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.     

Plasticizers for Zein: Their Effect on Tensile Properties and Water Absorption of Zein Films

Cast zein films are brittle at room conditions, so plasticizers are added to make them more flexible. The tensile properties of these films are known to be affected by the relative humidity (RH) of the ambient air. However, little is known about how the plasticizers are affected by RH. Cast zein films were plasticized with either glycerol (GLY), triethylene glycol (TEG), dibutyl tartrate (DBT), levulinic acid (LA), polyethylene glycol 300 (PEG), or oleic acid (OA). Mechanical properties and moisture content (MC) of the films were measured after one week of storage at 3, 20, 50, 70, 81, and 93% RH. The relative humidity of the films' storage had a great effect on the films' tensile properties. All the films' tensile strength and Young's modulus values decreased as RH increased. Films containing DBT, TEG, LA, or PEG showed an increase in the percent elongation with increasing RH. Films containing GLY, OA, or no plasticizer did not show any increase in percent elongation as RH increased. The changes seen in tensile properties with increasing RH are because of zein's hygroscopic nature. The absorbed water will further plasticize the zein. The type of plasticizer used determined the extent of the changes seen in the tensile properties of films stored at different RH values. Depending on the plasticizers used in the film, there were large differences in the amount of water absorbed. Films increasingly absorbed water depending on the plasticizer they contained in the order GLY > TEG > LA > PEG > NONE > DBT > OA. Films containing hygroscopic plasticizers like TEG absorbed too much water at high RH and became weak, but they absorbed enough water at lower RH values to not be brittle. While films containing the more hydrophobic plasticizer DBT were brittle at intermediate RH values, they had good mechanical properties at high RH values.     

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.     

Physical and Cooking Quality of Spaghetti Made from Whole Wheat Durum

The effects of cultivar on dough properties of ground whole wheat durum, and the effects of cultivar and drying temperature on the physical and cooking quality of spaghetti made from semolina and whole wheat were evaluated. Rankings of cultivars based on dough properties were similar for whole wheat and semolina. Dough made from whole wheat was weak and had poor stability. Whole wheat spaghetti had a rough reddish brown surface compared with the very smooth, translucent yellow color of spaghetti made from semolina. The reddish brown color of whole wheat spaghetti was enhanced by high‐temperature drying (70°C). Mechanical strength and cooking quality of spaghetti made from ground whole wheat or semolina varied with cultivar and with drying temperature. Compared with spaghetti made from semolina, whole wheat spaghetti had lower mechanical strength and cooked firmness and had greater cooking loss. Mechanical strength of whole wheat spaghetti was lower when dried at high temperature (70°C) than at low temperature (40°C). Conversely, the mechanical strength of spaghetti made from semolina was greater when dried at high temperature than at low temperature. Whole wheat and traditional spaghetti dried at high temperature had lower cooking losses than spaghetti dried at low temperature. When overcooked 6 min, firmness of spaghetti made from semolina or whole wheat was greater when dried at high temperature than at low temperature.     

Degradation behavior of soy protein-wheat gluten films in simulated soil conditions

Films containing soy protein and wheat gluten were exposed to simulated farmland soil mix over a period of 30 days and monitored for degradation. The simulated farmland soil mix (topsoil/sand/Sunshine compost/vermiculite, 59:6:25:10, wt %) was mixed and stored at ambient humidity (48-55%) and temperature (20-24 degrees C); the soil mix was constantly maintained at 15% moisture by weight. Research focused on evaluating the effectiveness of gluten and cysteine additions on biodegradable behavior in the simulated farmland soil conditions. The four types of films, soy protein (S:G 1:0); soy protein with cysteine addition (S:G 1:0 + CYS); soy protein-wheat gluten (S:G 4:1); and soy protein-wheat gluten with cysteine addition (S:G 4:1 + CYS), were prepared at pH 7. 0 for degradation studies. Soy protein-gluten film rapidly degraded with 50% weight loss in about 10 days and with up to 95% weight loss in 30 days. Tensile strength and elongation of all soy protein-gluten films significantly decreased in 3 days. However, cysteine addition delayed the degradation rate of soy protein-gluten films. Soy protein-wheat gluten film disintegrated after 20 days in the simulated farmland soil environment. These results suggest that wheat gluten and cysteine addition to soy protein-based films could delay degradation rates due to their high disulfide contents.     

Mechanical and water barrier properties of glutenin films influenced by storage time

The goal of this work was to study the effect of storage time on the functional properties of glutenin films plasticized with selected hydrophilic low molecular weight compounds: glycerol (GL), triethanolamine (TEA), and sorbitol (S). Glutenins were extracted from wheat gluten, and films were cast from film-forming solutions. The glutenin-based films were homogeneous, flexible, translucent, and easy to handle. Films were stored in an environmental chamber at 50 +/- 5% realtive humidity and 23 +/- 2 degrees C. Optical, mechanical, and water vapor permeability properties were monitored at regular intervals for 16 weeks. Films plasticized with GL and TEA had similar mechanical and water vapor barrier properties during the first few days of fabrication. Films plasticized with S were stronger, with better water vapor barrier properties. Mechanical and water vapor permeability properties of films plasticized with GL changed dramatically over time, whereas the properties of films plasticized with TEA and S remained stable during storage. Color properties of films plasticized with GL, TEA, and S did not change within the time period studied.     

Properties of chemically and physically treated wheat gluten films

Chemical (vapors of formaldehyde), physical (temperature, UV and gamma radiation), and aging treatments were applied to wheat gluten films. Changes in film mechanical properties, water vapor permeability, solubility, and color coordinates were investigated. An aging of 360 h led to a 75 and 314% increase in tensile strength and Young's modulus, respectively, and a 36% decrease in elongation. Severe thermal (above 110 degrees C, 15 min) and formaldehyde treatments highly improved the mechanical resistance of the films. Under these conditions, up to 376 and 654% increase in tensile strength and Young's modulus and up to 66% decrease in elongation have been observed. Water solubility was only slightly modified, whereas water vapor permeability was not affected. Color coordinates of films heated above 95 degrees C changed to a great extent. An almost total insolubilization of proteins in sodium dodecyl sulfate occurred for heat- and formaldehyde-treated films, due to the modification of protein network leading to changes in properties of the films.     

Effect of Processing on Functional Properties of Wheat Gluten Prepared by Cold‐Ethanol Displacement of Starch

Functional properties of gluten prepared from wheat flour are altered by separation and drying. Gluten was separated and concentrated by batterlike laboratory methods: development with water, dispersion of the batter with the displacing fluid, and screening to collect the gluten. Two displacing fluids were applied, water or cold ethanol (70% vol or greater, ‐13°C). Both the water‐displaced gluten (W‐gluten) and ethanol‐displaced‐ gluten (CE‐gluten) were freeze‐dried at ‐20°C as a reference. Samples were dried at temperatures up to 100°C using a laboratory, fluidized‐bed drier. Tests of functionality included 1) mixing in a mixograph, 2) mixing in a farinograph, and 3) the baked gluten ball test. Dough‐mixing functionality was assessed for Moro flour (9.2% protein) that was fortified up to 16% total protein with dried gluten. In the mixograph, CE‐gluten (70°C) produced improved dough performance but W‐gluten (70°C) degraded dough performance in proportion to the amount added in fortification. In the microfarinograph, there was a desirable and protein‐proportional increase in stability time for CE‐gluten (70°C) but no effect on stability for W‐gluten (70°C). Baking was evaluated using the baked gluten ball test and the percentage increase in the baked ball volume relative to the unbaked gluten volume (PIBV). PIBV values were as high as 1,310% for freeze‐dried CE‐gluten and as low as 620% for W‐gluten dried at 70°C. PIBV for CE‐gluten was reduced to 77% of the freeze‐dried control by fluid‐bed drying at 70°C. Exposure of CE‐gluten to 100°C air gave a PIBV that was 59% of the reference, but this expansion was still greater than that of W‐gluten dried at 70°C. The highest values of PIBV occurred at the same mixing times as the peak mixograph resistance.     

Effect of preparation conditions on protein secondary structure and biofilm formation of kafirin

Various extraction and drying conditions for the isolation of kafirin from dry-milled, whole grain sorghum have been investigated, with a view to optimizing extraction of the protein for commercial food coatings and packaging films. The addition of sodium hydroxide to an aqueous ethanol extractant increased the yield and solubility of kafirin. Subsequent heat drying at 40 degrees C was shown to cause the kafirin to aggregate as indicated by an increase in intermolecular beta-sheets. Extraction of the flour using ethanol (70%, w/w) with 0.5% (w/w) sodium metabisulfite and 0.35% (w/w) sodium hydroxide at 70 degrees C followed by freeze-drying of the protein was found to produce a yield of 54% kafirin with good film-forming properties. The kafirin films were assessed for their sensory properties, tensile strength, strain, and water vapor permeability. Fourier transform infrared spectroscopy was used to study the secondary structure of the extracted kafirins. The best films were made with kafirin containing a large proportion of nativelike alpha-helical structures with little intermolecular beta-sheet content as indicated by the Fourier transform infrared reflectance peak intensity ratios associated with these secondary structures. The principal factor affecting the secondary structure of the protein appeared to be the temperature at which the protein was dried. Heat drying resulted in a greater proportion of intermolecular beta-sheets. Any industrial-scale extraction must therefore minimize protein aggregation and maximize native alpha-helical structures to achieve optimal film quality.     

Study of the temperature effect on the formation of wheat gluten network: influence on mechanical properties and protein solubility

Modifications of mechanical properties of wheat dough during thermal treatments depend mainly on the capacity of wheat gluten proteins to establish intra- and intermolecular interactions when subjected to high-temperature processing. The present study investigates the effect of thermal treatments on the mechanical properties and protein solubility of wheat gluten-based network. The increase in treatment temperatures (from 80 to 135 C) induces an increase in mechanical resistance of the gluten network (tensile strength increases from 0.26 to 2.04 MPa) and a decrease in deformability (elongation decreases from 468 to 236%). The increase in temperature (from 80 to 135 C) also induces a very strong reduction of protein solubility in 2% SDS (from 68 to 0%) that could be correlated to the mechanical changes observed. It was concluded that the modifications of the wheat gluten network properties seem to depend mainly on the temperature level, as temperatures >108-116 C allow activation of thermosetting reactions.     

Oxygen permeability of films made from CO2-precipitated casein and modified casein

Oxygen permeabilities (OP) of CO(2)-casein (CO(2)CN), calcium caseinate (CaCN), and acylated casein (AcCN) films were determined as functions of % relative humidity (% RH), temperature, and plasticizer type. Tensile properties and water vapor permeabilities (WVP) were also measured. Plasticizers were glycerol (GLY) or a 3:1 ratio of GLY:poly(propylene glycol) (PPG), a hydrophobic plasticizer. OP of the CO(2)CN:GLY film was almost twice that of films containing either plasticizer at 35% RH, but its OP approached that of the other films at 70% RH. OP and WVP of films plasticized with GLY were greater than that for films plasticized with PPG. Plasticizer type had little impact on the tensile strength of CO(2)CN films while tensile strength of CaCN-GLY:PPG (3:1) films approximately doubled. Results show that structural dissimilarities in the films contribute to differences in OP only under conditions of low RH where the plasticizing effects of water are not significant.     

Properties of Flours and Starches as Affected by Rough Rice Drying Regime

Flours and starches from rough rice dried using different treatment combinations of air temperature (T) and relative humidity (RH) were studied to better understand the effect of drying regime on rice functionality. Rough rice from cultivars Bengal and Cypress were dried to a moisture content of ≈12% by three drying regimes: low temperature (T 20°C, RH 50%), medium temperature (T 40°C, RH 12%), and high temperature (T 60, RH 17%). Head rice grains were processed into flour and starch and evaluated for pasting characteristics with a Brabender Viscoamylograph, thermal properties with differential scanning calorimetry, starch molecular‐size distribution with high‐performance size‐exclusion chromatography (HPSEC), and amylopectin chain‐length distribution with high‐performance anion‐exchange chromatography with pulsed amperometric detection (HPAEC‐PAD). Lower head rice and starch yields were obtained from the batch dried at 60°C which were accompanied by an increase in total soluble solids and total carbohydrates in the pooled alkaline supernatant and wash water used in extracting the starch. Drying regime caused no apparent changes on starch molecular‐size distribution and amylopectin chain‐length distribution. Starch fine structure differences were due to cultivar. The pasting properties of flour were affected by the drying treatments while those of starch were not, suggesting that the grain components removed in the isolation of starch by alkaline‐steeping were important to the observed drying‐related changes in rice functionality.     

Production and characterization of films from cotton stalk xylan

Composite film production based on cotton stalk xylan was studied, and the mechanical and physical properties of the films formed were investigated. Xylan and lignin were separated from cellulose by alkali extraction and, then, lignin was removed using ethanol washing. Self-supporting continuous films could not be produced using pure cotton stalk xylan. However, film formation was achieved using 8-14% (w/w) xylan without complete removal of lignin during xylan isolation. Keeping about 1% lignin in xylan (w/w) was determined to be sufficient for film formation. Films were produced by casting the film-forming solutions, followed by solvent evaporation in a temperature (20 degrees C) and relative humidity (40%) controlled environment. The elastic modulus and hypothetical coating strength of the films obtained by using 8% xylan were significantly different from the ones containing 10-14% xylan. The water vapor transfer rates (WVTR) decreased with increasing xylan concentration, which made the films thicker. The glycerol addition as an additional plasticizer resulting in more stretchable films having higher WVTR and lower water solubility values. As a result, film production was successfully achieved from xylan, which was extracted from an agricultural waste (cotton stalk), and the film-forming effect of lignin on pure xylan has been demonstrated.     

Development and characterization of biodegradable films made from wheat gluten protein fractions

Gliadins and glutenins were extracted from commercial wheat gluten on the basis of their extractability in ethanol and used to produce film-forming solutions. Films cast using these gliadin- and glutenin-rich solutions were characterized. Glycerol was used as a plasticizer, and its effect on the films was also studied. Films obtained from the glutenin fraction presented higher tensile strength values and lower elongation at break and water vapor permeability values than gliadin films. Gliadin films disintegrated when immersed in water. The GAB isotherm model was used to describe the equilibrium moisture sorption of the films. The glycerol concentration largely modified mechanical and water vapor barrier properties of both film types.     

Improved Isolation of Zein from Corn Gluten Meal Using Acetic Acid and Isolate Characterization as Solvent

An improved means of isolating zein is needed to develop new uses for corn zein. We have measured the yield of zein and evaluated the ability of acetic acid to remove zein from corn gluten meal, distillers dried grains, and ground corn using acetic acid as solvent. Acetic acid removed zein more quickly, at lower temperatures, and in higher yields when compared with alcoholic solvents. After 60 min at 25°C, ≈50% of the zein in corn gluten meal was removed. A step change in yield from 43 to 50% occurs as the extraction temperature is increased from 40 to 55°C after mixing for 30 min at 25% solids. The protein composition of the zein removed from corn gluten meal using acetic acid is very similar to that of commercial zein by SDS‐PAGE. The zein obtained from corn gluten meal using acetic acid had higher amounts of fatty acids and esters according to IR analysis, leading to slightly lower protein content. Films made from zein extracted from corn gluten meal using acetic acid had lower tensile strength (≈60% lower) than films produced from commercial zein. Fibers with very small diameter (0.4–1.6 μm) can be produced by electrospinning using the AcOH solution obtained after corn gluten meal extraction.     

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.     

Drying kinetics of calcium caseinate

Drying is a major component of the cost of making caseinate-based films. We determined the drying curves for making calcium caseinate/glycerol films at low and high relative humidity at 21-34 degrees C. The drying curves exhibited a very long constant rate period followed by a single falling rate period. Much of the drying was in the constant rate period and preceded the actual film formation. Normally, calcium caseinate solutions are dried from about 5% solids, but it was possible to start with a more concentrated solution, 10% solids, to avoid much of the constant rate period. The resulting films were equal to those prepared starting at high initial moisture. An estimate of the drying costs indicated it is much cheaper to start with the more concentrated solutions.     

Thermoformed wheat gluten biopolymers

The quantity of available wheat gluten exceeds the current food use markets. Thermoforming is an alternative technical means for transforming wheat gluten. Thermoforming was applied here to wheat gluten under chemically reductive conditions to form pliable, translucent sheets. A wide variety of conditions, i.e., temperature, reducing agents, plasticizers and additives were tested to obtain a range of elastic properties in the thermoformed sheets. These properties were compared to those of commercially available polymers, such as polypropylene. Elasticity of the gluten formulations were indexed by Young's modulus and were in the range measured for commercial products when tested in the 30-70% relative humidity range. Removal of the gliadin subfraction of gluten yielded polymers with higher Young's modulus since this component acts as a polymer-chain terminator. At relative humidity less than 30% all whole gluten-based sheets were brittle, while above 70% they were highly elastic.     

Chemical modification of wheat protein-based natural polymers: cross-linking effect on mechanical properties and phase structures

Chemical modification of wheat protein-based natural polymer materials was conducted using glyoxal as cross-linker, and the cross-linking effect was studied on mechanical properties under different humidity conditions, the molecular motions of each component, and the phase structures/components of the whole materials. The cross-linking significantly enhanced the mechanical strength of wheat gluten (WG) materials under RH = 50%. The elongation of materials was also increased, which was in contrast to many cross-linked protein systems. The reaction mainly occurred in proteins and starch components, resulting in the formation of a stable cross-linked network with restricted molecular motions and modified motional dynamics. Although the plasticizer glycerol could also take part in the reaction with glyoxal or other components in WG especially when the glyoxal content was higher, the amount of glycerol involved in such reactions was very little. Glycerol was predominantly hydrogen-bonded with the network. The lipid component did not seem to take part in the cross-linking reaction; its mobility was promoted while its interaction with the protein-starch network was weakened after cross-linking. The formation of the cross-linked network did not enhance the hydrophobicity of the materials; the materials still adsorbed a high level of moisture under high humidity conditions (ca. RH = 85%) with no improvement in mechanical strength. In addition, further increasing the amount of glyoxal did not generate an additional strength improvement even at RH = 50%, possibly because the enhanced mobility of lipid promoted the component to be phase-separated from the WG system. To improve the water-resistant properties, the hydrophobicity of the protein macromolecules requires enhancement by other chemical modifications.