Effect of calcium and sodium caseinates on physical characteristics of soy protein isolate–lipid films

The effect of addition of caseinates to soy protein isolated (SPI) based films containing lipids (33% of oleic acid or 85:15 oleic acid (OA)–beeswax blend (BW)) on water vapour permeability (WVP), mechanical and optical properties was evaluated. SPI–lipids was combined with caseinates (sodium or calcium) in different SPI:caseinate ratios with the aim of improving water vapour barrier, mechanical and optical properties of SPI films containing lipids. Caseinate incorporation to SPI based films provoked an increase of elastic modulus and tensile strength at break, mainly for calcium caseinate. Both caseinates contributed to increase the water vapour barrier properties of soy protein-based films. Caseinates also provoked an increase of transparency of SPI based films and colour softening. The most effective combination was 1:1 sodium caseinate:SPI ratio, when film contains 85:15 oleic acid:beeswax ratio.     

Microstructure and optical properties of sodium caseinate films containing oleic acid–beeswax mixtures

The effect of internal and surface structure of films obtained from sodium caseinate (NaCas), containing glycerol and lipid mixtures of oleic acid (OA) and beeswax (BW) (1:0.3:0.5 protein:glycerol:lipid ratio) on optical properties (gloss and transparency) was studied. Gloss was measured at different angles of the incident light (20, 60 and 85°) using a gloss meter, and transparency was evaluated through Kubelka–Munt coefficients obtained from the film reflection spectra (400–700 nm). Film structure was analyzed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Control films (without lipid) exhibited the greatest transparency and gloss whereas lipid imparts opacity and loss of gloss to the film, especially as beeswax increased in the lipid mixture, due to the formation of greatest lipid aggregates in the internal and surface parts of the film. Good correlation was established among gloss, transparency and surface roughness parameters of the films.     

Antimicrobial, water vapour permeability, mechanical and thermal properties of casein based Zataraia multiflora Boiss. Extract containing film

Hydrophobic sodium caseinate based edible films were prepared by incorporating stearic and oleic acids. Films were produced with a protein/lipid ratio of 1.05. Antimicrobial films were produced based on the hydrophobic films by adding the essential oil of Zataraia multiflora Boiss. Water vapour permeability, microstructure, antimicrobial, mechanical and thermal properties of these films were studied. Water vapour permeability decreased from 2.18 × 10⁻⁹ to 7.81 × 10⁻¹¹ gPa⁻¹s⁻¹ m⁻¹ on the addition of lipid compounds to film. Scanning electron microscopy showed a partial phase separation of lipid compounds and protein. This fact was confirmed by obtaining two endothermic peaks for lipid containing films during Differential scanning calorimeter. The incorporation of fatty acids into the film structure increased the total specific thermal capacity. The presence of lipids and essential oil decreased tensile strength but increased the elongation at break. Films containing essential oil exhibited a large inhibitory effect on Staphylococcus aureus, as compared to Salmonella typhimurium and Escherichia coli O157:H7.     

Water sorption isotherms and phase transitions of sodium caseinate–lipid films as affected by lipid interactions

The water content–water activity–glass transition temperature relationships for sodium caseinate films containing glycerol were analyzed in caseinate based films containing oleic acid (OA) or beeswax (BW). Changes in the lipid phase transitions were also analyzed. Glass transitions of caseinate matrices as a function of water activity were modified by the presence of glycerol that plasticizes at low a_w values to a great extent, but which limits the water plasticization effect. Incorporation of oleic acid in the film also induced changes in the water plasticization effect, thus indicating that lipid interactions with polymeric matrix occur, which was also reflected in the lipid melting behavior. OA binding produced a weakening effect in the matrix. When the lipid was beeswax, no notable protein–lipid interactions were revealed from the phase transition analysis. So, different characteristics of film matrix fillers (active or inactive) can be deduced from phase transition analysis and allow us to explain the greatly different impact of these on the film properties.     

Effect of ferulic acid and α-tocopherol antioxidants on properties of sodium caseinate edible films

Edible films, based on sodium caseinate containing three different concentrations of ferulic acid or α-tocopherol (20, 40 and 60 mg/g sodium caseinate), were obtained in order to evaluate the effect of these compounds on properties of the caseinate matrices. Special emphasis was placed on their effect on the films’ oxygen barrier properties, which are decisive in the prevention of the oxidation of foods containing lipids. Films were characterized as to their tensile, optical and surface properties as well as their barrier properties to water vapor, oxygen and aroma compounds (n-hexanal and n-hexanol). Ferulic acid was more efficient at reducing oxygen and n-hexanal permeability than α-tocopherol. Although ferulic acid slightly increased the stiffness of films at low concentration, in general, both antioxidants slightly reduce mechanical resistance, water vapor permeability, gloss and transparency of the films.     

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.     

Characterization of sodium caseinate-based edible films incorporated with cinnamon or ginger essential oils

Film-forming emulsions were formulated with sodium caseinate and two essential oils (cinnamon or ginger) and films were obtained by casting. At the low oil proportion being tested (maximum ratio protein:oil 1:0.100), the lipid did not affect the mechanical behaviour of the protein films. The water vapour permeability was slightly reduced by both oils. Cinnamon oil greatly affected the optical properties of the films. Ginger oil resulted in lipid droplet aggregation observable by Scanning Electron Microscopy in dried films, surface irregularities and gloss decrease. Neither of the oils improved the ability of sodium caseinate films to act as protection against lipid oxidation, despite the fact that, in a spectrophotometric method, isolated cinnamon oil proved to be very a strong antioxidant.     

Caseinate films modified with tung oil

Sodium caseinate/tung oil composite films were prepared through emulsification in order to reduce the water affinity of the protein-based film. Addition of lipid leads to milky films, resulting in a sharp increase in opacity. Uneven lipid distribution was evidenced by SEM in films prepared with 15% tung oil, which most likely arose from the limited dispersion capability of the lipids. Tung oil content also affects the film mechanical response, increasing tensile strength and elastic modulus but decreasing deformability. Contact angle measurements, besides water absorption tests, confirm lower hydrophilicity of the samples. However, tung oil incorporation into the caseinate matrix did not affect significantly the WVP at any of the three levels used, probably due to pore formation. The advantages of cross-linking composite films using heat were also addressed.     

Structure and properties of nanocomposite films based on sodium caseinate and nanocellulose fibers

Films made from sodium caseinate and nanocellulose were prepared by dispersing the fibrils into film forming solutions, casting and drying. Composite films were less transparent and had a more hydrophilic surface than neat sodium caseinate ones. However, the global moisture uptake was almost not affected by filler concentration. Addition of nanocellulose to the neat sodium caseinate films produced an initial increase in the barrier properties to water vapor, and then, it decreases as filler content increased. This was explained in terms of additional detrimental changes (cracks and bubble formation) induced in the morphological structure of the film by the reinforcement.The tensile modulus and strength of composite films increased significantly with increasing cellulose concentrations, while the values of elongation decreased. In the same way it was found that the storage modulus increases considerably with filler addition in the low temperature range (<60 °C), though the effect of temperature on the films performance is even more dramatic, as expected in protein-based materials.     

Effect of sodium caseinate on properties and ageing behaviour of corn starch based films

The effect of sodium caseinate addition on corn starch films was studied in terms of microstructural, mechanical, optical and water and oxygen barrier properties and the changes they underwent during their 5 weeks' storage under controlled conditions. The influence of the polymer mixture on the degree of crystallization of the films was also analysed. The following starch: protein ratios were considered. 100:0, 75:50, 50:50 and 0:100. SEM Microstructure analysis revealed the compatibility of both hydrocolloids since no phase separation was observed. The addition of sodium caseinate to the starch films provided films that were less stiff and resistant to fracture but more flexible and deformable than pure starch films, with similar water vapour permeability values. The films became more permeable to oxygen as their sodium caseinate content increased in line with the higher permeability values of the protein film. Incorporating sodium caseinate to starch films provoked a slight increase in transparency, but a loss of gloss, which also decreased in composite films during storage. The re-arrangement of polymer chains during storage caused a loss of mechanical resistance, stretchability and gloss in composite films.     

Use of sodium caseinate/glycerol edible films to reduce lipid oxidation in sliced turkey meat

The objective of this study was to investigate the influence of sodium caseinate films containing glycerol [glycerol:protein ratio 0.32 (w/w)] on lipid oxidation in cooked turkey breast meat slices. Slices were wrapped in films of different thickness (22, 42, and 58 μm) and were stored at 4 °C for 1, 2, 3 and 4 days. Lipid oxidation was measured using TBARS and hexanal assays on each day of storage while an olfactory sensory analysis was carried out on all the samples after 4 days of storage. TBARS values and hexanal levels of unwrapped samples (~6.0 mg MDA/kg and ~8.0 mg hexanal/kg) were significantly (P ≤ 0.05) higher than those of the casein film wrapped samples (~3.0 mg MDA/kg and ~3.0 mg hexanal/kg). Sensory analysis also showed significant (P ≤ 0.05) differences between wrapped samples and unwrapped samples, the former being perceived as less rancid. Thus wrapping in caseinate films may help reduce lipid oxidation in cooked turkey meat.     

Water Vapor Permeability of Caseinate-Based Edible Films as Affected by pH, Calcium Crosslinking and Lipid Content

Edible films were cast from solutions of sodium or calcium caseinate and from emulsions of these proteins with acetylated monoglyceride, beeswax, and stearic acid. The water vapor permeabilities of the films were evaluated at 25°C using the ASTM E96–80 method, modified to calculate the % relative humidity at the film underside. Adjustment to pH 4.6 (isoelectric point), calcium ion crosslinking and combined effects of calcium ascorbate buffer (pH 4.6) reduced water vapor permeability of sodium caseinate films by 36%, 42%, and 43%, respectively. Calcium caseinate-beeswax emulsion films had water vapor permeabilities up to 90% lower than pure sodium caseinate films. Water vapor permeability varied by a factor of two depending on emulsion film orientation, indicating nonisotropic structure.     

Study of the retention and release of n-hexanal incorporated into soy protein isolate–lipid composite films

This work deals with the study of the kinetic of aroma release, which had been previously incorporated into soy protein isolate (SPI)–lipid composite films. The aim was to determine the influence of type and amount of lipidic material on aroma (n-hexanal) release and retention, as well as the apparent diffusion coefficients. To carry out this study it have been employed SPI-based films containing two SPI:LIPID ratios (1:0.25 and 1:0.5), and two types of lipids, oleic acid (OA) and beeswax (BW), in OA:BW ratios 100:0, 70:30, 50:50, 30:70 and 0:100. The measurements were performed by a gas chromatography technique. The films that showed more retention were SPI:LIPID 1:0.5 100% BW and control film. Concerning release rate, films containing BW as unique lipid material gave the lowest aroma release rate. Apparent diffusion coefficients (D_app) of all films are in the same order of magnitude (10⁻¹⁵ m² s⁻¹). D_app decreases when BW increases in the film matrix and when oleic acid amount decreases. In conclusion, for encapsulating n-hexanal, SPI-BW films demonstrated the best performances, followed by control film (without lipids).     

Mechanical and barrier properties of sodium caseinate–anhydrous milk fat edible films

Edible films were cast from solutions of sodium caseinate (NaCAS) and from emulsions of this protein with anhydrous milk fat (AMF). The moisture sorption isotherms, mechanical properties [tensile strength (TS) and elongation] and water vapour and oxygen permeabilities were determined for films based on NaCAS as a function of AMF concentration. AMF concentration significantly affected TS (P < 0.001) and elongation (P < 0.05). The increase of lipid content led to a loss of mechanical efficiency, but had little influence on water vapour barrier properties. No significant difference (P > 0.05) occurred between oxygen permeability of films at each lipid concentration.     

Edible composite films of wheat gluten and lipids: water vapour permeability and other physical properties

Edible composite films comprised of wheat gluten as the structural matrix and various concentrations of different lipids as the moisture barrier component were tested for water vapour permeability, dispersion in water, opacity and mechanical properties. the effects of lipids on the functional properties of gluten-based composite films depended on the lipid characteristics and on the interactions between the lipid and the protein structural matrix. Beeswax, a solid and highly hydrophobic lipid, was the most effective lipid for improving moisture barrier properties of films; but these films were opaque, weak and disintegrated easily in water. Combining wheat gluten proteins with a diacetyl tartaric ester of monoglycerides reduced water vapour permeability, increased strength and maintained transparency.     

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).     

Preparation and properties of pullulan–alginate–carboxymethylcellulose blend films

Pullulan, alginate, and carboxymethylcellulose (CMC) films were solvent cast from aqueous polymer solution. At 55% RH and 20 °C, their tensile strength and elongation at break were 67 MPa and 11%, 49 MPa and 5.2%, and 45 MPa and 5.8%, respectively. Pullulan films had lower water vapor permeability than alginate and CMC films (4.4 × 10⁻⁷, 9.7 × 10⁻⁷, and 1.3 × 10⁻⁶ g m/Pa h m², respectively), but dissolved in water quicker than alginate and CMC films. By incorporating alginate and CMC into pullulan, water barrier and mechanical properties were weakened significantly. Blending pullulan with alginate or CMC up to about 17–33% (w/w total polymer) reduced film solubilization time in water. The addition of glycerol further reduced tensile strength, increased elongation at break, weakened water barrier properties, but enhanced solubilization in water. FTIR results indicated that blending pullulan with alginate and CMC resulted in weaker hydrogen bonds acting on –OH groups compared to the pure pullulan.     

Tensile and moisture barrier properties of whey protein–beeswax layered composite films

BACKGROUND: There is a lack of research on producing layered protein–lipid composite films with improved tensile and barrier properties compared to films from individual components. Several film‐forming parameters were hypothesized to influence the extent to which lipids were either dispersed within or layered upon whey protein films. Film‐forming parameters investigated were ratio of whey protein isolate (WPI) to beeswax (BW), homogenization method, sodium chloride (NaCl) concentration, and BW particle size. RESULTS: Film percent elongation (E) increased, while tensile strength (TS) and elastic modulus (EM) decreased when BW was incorporated into WPI films, demonstrating a lubricant effect of the BW. Mean water vapor permeability values for WPI film decreased by 57% when the film composition was modified by the addition of 40% BW. BW phase separation was observed in all of the tested films. Particle size of BW in the film‐forming emulsions was larger in the presence of NaCl (100 mmol L^?1), indicating a neutralization of particle charge. However, the addition of NaCl did not improve the moisture barrier of WPI‐BW film over the range of film‐forming conditions used in the study. CONCLUSION: The results from this study are useful in determining formulations and conditions for the production of composite films from WPI and BW with improved tensile and moisture barrier properties. Copyright © 2008 Society of Chemical Industry     

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.     

Caseinate at Low Temperatures: Calcium Use in β-Casein Extraction by Microfiltration

Calcium-induced modifications of 2% sodium caseinate at 4°C and β-casein extraction by microfiltration on membranes were studied. Pore diameters and tangential flow rates were investigated. Calcium addition up to 3 g.L^?1 was followed by a pH decrease, particle size increase and a shift of casein towards colloidal state. The higher purity of β-casein in the soluble fraction was obtained between 1 and 1.5 g.L^?1 of added calcium. Increasing calcium to 1 g.L^?1 induced hydraulic resistance increase, and higher retention of β-casein. Particle size increases were related to physicochemical modifications induced by the calcium addition.