binding of curcumin to NaCas and the electrostatic complexes were confirmed by UV‐vis and fluorescence spectra and Fourier transform infrared spectroscopy (FT‐IR). The electrostatic complexes showed a higher binding constant and protected curcumin better than the native NaCas. This study suggests that the electrostatic complexes may be a superior carrier to NaCas at an acidic environment.     

酪蛋白酸钠流变特性的研究

研究了酪蛋白酸钠溶液的流变特性.酪蛋白酸钠属于假塑性流体,粘度与浓度成对数相关性,其流变特性受温度、pH、盐种类及盐浓度等因素的影响.     

Binding of resveratrol with sodium caseinate in aqueous solutions

The interaction between resveratrol (Res) and sodium caseinate (Na-Cas) has been studied by measuring fluorescence quenching of the protein by resveratrol. Quenching constants were determined using Stern–Volmer equation, which suggests that both dynamic and static quenching occur between Na-Cas and Res. Binding constants for the complexation between Na-Cas and Res were determined at different temperatures. The large binding constants (3.7–5.1 × 10⁵ M⁻¹) suggest that Res has strong affinity for Na-Cas. This affinity decreases as the temperature is raised from 25 to 37 °C. The binding involves both hydrogen bonding and hydrophobic interaction, as suggested by negative enthalpy change and positive entropy change for the binding reaction. The present study indicates that Na-Cas, a common food protein, may be used as a carrier of Res, a bioactive polyphenol which is insoluble in both water and oils.     

Interference of sodium caseinate in the TBARS assay

One of the most common methods of measuring lipid oxidation in foods is the quantification of malonaldehyde by reaction with 2-thiobarbituric acid (TBA) in the so called TBA-reactive substances (TBARS) assay. Different variants of the TBARS assay include those in which the food sample reacts directly with the TBA reagent and those that involve collection of a distillate from the food before reaction with TBA. Interference of sodium caseinate (NaCas) in a TBARS assay involving direct reaction of TBA with a food sample was observed while exploring the possible retardation of lipid oxidation in sliced turkey meat coated with a NaCas-containing edible film. This short report shows the extent of interference encountered and illustrates the importance of validating the TBA method for particular applications.     

螯合剂六偏磷酸钠提取甜菜果胶工艺优化

用钙离子螯合剂六偏磷酸钠(SHMP)溶液从甜菜干粕中提取果胶,并对提取工艺进行优化。在单因素试验的基础之上,对影响果胶得率的主要因素进行Box-Benhnken中心组合实验设计;建立六偏磷酸钠提取甜菜果胶的二次回归模型。实验结果表明,甜菜果胶的最佳提取工艺为提取时间2.4h,螯合剂SHMP质量分数1.25%,提取温度88℃,此时果胶产率为14.32%,与模型预测值接近。同时,采用间羟联苯法测定出果胶样品的半乳糖醛酸含量为73.12%。红外光谱的数据表明,果胶样品具有果胶分子的结构特征,并初步判断为低酯果胶。     

Factors affecting the acid gelation of sodium caseinate

Acid gelation, turbidity and particle size development of dispersions of sodium caseinate and other protein fractions were studied. Sodium caseinate dispersions became particulate prior to the onset of gelation. Casein particles had enhanced stability to gelation in the presence of sodium chloride. Removal of the hydrophilic part of the κ-casein molecule through renneting and acidification of the soluble sodium para-caseinate resulted in increased gelation pH. Removal of most of the κ-casein through ethanol fractionation of sodium caseinate resulted in an α_s1-β-fraction, which was markedly destabilised at higher pH values during acidification in the presence of sodium chloride. Preheated β-lactoglobulin/sodium caseinate dispersions had similar acid gelation profiles in the presence of sodium chloride with or without N-ethylmaleimide, suggesting that secondary thiol-disulphide interchange reactions between κ-casein and pre-heated β-lactoglobulin aggregates did not effect the gel point and final storage modulus in the short time-frame (120 min) of acidification. It was found that κ-casein and sodium chloride played a significant role in both particle development and subsequent stability of sodium caseinate dispersions on acidification.     

Influence of pectin structure on the interaction with bile acids under in vitro conditions

Structural parameters of pectin (a polysaccharide and important component of dietary fibre) influence the interaction with bile acids (BA). The effect of experimental conditions (concentration of pectin, BA and Ca²⁺) on such interactions was studied at pH 6.0. Series of pectins were used, prepared from virtually fully esterified pectin by gradual de-esterification with alkali or with pectinesterase from oranges. Further amidated and acetylated pectins were also tested. The greatest interaction with BA was found with a very highly esterified pectin under in vitro conditions. The interaction diminished with decreasing degrees of esterification (DE). This decrease was more intensive for pectins possessing a blockwise arrangement of free -COOH groups. Derivatives of pectin generally interacted less with BA. These results were principally confirmed with commercial pectins, with pectins prepared on a pilot-plant scale and with pectins originating from a defined botanical source. The interactions of these preparations with BA were less intensive than with those of pectins having an ideal random distribution of free -COOH groups in the polysaccharide molecules at the same DE. The interaction with pectin is also likely to be influenced by the structure of BA.     

酶法脱磷酸化修饰酪蛋白酸钠及其体外模拟消化

以小牛肠碱性磷酸酶修饰酪蛋白酸钠(sodium caseinate,SC)为研究对象,制备得到4种磷酸化水平的SC。采用尿素电泳、微波消解-紫外可见吸收光谱和超高效液相-电喷雾-离子化-飞行时间质谱等表征手段,从不同角度鉴定了SC的脱磷酸化程度,并在模拟婴幼儿胃、肠液中考察了不同的脱磷酸化程度对SC体外消化的影响。结果表明,SC脱磷酸化程度越高,在模拟胃液中分散程度越均匀,降解速度越快;并且在模拟肠液中进一步降解时所产生的多肽分子量越小,消化性越好。     

The effect of the glucono-δ-lactone/caseinate ratio on sodium caseinate gelation

The influence of the acidification rate and the final pH on the properties of sodium caseinate gels (2–6%, w/v) prepared by acidification with glucono-δ-lactone (GDL) at 10 °C was investigated. The rheological properties of the systems were analysed under shear at incipient gelation and under uniaxial compression throughout the entire gelation process. The water holding capacity (WHC) of these gels and their amount of soluble protein in different media were also evaluated. Up to ∼50% of the total κ-casein content was soluble in gels with a higher amount of GDL, and this contributed to the high WHC observed under this condition. The acidification rate did not affect the rheological properties measured under shear during gelation, but the GDL/caseinate ratio used had a significant effect on the steady-state properties. Fast acidification resulted in lower Young's modulus and stress at fracture values, but higher residual stress values and relaxation times. In contrast, slow acidification produced a more interconnected network probably because of the extensive reorganization or rearrangement within the segments near the isoelectric point.     

Properties of sodium caseinate film-forming dispersions and films

The flow properties of sodium caseinate (NaCAS) film-forming dispersions were studied as a function of protein and glycerol concentration. Apparent viscosity vs. concentration profiles showed a disruption at about 10% (wt/wt) NaCAS. This was interpreted in terms of protein-water and protein-protein interactions. The presence of glycerol in the NaCAS film-forming suspensions reduced the viscosity of aqueous NaCAS as a consequence of decreasing protein-protein and protein-solvent interactions through the hydrogen bonding formation between the glycerol, the polypeptide chain of NaCAS, and water molecules. For higher concentration of glycerol, viscosity of NaCAS dispersions increased as a result of increasing total solid content. The glass transition temperature for solid films of 10% (wt/wt) NaCAS decreased with the glycerol content. The glycerol-protein interactions reduced the protein-protein interaction and, thus, increased the intermolecular spacing, leading to higher protein chain mobility and water vapor permeability.     

酪朊酸钠的酶解及分离分析

利用复合蛋白酶水解酪朊酸钠制备营养性酪蛋白小分子肽，对水解的工艺参数，小分子肽的得率变化及酶解液溶解性进行了系统的研究，并对酶解产物进行了SDS-PAGE电泳实验和氨基酸组成分析。