Effect of phosphatase/transglutaminase treatment on molar mass distribution and techno-functional properties of sodium caseinate

Sodium caseinate was enzymatically dephosphorylated by alkaline or acid phosphatase prior to incubation with microbial transglutaminase. It was demonstrated that a higher degree of protein cross-linking by transglutaminase was achieved in dephosphorylated sodium caseinate than in non-dephosphorylated sodium caseinate. During transglutaminase treatment, about 70% protein polymers >200.000 g/mol were produced from untreated sodium caseinate, but about 90% protein polymers >200.000 g/mol from dephosphorylated sodium caseinate. Phosphatase/transglutaminase-treated sodium caseinate exhibited techno-functional properties similar to transglutaminase-treated sodium caseinate, but performed improved interfacial stabilisation behaviour as well as higher viscosity.     

Laccase-aided protein modification: Effects on the structural properties of acidified sodium caseinate gels

Trametes hirsuta laccase (EC 1.10.32) alone was not able to cross-link proteins effectively unless high dosages were used. Incorporation of ferulic acid enhanced the formation of intermolecular cross-links. Cross-linking was more effective when the reaction was carried out at 45 °C rather than at room temperature. Size exclusion chromatography showed that ferulic acid monomers disappeared from the solution in the presence of laccase. Force at rupture point of the caseinate gels treated with laccase without ferulic acid was not significantly different from the control, while stronger gels were achieved when ferulic acid was present. Rheological measurements showed that laccase treatment together with ferulic acid resulted in higher G′ values than the control. Gels were analyzed with confocal laser scanning microscope. A finer network was observed when the enzyme was used together with ferulic acid. Slight proteolytic activity resulted in a negative effect on the gel firmness and microstructure when laccase was used without ferulic acid.     

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.     

Effect of dielectric barrier discharge atmospheric cold plasma treatment on structural,thermal and techno-functional characteristics of sodium caseinate

The present work aimed to study the effect of dielectric barrier discharge (DBD) atmospheric cold plasma (CP) on the structure-function relationship of sodium caseinate. The caseinate powder was subjected to CP for 0, 2.5, 5 and 10 min, and its physicochemical, structural, thermal, emulsifying and film-forming properties were investigated. The FTIR spectra revealed a higher β-structures and a diminished-random coil conformation after CP treatment. The DSC profiles confirmed higher glass transition in CP-processed caseinates. The CP-treated caseinates exhibited higher interfacial activity and developed emulsions with smaller particle size and higher physical stability. The SEM images and mechanical analysis of produced caseinate film showed that CP treatment up to 5 min promoted the formation of a more uniform microstructure and reinforced the tensile strength. These findings propose that CP treatment may be efficiently employed to mildly modify caseinate structure and improve its techno-functional properties.Industrial relevanceCold plasma (CP) is an emerging eco-friendly efficient technology, which has gained increasing attention in the food and pharmaceutical industries. It is a potent and outstanding technique for non-thermal microbial decontamination, enzyme deactivation, surface modification, functionalization, and etching of coating materials. The CP may provide opportunities in a targeted modification of the structure and interfacial performance of biopolymers. This work demonstrates the potential of CP for mild modification of the structure, emulsifying and film-forming properties of sodium caseinate powder while maintaining its appearance features. Sodium caseinate treated by plasma can develop an emulsion with significantly higher physical stability and edible film with augmented mechanical strength, opening a wide range of promising applications in food and pharmaceutical industries such as the development of tailor-made protein-based films, coatings, emulsions, and emulsion films.     

New insights into the microencapsulation properties of sodium caseinate and hydrolyzed casein

The aim of the present study was to describe the fundamental physical characteristics of spray-dried carrier matrices based on sodium caseinate and casein hydrolyzate and microcapsules as well as their impact on the stability of a microencapsulated functional ingredient. Spray-dried carrier matrix was characterized by different physical methods (helium pycnometry, nitrogen displacement for surface area analysis, X-ray photoelectron spectroscopy, positron annihilation lifetime spectroscopy). Surface viscoelasticity of protein-stabilized oil–water interfaces was analyzed using dynamic pendant drop tensiometry. Fish oil was microencapsulated and microencapsulation efficiency as well as oxidative stability over time was monitored.     

酪蛋白酸钠膜的DSC分析

采用差示扫描量热法(DSC)分析,研究不同相对湿度(RH)条件下,酪蛋白酸钠(NaCas)膜的热特性以及谷氨酰胺转移酶(TGase)改性对热特性的影响。对于NaCas膜,无论是对照膜还是TGase改性膜,蛋白膜的热稳定性随着RH的增高而下降。TGase改性改变了NaCas膜吸热峰出现的位置与数量。在同一RH时,TGase改性膜更易失去水分。TGase改性使NaCas膜的耐热特性发生了明显改变,可能是TGase作用改变了NaCas的不同组分的耐热特性所致。      

Physical properties of edible films made from mixtures of sodium caseinate and WPI

The physical properties of thin films (25–30 μm) made from mixtures of sodium caseinate (NaCas) and whey protein isolate (WPI) were investigated. Films were formed by mixing solutions of NaCas (2.5% w/w protein), plasticised with glycerol (NaCas–gly) at a glycerol:protein ratio of 0.32, with WPI solutions (2.3% w/w protein), plasticised (WPI-gly) at a glycerol:protein ratio 0.37. Tensile and water barrier properties of films formed from mixtures of NaCas–gly and WPI-gly were similar to films containing NaCas–gly only. Films containing only WPI-gly had higher maximum load and elastic modulus values than the mixed films. Increasing the NaCas–gly content of the films from 25 to 100% greatly increased solubility. This increased film solubility may increase the number of food applications for protein-based films.     

Comparative study of the functional properties of bovine globin isolates and sodium caseinate

Two methods used for extraction of globin from bovine blood were tested in terms of effiency, protein recovery and solvent residues. A comparative study with commercial sodium caseinate was made concerning the chemical composition and the functional properties of these proteins. Also, the effect of the NaCl addition on these properties was evaluated. Although the efficiency of the carboxymethyl-cellulose method was inferior than that of the acidified acetone, the absence of residual organic solvents in the globin makes it a more reliable method to prepare globins to be used in foodstuff. The chemical composition of proteins was affected by the method of extraction and the iron content of the globin obtained by the former method was more than three times higher than that using CMC. In general, the NaCl additon was harmful for the functional properties of the studied proteins, mostly for a salt concentration close to that used in meat products (0.25 mol/l).     

Assessment of interfacial and foaming properties of bovine sodium caseinate glycated with galactose

The impact of the initial and advanced stages of glycation of sodium caseinate (SC) with galactose on the interfacial and foaming properties has been investigated at pH 7 and 5. At pH 7, the most remarkable result was the higher stabilizing foam capacity of glycoconjugates as compared to native and heat treated SC, as a result of the higher elastic character and cohesion of the interfacial film formed by glycated SC. At pH 5, native and control heated SC underwent a significant loss of solubility, resulting in a worse dynamic of adsorption at the interface of such systems and the formation of fluid and poorly resistant films. However, solubility of glycated SC remained relatively high, so that, at this pH, only SC glycoconjugates showed interfacial characteristics suitable to stabilize the foam during its formation as well as against mechanisms of foam destabilization at long term. This behavior was attributed to the higher adsorption efficiency and degree of interfacial interaction exhibited by the SC glycoconjugates. These findings highlight the beneficial effect of glycation on the foaming properties of SC which could contribute to broadening the applicability of SC as a foaming agent, mainly in acid foods.     

Structure and properties of nanocomposite films based on sodium caseinate and nanocellulose fibers

Films made from sodium caseinate and nanocellulose were prepared by dispersing the fibrils into film forming solutions, casting and drying. Composite films were less transparent and had a more hydrophilic surface than neat sodium caseinate ones. However, the global moisture uptake was almost not affected by filler concentration. Addition of nanocellulose to the neat sodium caseinate films produced an initial increase in the barrier properties to water vapor, and then, it decreases as filler content increased. This was explained in terms of additional detrimental changes (cracks and bubble formation) induced in the morphological structure of the film by the reinforcement.The tensile modulus and strength of composite films increased significantly with increasing cellulose concentrations, while the values of elongation decreased. In the same way it was found that the storage modulus increases considerably with filler addition in the low temperature range (<60 °C), though the effect of temperature on the films performance is even more dramatic, as expected in protein-based materials.     

Effect of transglutaminase on rheological properties and microstructure of chemically acidified sodium caseinate gels

The mechanical properties and microstructure of 2.7% and 4.5% sodium caseinate gels chemically acidified by glucono-δ-lactone (GDL) and cross-linked by microbial transglutaminase (TG) were studied. The acidification was performed at different temperatures. According to SDS–PAGE TG clearly caused polymerisation of caseinate irrespective of the treatment temperature (4–50 °C), The cross-linking of the proteins was more extensive at temperatures 22–50 °C. Low amplitude viscoelastic measurements showed that 4.5% caseinate gels acidified at 50 °C were formed much faster than gels acidified at 22 °C. TG only slightly increased the time of gelling. Control gels prepared without TG at temperatures of 4, 22, 37 and 50 °C were mechanically weak. Examination of the control gels with a confocal laser scanning microscope showed that gels formed at 37 and 50 °C were coarse and porous with large cavities between particle aggregates, whereas those formed at 22 °C were much more homogeneous. The TG-treated and acidified sodium caseinate dispersions formed firm gels, indicating cross-linking of casein proteins. Interestingly, the strongest gels were formed at 22 and 37 °C. TG treatment improved the homogeneity of the gel structure at temperatures of 37 and 50 °C. The hardness of TG-treated gels acidified at 4 °C increased during 1 week of storage.     

Structure and mechanical properties of sodium and calcium caseinate edible active films with carvacrol

Edible active films based on sodium caseinate (SC) and calcium caseinate (CC) plasticized with glycerol (G) at three different concentrations and carvacrol (CRV) as active agent were prepared by solvent casting. Transparent films were obtained and their surfaces were analysed by optical microscopy and scanning electron microscopy (SEM). The influence of the addition of three different plasticizer concentrations was studied by determining tensile properties, while Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to evaluate the structural and thermal behavior of such films. The addition of glycerol resulted in a reduction in the elastic modulus and tensile strength, while some increase in the elongation at break was observed. In general terms, SC films showed flexibility higher than the corresponding CC counterparts. In addition, the presence of carvacrol caused further improvements in ductile properties suggesting the presence of stronger interactions between the protein matrix and glycerol, as it was also observed in thermal degradation studies. FTIR spectra of all films showed the characteristic bands and peaks corresponding to proteins as well as to primary and secondary alcohols. In summary, the best results regarding mechanical and structural properties for caseinates-based films containing carvacrol were found for the formulations with high glycerol concentrations.     

Effect of sodium caseinate on properties and ageing behaviour of corn starch based films

The effect of sodium caseinate addition on corn starch films was studied in terms of microstructural, mechanical, optical and water and oxygen barrier properties and the changes they underwent during their 5 weeks' storage under controlled conditions. The influence of the polymer mixture on the degree of crystallization of the films was also analysed. The following starch: protein ratios were considered. 100:0, 75:50, 50:50 and 0:100. SEM Microstructure analysis revealed the compatibility of both hydrocolloids since no phase separation was observed. The addition of sodium caseinate to the starch films provided films that were less stiff and resistant to fracture but more flexible and deformable than pure starch films, with similar water vapour permeability values. The films became more permeable to oxygen as their sodium caseinate content increased in line with the higher permeability values of the protein film. Incorporating sodium caseinate to starch films provoked a slight increase in transparency, but a loss of gloss, which also decreased in composite films during storage. The re-arrangement of polymer chains during storage caused a loss of mechanical resistance, stretchability and gloss in composite films.     

Physicochemical characterization of plasma-treated sodium caseinate film

Sodium caseinate films were physico-chemically characterized for the effects of atmospheric dielectric barrier discharge (DBD) plasma as function of applied voltage and treatment times. Surface roughness of plasma treated films at both 60 and 70 kV was found to be significantly (p ≤ 0.05) higher than the control. Glass transition temperature of all the films after plasma treatment was found to be less than the control film. The increase in the O/C atomic ratio shows the formation of new oxygen-containing groups on the film surface. XRD and FT-IR spectra suggest a disruption in the inter-helical structure without any change in the helical configuration of the protein molecules. Increase in the hydrophilicity of the sodium caseinate film was also observed after DBD plasma, but no significant (p > 0.05) increase in the WVTR and OTR was noticed, showing the suitability of the film for novel processes such as in-package plasma decontamination of food.     

Barrier properties of sodium caseinate films as affected by lipid composition and moisture content

This work analyses the effect of lipid addition (oleic acid, beeswax and oleic acid-beeswax mixtures) as well as the influence of the relative humidity (RH), or the equilibrium water content of the films, on the permeability of sodium caseinate based films to water vapor and gas (oxygen and carbon dioxide). The effect that lipid addition had on the gas and water vapor permeability was dependent both on the composition of oleic acid-beeswax mixtures and the film’s moisture content. The addition of lipid mixtures reduced water vapor transfer as compared to the control films (without lipid), whereas pure oleic acid or beeswax were less effective. Both control films and films prepared with pure beeswax showed the lowest O₂ and CO₂ permeability, whereas the incorporation of oleic acid exponentially increased these values. A linear increase in water vapor and gas permeability was observed when the water content of the film rose, due to its plasticizing effect, which led to an increase in the molecular mobility. Predictive equations for water vapor permeability (WVP) and gas permeability were established as a function of water content and lipid composition.     

酪朊酸钠酶解液的超滤分离研究

对酪朊酸钠酶解液进行超滤实验,研究了酶解液的透过液体积与操作时间、平均透过速率之间的关系,并对比了透过液、截留液和酶解液中可溶性蛋白得率、小分子肽得率的变化,通过SDS-PAGE电泳实验分析了透过液和截留液的分子量分布情况.     

Proteomic characterisation of heat-induced hydrolysis of sodium caseinate

The hydrolysis of sodium caseinate during heating for up to 120 min at pH 7.0 and 130 °C was investigated. The formation of 2% trichloroacetic acid (TCA)-soluble peptides was studied using spectrofluorimetry and high resolution liquid chromatography-mass spectrometry (LC-MS), whereas sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to study hydrolysis of the caseins. LC-MS and spectrofluorimetry showed an increase in 2% TCA-soluble peptides over time, confirming that proteolysis had occurred, whereas SDS-PAGE showed a decrease in band intensity for the main caseins over time. In total, 1023 casein-derived peptides were identified. For eleven of the most abundant peptides, release and breakdown were modelled. Peptide bonds containing Pro, Ser, Asn and/or Asp were preferentially hydrolysed during heating. The production of peptides in this manner may represent a novel alternative to enzymatic hydrolysis strategies.     

Functionality of Bacillus proteinase hydrolysates of sodium caseinate

Sodium caseinate (NaCN) was digested with Protamex, a Bacillus proteinase, at 40°C and pH 7.0 to degree of hydrolysis (DH) values of 2.7%, 5.3% and 13.3%. The solubility, emulsifying, foaming and viscosity properties of the hydrolysates were investigated between pH 2.0 and 10.0. Foam expansion of >1300% was observed for the 5.3% DH hydrolysate at pH 4.0, compared to 670% for unheated NaCN. Significantly improved foam expansion properties (P<0.005) were observed over the entire pH range examined for the 13.3% DH hydrolysate compared to unheated or heat-treated NaCN. Hydrolysis resulted in significantly improved solubility (P<0.005) around the isoelectric point and significant improvements in the emulsifying activity and stability (P<0.005) at alkaline pH compared to unheated NaCN. Hydrolysis with Protamex increased the apparent viscosity of NaCN at the isoelectric point. Reversed-phase HPLC profiles showed that high DH samples contained high levels of hydrophilic peptides.     

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.