Effect of pH and ethanol content of solvent on rheology of zein solutions

Zein, a corn protein, is a mixture of the polypeptides α-, γ-, β-, and δ-zein. α-Zein and γ-zein comprise 70–85% and 10–20% of total zein mass, respectively. Both peptides have similar amino acid composition, except γ-zein is rich in cysteine. The presence of cysteine has been associated with gelation of zein solutions. A common solvent for zein is aqueous ethanol. Preliminary results suggested that pH and ethanol content affect the rheology of zein solutions. Our objective was to investigate the effect of ethanol content (65–90%) and pH of the solvent (2, 6, and 12) on rheological properties of zein solutions (20% w/w) containing γ-zein. Steady shear tests and oscillatory time sweeps were performed to determine flow behavior and gelation time of zein solutions. Results indicated that α-zein solutions were nearly Newtonian while those containing γ-zein showed shear thinning behavior. At high pH, γ-zein increased the consistency index (K) and shortened gelation time. Results were attributed to the cysteine in γ-zein. High pH promoted formation of disulfide bonds leading to higher K values and shorter gelation times. Results of this work are expected to be useful in the design of zein extraction processes and the development of new zein applications.     

Two fraction extraction of α-zein from DDGS and its characterization

Zein was recovered from corn distiller's dried grains with solubles (DDGS) by a modified method using 70% (w/w) aqueous 2-propanol (70-IPA) or 70% (v/v) aqueous ethanol (70-EtOH) solvents, and a commercial method using 88% (w/w) aqueous 2-propanol (88-IPA). Yield, purity, and film properties of the isolated zein were determined. The modified procedure extracted two fractions of zeins: a mostly α-zein fraction, and a mostly γ-zein fraction. The modified method increased α-zein yield from 4% to 14%. Enzyme cellulase pretreatment did not improve zein yield, but grinding did. The α-zein fraction showed electrophoretic bands at 40, 22, 19, and 10 kDa, corresponding to α-zein dimer, α₁-zein, α₂-zein, and δ-zein, respectively. The α-zein of DDGS retained its film forming capability. The α-zein film of unmodified DDGS was cloudy and rough, unlike the clear and smooth films of α-zeins isolated from corn gluten meal and enzyme-treated DDGS.     

Rheological properties of kafirin and zein prolamins

The possibility of forming dough from kafirin was investigated and laboratory prepared kafirin was formed into a viscoelastic dough system. Measurements with Contraction Flow showed that dough systems prepared from kafirin and from commercial zein had the required extensional rheological properties for baking of leavened bread. The extensional viscosity and strain hardening of the kafirin and zein dough systems were similar to those of gluten and wheat flour doughs. The kafirin dough system, however, unlike the zein dough system rapidly became very stiff. The stiffening behaviour of the kafirin dough system was presumed to be caused by cross-linking of kafirin monomers. SDS-PAGE showed that the kafirin essentially only contained α- and γ-kafirin, whereas the zein essentially only contained α-zein. Since γ-kafirin contains more cysteine residues than the α-prolamin it is more likely to form disulphide cross-links, which probably caused the differences in stiffening behaviour between kafirin and zein dough systems. Overall the kafirin dough system displayed rheological properties sufficient for baking of porous bread. Kafirin like zein appears to have promising properties for making non-gluten leavened doughs.     

Effect of thermal modification on the properties of narrow-leaved ash and chestnut

The concept of thermal modification has evolved from a challenging research program to commercial reality in several European countries in recent years. The aim of this study is to determine the change of various physical properties (oven-dry density, air-dry density, weight loss, swelling and anti-swelling efficiency (ASE)), compression strength parallel to grain, colour difference (ΔE), glossiness and surface roughness of narrow-leaved ash (Fraxinus angustifolia Vahl.) and chestnut (Castanea sativa Mill.) woods after heat treatment under different temperatures and durations. For this study two different temperatures (160 °C and 180 °C) and two different durations (2 h and 4 h) were considered. A stylus method was employed to evaluate the surface characteristics of the samples. Roughness measurements by the stylus method were made in the direction perpendicular to the fiber. Four main roughness parameters which are mean arithmetic deviation of profile (R_a), mean peak-to-valley height (R_z), root mean square roughness (R_q), and maximum roughness (R_y) obtained from the surface of wood were used to evaluate the effect of heat treatment on the surface characteristics of the specimens. The properties studied were significantly different (p = 0.05) at two temperatures and two durations of heat treatment. Based on the findings of this study, the results showed that oven-dry density, air-dry density, swelling, compression strength parallel to grain and surface roughness decreases with increasing heat treatment temperature and time.     

Wettability and surface roughness of thermally modified plywood panels

The objective of this research was to investigate the wettability and surface roughness properties of the plywood panels under thermal modification. The plywood panel specimens were subjected to thermal modification under atmospheric pressure and presence of air at a temperature of 150, 170 or 190 °C for 60 min. The contact angle measurements were obtained by using a KSV Cam-101 Scientific Instrument connected with a digital camera and computer system. The roughness measurements, average roughness (R_a) and maximum roughness (R_max), were performed based on both parallel and perpendicular to the grain using a fine stylus tracing technique. Statistical analyses showed significant differences in the surface roughness and contact angle values of the plywood panels following thermal modification.     

Nano-structure and properties of maize zein studied by atomic force microscopy

Atomic force microscopy was used to investigate the nanostructure of zein from maize (Zea mays). In aqueous ethanol solution zein exists as small globules with diameters between 150 and 550 nm. The mechanism of zein film formation was also explored. The characteristic film structure consists of a meshwork composed of doughnut structures formed from asymmetric rods joined to each other.     

Dynamic water vapour sorption in gluten and starch films

Water sorption of gluten and wheat starch films as a function of water activity was studied using gravimetric step-change sorption experiments. Films of different thicknesses were used with the aim to vary the characteristic diffusion time and to get insights in the contribution of the polymer-chain rearrangement in the sorption behaviour. It is shown that both starch and gluten are in the glassy state for a water activity a_w below 0.9. From comparison of the dynamical sorption curves with a Fickian diffusion model, it is shown that water diffusion in gluten films seems Fickian for a_w < 0.7, and non-Fickian for a_w > 0.7, while for starch films, non-Fickian sorption behaviour is observed for a_w > 0.1. The results show that polymer-chain rearrangement and the stress built up in the matrix play an important role in the sorption dynamics of these films. Even when the material is in the glassy state matrix relaxation phenomena play a role in the sorption behaviour of starch and gluten.     

Impact of different isolation procedures on the functionality of zein and kafirin

Commercial corn prolamin (zein) aggregates in water at elevated temperatures into an extensible, viscoelastic gluten-like substance. This specific functionality of zein can be used in the production of gluten-free bread from true dough systems and not from batters. The present study examined laboratory-scale isolation of such functional zein from dry milled corn. RP-HPLC indicated that successful isolation procedures resulted in relatively pure α-zeins, with a maximum ratio of (β + γ)/α-zeins of about 10%. In the present study, such functional zeins were obtained by using 70% ethanol as the extractant, without added alkali or reducing agent in the main extraction step. In contrast, films could be cast from a wider range of zein isolates, also with higher ratios of (β + γ)/α-zeins. Isolation of the analogous prolamin (kafirin) from dry milled sorghum required a more hydrophobic extractant such as 83% isopropanol to achieve partial functionality. Such kafirin was able to aggregate in warm water, preferably when a reducing agent was added; however, it quickly became firm and lost its extensibility. The present study suggests that hydrophobic interactions rather than disulfide bonds are the key to gluten-like functionality of zein and kafirin.     

Melt-processed blends of zein with polyvinylpyrrolidone

Melt-processed blends of zein and polyvinylpyrrolidone (PVP) of varying molecular weights (55K, 360K and 1.3M) were compared based on mechanical and thermal properties. Generally, all samples stored at 50% RH exhibited a slight improvement in tensile strength, with the PVP360K samples showing the greatest improvement. At the higher levels of PVP, samples stored at 70% RH showed a decrease in tensile strength. Elongation was also more significantly impacted at higher humidity, with the higher levels of PVP causing greater elongation increases. Differential scanning calorimetry data for the blends showed single T_g values intermediate between the zein and PVP controls. Kinetic thermogravimetric data suggested a multi-step degradation interaction for the zein/PVP blends. Scanning electron microscope imaging of compression molded samples showed homogeneous surface contours for even the 20% PVP1.3M blend. Melt-processed blends of zein with polyvinylpyrrolidone of various molecular weights appear to be compatible. This work represents the first melt-processed blend of zein with PVP to generate a compatible blend.     

Wettability and roughness characteristics of modified wood boards using a hot-press

The aim of this study was to investigate the effect of the thermal modification process by hot-press on the wettability and surface roughness characteristics of the eucalyptus wood boards. The roughness measurements, average roughness (R_a), and maximum roughness (R_max) were taken both parallel and perpendicular to the grain using a fine stylus tracing technique. Contact angle measurements were obtained using a goniometer system connected to a digital camera and computer system. The results showed that surface roughness values of the modified wood boards using a hot-press significantly decreased with increasing press pressure and with decreasing temperature. The contact angle measurements indicated that the thermal modification had a significant influence on the surface wettability of the wood boards. Statistical analyses showed significant differences in the surface roughness and contact angle values of the wood boards following thermal modification. The results acquired in this work provide important information for future research and utilization of the thermally modified wood boards.     

Improved viscoelastic zein–starch doughs for leavened gluten-free breads: Their rheology and microstructure

Gluten-free bread was prepared from commercial zein (20 g), maize starch (80 g), water (75 g), saccharose, NaCl and dry yeast by mixing above zein's glass transition temperature (T_g) at 40°C. Addition of hydroxypropyl methylcellulose (HPMC, 2 g) significantly improved quality, and the resulting bread resembled wheat bread having a regular, fine crumb grain, a round top and good aeration (specific volume 3.2 ml/g). In model studies, HPMC stabilized gas bubbles well. Additionally, laser scanning confocal microscopy (LSCM) revealed finer zein strands in the dough when HPMC was present, while dynamic oscillatory tests showed that HPMC rendered gluten-like hydrated zein above its T_g softer (i.e. |G*| was significantly lower). LSCM revealed that cooling below T_g alone did not destroy the zein strands; however, upon mechanical impact below T_g, they shattered into small pieces. When such dough was heated above T_g and then remixed, zein strands did not reform, and this dough lacked resistance in uniaxial extension tests. When within the breadmaking process, dough was cooled below T_g and subsequently reheated, breads had large void spaces under the crust. Likely, expanding gas bubbles broke zein strands below T_g resulting in structural weakness.     

Optimization of elecrospinning process of zein using central composite design

Biodegradable edible sub-micron electrospun zein fibers were prepared using acetic acid as solvent. The solution concentration at three levels: 22, 26 and 30 w/v %, the electrospinning voltage at three levels: 10, 20 and 30 kV, the solution flow rate at three levels: 4, 8 and 12 ml/h and the distance between needle tip and collector at three levels: 10, 15 and 20 cm were studied. Central composite design (CCD) was utilized to modeling the effect of electrospinning parameters of zein solution on average fiber diameters and the data were analyzed using response surface methodology (RSM). Coefficient of determination, R², of fitted regression model was higher than 0.9 for response. The analysis of variance table showed that the lack of fit was not significant for response surface model at 95 %. Therefore, the model for response variable was highly adequate. Results also indicated that the solution concentration had significant influence (P<0.0001) on morphology and diameter of fibers. By increasing the solution concentration, uniform and bead-free fibers were obtained. As the solution concentration was increased, the average fiber diameters were also increased. Furthermore, the electrospinning voltage had significant effect (P<0.0001) on average fiber diameters. By increasing the electrospinning voltage, the average fiber diameters increased. The solution flow rate and the distance between needle tip and collector had no significant influence on the average fiber diameters. According to model optimization, the minimum average fiber diameter of electrospun zein fiber is given by following conditions: 24 w/v % zein concentration, 10 kV of the applied voltage, 10 cm of needle tip to collector distance, and 4 ml/h of solution flow rate.     

Hyperspectral remote sensing of yellow mosaic severity and associated pigment losses in Vigna mungo using multinomial logistic regression models

Yellow mosaic disease (YMD) has been a serious threat to blackgram cultivation especially during post-monsoon season. Visual assessment of disease severity is qualitative and time consuming. Rapid and non-destructive estimation of YMD by hyperspectral remote sensing has not been attempted so far on any of its hosts. Field studies were conducted for two seasons with eight blackgram genotypes having differential response to YMD. Comparison of mean reflectance spectra of the healthy and YMD infested leaves showed changes in all the broad band regions. However, reflectance sensitivity analysis of the narrow-band hyperspectral data revealed a sharp increase in reflectance from the diseased leaves compare to healthy at 669 (red), 505 and 510 nm (blue). ANOVA showed a significant decrease in leaf chlorophyll (p < 0.0001) with increase in disease severity, while no such relationship was observed for relative water content. By plotting coefficients of determination (R²) between leaf chlorophyll and percent reflectance at one nm wavelength interval, two individual bands (R₅₇₁; R₇₀₅) and two band ratios (R₅₇₁/R₇₂₁; R₇₀₅/R₅₉₃) with highest R² values were selected. These bands showed a significant linear relationship with SPAD chlorophyll readings (R² range 0.781–0.814) and spectrometric estimates of total chlorophyll content (R² range 0.477–0.565). Further, the relationship was stronger for band ratios compared to single bands. With optimal spectral reflectance ratios as inputs, disease prediction models were built using multinomial logistic regression (MLR) technique. Based on model fit statistics, reflectance ratios R₅₇₁/R₇₂₁ and R₇₀₅/R₅₉₃ were found better than the individual bands R₅₇₁ and R₇₀₅. Validation of MLR models using an independent test data set showed that the overall percentage of correct classification of the plant into one of the diseased categories was essentially same for both the ratios (68.75%). However, the MLR model using R₇₀₅/R₅₉₃ as dependent variable was of greater accuracy as it gave lower values of standard errors for slopes (β_G range 9.79–36.73) and highly significant estimates of intercept and slope (p < 0.05). Thus the models developed in this study have potential use for rapid and non-destructive estimation of leaf chlorophyll and yellow mosaic disease severity in blackgram.     

Characterization of zein modified with a mild cross-linking agent

Zein, a predominant corn protein, is an alcohol-soluble protein extracted from corn and is an excellent film former. The characteristic brittleness of zein diminishes its usefulness as a film. It is well known that zein has a propensity for forming aggregates in solution. When zein molecules were cross-linked with 1-[3-dimethylaminopropyl]-3-ethyl-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), it was found that the film-forming property was improved and the aggregation phenomenon in solution was suppressed. At the air/water interface, native zein forms brittle film with rough surface, whereas cross-linked zein forms rigid film with very smooth and even surface. Tensile strengths of the films were shown to be greatly increased by cross-linking. Objectives of this study are to determine the cross-linking mechanism of zein, the optimum reaction conditions, characteristics of the reaction product, and mechanical properties of cross-linked zein film. Through viscosity and dynamic light scattering, the cross-linking reaction was monitored. Optimum amount of EDC and NHS was determined to be 30 mg each per gram of zein. The cross-linking of zein with EDC and NHS seemed to be self-terminating because the cross-linking reaction did not proceed to precipitation.     

Film morphology of supramolecule CPES/ASO and its performance on cotton substrates

The supramolecule CPES/ASO was self-assembled from carboxylated polyether-block-polydimethylsiloxane (CPES) and N-β-aminoethyl-γ-aminopropyl polysiloxane (ASO) in ethyl acetate solution. The film morphology and performance of CPES/ASO on cotton substrates were investigated by field emission scanning electron microscope (FESEM), atomic force microscope (AFM), X-ray photoelectron microscope (XPS), and so on. The results indicated that a polysiloxane resin film was coated on the treated fiber surface and able to decrease the root mean square roughness (R _q ) of the treated fiber conspicuously. Morphology of higher peaks circled by many smaller peaks was observed on the film surface, which was partly similar to that of CPES/ASO on the silicon wafer. Besides, when the mass ratio of CPES to ASO was 2:1, the fabric treated by CPES/ASO showed the best softness and had a comfortable oily tactile.     

Dynamic of water activity in maize hybrids is crucial for fumonisin contamination in kernels

The dynamic of water activity (a_w) and humidity (h) of maize (Zea mays L.) kernels and their relevance for fumonisin (FUM) accumulation in kernels was studied in 10 commercial hybrids grown in 5 locations of North Italy, in 2007 and 2008. The dynamic of both a_w and h in maize kernels was different in diverse hybrids and was accurately described by monomolecular and linear regression, respectively, using degree-days (base 0 °C) accumulated between female flowering and harvest as an independent variable (R² = 0.61-0.96, depending on the hybrid). FUM contamination at harvest was predicted by using a_w as an independent variable in a logistic regression which provided 67% of correct prediction of cases with FUM ≥ 4000 μg/kg of kernel; accuracy of prediction increased to 72% by using both a_w and ECB severity as independent variables. The use of h as independent variable provided 71% correct predictions, but specific correction factors were necessary for each hybrid. Results showed that “slow dry down” hybrids were more prone to FUM accumulation, irrespective of their season length. The identification of factors able to drive a_w dynamic in maize kernels and their genetic bases may then provide a crucial contribution in breeding maize for resistance to FUM contamination.     

Ethanolic extraction of zein from maize

Zein can be extracted from maize (Zea mays) using ethanol solutions, and recovered from the extract by diluting with water. Dilution to 40% ethanol will precipitate a mixture of zein and maize lipid with ∼15% lipid. For possible zein applications, such as film production, purer zein is required. Most of the lipid can be removed from the precipitate by selective re-extraction with hexane or ethanol, but this is expensive. A precipitate containing 90% or more of the protein in the extract, with less than 10% lipid, can be obtained by diluting the extract in stages. An initial dilution will precipitate a solid with 75% or more lipid, this precipitate can be centrifuged from the extract and the centrifugate diluted to precipitate a solid of 70% or more zein. The mass and composition of solid centrifuged from a maize extract that was diluted in several steps to characterize the composition of precipitates so formed. The lipid content of a zein product precipitated from an extract diluted from 55% ethanol to 50% is significantly lower than the content of precipitate of an extract diluted in a single step to 40% ethanol.     

Improved viscoelastic zein–starch doughs for leavened gluten-free breads: Their rheology and microstructure

Gluten-free bread was prepared from commercial zein (20 g), maize starch (80 g), water (75 g), saccharose, NaCl and dry yeast by mixing above zein's glass transition temperature (T_g) at 40°C. Addition of hydroxypropyl methylcellulose (HPMC, 2 g) significantly improved quality, and the resulting bread resembled wheat bread having a regular, fine crumb grain, a round top and good aeration (specific volume 3.2 ml/g). In model studies, HPMC stabilized gas bubbles well. Additionally, laser scanning confocal microscopy (LSCM) revealed finer zein strands in the dough when HPMC was present, while dynamic oscillatory tests showed that HPMC rendered gluten-like hydrated zein above its T_g softer (i.e. |G*| was significantly lower). LSCM revealed that cooling below T_g alone did not destroy the zein strands; however, upon mechanical impact below T_g, they shattered into small pieces. When such dough was heated above T_g and then remixed, zein strands did not reform, and this dough lacked resistance in uniaxial extension tests. When within the breadmaking process, dough was cooled below T_g and subsequently reheated, breads had large void spaces under the crust. Likely, expanding gas bubbles broke zein strands below T_g resulting in structural weakness.     

Removal of surface lipids improves the functionality of commercial zein in viscoelastic zein-starch dough for gluten-free breadmaking

Maize prolamin (zein), together with starch, hydroxypropyl methylcellulose, sugar, salt, yeast and water can form wheat-like cohesive, extensible, viscoelastic dough when mixed above room temperature (e.g. 40 °C). This dough is capable of holding gas. However, it is excessively extensible, and when used for hearth-type rolls, it tends to become flat. Bench-scale defatting of zein with chloroform at room temperature significantly (P < 0.05) improved specific volume (4.5 ml/g vs. 3.3 ml/g) and shape of the rolls (width-to-height 2.0 vs. 3.9). The total lipid content determined by accelerated solvent extraction (100 °C, 69 bar, chloroform), however, only decreased from 8.0 to 6.6% due to this bench-scale defatting. Staining experiments with Naphthol Blue Black suggested that bench-scale defatting removed surface lipids from the zein particles, and thus facilitated their aggregation. Aggregation experiments with zein and water at 40 °C, and laser scanning confocal microscopy with zein-starch dough confirmed that zein particles aggregated more easily when surface-defatted. Dynamic oscillatory temperature sweeps demonstrated that surface-defatting lowered the temperature at which protein cross-linking occurred by 2 °C. This research can help to produce superior gluten-free bread and could also possibly contribute to the better understanding of wheat dough.     

Digitization of farinogram plots and estimation of mixing stability

Twenty-four farinograms and accompanying flour characteristics obtained from a bakery were used to get additional information for baking characteristics of flours. Farinograms were digitized and four novel parameters were included for comparison: a and b were extracted from an equation of the form y = ae^−bt; the height of the upper curve and the width of the farinograph curve at a time value equal to the dough development time. Stepwise multiple regressions were carried out relating bread volume to novel and existing parameters (water absorption, development time, arrival time, departure time, stability and degree of softening). Results indicated that four farinogram parameters, resistance, water absorption, a and b were related to bake height with an overall value of 61%. A relatively weak correlation (R = 0.44, P < 0.05) was detected between specific loaf volume and bake height.