微生物转谷氨酰胺酶催化酪蛋白酸钠聚合物的功能特性研究

研究了微生物转谷氨酰胺酶(TGase)催化酪蛋白酸钠聚合对其功能特性的影响。结果显示,随着催化时间的增加,其各组份含量不断减少,同时生成的聚合物含量不断增加,比较了TGase催化不同酪蛋白的聚合速率,结果显示转谷氨酰胺酶较易催化α-和β-酪蛋白,而不易催化κ-酪蛋白TGase催化聚合酪蛋白酸钠能明显改善其乳化性能,聚合时间越长,乳化指数越高,而乳化稳定性随聚合时间先升后降,4h时最高TGase催化酪蛋白酸钠还可提高其热稳定性,然而对其起泡性影响不大     

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 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.     

Physical properties and antilisterial activity of bioactive edible films containing Lactobacillus plantarum

Bioactive polymeric films were developed from the incorporation of Lactobacillus plantarum into polysaccharide or protein edible films. Lactic acid bacteria (LAB) were added directly to the film forming solution and films were obtained by casting. Four different biopolymers were tested: sodium caseinate, pea protein, methylcellulose and hydroxypropylmethylcellulose. In order to study the impact of the incorporation of the protective culture into the biopolymer matrix, the water vapour permeability (WVP), optical and mechanical properties of the dry films were evaluated. Furthermore, survival of L. plantarum and the antimicrobial potential of bioactive films against Listeria innocua were studied. Whereas optical and mechanical properties of the films were not notably altered by the LAB incorporation, WVP values increased for all biopolymers. Viability of the strain was lower in cellulose derivative matrices than in protein films, although bacteriocin production in the newly prepared films was greater in these matrices. As a result, a significant antimicrobial activity against L. innocua was observed for polysaccharide matrices, which was not observed for protein films, where the bacteriocin production is delayed. In pea protein films the maximum bacteriocin production occurs at 15 storage days and afterwards decreases. So, the nature of the biopolymer and the knowledge of time when an adequate bacteriocin concentration is produced are key to use bioactive films in an effective way.     

酪蛋白酸钠溶液粘度变化的数学模型

研究了浓度为１２－２０％酪蛋白酸钠溶液在６６－９０℃的粘度变化。在ＰＨ值为６．８－７．５的范围内，ＰＨ值对酪蛋白酸钠的粘度没有显著的影响。酪蛋白酸钠溶液粘度的和与溶液的浓度和温度都叶线性关系（Ｒ＾２〉９５％）。酪蛋白酸钠溶液的粘度浓度方程的斜率和截距都与温度呈二次方程的关系（Ｒ＾２＝９４．９１％，Ｒ＾２＝９３．５９％），并由此推导出关于浓度和温度对酪蛋白酸钠溶液粘度相互 半对数方程（Ｒ＾２＝９４．     

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.     

Physical properties and antioxidant capacity of starch–sodium caseinate films containing lipids

Biodegradable films based on starch, sodium caseinate, glycerol and lipids (oleic acid and/or α-tocopherol) were obtained and evaluated in terms of microstructure, mechanical behaviour, barrier and optical properties and antioxidant capacity. The effect of film storage time on these properties was also analysed. The lipid incorporation provoked phase separation due to the different interaction between each polymer and lipids, although structural rearrangement of components during storage could be deduced from the change in mechanical behaviour. After storage, all films showed similar mechanical properties, but lipid containing films were more stretchable. Lipid addition did not induce a notable decreased in water vapour permeability of the films, but oxygen permeability highly increased when they contained oleic acid. All films were highly transparent, with very small differences among formulations, although their gloss values increased when lipids were added. The incorporation of α-tocopherol greatly increased the antioxidant capacity of the films which affected oxygen permeability.     

酪蛋白钠稳定肉糜机理的研究

通过对添加酪蛋白钠预制乳剂香肠样品与对照样的扫描电镜照片的分析，证明了酪蛋白钠可在脂肪球表面形成１μｍ强韧亲水蛋白膜，稳定了肉糜的脂肪蛋白质水体系     

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.     

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.     

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。     

混合蛋白酶水解酪朊酸钠工艺的研究

以酪软酸钠为原料,采用混合蛋白酶水解,本文对酶水解工艺参数,小分子肽得率变化进行了系统的研究。本文得出结论:碱性蛋白酶和中性蛋白酶混合使用酶解酪朊酸钠的最适宜条件为:温度为45,pH为6.5,酶解时间为24小时,底物浓度为10%,酶用量为1.55?04u/g.     

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.     

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.     

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.     

Preparation,characterisation and selected functional properties of sodium caseinate–maltodextrin conjugates

Sodium caseinate (NaCN)–maltodextrin (Md40 or Md100) conjugates were prepared by a Maillard-type reaction by dry heat treatment of mixtures of NaCN and Md at 60 °C and 79% relative humidity for 4 days. Minimal levels of coloured reaction products were formed during conjugate preparation. Conjugation resulted in a 35.6% and a 36.2% loss of available amino groups in the NaCN, and a 17.8% and a 25.7% loss of available reducing groups in Md40 and Md100, respectively. SDS–PAGE and gel permeation chromatography confirmed conjugation. When assessed in the pH range 2.0–8.0 at 20 °C and 50 °C, conjugates had improved solubility compared to NaCN, particularly around the isoelectric point of the protein. The emulsifying properties of NaCN–Md conjugates were assessed in oil-in-water (o/w) emulsions and in model cream liqueurs. The conjugate stabilised o/w emulsions and liqueurs showed improved stability when compared to NaCN stabilised o/w emulsions and liqueurs. These results indicate a potential for these NaCN–Md conjugates as speciality functional food ingredients.     

Development of a novel bioactive packaging based on the incorporation of Lactobacillus sakei into sodium-caseinate films for controlling Listeria monocytogenes in foods

A novel packaging technology was developed based on the incorporation of Lactobacillus sakei cells into sodium-caseinate (SC) edible films. Incorporation was based either on direct addition of the cells in the film forming solution used for casting or by surface spraying of the culture on the preformed film, resulting in a population density of 10⁶ cfu/cm². Addition of sorbitol in the film matrix increased the viability of the cells, greater than 90%, upon storage under both refrigeration and ambient temperature conditions for 30 days. Incorporation of the viable protective culture did not affect the mechanical properties and the physico-chemical properties of the film. Application of the films to both laboratory medium (agar) and a food model system (fresh beef) inoculated with Listeria monocytogenes resulted in a rapid growth of L. sakei immobilized in the film following contact with the wet medium or the food surface and a significant inhibition of the pathogen growth compared to the control samples under both constant and dynamic storage temperature protocols. The present study indicated that biopolymer-based antimicrobial films containing cells of a protective culture can be used as an effective packaging technology for improving food safety.     

Influence of the chain-length distribution of inulin on the rheology and microstructure of prebiotic dairy desserts

The changes in rheological properties and microstructure of inulin-enriched custard desserts were studied for a seven-day period of refrigerated storage. Desserts prepared with 7.5% short-chain inulin (CLR), long-chain inulin (TEX), native inulin (IQ), and a mixture of short and long-chain inulin (MIX) were compared. Rheological changes and inulin aggregates formation were not observed in CLR samples during the seven-day storage period. However TEX, MIX and IQ samples formed inulin aggregates and consequently became more thixotropic, consistent and elastic. These rheological changes, the rate of the inulin aggregates formation and the percentage of volume occupied by them varied among samples in the following order TEX > MIX > IQ. Although the same trend was observed for both skimmed-milk and whole-milk samples the effects of inulin type and storage time on rheology and microstructure were less pronounced in the whole-milk samples.     

酪朊酸钠磷酸化结果验证方法研究

酪朊酸钠是一种天然乳化剂，具有良好的乳化，发泡，粘着等功能症，但由于其蛋白质的疏水性度高，影响了其乳化功能性，在总结前人经验的基础上，对其进行了三聚磷酸钠改性。通过对磷酸酪朊 酸钠的差热分析曲线和等电点的测定结果的分析讨论，证明了酪朊酸钠在ＰＨ７－９之间三聚磷酸钠进行改性是成功的，通过三聚磷酸钠改性，发迹了酪朊酸的蛋白质酸结构，酪朊钠分子中加入磷酸酪键是有可能的。