Drying temperature effect on water vapor permeability and mechanical properties of whey protein-lipid emulsion films

The water vapor permeability (WVP) and mechanical properties of whey protein isolate (WPI) and WPI-lipid emulsion films dried at different conditions were investigated. As drying temperature increased, WVPs decreased significantly. Significantly lower WVP was observed for emulsion films compared to WPI films. WPI-Beeswax (BW) and WPI-anhydrous milkfat fraction emulsion films dried at 80 degrees C and 40% RH gave the lowest WVP compared to 25 degrees C, 40% RH and 40 degrees C, 40% RH. A large drop in WVP of WPI-BW emulsion films was observed at 20% BW content. The decrease in WVP for emulsion films as drying temperature increased could be due to change in the lipid crystalline morphology and/or lipid distribution within the matrix. Mechanical properties of WPI and WPI-lipid emulsion films, on the other hand, were not modified by drying conditions.     

Ascorbic acid-containing whey protein film coatings for control of oxidation

A formulation for the whey protein isolate film or coating incorporating ascorbic acid (AA-WPI film or coating) was developed. Tensile and oxygen-barrier properties of the AA-WPI film were measured. Antioxidant effects of the AA-WPI coating on roasted peanuts were studied by comparing the values of peroxide (PO), thiobarbituric acid reactive substance (TBARS), and free-radical-scavenging activity, determined with noncoated peanuts and peanuts coated with WPI with and without ascorbic acid during storage at 21% relative humidity (RH) and 23, 35, and 50 degrees C. The incorporation of AA reduced elongation of WPI films. The oxygen-barrier property of the WPI film was significantly improved by incorporation of AA. The AA-WPI coating retarded lipid oxidation in peanuts significantly at 23, 35, and 50 degrees C. The AA-WPI coated peanuts were more red than noncoated peanuts at all storage temperatures.     

Kinetics of sucrose crystallization in whey protein films

The kinetics of sucrose crystallization in whey protein isolate (WPI) films was studied at 25 degrees C in four different relative humidity environments: 23, 33, 44, and 53%. The effects of protein matrix, crystallization inhibitors, and storage environment on the rate constants of sucrose crystallization were determined using the Avrami model of crystallization. It was found that a cross-linked, denatured whey protein (WP) matrix more effectively hindered sucrose crystallization than a protein matrix of native WP. The crystallization inhibitors tested were lactose, raffinose, modified starch (Purity 69), and polyvinylpyrrolidone (Plasdone C15). Raffinose and modified starch were determined to be the more effective inhibitors of sucrose crystallization. At lower relative humidities (23, 33, and 44%), the cross-linked protein matrix played a more important role in sucrose crystallization than the inhibitors. As relative humidity increased (53%), the crystallization inhibitors were more central to controlling sucrose crystallization in WPI films.     

Aging of whey protein films and the effect on mechanical and barrier properties

This work focuses on the aging of whey protein isolate (WPI) films plasticized with glycerol (G) and sorbitol (S). The films were cast from heated aqueous solutions at pH 7 and dried at 23 degrees C and 50% relative humidity (RH) for 16 h. They were stored in a climate room (23 degrees C, 50% RH) for 120 days, and the film properties were measured at regular intervals. The moisture content (MC) of the WPI/G films decreased from 22% (2 days) to 15% (45 days) and was thereafter constant at 15% (up to 120 days). This affected the mechanical properties and caused an increased stress at break (from 2.7 to 8.3 MPa), a decreased strain at break (from 33 to 4%), and an increased glass transition temperature (T(g)) (from -56 to -45 degrees C). The barrier properties were, however, unaffected, with constant water vapor permeability and a uniform film thickness. The MC of the WPI/S films was constant at approximately 9%, which gave no change in film properties.     

Effects of pH and the gel state on the mechanical properties, moisture contents, and glass transition temperatures of whey protein films.

The mechanical properties, moisture contents (MC), and glass transition temperature (T(g)) of whey protein isolate (WPI) films were studied at various pH values using sorbitol (S) as a plasticizer. The films were cast from heated aqueous solutions and dried in a climate chamber at 23 degrees C and 50% relative humidity (RH) for 16 h. The critical gel concentrations (c(g)) for the cooled aqueous solutions were found to be 11.7, 12.1, and 11.3% (w/w) WPI for pH 7, 8, and 9, respectively. The cooling rate influenced the c(g), in that a lower amount of WPI was needed for gelation when a slower cooling rate was applied. Both cooling rates used in this study showed a maximum in the c(g) at pH 8. The influence of the polymer network on the film properties was elucidated by varying the concentration of WPI over and under the c(g). Strain at break (epsilon(b)) showed a maximum at the c(g) for all pH values, thus implying that the most favorable structure regarding the ability of the films to stretch is formed at this concentration. Young's modulus (E) and stress at break (sigma(b)) showed a maximum at c(g) for pH 7 and 8. The MC and epsilon(b) increased when pH increased from 7 to 9, whereas T(g) decreased. Hence, T(g) values were -17, -18, and -21 degrees C for pH 7, 8, and 9, respectively. E and sigma(b) decreased and epsilon(b) and thickness increased when the surrounding RH increased. The thickness of the WPI films also increased with the concentration of WPI.     

Oxygen permeability and mechanical properties of films from hydrolyzed whey protein

The effects of whey protein hydrolysis on film oxygen permeability (OP) and mechanical properties at several glycerol-plasticizer levels were studied. Both 5.5% and 10% degree of hydrolysis (DH) whey protein isolate (WPI) had significant effect (p 0.05) occurred for film OP between unhydrolyzed WPI, 5.5% DH WPI, and 10% DH WPI films at the same glycerol content. Hydrolyzed WPI films of mechanical properties similar to those of WPI films had better oxygen barrier. Therefore, use of hydrolyzed WPI allowed achievement of desired film flexibility with less glycerol and with smaller increase in OP.     

Effects of alpha-tocopherol, beta-carotene, and soy isoflavones on lipid oxidation of structured lipid-based emulsions

Structured lipids (SLs) are triacylglycerols that have been modified to change the fatty acid composition and/or positional distribution in the glycerol backbone by chemically and/or enzymatically catalyzed reactions and/or genetic engineering. Ten percent oil-in-water emulsions were formulated with a canola oil/caprylic acid SL and stabilized with 0.5% whey protein isolate (WPI) or sucrose fatty acid ester (SFE). The effects of alpha-tocopherol, beta-carotene, genistein, and daidzein (added at 0.02 wt % of oil) on lipid oxidation were evaluated over a 15-day period in emulsion samples. Significantly (p < 0.05) less total oxidation (calculated from peroxide value and anisidine value measurements) occurred in the WPI emulsions compared to their SFE counterparts. In this study, alpha-tocopherol, beta-carotene, and both soy isoflavones exhibited prooxidant activities in SFE emulsions. Because of their ability to exhibit prooxidant activity under certain conditions, manufacturers must experiment with these compounds before adding them to SL-based products as functional ingredients.     

Effects of protein and peptide addition on lipid oxidation in powder model system

The effect of protein and peptide addition on the oxidation of eicosapentaenoic acid ethyl ester (EPE) encapsulated by maltodextrin (MD) was investigated. The encapsulated lipid (powder lipid) was prepared in two steps, i.e., mixing of EPE with MD solutions (+/- protein and peptides) to produce emulsions and freeze-drying of the resultant emulsions. EPE oxidation in MD powder progressed more rapidly in the humid state [relative humidity (RH) = 70%] than in the dry state (RH = 10%). The addition of soy protein, soy peptide, and gelatin peptides improved the oxidation stability of EPE encapsulated by MD, and the inhibition of lipid oxidation by the protein and the peptides was more dramatic in the humid state. Especially, the oxidation of EPE was almost perfectly suppressed when the lipid was encapsulated with MD + soy peptide during storage in the humid state for 7 days. Several physical properties such as the lipid particle size of the emulsions, the fraction of nonencapsulated lipids, scanning electron microscopy images of powder lipids, and the mobility of the MD matrix were investigated to find the modification of encapsulation behavior by the addition of the protein and peptides, but no significant change was observed. On the other hand, the protein and peptides exhibited a strong radical scavenging activity in the powder systems as well as in the solution systems. These results suggest that a chemical mechanism such as radical scavenging ability plays an important role in the suppression of EPE oxidation in MD powder by soy proteins, soy peptides, and gelatin peptides.     

Storage stability of ascorbic acid incorporated in edible whey protein films

The stability of ascorbic acid (AA) incorporated in whey protein isolate (WPI) film and the related color changes during storage were studied. No significant loss of AA content was found in any films prepared from pH 2.0 casting solution stored at 30% relative humidity (RH) and 22 °C over 84 days. Total visible color difference (ΔE*(ab)) of all films slowly increased over storage time. The ΔE*(ab) values of pH 3.5 films were significantly higher than those of pH 2.0 films. The stability of AA-WPI films was found to be mainly affected by the pH of the film-forming solution and storage temperature. Oxidative degradation of AA-WPI films followed Arrhenius behavior. Reduction of the casting solution pH to below the pK(a1) (4.04 at 25 °C) of AA effectively maintained AA-WPI storage stability by greatly reducing oxidative degradation, whereas anaerobic and nonenzymatic browning were insignificant. The half-life of pH 2.0 AA-WPI film at 30% RH and 22 °C was 520 days.     

Structural changes imposed on whey proteins by UV irradiation in a continuous UV light reactor

The objective of this study was to investigate the structural changes of whey proteins during exposure in a continuous-flow UV reactor. Varying UV irradiation dosages were obtained by controlling the flow rate and the mixing speed. Whey protein isolate (WPI) solutions at concentrations of 1% and 5% (w/v) were circulated at flow rates ranging from 30 to 800 mL·min(-1), and changes in physicochemical properties of the proteins were investigated. Intrinsic fluorescence spectra and surface hydrophobicity measurements suggested changes in the tertiary structure of the proteins with UV exposure. The UV treatment also increased the concentration of total and accessible thiol groups in 1% WPI solutions, while no change was measured in 5% WPI solutions. Size-exclusion chromatography demonstrated the formation of UV-induced aggregates and oxidation products (N-formylkynurenine and dityrosine) of aromatic amino acids. Furthermore, the UV-induced changes in protein conformation increased the susceptibility of whey proteins to pepsin hydrolysis.     

Kinetics of moisture-induced hydrolysis in powder blends stored at and below the deliquescence relative humidity: investigation of sucrose-citric acid mixtures

Previous studies have shown that deliquescent organic compounds frequently exhibit chemical instability when stored in environmental conditions above their deliquescence relative humidity (RH). The goal of the current study was to investigate the effect of atmospheric moisture on the long-term chemical stability of crystalline sucrose-citric acid mixtures following storage at RHs at and below the mutual deliquescence relative humidity (MDRH). Interestingly, it was found that sucrose hydrolysis can occur below the MDRH of 64% and was observed for samples stored at 54% RH. However, hydrolysis was not seen for samples stored at 33 or 43% RH. The rate of sucrose hydrolysis could be modeled by taking into account the rate and extent of moisture uptake, which in turn was dependent on the composition of the powder and the storage RH. A reaction mechanism initiated by capillary condensation and involving additional deliquescence lowering by the degradation products formed as a result of sucrose hydrolysis (glucose and fructose) was proposed.     

Oxidation of encapsulated oil in tailor-made cellular solid

A cellular alginate solid containing oil was prepared by freeze-drying. The oil was incorporated in the matrix by emulsification in the pre-gel state. The alginate-oil gels were immersed in 60 degrees Brix sucrose solution for various periods, before freeze-drying. The extent of the collapse expressing the reduction in sample volume was affected by immersion duration and freeze-drying conditions. Sucrose diffusion during immersion followed an exponential pattern. Effective diffusivity calculated using nonlinear regression gave a value of 3.64 x 10(-)(10) m(2)/s. The effect of relative humidity on water content calculated on a dry basis excluding sucrose showed a significant increase in water content at 75% RH. Image analysis was utilized to quantify the area of the encapsulated oil droplets. The area of the droplets was divided into four subregions defined as (0.02-0.1) x 10(-)(12), (0. 1-1.0) x 10(-)(12), (1-10) x 10(-)(12), and (10-100) x 10(-)(12) m(2). A distribution resembling a Gaussian bell distribution with a maximum of 54% for the (1-10) x 10(-)(12) m(2) area range was found. The number of oil droplets was almost constant for the first three area regions, and then decreased markedly. Oxidation index was not effected by porosity at 0 and 22% RH. A 75% RH and porosity above a critical value of ca. 0.45 was found to increase oxidation significantly. Samples immersed for less than 5.5 h in sucrose solution were mechanically stronger after equilibration at 0 and 22% RH when compared to their counterpart equilibrated at 75% RH. Immersion for more than 24 h resulted in similar mechanical strength irrespective of the RH.     

Protein-stabilized nanoemulsions and emulsions: comparison of physicochemical stability, lipid oxidation, and lipase digestibility

The properties of whey protein isolate (WPI) stabilized oil-in-water (O/W) nanoemulsions (d(43) ≈ 66 nm; 0.5% oil, 0.9% WPI) and emulsions (d(43) ≈ 325 nm; 0.5% oil, 0.045% WPI) were compared. Emulsions were prepared by high-pressure homogenization, while nanoemulsions were prepared by high-pressure homogenization and solvent (ethyl acetate) evaporation. The effects of pH, ionic strength (0-500 mM NaCl), thermal treatment (30-90 °C), and freezing/thawing on the stability and properties of the nanoemulsions and emulsions were compared. In general, nanoemulsions had better stability to droplet aggregation and creaming than emulsions. The nanoemulsions were unstable to droplet flocculation near the isoelectric point of WPI but remained stable at higher or lower pH values. In addition, the nanoemulsions were stable to salt addition, thermal treatment, and freezing/thawing (pH 7). Lipid oxidation was faster in nanoemulsions than emulsions, which was attributed to the increased surface area. Lipase digestibility of lipids was slower in nanoemulsions than emulsions, which was attributed to changes in interfacial structure and protein content. These results have important consequences for the design and utilization of food-grade nanoemulsions.     

Effect of water activity on the release characteristics and oxidative stability of D-limonene encapsulated by spray drying

The stability of encapsulated D-limonene, which was prepared by spray drying, was studied in view of the release characteristics and oxidation stability. Gum arabic, soybean water-soluble polysaccharide, or modified starch, blended with maltodextrin were used as the wall materials. The powders were stored under the conditions of 23-96% relative humidity at 50 degrees C. The release rate and the oxidation rate were closely related to the relative humidity. The relationship was not simple. Initially, the release rate and the oxidation rate increased with increasing water activity, but around the glass transition temperature, the rates decreased sharply to increase again at a further increase of water activity. The results could be explained by a change in the powder structure, where a glass capsule matrix was changed into rubbery state during storage.     

Effect of conductivity control on the separation of whey proteins by bipolar membrane electroacidification

Since the limiting factor of the bipolar membrane electroacidification (BMEA) process at 20% WPI (whey protein isolate) was hypothesized to be the lack of mobile ion inherent to the protein solution at pH 5.0, the aim of the present work is to study the effect of the conductivity control on the precipitation behavior of whey protein. BMEA performances were evaluated by measuring electrodialytic parameters, protein kinetic precipitation, molecular profiles, and isolate chemical composition and purity. The highest protein precipitation with 10% WPI solution was obtained at pH 4.6 and at a conductivity level of 200 microS/cm maintained with many 0.4-mL additions of 1.0 M KCl (200 microS[+]), with a 46% precipitation of the total protein, beta-lg composing the main part of the precipitated protein. With a 20% WPI solution, it was possible to reach pH 4.65 with conductivity control at 350 microS/cm. However, the 27% protein precipitation was still low. The changes in viscosity as pH decreases observed at 20% WPI would decreased the final precipitation rate of beta-lg, since the viscosity of the 20% WPI dispersion was very different.     

Stability of spray-dried tuna oil emulsions encapsulated with two-layered interfacial membranes

omega-3 Fatty acids have numerous health benefits, but their addition to foods is limited by oxidative rancidity. Spray-drying tuna oil-in-water emulsion droplets with a coating of lecithin and chitosan multilayer system could produce emulsion droplet interfacial membranes that are cationic and thick, both factors that can help control lipid oxidation. Physicochemical and oxidative stability of the spray-dried emulsions were determined as a function of storage temperature and relative humidity (RH). The combination of ethylenediaminetetraacetic acid (EDTA) and mixed tocopherols was able to increase the oxidative stability of dried emulsions. Lipid oxidation was more rapid during storage at low relative humidity (11% and 33% compared to 52% RH). At high moisture, physical modifications in the sample were observed, including reduced dispersibility and formation of brown pigments. Sugar crystallization or Maillard products produced at the higher humidities may have inhibited oxidation. Overall, spray-dried tuna oil-in-water emulsions stabilized by lecithin-chitosan membranes were more oxidatively stable than bulk oils and thus have excellent potential as an omega-3 fatty acid ingredient for functional foods.     

Lipid oxidation in corn oil-in-water emulsions stabilized by casein,whey protein isolate,and soy protein isolate

Proteins can be used to produce cationic oil-in-water emulsion droplets at pH 3.0 that have high oxidative stability. This research investigated differences in the physical properties and oxidative stability of corn oil-in-water emulsions stabilized by casein, whey protein isolate (WPI), or soy protein isolate (SPI) at pH 3.0. Emulsions were prepared with 5% corn oil and 0.2-1.5% protein. Physically stable, monomodal emulsions were prepared with 1.5% casein, 1.0 or 1.5% SPI, and > or =0.5% WPI. The oxidative stability of the different protein-stabilized emulsions was in the order of casein > WPI > SPI as determined by monitoring both lipid hydroperoxide and headspace hexanal formation. The degree of positive charge on the protein-stabilized emulsion droplets was not the only factor involved in the inhibition of lipid oxidation because the charge of the emulsion droplets (WPI > casein > or = SPI) did not parallel oxidative stability. Other potential reasons for differences in oxidative stability of the protein-stabilized emulsions include differences in interfacial film thickness, protein chelating properties, and differences in free radical scavenging amino acids. This research shows that differences can be seen in the oxidative stability of protein-stabilized emulsions; however, further research is needed to determine the mechanisms for these differences.     

Effects of the addition of amino acids and peptides on lipid oxidation in a powdery model system

The effects of the addition of amino acids and peptides on the oxidation of eicosapentaenoic acid ethyl ester (EPE) encapsulated by maltodextrin (MD) were investigated. The encapsulated lipid was prepared in two steps, that is, by mixing of EPE with MD solutions (+/-amino acids and peptides) to produce emulsions and freeze-drying of the resultant emulsions. The addition of amino acids and peptides improved the oxidation stability of EPE encapsulated with MD, and the inhibition of lipid oxidation by the amino acids and peptides was more effective at 70% relative humidity (RH). Met, Arg, and Trp were effective amino acids for antioxidation at RH = 10 and 40%, whereas at RH = 70%, His was the most effective amino acid, preventing the oxidation of EPE almost perfectly. Carnosine also exhibited a strong antioxidant effect at RH = 70%, but the effect of anserine was inferior. The addition of Met + Trp or Met + Arg inhibited the oxidation of EPE encapsulated with MD at RH = 40%. Cys accelerated the oxidation of EPE, indicating that the thiyl radical may act as a pro-oxidant. No close relationship was observed between the radical scavenging abilities of amino acids and peptides measured in the aqueous diphenylpicrylhydrazyl solution and their antioxidative effects in the powdery system. It is possible that the radical-scavenging ability of amino acids and peptides detected by ESR in the powder system is responsible for the antioxidative activity of these compounds.     

Maillard reaction and protein cross-linking in relation to the solubility of milk powders

Protein changes in relation to solubility, Maillard reaction (MR), and protein cross-linking in whole milk powder (WMP), skim milk powder (SMP), and whey protein concentrate (WPC) stored at different relative humidities (RHs) were investigated by chemical and electrophoretic methods. WMP and SMP reached minimum solubility rapidly, while WPC showed no change in solubility. The loss of solubility corresponded with development of high-molecular-weight protein complexes observed by two-dimensional electrophoresis. The maximal MR rate occurred at 66% RH for WMP and SMP (high lactose/protein ratios) and 84% RH for WPC (low lactose/protein ratios) based on the furosine and hydroxymethylfurfural contents. However, browning was greatest at 84% RH in all powders. The minimum solubility corresponded with the casein and fat contents. The retention of solubility and minimal protein cross-linking of WPC compared to casein-containing powders suggest that the casein content and cross-linking strongly influence the decrease in the solubility of milk powder.     

Preparation and characterization of beta-carotene nanodispersions prepared by solvent displacement technique

This work demonstrated the preparation of protein-stabilized beta-carotene nanodispersions using the solvent displacement technique. The emulsifying performance of sodium caseinate (SC), whey protein concentrate (WPC), whey protein isolate (WPI), and a whey protein hydrolysate (WPH, 18% degree of hydrolysis) was compared in terms of particle size and zeta-potential of the nanodispersions. SC-stabilized nanodispersions exhibited a bimodal particle size distribution: large particles (stabilized by casein micelles) with a mean particle size of 171 nm and small particles (stabilized by casein submicelles) of 13 nm. This was confirmed with transmission electron microscopy analysis. Most of the beta-carotene precipitated (87.6%) was stabilized in the small particles. On the other hand, the nanodispersions stabilized by the whey proteins were polydispersed with larger mean particle sizes. The mean particle size of WPC and WPI was 1730 and 201 nm, respectively. The SC-stabilized nanodispersion was expected to be more stable as indicated by its higher absolute zeta-potential value (-31 mV) compared to that of WPC (-15 mV) and WPI (-16 mV). Partially hydrolyzed whey protein possessed improved emulsifying properties as shown by WPH-stabilized samples. It was interesting to note that increasing the SC concentration from 0.05 to 0.5 wt % increased the particle size of beta-carotene stabilized by casein micelles, while the reverse was true for those stabilized by SC submicelles. Microfluidization at 100 MPa of SC solution dissociated the casein micelles, resulting in a decrease in mean particle size of the casein micelle-stabilized particles when the SC solution was used to prepare nanodispersions. The results from this work showed that protein-stabilized beta-carotene nanodispersions could be prepared using the solvent displacement technique.