Disruption and sedimentation of casein micelles and casein micelle isolates under high-pressure homogenization

Native casein micelles were isolated from raw skim milk by ultrafiltration (< 30 kDa) or microfiltration (< 0.2 μm) and subjected to high-pressure homogenization (HPH) at 100, 200, 250, 300, and 350 MPa. Of particular interest was the effect of HPH on casein micelle size in solutions varying in ionic strength (0, 5, 10, and 15 mM CaCl₂) and micelle size populations. Particle size distribution reflected an initial decrease in micelle diameter in all samples at 100 MPa. In samples containing 10 and 15 mM CaCl₂, there was an abrupt increase in particle size and subsequent casein precipitation followed by sedimentation upon centrifugation at elevated pressures (300 and 350 MPa). The amount of sedimentable casein protein increased as CaCl₂ concentration (10 and 15 mM) and pressure (300 and 350 MPa) increased as determined by UV absorbance of sample supernatant. SDS-PAGE indicated extensive micellar disruption at elevated pressures (300 and 350 MPa) and confirmed that the sedimented portion of the samples contained casein proteins and minimal amounts of whey proteins. Results indicated that through HPH treatment casein micelle size can be modified based on CaCl₂ concentration and pressure applied. Based on these findings, HPH in combination with an appropriate suspending medium has the ability to modify micelles to a desired size for a number of potential applications.Industrial relevanceThe modification of structure-function properties of the casein micelle from bovine milk by using high-pressure homogenization is relevant in (1) the development of new ingredients to change rheological/textural properties of dairy based foods, and (2) the discovery of new and/or improved functionalities for protein quaternary structures.     

Rehydration of casein powders: effects of added mineral salts and salt addition methods on water transfer

Enrichment of milk with micellar casein decreases water transfer during the rehydration of milk powders. In this study, the effects of the ion environment and the ion addition method on the rehydration kinetics were found to be dependent on the changes in the micellar casein. For example, adding citrate or phosphate solution to the micellar casein suspension before drying considerably increased rehydration rates and this was related to the destruction of the micelle structure. Water transfer in the casein suspension was improved by adding NaCl during rehydration: this effect may be explained by the more hygroscopic nature of NaCl rather than by extensive modification of the micellar structure. The addition of CaCl₂ considerably affected micelle organization and led to the formation of insoluble structures during spray drying.     

Characterization of high-milk-protein powders upon rehydration under various salt concentrations

Rehydration of native micellar casein and native whey isolate protein powders was followed in different ionic environments. Solutions of NaCl and CaCl₂ in the concentration range of 0 to 12% (wt%) were used as rehydration media. The rehydration profiles obtained were interpreted in terms of wetting, swelling, and dispersion stages by using a turbidity method. Two behaviors were observed depending on the salt concentration. For native micellar casein powder, a significant change was observed between 3 and 6% NaCl and between 0.75 and 1.5% CaCl₂. The first behavior (low salt concentration) presents a typical rehydration profile: quick wetting, swelling, and long dispersion stage. The dispersion stage of the second behavior (high salt concentration) was significantly shortened, indicating a strong modification of the protein backbone. The rehydration of whey protein powder was less influenced by salts. At low salt concentrations, a typical profile for whey powders was observed: wetting with lump formation and no swelling followed by a quick dispersion. At high CaCl₂ concentrations, no turbidity stabilization was observed, indicating a possible protein unfolding and denaturation. Additionally, the changes in secondary structures of the 2 proteins upon salt increase were followed by Fourier transform infrared spectroscopy and confirmed the different profiles observed.     

Shelf life of alginate beads containing lactobacilli and bifidobacteria: characterisation of microspheres containing Lactobacillus delbrueckii subsp. bulgaricus

Capsules, containing different microorganisms (Lactobacillus plantarum, L. casei, L. delbrueckii subsp. bulgaricus, L. delbrueckii subsp. delbrueckii, L. reuteri, L. rhamnosus, Bifidobacterium breve and B. animalis subsp. lactis), were produced through a simple extrusion protocol and dipped in a CaCl₂ solution (0.5% or 8%). Beads were characterised, to assess the encapsulation yield (EY) and the shelf life at 4 °C (defined as the time to retain inside a cell count of 6 log CFU g^?1); then, L. delbrueckii subsp. bulgaricus was used as target for system optimisation, through the study of the kinetic of cell release, as a function of the concentration of CaCl₂ solution, agitation (150 rpm) and recycling. The EY was 50% or higher, and the shelf life was at least 30 days. Concerning beads containing L. delbrueckii subsp. bulgaricus, the release of cells from capsules followed a biphasic (diauxic) trend and the microsphere could be used successfully for two times, as only after third reuse, the amount of release cells decreased.     

Water holding capacity of sodium-reduced chicken breast myofibrillar protein gel as affected by combined CaCl2 and high-pressure processing

The water holding capacity (WHC) of sodium-reduced (0.3 m sodium chloride, corresponding to the salt percentage (w/v) of 1.755%) myofibrillar protein (MP) gel in response to combined calcium chloride (CaCl₂, 20, 60, 100 mm ) and high-pressure processing (HPP, 200 MPa, 10 min) was investigated. The results showed that 200 MPa + 20 mm CaCl₂ synergistically increased the WHC of MP gel via reducing particle size of MP solutions, strengthening hydrogen-bonding and disulphide-bonding, promoting formation of β-sheet and uncoiling of α-helix, exposing tryptophan residues, enhancing hydrophobic interactions of aliphatic residues and forming a compact and continuous networked gel structure. However, high concentrations (≥60 mm ) of CaCl₂ could attenuate the enhancing effects of HPP on the WHC by inducing decreased hydrogen bonds, fewer tryptophan residues exposed and coarser and aggregated gel structures with large cavities. Therefore, a combined moderate HPP and low concentration of CaCl₂ is a potential alternative for developing sodium-reduced meat products.     

Effect of palmitoylated alginate microencapsulation on viability of Bifidobacterium longum during freeze-drying

In the present research the viability of microencapsulated Bifidobacterium longum 15708 by extrusion and spray technique was investigated. Native (NA) and O-palmitoylated (PA) alginate were used as matrix for immobilization. Beads obtained by extrusion were characterized to assess the encapsulation yield (EY). Higher EY (67%) was found for bacteria immobilized in 3% PA. The effects of freeze drying on viability of entrapped B. longum were evaluated. Results indicated that microbeads obtained by spray were the most effective in preserving bacterial viability with a loss of viability of 2 log after 24 h as compared to extrusion beads and free cells where a loss of 2.9 and 2.75 log were respectively observed. No significant difference (P > 0.05) between NA and PA was observed. Scanning electron microscopy (SEM) analysis of beads showed globular structures and confirmed differences between the NA and PA alginates as to their appearance (porosity, fatty acid content), while the use of spray contributes to reduce the size of beads by 1/10. Present results showed that several alternatives such as beads size, alginate concentration, as well as polymer functionalization can be managed to allow probiotic viability.     

Tuning the properties of β-lactoglobulin nanofibrils with pH,NaCl and CaCl2

We investigated the effects of pH (1.6–2.4), NaCl and CaCl₂ (0–100 mm) on the kinetics of β-lactoglobulin fibril formation during heating at 80 °C. The morphology of fibrils was also examined. At pH 1.8–2.4 fibril formation occurred slightly faster with decreasing pH. At pH 1.6 fibril formation during the growth phase occurred much faster than at any other pH. Fibril morphology was unchanged between pH 1.6 and pH 2.0. Addition of NaCl or CaCl₂ accelerated fibril formation during the growth phase, and CaCl₂ shortened the lag phase as well. Worm-like fibrils were seen at ≥60 mm NaCl or ≥33 mm CaCl₂, and these had a persistence length which was much shorter than the long semi-flexible fibrils formed without salts. The efficiency of fibril formation can be substantially enhanced by varying pH and salt concentration.     

Pulsed electric field treatment prior to freezing carrot discs significantly maintains their initial quality parameters after thawing

The interaction of pulsed electric fields (PEF) with different cryoprotectant and texturizing agents in quality retention of carrot discs was analysed. Increasing the permeability properties by PEF may lead to better accessibility of intracellular materials to freezing and thus reducing the freezing time, leading to better maintaining the texture after thawing. Carrot discs of 5 mm thickness were immersed in different solutions of CaCl₂, glycerol, trehalose and tap water, and subsequently were treated with PEF (1 kV/cm, 100 pulses, 4 Hz). Then, the samples were drained and packed along with a control group in separate prepared polypropylene pouches. All the samples were frozen at ?18 °C for 24 h and thawed during 3 h at ambient temperature (20 °C) the following day. The quality of the thawed carrot discs was certified by measuring weight loss, firmness, microscopic studies and CIE colorimetric attributes. All the PEF‐treated samples, no matter what solution they were soaked in, could significantly (P < 0.05) maintain the firmness as well as colour attributes. However, it was deducted that application of CaCl₂ in conjunction with PEF can result in a firmer texture. Firmness analyses determined that application of PEF alone results in 5.84 N, while its combination with CaCl₂ leads to higher value of 6.63 N. Firmness in control samples was found to be 3.46 N. The SEM studies supported the results of firmness analysis and depicted more integrity in the cell walls of the samples treated with CaCl₂ and glycerol. The weight loss values varied among different samples, and the highest amount and lowest amount were reported in CaCl₂ and solely PEF‐treated samples, respectively. There was no significant difference between the colour attributes measured in different groups including control sample (P > 0.05).     

Influence of CaCl2 on the water vapor permeability and the surface morphology of mesquite gum based edible films

Oil-in-water (O/W) emulsions with a dispersed phase mass fraction (φ_m) of 0.175 were prepared by dispersing a blend of candelilla wax/mineral oil (2:1 ratio) in 10 g of mesquite gum per 100 g of water containing either CaCl₂ (0.0, 0.1, 0.2, 0.3, 0.4 or 0.5 g) alone or combined with 1.5 g of glycerol. The mean volumetric droplet size (d_3,0), the rate of droplet coalescence (C) and the viscosity-shear rate behavior of the emulsions were affected by the addition of CaCl₂ alone or combined with glycerol. The Carreau-Yasuda model fitted best the viscosity-shear rate data of all the emulsions. The surface morphology of the edible films, analyzed by Atomic Force Microscopy (AFM), exhibited a strong dependence on the CaCl₂ concentration. Maximum roughness occurred with a CaCl₂ concentration of 0.3 g per 100 g. Films with glycerol showed significantly higher roughness than those with only CaCl₂. Water vapor permeability (WVP) was significantly lowered as the concentration of CaCl₂ increased from 0.1 to 0.3 g per 100 g in the coatings, but increased again at CaCl₂ concentrations of 0.4-0.5 g per 100 g. Coatings containing glycerol displayed significant higher WVP.     

Effect of pulsed vacuum and ultrasound osmopretreatments on glass transition temperature, texture, microstructure and calcium penetration of dried apples (Fuji)

The effect of pulsed vacuum and ultrasound pretreatments on glass transition, texture, rehydration, microstructure and other selected properties of air- and freeze-dried apples (Fuji) were investigated. Apple cylinders (15 mm height × 15 mm diameter) were first osmoconcentrated in a 60 g/100 g high-fructose corn syrup solution containing 7.5 g/100 g Gluconal Cal^® combined with agitation, pulsed vacuum (PV), or ultrasound for 3 h, then hot-air or freeze dried. Changes in glass transition temperature, hardness, crispness, and rehydration rate were measured, microstructure was observed using scanning electronic microscopy (SEM), and calcium ions distributions were analyzed by a laser ablation inductively coupled mass spectrometry (LA-ICP-MS). Under the same drying method, ultrasound led to a higher glass transition temperature, lower water activity, moisture content and rehydration rate, severer structure collapse, less cavities and calcium uptake than PV did. Different osmoconcentration pretreatment had no significant (P < 0.05) effect on the hardness, crispness, shrinkage and rehydration rate. Compared to hot-air drying, freeze-dried apples showed the porous structure, minimal shrinkage, softer texture, better rehydration capacity, lighter color, and slightly lower glass transition temperature.     

The interaction of pulsed electric fields and texturizing ‐ antifreezing agents in quality retention of defrosted potato strips

The combination of pulsed electric fields (PEF) and texturizing and antifreeze agents on quality retention of defrosted potato strips were studied. Potato strips (10 mm thickness, 100 g) were placed in different solutions (1% w/v) of CaCl₂, glycerol, trehalose as well as NaCl and sucrose, treated with PEF (0.5 kV cm^?1, 100 pulses, 4 Hz). Then, all the samples were soaked in the same solutions for 10 min. After draining, samples were packed into polypropylene pouches and stored at ?18 °C for 12 h. Samples were thawed out at room temperature (20 °C) in 3 h. Untreated controls and PEF treated control samples were also frozen and thawed in similar conditions. To assess the potato strip quality, the thawed samples were analysed for moisture content, weight loss, firmness and colour attributes. The results indicate that PEF treatment by itself is not a suitable pre‐treatment method for frozen potato strips and should be assisted by CaCl₂ and trehalose treatment to prevent softening after defrosting. Firmness analyses determined that application of PEF alone results in 2.38 N. However, PEF in combination with CaCl₂ and trehalose result in 2.97 N and 2.99 N, respectively, which are both significantly firmer than the samples solely treated with PEF. CaCl₂ and trehalose were effective in not only maintaining the structural integrity of the cells, but also retaining colour attributes. The L* value was found to be higher (P < 0.05) in CaCl₂ and trehalose treated samples (58.95 and 57.21, respectively), as compared to PEF treated samples (53.97) denoting a darker colour. Application of CaCl₂ and trehalsoe in combination with PEF also resulted in significantly less weight loss after thawing.     

Influence of pulsed electric fields (PEF) with calcium addition on the texture profile of cooked black beans (Phaseolus vulgaris) and their particle breakdown during in vivo oral processing

This study investigated the use of pulsed electric fields/PEF (electric field strengths 1–2 kV/cm, specific energy 9–127 kJ/kg) to facilitate calcium uptake into black beans in preserving their hardness from thermal degradation during subsequent cooking (1 h, 70–90 °C). Increasing specific energy reduced CaCl₂ concentration in PEF processing media to 100 ppm to improve the hardness of cooked black beans. Those pre-treated at lower energy required min. 300 ppm CaCl₂. Cooked black beans with PEF-pretreatment shared similar hardness as without PEF but unexpectedly chewier (18–43% more energy to disintegrate the beans). In vivo mastication study showed particle size at 18 and 24 s of mastication was significantly different (p < 0.05) wherein “PEF without CaCl₂” had the smallest particles compared to “No PEF with CaCl₂” and “PEF with CaCl₂”. The outer seed coats of PEF-pretreated beans were easily masticated to smaller and consistent particles. This implies that PEF improved particle breakdown during mastication.     

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.     

Improvement of the storage process for cracked table olives

The aim of this work was to improve the storage method for cracked table olives. First, a study was carried out of the washing phase in 5% (wt/vol) NaCl brine with ascorbic acid and sodium metabisulphite added to it. Its use removed half the proportion of the initial sugar content in the flesh and markedly decreased the content of polyphenols in the fruits, confirming the effectiveness of this treatment. Washing with 5% NaCl and sodium metabisulphite was selected and applied in storage phase which follows. Storage of the washed cracked olives produced an additional decrease in sugars and polyphenols in the flesh, although the product still retained a fairly high concentration of residual sugars at the end of the storage period. The growth of lactic acid bacteria in this phase was prevented by the high NaCl level (10–13% at the equilibrium) but yeast growth, followed by a decline phase, was found in all storage systems studied. The use of a CO₂ atmosphere led to a partial inactivation of yeasts for about 300 h and showed a protective effect on polyphenols. Application of ozone had a favourable effect on initial solubilisation of sugars and polyphenols but caused a negative effect on fresh appearance, colour retention and polyphenol degradation. CaCl₂ + MgCl₂ treatment led to a significantly faster decline phase of yeasts. A tentative improved process for cracked olive storage may consist of a previous washing of olives for 24 h with a 5% NaCl solution (optionally added with 0.1% sodium metabisulphite), and a subsequent brining in a 15% NaCl solution with 0.25% CaCl₂ + 0.20% MgCl₂ or in a 15% NaCl brine under CO₂ atmosphere.     

α-AMYLASE COMPONENTS IN EXCISED,INCUBATED BARLEY EMBRYOS*

Excised embryos from kernels of Betzes and Bonanza barley were incubated on sand for 3 days in the presence of CaCl₂ (10-3³M), CaCl₂ + gibberellic acid (10-⁴M), CaCl₂ + casein hydrolysate (0·2%) and a mixture of all three. α-Amylase components in these embryos were analysed quantitatively by chromato-focusing. The α-amylase I component predominated in all samples. Addition of gibberellic acid or casein to the incubation medium did not increase α-amylase synthesis but addition of casein did appear to lower the proportion of α-amylase I synthesised.     

The effects of particle size on the physicochemical properties of optimized astaxanthin-rich Xanthophyllomyces dendrorhous-loaded microparticles

To improve the entrapment efficiency (EE) of astaxanthin-rich Xanthophyllomyces dendrorhous (ASX)-loaded calcium alginate gel (ASX-CAG) microparticles, we used a response surface methodology to optimize preparation conditions including the ratio of ASX to total material (X₁), alginate concentration (X₂), and CaCl₂ concentration (X₃). The EE and the mean size of the ASX-CAG microparticles were 76.7 g/100 g and 210.26 μm, respectively, after preparation under optimal conditions: 24 g ASX/100 g total material, 1.0 g/100 g alginate, and 200 mmol/L CaCl₂. The effects of particle size on different characteristics were evaluated with increasing microparticle size; an increase in microparticle size significantly increased EE and the antioxidant activity of ASX, but resulted in a decrease in the release of entrapped ASX. Most importantly, the lipid peroxidation inhibitory activity of encapsulated ASX (55.1%) was significantly higher and longer-lasting than that of non-encapsulated ASX (40.5%) after 36 h of storage as determined using the thiobarbituric acid method.     

Effect of different pre-treatments and dehydration methods on quality characteristics and storage stability of tomato powder

Dehydration process was carried out for tomato slices of var. Avinash after giving different pre-treatments such as calcium chloride (CaCl₂), potassium metabisulphite (KMS), calcium chloride and potassium metabisulphite (CaCl₂+KMS), and sodium chloride (NaCl). Untreated samples served as control. Solar drier and continuous conveyor (tunnel) drier were used for dehydration. Quality characteristics of tomato slices viz. moisture content, sugar, titratable acidity, lycopene content, dehydration ratio, rehydration ratio and non-enzymatic browning (NEB) as affected by dehydration process were studied. Storage study was also carried out for a period of 6 months for tomato powder packed into different types of packaging materials viz. metalized polyester (MP) film and low density polyethylene. Changes in lycopene content and NEB were estimated during storage at room temperature. Pre-treatment of 5 mm thickness of tomato slices with CaCl₂ in combination with KMS and drying using a tunnel drier with subsequent storage of product in MP bags was selected as the best process.     

Effect of chloride salt mixtures on selected attributes and mineral content of fermented cracked Aloreña olives

Sodium chloride is essential in table olive fermentation, storage and packing to guarantee safety and flavor. However, consumers are progressively concerned about sodium intake. In this work, the effect of selected attributes and mineral contents of fermented cracked Aloreña olives as a function of different chloride salt mixtures were studied, using a simplex lattice design with constrains (NaCl + CaCl₂ + KCl = 0.110 kg/l). The best fruit colour was observed at half proportions of KCl and NaCl or CaCl₂; optimum firmness was around the centre of the triangular coordinates but close to the line connecting CaCl₂ and NaCl vertexes; and the best overall quality was obtained in the 0.037 kg/l NaCl and 0.073 kg/l KCl mixture. The concentrations in the fermented olive flesh of the involved elements depended on their initial levels and on the CaCl₂ × NaCl and CaCl₂ × KCl interactions. Results demonstrate that sodium chloride can be replaced in table olives, at least partially, with potassium or calcium chlorides.     

Effect of spray freeze drying on the structural modification and rehydration characteristics of micellar casein powders

Micellar casein (MC) is usually spray-dried into powder form for transportation and storage. However, the micellar structure maintained by colloidal calcium phosphate (CCP) and hydrophobic forces leads to poor rehydration ability of MC powders, which limits its potential applications. Here, spray freeze drying (SFD) with controlled droplet size was used to produce MC powders. Their effects on the structure of MC and the subsequent rehydration characteristics including wetting, dispersion and dissolution were investigated. The results showed SFD powders obtained from smaller droplet size caused more than 50% of serum Ca²⁺ and PO₄³⁻ to release from the micellar structure. These powder particles exhibited extremely high porosity (92%) and spherical morphology, which thus greatly shortened their wetting time. Furthermore, the smallest droplets during SFD were believed to produce the MC powders with the quickest dispersion and best solubility, as over 80% of the solids could be completely dissolved in just 15 min.     

Interaction of β‐casein with (−)‐epigallocatechin‐3‐gallate assayed by fluorescence quenching: effect of thermal processing temperature

The interactions between the flavan‐3‐ol (?)‐epigallocatechin‐3‐gallate (EGCG) and bovine β‐casein in phosphate‐buffered saline (PBS) of pH 6.5 subjected to thermal processing at various temperatures (25–100 °C) were investigated using fluorescence quenching. The results indicated that different temperatures had different effects on the structural changes and EGCG‐binding ability of β‐casein. At temperatures below 60 °C, the β‐casein–EGCG interaction changed little (P > 0.05) with increasing temperature. At temperatures above 80 °C, native assemblies of β‐casein in solution dissociated into individual β‐casein molecules and unfolded, as demonstrated by a red shift of the maximum fluorescence emission wavelength (λ_max) of up to 8.8 nm. The highest quenching constant (K_q) and the number of binding sites (n) were 0.92 (±0.01) × 10¹³ m ^?1 s^?1 and 0.73 (±0.02) (100 °C), respectively. These results provide insight into the potential of interactions between β‐casein–EGCG that may modulate bioactivity or bioavailability to be altered during thermal process.