Influence of milk proteins on the pasting behaviour and microstructural characteristics of waxy maize starch

Gelatinisation of 5 wt% waxy maize starch (WMS) under shear (16.8 s⁻¹), alone and in mixtures with 5 wt% α-lactalbumin (α-lac), β-lactoglobulin (β-lg), α-caseinate or β-caseinate, showed reinforcement of the starch granule structure by both caseinates, but not by the whey proteins (α-lac and β-lg). Reinforcement was evident from (i) later onset of increase in viscosity on heating; (ii) higher gelatinisation temperature by differential scanning calorimetry; (iii) micrographs showing reduced swelling during heating and in the final pastes obtained on cooling; and (iv) elimination of a characteristic “secondary swelling peak” observed for WMS immediately after completion of heating to 95 °C and attributed to fracture of a restricting layer of lipid and protein at the surface of the granules. A likely mechanism of reinforcement is binding of caseinate to the lipid–protein layer. Images from confocal laser scanning microscopy with fluorescent labelling of protein showed attachment of aggregated β-caseinate to the surface of WMS granules in mixtures that had been heated (under shear) to 70 °C. Corresponding images for mixtures with α-caseinate (which is less aggregated) showed penetration of protein to the interior of the granules, which would allow binding to occur on the inside of the surface layer as well as the outside. The inability of the more hydrophilic whey proteins to reinforce the WMS granules suggests that binding of caseinates to the lipid–protein layer occurs predominantly by hydrophobic association. The understanding that caseinates make gelatinised WMS granules smaller and tougher could be useful in product formulation.     

PFG-NMR self-diffusion in casein dispersions: Effects of probe size and protein aggregate size

The self-diffusion coefficients of different molecular weight PEGs (Polyethylene glycol) and casein particles were measured, using a pulsed-gradient nuclear magnetic resonance technique (PFG-NMR), in native phosphocaseinate (NPC) and sodium caseinate (SC) dispersions where caseins are not structured into micelles. The dependence of the PEG self-diffusion coefficient on the PEG size, casein concentration, the size and the mobility of casein obstacle particles are reported. Wide differences in the PEG diffusion coefficients were found according to the casein particle structure. The greatest reduction in diffusion coefficients was found in sodium caseinate suspensions. Moreover, sodium caseinate aggregates were found to diffuse more slowly than casein micelles for casein concentrations >9 g/100 g H₂O. Experimental PEG and casein diffusion findings were analyzed using two appropriate diffusion models: the Rouse model and the Speedy model, respectively. According to the Speedy model, caseins behave as hard spheres below the close packing limit (10 g/100 g H₂O for SC (Farrer & Lips, 1999) and 15 g/100 g H₂O for NPC (Bouchoux et al., 2009)) and as soft particles above this limit. Our results provided a consistent picture of the effects of diffusant mass, the dynamics of the host material and of the importance of the casein structure in determining the diffusion behavior of probes in these systems.     

Effect of water content on the mobility of solute molecules and of protein side chains in casemate preparations

The effect of water content on the mobility of small solute molecules and of casein side chains was studied by electron spin resonance in caseinate/water systems. The immobilization of nitroxide probes of different sizes and properties were followed during progressive dehydration of concentrated caseinate preparations (3 g H₂O/g dry protein). Above a characteristic minimum moisture content a linear relationship was observed between the rotational diffusivity and water content. The slope of the straight lines depended upon the size of the probe and upon the nature of the interactions with the protein. Nitroxide labels were covalently bound to caseinate and the changes in the flexibility of the side chains as hydration changed were followed. The results are discussed in relation to the solvent properties of water, and to recent suggestions concerning the significance, for stability, of the glass transition phenomenon in such materials.     

The rennet coagulation mechanisms of a concentrated casein suspension as observed by PFG-NMR diffusion measurements

Pulsed field gradient-nuclear magnetic resonance (PFG-NMR) was used to monitor the diffusion of caseins throughout the rennet coagulation of a highly concentrated casein suspension. Two types of casein species were distinguished according to their diffusing properties and attributed to the dissolved casein fraction, i.e. dissociated caseins and caseinomacropeptides (CMP), and casein particles, respectively. The NMR signal intensity coming from the dissolved casein fraction, which is related to the number of protons it contains, increased all along the experiment whereas the opposite tendency was observed for casein particles. This was explained by the increasing amount of CMP in the whey and the reciprocal loss of protons contained by casein particles, and used to quantitatively estimate the kinetics of the chymosin action. The diffusion of the dissolved casein fraction remained nearly constant during the coagulation process whereas, as revealed by rheometry measurements, the diffusion of casein particles was very sensitive to the structural reorganization of the sample. It decreased by about 35% during the sol–gel transition and increased in similar proportions during the succeeding rise in gel porosity. Our results also provide different types of information on the respective behaviors of dissociated caseins and casein particles during the course of the process, the most remarkable one being that all the casein particles did not aggregate during the sol–gel transition of our sample. This strongly suggests that the rennet gelation of a concentrated dairy solution may be better visualized by the formation of a network backbone during the sol–gel transition which is thereafter reinforced upon further incorporation of casein particles.     

Effect of sesame protein isolate in partial replacement of milk protein on the rheological,textural and microstructural characteristics of fresh cheese

Soft cheeses were manufactured from bovine milk with the addition of 0–12% sesame protein isolate (SPI) were utilised to investigate rheology, texture and microstructure at different stages of cheese making. SPI addition reduced the speed of milk fermentation, kappa‐casein proteolysis of rennet and elongated the time of cheese curd formation. Renneted milk storage modulus G′_60min was decreased and coagulation time increased with increasing SPI content. Low SPI supplements (4% and 8%) enhanced the hardness, cohesiveness, adhesiveness and gumminess of the soft cheese, while high SPI addition (12%) deteriorated the texture. In the cheese curd gel matrix, SPI distributed as specific SPI‐gel clusters on the surface of curd fractures, stacked or fused with ball‐shaped casein micelles and wrapped up to casein gel strands. In summary, SPI actively interacted with casein colloid throughout the cheese making process.     

Selection of marker peptides from casein phosphopeptide and application for quantification in infant formula

ABSTRACT

Casein phosphopeptides (CPPs) have been used worldwide as a nutritional supplement. However, the peptide components have been unknown; as a consequence, few quantification methods of CPP in infant formula were reported. This study introduced a quantification method based on peptide marker and corresponding peptide selection strategy using a simplified model with four commercial types of CPP. The peptides from four commercial CPPs were first identified. Due to the great variety of CPPs, two marker selection strategies were adopted: on one hand, universal marker peptide VLPVPQK can be used for the quantification of all four commercial CPPs, if the CPP can be obtained as a standard. On the other hand, the specific marker peptide LYQEPVLGPV can be used for identification and quantification of commercial CPP type K content in infant formula with a fixed calculation factor. In the simplified model, the combination use of the two markers can meet most of the requirements of CPP analysis in infant formula. The method validation revealed that this was suitable for the routine analysis laboratories without proteomics backgrounds. This selection strategy was suggested for the large-scale marker peptide selection with all commercial CPPs, which can give a comprehensive solution of CPP quantification in infant formula.

Abbreviations: CPP: Casein phosphopeptides; LC: Liquid chromatography; TQMS: Triple quadrupole mass spectrometry; MRM: Multiple reaction monitoring; RSD: Relative standard deviation; L*: [¹³C₆, ¹⁵N]-leucine; SSSEE: Peptides sequence of serine-serine-serine-glutamic acid-glutamic acid     

Effect of a new emulsifier containing sodium stearoyl-2-lactylate and carrageenan on the functionality of meat emulsion systems

The emulsion capacity and stability of a new emulsifier containing sodium stearoyl lactylate plus iota carrageenan (SSL/iC) in comparison to caseinate and soy isolate was analysed. The emulsion capacity and stability of SSL/iC in oil/water (O/W) model system emulsions was higher than shown by caseinate and soy isolate. However, the O/W emulsion stability was negatively affected by sodium chloride addition, but positively affected by an increase in temperature. Meat batters were made with caseinate, soy isolate, and SSL/iC at the minimum concentration that showed a good performance (>75% stability) in the O/W emulsions. The emulsifier SSL/iC produced high cook yields and good stability when used in meat batters. However, the cooked meat batters containing SSL/iC showed texture characteristics highly detrimental to the sensory analysis. On the other hand, the addition of 2% potato starch reduced the differences in texture parameters among the samples made with the different emulsifiers.     

超滤法纯化酪蛋白凝乳酶水解物中的酪蛋白糖巨肽

研究超滤法分离纯化了(CGMP)的条件,得到超滤的最佳条件是在室温下,压差为0.02 MPa,浓缩比为8.通过此方法得到比较纯的CGMP,蛋白回收率为1.77%,糖基化程度(唾液酸/蛋白质)为70.1μg/mg,并且此方法适用于工业化生产.     

Chaperone‐like activity of β‐casein and its effect on residual in vitro activity of horseradish peroxidase

In this study, the residual activity horseradish peroxidase was used as a novel marker of chaperone‐like activity of β‐casein under elevated temperature. It was shown that β‐casein does affect residual activity of horseradish peroxidase (HRP) depending on the concentration and molar ratio between proteins. Incubating HRP (0.1 mg mL^?1) for 10 min at 72 °C resulted in residual activity of 59 ± 5%, while addition of 1 mg mL^?1 β‐casein resulted in increase in residual activity up to 85 ± 1%. Increased residual activity is not merely attributed to an effect of higher total protein concentration, as similar experiment with bovine serum albumin resulted in residual activity of horseradish peroxidase that was significantly lower than without any addition. The effect of β‐casein on HRP disappears when pH is below the isoelectric point of β‐casein. It was also proven by light scattering studies that β‐casein interacts with horseradish peroxidase when the temperature was increased from 25 to 70 °C whereas interactions seem to cease when temperature was lowered back to 25 °C. This study highlights how specific proteins can influence enzyme activity, which is of potential importance for various industries such as enzyme manufacturers and food industry.     

Soft Matter Engineering for the Fabrication of Functionalized Casein Microparticles

The structural features of the most abundant milk protein casein can be exploited for the targeted production of microparticles with desired properties. After the addition of pectin, the so-called casein micelles reversibly form aggregates of several µm in size, which change their shape due to shear and elongation forces. The soft properties are crucial for the subsequent solidification into stable casein microparticles during film drying. Based on pH-dependent experiments, we show how we analyze and tailor the swelling and disintegration properties of the microparticles for future controlled and instant release applications.