Rheology and structure of mixtures of ι-carrageenan and sodium caseinate

Mixtures of ι-carrageenan (IC) and sodium caseinate (SC) were investigated and the results are compared with a similar study of mixtures of κ-carrageenan (KC) and SC. Segregative phase separation was observed at high biopolymer concentrations and the binodal was determined. At low IC concentrations, SC formed aggregates involving a very small amount of IC that were characterized with light scattering. The influence of adding SC on the gelation of IC during cooling and the shear modulus of the gels was studied in the presence of NaCl or KCl. The main conclusion of this work is that SC binds to both IC and KC, in the coil conformation as well as in the helix conformation, but that its effect on the rheology is much weaker for IC than for KC.     

Characterisation of binding of iron to sodium caseinate and whey protein isolate

The fortification of dairy products with iron is an important approach to delivering iron in required quantities to the consumer. The binding of iron (ferrous sulfate) to two commercial milk protein products, sodium caseinate and whey protein isolate (WPI), dissolved in 50 mM HEPES buffer, was examined as a function of pH and iron concentration. Sodium caseinate had more sites (n = 14) than WPI (n = 8) for binding iron, and the affinity of caseinate to bind iron was also higher than that of WPI. These differences were attributed to the presence of clusters of phosphoserine residues in casein molecules, which are known to bind divalent cations strongly. The amount of iron bound to sodium caseinate was found to be independent of pH in the range 5.5–7.0, whereas acidification (pH range 7.0–3.0) caused a marked decrease in the amount of iron bound to WPI.     

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.     

Quantification of free and protein-bound trans-resveratrol metabolites and identification of trans-resveratrol-C/O-conjugated diglucuronides - two novel resveratrol metabolites in human plasma

The polyphenol trans-resveratrol (t-RES) is present as t-RES-3-O-beta-D-glycoside, termed piceid, in several plant-derived foods. Although data on the metabolism and on in vivo effects of t-RES have been reported, quantitative data on the metabolites formed after dietary intake of t-RES or piceid are still lacking. In this study, 85.5 mg of piceid per 70 kg of body weight (bw) were administered to healthy volunteers in a bolus dose. t-RES metabolites formed in plasma and urine were identified and quantified by LC-MS/MS, NMR, and HPLC-DAD analysis using chemically synthesized t-RES conjugate standards. In addition, the amount of t-RES metabolites bound noncovalently to plasma proteins was determined for the first time in humans. The metabolites identified and quantified were t-RES-3-sulfate, t-RES-3,4'-disulfate, t-RES-3,5-disulfate, t-RES-3-glucuronide and t-RES-4'-glucuronide, with t-RES-sulfates being the dominant conjugates in plasma and urine. Besides these metabolites, two novel t-RES-C/O-conjugated diglucuronides have been identified and quantified in plasma and urine. Moreover, it could be shown that up to 50% of the plasma t-RES-3-sulfate, t-RES-disulfates, and the novel t-RES-C/O-diglucuronides were bound to proteins. Total recovery of the dietary administered piceid in urine ranged between 13.6 and 35.7%.     

Impact of enzyme preparation and degree of hydrolysis on peptide profile and nitrogen solubility of sodium caseinate hydrolysates

The solubility of casein ingredients is limited under certain pH conditions. Therefore, sodium caseinate (NaCN) was hydrolysed at laboratory scale with four enzyme preparations (Alcalase, Prolyve, FlavorPro Whey and pepsin) yielding hydrolysates having degree of hydrolysis (DH) values between 0.19 ± 0.11 and 19.25 ± 0.73%. The nitrogen solubility index (NSI) over the pH range 2.0–8.0 was affected by (i) the specificity of the enzyme preparation, (ii) the DH and (iii) the presence of unhydrolysed NaCN within the hydrolysate. The trends observed at laboratory scale (<5 L) were also seen with the semi‐pilot‐scale (300 L) hydrolysates generated with Alcalase and FlavorPro Whey. Removal of unhydrolysed NaCN from the FlavorPro Whey hydrolysate using a 5‐kDa ultrafiltration (UF) membrane increased NSI. This study has highlighted the importance of carefully selecting the proteolytic preparation along with the DH to design casein‐based ingredients with enhanced technofunctional properties.     

Binding of olive oil phenolics to food proteins

In this paper we investigate the interaction of phenolics extracted from olive oil with different food proteins (sodium caseinate, bovine serum albumin, β‐lactoglobulin and gelatin). Binding parameters are estimated using different experimental techniques: gel filtration, HPLC, isothermal titration calorimetry and NMR diffusion measurements. For comparison, the binding properties of gallic acid and tannic acid are also studied. The affinity of olive oil phenolics for the different food proteins is found to be relatively weak (compared with tannic acid). Binding constants are measured for the different phenolics in the extract: tyrosol and hydroxytyrosol do not (or very weakly) bind to the proteins, whereas other phenolics in the extract had binding constants of the order 10²–10⁴ M ^?1. The binding parameters determined have been discussed in relation to the possible effect of proteins on sensory properties (bitterness) of food emulsions containing olive oil. Copyright © 2004 Society of Chemical Industry     

Binding,stability, and antioxidant activity of curcumin with self-assembled casein–dextran conjugate micelles

This work studied the potential of self-assembled micelles of casein–dextran conjugates (CD) as a protective carrier for bioactive curcumin. CD was prepared through the Amadori rearrangement of the Maillard reaction. In casein micelles and CD micelles, the addition of curcumin can quench the intrinsic fluorescence of casein gradually. According to the double logarithm equation, the binding constants were determined as 3.9 × 10⁴ and 1.8 × 10⁵ M^?1 for the binding of curcumin with casein micelles and CD micelles, respectively. The higher affinity of hydrophobic binding of curcumin with CD micelles was ascribed to the more hydrophobic and compact structure of casein core surrounded by the hydrophilic dextran shell, which was supported by the fluorescence spectrum and fluorescence anisotropy of curcumin. Furthermore, CD micelles were found to be superior to casein micelles for improving the stability and radical scavenging activity of curcumin.     

Effects of milk supplementation with skim milk powder, whey protein concentrate and sodium caseinate on acidification kinetics, rheological properties and structure of nonfat stirred yogurt

Milk supplementation with milk proteins in four different levels was used to investigate the effect on acidification and textural properties of yogurt. Commercial skim milk powder was diluted in distilled water, and the supplements were added to give different enriched-milk bases; these were heat treated at 90 °C for 5 min. These mixtures were incubated with the bacterial cultures for fermentation in a water bath, at 42 °C, until pH 4.50 was reached. Chemical changes during fermentation were followed by measuring the pH. Protein concentration measurements, microbial counts of Lactobacillus bulgaricus and Streptococcus thermophilus, and textural properties (G′, G″, yield stress and firmness) were determined after 24 h of storage at 4 °C. Yogurt made with milk supplemented with sodium caseinate resulted in significant properties changes, which were decrease in fermentation time, and increase in yield stress, storage modulus, and firmness, with increases in supplement level. Microstructure also differed from that of yogurt produced with milk supplemented with skim milk powder or sodium caseinate.     

Influence of pH and biopolymer ratio on sodium caseinate—guar gum interactions in aqueous solutions and in O/W emulsions

Many colloidal food systems contain both proteins and polysaccharides. In the present study, the phase behaviour of mixed sodium caseinate—guar gum aqueous solutions was investigated: segregative phase separation was observed in solutions containing at least 0.04% of guar gum and 1.6% of sodium caseinate, thus indicating the limited compatibility of the polysaccharide and the protein.In addition, the functionality of guar gum as gravitational stabilizer in sodium caseinate stabilized 25% O/W emulsions was checked. At pH conditions significantly larger than the iso-electric point (IEP) of sodium caseinate, addition of small amounts of guar gum (0.1–0.2%) gave raise to fast serum separation, which was thought to be due to depletion flocculation. Increasing the polysaccharide concentration and/or the oil volume fraction limited the degree of phase separation, since depletion flocculation induced a sufficiently strong three-dimensional network to withstand gravity effects.Considering different guar gum concentrations at pH 5.0, 5.5, 6.0 and 6.5, it became obvious that the phase separation behaviour in the absence of guar gum was largely affected by the pH, whereas in the presence of at least 0.1% of guar gum it became mainly affected by the guar gum concentration. Hereby, higher guar gum concentrations introduced a longer delay time before separation could effectively be detected. As laser diffraction particle size analysis results were not significantly affected by guar gum addition, it was concluded that the guar gum-induced flocculation was weak in nature and largely reversible.Combining all results, it was concluded that guar gum could effectively be used to prevent phase separation problems that could occur due to flocculation around the protein's IEP, provided that at least 1.0% of guar gum is added to ensure depletion stabilization by formation of a sufficiently strong three-dimensional network to overcome separation effects. Increasing the ionic strength through addition of salt further reinforces the network in order to prevent its collapse due to gravity.     

Development of multiple emulsions based on the repulsive interaction between sodium caseinate and LBG

The stability of oil-in-water, water-in-water and multiple emulsions containing sodium caseinate (Na-CN) and/or locust bean gum (LBG) at pH 5.5 was investigated with different compositions using a visual analysis (creaming and/or phase separation), optical microscopy and rheological measurements. Oil-in-water emulsions (O/W) were produced by high pressure homogenization, which promoted the formation of very small droplets (∼0.4 μm) and hindered the destabilization process. In the second step of this study, a visual phase diagram was constructed in order to identify the concentrations of sodium caseinate (Na-CN) and locust bean gum (LBG) that led to phase separation at pH 5.5. A mixed solution composed of 3% (w/v) Na-CN and 0.3% (w/v) LBG was chosen to produce the water-in-water and multiple emulsions. After centrifugation, the solution was separated into an upper phase rich in polysaccharide (PS) and a bottom phase rich in protein (PR), which were mixed in different proportions (1:3, 1:1, 3:1), forming the water-in-water (W/W) emulsions. The stability, microstructure and rheological properties of the W/W emulsions depended strongly on the composition of the biopolymers. An increase in the polysaccharide concentration in the W/W emulsions led to the production of more viscous and stable systems. Multiple emulsions with different characteristics were prepared and also depended on the biopolymer composition. The system with the highest polysaccharide content was the only one that showed an O/W/W structure, while the others presented the microstructure of an O/W-W/W emulsion.     

Effects of solvent and alkaline earth metals on the heat-induced precipitation process of sodium caseinate

The precipitation temperatures of sodium caseinate in H₂O and D₂O in the presence of Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ were investigated through fluorescence, turbidity and conductivity experiments.     

干红葡萄酒中白藜芦醇的含量与分布

对影响葡萄酒中白藜芦醇含量的因素进行了系统的研究.结果表明:葡萄浆果中的白藜芦醇主要分布在果皮上;发酵温度及酵母菌、乳酸菌种类对葡萄酒中白藜芦醇含量有一定的影响,而果胶酶对其几乎没有影响;产地、年份等生态条件的差异导致了葡萄酒中白藜芦醇含量的差异;国产干红葡萄酒中白藜芦醇含量差异明显.     

液相色谱-质谱法检测保健食品中白藜芦醇及白藜芦醇苷

目的 建立液相色谱-质谱法(liquid chromatography-mass spectrometry,LC-MS)分析保健食品中白藜芦醇及白藜芦醇苷顺反结构(顺式白藜芦醇、反式白藜芦醇、顺式白藜芦醇苷、反式白藜芦醇苷)含量的分析方法.方法 保健食品经80％乙醇于低温条件下避光提取,经液相色谱柱分离后,在多反应监测...     

Heating of milk alters the binding of curcumin to casein micelles. A fluorescence spectroscopy study

Curcumin, a polyphenolic compound present in turmeric, is a hydrophobic molecule that has been shown to bind to casein micelles. The present work tested the hypothesis that surface changes in the casein micelles caused by heat-induced interactions with the whey proteins would affect the binding of curcumin. Binding was quantified by direct and tryptophan quenching fluorescence spectroscopy. Curcumin binds to the hydrophobic moieties of the casein proteins, with a 10 nm blue shift in its fluorescence emission peak, and causes quenching of the intrinsic fluorescence spectra of the proteins. The fluorescence intensity of curcumin increased after heating of milk at 80 °C for 10 min; a similar trend in the binding constants was also observed with casein micelles separated from the soluble proteins by centrifugation. There was an increase in the non-specific interactions with heating milk at 80 °C for 10 min, both in milk as well as in casein micelles separated from the serum proteins. The increased capacity of milk proteins to bind curcumin after heat treatment can be attributed to whey protein denaturation, as whey proteins bind to the surface of casein micelles with heating.     

葡萄采后紫外线(UV)处理对白藜芦醇的诱导作用

采用不同剂量的紫外线(254nm)照射处理采后赤霞珠、玫瑰香葡萄,室温避光贮藏24小时后检测葡萄果皮中白藜芦醇的含量变化,以及葡萄可溶性固形物、总酸、总酚和花色素的含量,结果发现:1)在赤霞珠、玫瑰香葡萄果皮中检测到反式白藜芦醇,但未检测到顺式白藜芦醇;2)UV照射处理显著影响了葡萄的花色素、可溶性固形物含量;3)低剂量的UV照射对葡萄果皮中白藜芦醇具有诱导作用,明显提高了白藜芦醇含量,而高剂量UV处理后白藜芦醇含量呈降低趋势.     

Interactions between pig gastric mucin and sodium caseinate in solutions and in emulsions

The interactions between pig gastric mucin (PGM) and sodium caseinate (Cas) were studied in solutions and in Cas-stabilized emulsions with respect to the ratio of the two components and the pH (1–7) with an emphasis on pH cycling, using absorbance, zeta potential, light scattering, creaming and microscopy measurements. In solutions, pH-reversible interactions were observed at pH 3 or lower, down to pH 1. Zeta potential measurements suggest that interactions are electrostatic in nature at pH 3, while the negligible charge of PGM allows for some attractive interactions with positively charged Cas at pH 1. Caseinate-stabilized oil-in-water emulsions are stable toward coalescence at pH 1 and pH 7; some coalescence is observed at pH 3. Addition of PGM results in flocculation, either due to depletion (pH 7), or due to bridging flocculation and Cas–PGM interactions similar to those observed in solution (pH 1 and pH 3). The flocculation is reversible, as is shown in pH cycling at pH 1 to pH 7, then to pH 1. Overall, the above can be of interest as an examination of the fate of emulsions in pH transitions and cycling in the human gastrointestinal tract.     

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.