响应面法优化酪蛋白酸钙生产工艺

以食品级干酪素为原料,以制备的酪蛋白酸钙中钙含量为指标,采用单因素实验、中心组合(Box-Benhnken)试验设计与响应曲面分析法,研究了酪蛋白酸钙的生产工艺。在单因素实验的基础上采用3因素3水平的响应曲面分析法,以酪蛋白酸钙中钙含量为指标,考察溶液pH、溶液浓度与Ca(OH)2添加量对酪蛋白酸钙制备的影响,建立了酪蛋白酸钙制备中钙含量与各影响因子的回归方程,确定了最佳工艺条件。结果表明:最佳制备工艺为溶液pH值为7.16、料液浓度为5.97%、Ca(OH)2添加量为1.716%,在此条件下制备的酪蛋白酸钙中钙含量为1.639%,与预测值1.642%相差不显著。该工艺酪蛋白酸钙得率高,所得产品含钙量较高,产品具有较好的品质。     

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.     

The effects of xanthan conformation and sucrose concentration on the rheological properties of acidified sodium caseinate–xanthan gels

Xanthan solution transitions caused by annealing at different temperatures were studied by oscillatory rheology. The rheological behaviour of solutions evaluated at 10 °C showed different irreversible xanthan transitions, depending on the annealing temperature. The effect of xanthan conformation and caseinate, xanthan and sucrose concentrations on the mechanical and stress relaxation properties of acidified dairy gels were also investigated. Xanthan transitions produced different structural characteristics in mixed gels, as observed by their relaxation time and residual stress. The amount of sucrose played an important role in the network formation of gels and on the final elasticity. Intermediate concentrations of sucrose yielded gels that were finer than those obtained with low sucrose content, whereas at high amounts of this co-solute, the gels became more fragile. This quadratic effect of sucrose occurred at lower sucrose contents than in protein–sucrose or polysaccharide–sucrose systems. The mechanical properties at equilibrium were affected only by the strength of the interactions between caseinate and xanthan.     

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.     

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 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.     

Elution of sodium caseinate from agar-based gel matrixes in simulated gastric fluids

Elution of sodium caseinate from agar/psyllium composite gels was investigated in simulated gastric fluids to determine predominant mechanical parameters of gels for the elution kinetics and to predict the kinetics using the parameters. When the concentration of agar was fixed at 0.5% in the composite gels, elastic moduli determined by creep tests decreased with increasing concentration of psyllium, while viscosities increased. Compression load upon syringing through an enteral tube increased with increasing concentration of psyllium, whereas the surface-volume diameter d_3,2 of gel particles after syringing decreased. The elution kinetics of sodium caseinate from cylindrical gels was described using two different diffusion coefficients; D₁ and D₂ (D₁ > D₂) and the diameter of gels. Both diffusion coefficients decreased with increasing concentration of psyllium, resulting in 1.9 × 10⁻⁶ (for D₁) and 6.7 × 10⁻⁸ (for D₂) cm²/min by 1.5% addition, which corresponded to approx. 30% and 45% of the control (i.e., 0% psyllium), respectively. The fraction ratio of sodium caseinate having D₁ was not sensitive to psyllium concentration; approx. 80%–85% in the concentration range tested. D₁ was inversely proportional to viscosities determined by creep tests, particularly one from the Voigt body η₁ in the 4-element mechanical model. When cube gels were divided into smaller ones without changing the total volume, elution rates were inversely proportional to the cube length, where the diffusion coefficients did not change. The elution kinetics of sodium caseinate from the gel matrixes was anticipated using η₁ of gels before syringing and d_3,2 of gel particles after syringing when the usage of gels for percutaneous endoscopic gastrostomy is assumed.     

Oil-in-water emulsions stabilized by sodium caseinate: Influence of pH,high-pressure homogenization and locust bean gum addition

The effect of pH, addition of a thickening agent (locust bean gum) or high-pressure homogenization on the stability of oil-in-water emulsions added by sodium caseinate (Na-CN) was evaluated. For this purpose, emulsions were characterized by visual analysis, microstructure and rheological measurements. Most of the systems were not stable, showing phase separation a few minutes after emulsion preparation. However, creaming behavior was largely affected by the pH, homogenization pressure or locust bean gum (LBG) concentration. The most stable systems were obtained for emulsions homogenized at high pressure, containing an increased amount of LBG or with pH values close to the isoelectric point (pI) of sodium caseinate, which was attributed to the size reduction of the droplets, the higher viscosity of continuous phase and the emulsion gelation (elastic network formation), respectively. All the studied mechanisms were efficient to decrease the molecular mobility, which slowed down the phase separation of the emulsions. In addition, the use of sodium caseinate was also essential to stabilize the emulsions, since it promoted the electrostatic repulsive interactions between droplets.     

Effect of added calcium chloride on the physicochemical and rheological properties of aqueous mixtures of sodium caseinate/sodium alginate and respective oil-in-water emulsions

Changes induced by addition of calcium chloride in particle size distribution and electrokinetic potential were determined in sodium caseinate/sodium alginate mixtures dissolved in water or acetate buffer at ambient temperature. Rheological properties of aqueous mixtures and respective oil-in-water emulsions (30% oil w/w) were evaluated using a low-stress rheometer. Stability and particle diameter of emulsions were measured. Caseinate and alginate solutions were negatively charged and showed negative electrokinetic potential; however values of mixtures were between those of the values for the individual hydrocolloids. When calcium ions were added the electrokinetic potential diminished while the negative charge was preserved. Aqueous mixtures of caseinate and alginate showed average particles size between of those of caseinate or alginate samples. We observed low viscosity values and Newtonian behavior for both caseinate (1 and 2%) and alginate (0.1%). Addition of 5 mM CaCl₂ to alginate solutions induced shear-thinning behavior as well as the development of viscoelasticity. Both the viscosity and the elastic modulus of these polysaccharide solutions were attenuated by the presence of protein or dispersed oil in mixtures or emulsions, respectively. High average particle diameter of emulsions prepared was obtained (close to 10 μm), however, stability of emulsions was possible only with the addition of CaCl₂ to the mixtures, in both water and acetate buffer. In these cases elastic behavior predominated to viscosity in the formation of emulsions, confirming the prevalence of aqueous phase rheology on emulsions.     

Preparation and characterization of phytosterol-loaded nanoparticles with sodium caseinate/dextran conjugates

Sodium caseinate (SC)/dextran conjugates were prepared via Maillard reaction under controlled dry-heating conditions. Moreover, the nanoparticles of phytosterols (PS) encapsulated by SC or SC/dextran were produced using the emulsion evaporation method. The encapsulation efficiency (78.81 ± 5.22%) of PS in SC/dextran nanoparticles was higher than that (73.5 ± 2.78%) in SC nanoparticles. Compared with the compact and dense structure of SC nanoparticles, SC/dextran nanoparticles existed as relatively loose aggregates. The result of differential scanning calorimetry demonstrated that the encapsulation of PS greatly decreased its crystallinity. The released rates of PS from SC and SC/dextran nanoparticles under acidic gastric conditions were 8.59% and 4.73%, respectively. After 7 h of intestinal digestion, the released rate (52.19%) of PS from SC/dextran nanoparticles was significantly higher than that from SC (32.67%) nanoparticles. Therefore, SC/dextran conjugates prepared by the Maillard reaction are more suitable to be used as wall material for the nano-encapsulation of PS.     

Characterization and improvement of rheological properties of sodium caseinate glycated with galactose, lactose and dextran

The aim of this work was to investigate the effect of non-enzymatic glycosylation with galactose, lactose, and 10 kDa dextran on the rheological properties of sodium caseinate. To promote the formation of covalent complexes, the reaction was done in solid state (a_w = 0.67), pH 7.0 (0.1 M sodium phosphate buffer), and temperature set at 50 and 60 °C. The progress of Maillard reaction was indirectly traced by measuring the formation of the Amadori compound, through furosine (2-furoylmethyl-lysine) analysis, and brown polymers, and the resulting glycoconjugates were characterized by LC/ESI-MS and SEC. Results showed a higher reactivity of galactose than lactose and dextran to form the glycoconjugates, due to its smaller molecular weight. Glycation with galactose and lactose increased the viscosity of caseinate and also altered its flow characteristics from Newtonian to shear-thinning. Oscillatory testing showed a higher elastic modulus (G′) in glycoconjugates when compared to non-glycated caseinate, especially with galactose, where a gel-like behaviour was observed after long incubation times. Glycation with dextran did not produce substantial improvements in the rheological properties of caseinate, probably due to the limited extent of the reaction. Our results show that by controlling the rate and extent of the Maillard reaction is a technologically feasible operation to improve the viscosity and gelling properties of sodium caseinate-based ingredients.     

Rheological and thermal properties of milk gels formed with κ-carrageenan. I. Sodium caseinate

Mixed gels, formed by κ-carrageenan, and sodium caseinate were studied by differential scanning calorimetry (DSC) and rheometry. DSC showed that during gelation (i.e. cooling) the thermal behaviour of κ-carrageenan was almost uninfluenced by the presence of sodium caseinate. Thus the interaction of κ-carrageenan with sodium caseinate has little (or no) effect on the carrageenan's coil-to-helix transition. In contrast, during melting, added sodium caseinate strongly modified the thermal behaviour. The DSC peak became progressively broader with addition of sodium caseinate, indicating that the junction zones are highly heterogeneous in the mixed gel. Rheometry showed that sodium caseinate strongly influences the storage modulus (G′). In experiments in which the concentration of sodium caseinate was fixed and that of κ-carrageenan varied, plots of G′ vs. concentration of κ-carrageenan were biphasic, with an abrupt change in slope at a concentration that increased linearly with the concentration of sodium caseinate. When the concentration of κ-carrageenan was constant and that of sodium caseinate varied, G′ as a function of concentration of sodium caseinate passed through a minimum. This behaviour could be modelled quantitatively, by assuming that: (a) the sodium caseinate adsorbs κ-carrageenan, but with a limited adsorptive capacity; (b) sodium caseinate aggregates (sub-micelles) with adsorbed κ-carrageenan can associate via interaction between free ends of adsorbed κ-carrageenan chains and form a gel network; and (c) the contributions to G′ from the sodium caseinate–κ-carrageenan network and the network formed by κ-carrageenan alone are additive. At low κ-carrageenan to sodium caseinate ratios, the sodium caseinate and κ-carrageenan combine to form a mixed gel. As the ratio of κ-carrageenan to sodium caseinate increases, the sodium caseinate becomes saturated and no further association with κ-carrageenan can occur—the increase in G′, as further κ-carrageenan is added, comes from a gel network formed by κ-carrageenan alone.     

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.     

Influence of calcium on tensile, optical and water vapour permeability properties of sodium caseinate edible films

The influence of calcium on sodium caseinate edible films with and without lipid addition (oleic acid (OA)–beeswax (BW) mixtures) was investigated through the analysis of tensile, optical and water vapour barrier properties. Calcium was added by substitution of sodium caseinate by calcium caseinate. Calcium caseinate films have less transparency and more rigidity but they have lower water vapour permeability values than sodium caseinate films. The effect of substitution was different for films with and without lipids. Calcium caseinate increased tensile strength and decreased elongation of films, depending on the level of substitution and lipid presence. Among control films (without lipid), water vapour permeability was reduced when calcium caseinate was present, reaching values of 3.9 (±0.2) g mm kPa⁻¹ h⁻¹ m⁻². Nevertheless, in the films containing lipids, this reduction was inhibited when the level of sodium caseinate substitution exceeded 50%. Film transparency and gloss was reduced by calcium caseinate and lipid presence, although pure calcium caseinate films were glossier. When taking all the studied variables into account, the films prepared with 2:1 NaCas:CaCas ratio and 70:30 OA:BW ratio showed the most adequate properties.     

Encapsulation of bixin in sodium caseinate to deliver the colorant in transparent dispersions

Bixin, the major colorant component of annatto, is water insoluble and sensitive to degradation by temperature, pH, and light stresses. In this work, we studied an encapsulation process by spray drying warm 40% v/v aqueous ethanol solution with dissociated sodium caseinate (NaCas) and dissolved bixin. Upon hydration of spray-dried powder, transparent dispersions were observed at a wide pH range away from the isoelectric point (pI) of NaCas. The stability of bixin was much improved and the consistent yellow color was obtained. The volume–length mean particle diameters of capsules were around 250 nm in dispersions, slightly bigger than that of NaCas, based on dynamic light scattering, but the difference was not observed based on atomic force microscopy. Capsules and the mixture of NaCas and bixin showed different fluorescence and FTIR spectra. At pH near the pI of casein, soluble soybean polysaccharides adsorbed strongly onto capsules and stabilized them from aggregation. The simple encapsulation approach studied in the present work showed a promising process to enhance the stability and dispersibility of carotenoids using NaCas as a carrier, especially in transparent dispersions.     

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.     

Interfacial composition and stability of emulsions made with mixtures of commercial sodium caseinate and whey protein concentrate

The interfacial composition and the stability of oil-in-water emulsion droplets (30% soya oil, pH 7.0) made with mixtures of sodium caseinate and whey protein concentrate (WPC) (1:1 by protein weight) at various total protein concentrations were examined. The average volume-surface diameter (d₃₂) and the total surface protein concentration of emulsion droplets were similar to those of emulsions made with both sodium caseinate alone and WPC alone. Whey proteins were adsorbed in preference to caseins at low protein concentrations (<3%), whereas caseins were adsorbed in preference to whey proteins at high protein concentrations. The creaming stability of the emulsions decreased markedly as the total protein concentration of the system was increased above 2% (sodium caseinate >1%). This was attributed to depletion flocculation caused by the sodium caseinate in these emulsions. Whey proteins did not retard this instability in the emulsions made with mixtures of sodium caseinate and WPC.     

Assessment of physical and mechanical properties of sodium caseinate and stearic acid based film-forming emulsions and edible films

Edible films were prepared using sodium caseinate (6–8 g/100 g) and stearic acid (0–2 g/100 g). Effects of the ratio of stearic acid and sodium caseinate to water on the water vapor permeability (WVP) and mechanical properties of the prepared films were evaluated. Film-forming emulsions were also tested for rheological properties and surface tension. Changes in the ratios of sodium caseinate and stearic acid to water had significant effects on WVP (p < 0.05) and surface tension (p < 0.01). Higher values of consistency coefficient and elastic modulus were obtained in the presence of higher stearic acid. In addition, increase in stearic acid content increased the rate of water loss and gain of elastic modulus at the early stage of drying and resulted in production of less flexible film. The resultant edible film prepared with 6 g/100 g sodium caseinate and 2 g/100 g stearic acid showed the lowest WVP of 1.368 (g mm/m² h kPa).     

Water soluble inner aqueous phase markers as indicators of the encapsulation properties of water-in-oil-in-water emulsions stabilized with sodium caseinate

The aim of this study was to evaluate the suitability of Methylene Blue (MB) and Vitamin B₁₂ (Vit-B₁₂) as water soluble inner aqueous phase (W₁) markers for measuring the encapsulation efficiency and stability of water-in-oil-in-water (W₁/O/W₂) double emulsions stabilized by sodium caseinate (NaCN). The encapsulation efficiency and stability were determined by centrifugation of the double emulsion to separate the cream phase (W₁/O) and the outer aqueous phase (W₂) and measuring the concentration of marker in W₂ by absorbance spectrophotometry. To validate this method the marker concentration measurable and the stability of the marker in W₂ were measured. Both markers could be accurately measured in W₂ and there was no change in the concentration of marker on storage of a W₂ solution for 7 days at 45 °C. The recovery yields of MB and Vit-B₁₂ in the recovered W₂ of an oil-in-water (O/W₂) emulsion, determined using the procedure normally used for measuring encapsulation efficiency and stability, were 78% and 99%, respectively, and 52 and 100%, respectively. Double emulsions had encapsulation efficiency of 61.9 ± 21.4% and 16.6 ± 1.1% and encapsulation stability of 62.0 ± 22.6% and 10.7 ± 0.7% for MB and Vit-B₁₂, respectively. Recovery yield and encapsulation efficiency/stability data for MB indicate that it is not a suitable marker for measuring the encapsulation properties of NaCN stabilized double emulsions while similar data for Vit-B₁₂ indicate that it is a suitable marker for studying the encapsulation properties of double emulsions stabilized with NaCN. Methods used in other studies to measure encapsulation properties of double emulsions are discussed in light of the results obtained in this study.     

An investigation on the effect of pigments on the texture ability and mechanical properties of polypropylene BCF yarns

Abstract

In this work, the effect of five pigments on the mechanical and texturing properties of polypropylene BCF yarns has been investigated. The results showed that depending on the type, pigments may have a significant decreasing or increasing effect on the mechanical properties of polypropylene BCF yarns, although some of these differences may not be practically significant. As far as the bulk properties of the BCF yarns are concerned, a trend could not be established for the effect of pigments on crimp contraction and crimp modulus, but increasing the amount of pigments decreased the crimp stability of all BCF yarns. XRD and DSC analyses showed that the addition of pigments decreased the crystallinity index of the yarns depending on the type of pigment. DSC analysis showed a higher onset melting point after adding pigments with the exception of white one. FTIR spectra show no considerable reaction or interaction between polypropylene and the pigments employed in the masterbatch.