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1.
Rheology of zein solutions in aqueous ethanol.   总被引：3，自引：0，他引：3  
Aqueous ethanol solutions prepared with commercial zein exhibited Newtonian behavior. Temperature, zein concentration, and ratio of water to ethanol affected viscosity of the zein solutions. The influence of temperature on zein solution viscosity was expressed by an Arrhenius-type equation. As zein concentration increased, solution viscosity exponentially increased. Generally speaking, viscosity decreased when the ethanol concentration increased. Parameters were estimated for an Arrhenius-type equation to describe the viscosity as a function of temperature, zein concentration, and ethanol concentration.  相似文献   

2.
A new class of zein additives was investigated, thiocyanate salts. Ammonium, potassium, guanidine (GTC), and magnesium thiocyanate salts were added to solutions of zein in with various amounts of tri(ethylene glycol) (TEG), cast as films, and then tested to determine the impact that each salt had on properties. The presence of these salts affected solution rheology and intrinsic viscosity, demonstrating that the salts interacted with the protein. It was found that these salts acted as plasticizers, as they lowered the glass transition temperature of zein when evaluated with differential scanning calorimetry. In zein films in which TEG was present, these salts increased elongation and reduced tensile strength. However, unlike traditional plasticizers (such as TEG), when the salts were used as the only additive, elongation was not increased and tensile strength was not decreased. Of the salts tested, GTC in combination with TEG was found to increase elongation the most. The impact of salts on elongation was greatly affected by the relative humidity in which the samples were stored.  相似文献   

3.
There continues to be interest in developing solvent‐resistant articles from biobased renewable materials to successfully compete with petrochemical products. It was previously shown that reaction of zein with polyethylenemaleic anhydride (PEMA) provides articles that are solvent resistant. The gelation kinetics for the reaction of PEMA with zein was investigated rheologically to better understand this chemistry. The reaction of the nucleophilic groups on zein with the anhydrides on PEMA is the main cause for the gelation reaction. The gelation time was defined as being the point when the elastic modulus (G′) and viscous modulus (G″) cross. In this work, the rate of reaction, in terms of time to gelation, was studied in N,N‐dimethylformamide solution for which the amount of PEMA, the reaction temperature, and the overall reaction concentration were varied. Exponential relationships were found between the gelation time and % PEMA, temperature, and % solids, as well as between elastic modulus with either % PEMA or % solids. The concentration of PEMA had the largest impact on gelation time, for which going from 2.5% PEMA to 6% PEMA reduced the gelation time from 63,114 to 1,576 s. The temperature dependence of this gelation reaction was well described by an Arrhenius plot with an apparent activation energy of 50.5 kJ/mol.  相似文献   

4.
An acidic method of zein extraction from DDGS   总被引：3，自引：0，他引：3  
Zein with a higher intrinsic viscosity and phosphorus content, similar protein content, lower yellowness, and at potentially much lower cost than commercially available zein was obtained from distillers dried grains with solubles (DDGS). A novel extraction method using acidic conditions in the presence of a reducing agent has been used to obtain about 10% aqueous ethanol soluble zein from DDGS. The optimum pH, time, temperature, and amount of reducing agent that can produce zein with high quality and yield have been developed. In addition to the zein, about 17% oil based on the dry weight of DDGS has also been obtained during zein extraction. The zein obtained from this research is expected to be suitable for use as fibers, films, and binders and in paints.  相似文献   

5.
Batch extraction of zein from dry‐milled whole corn with ethanol was optimum with 70% ethanol in water, an extraction time of 30–40 min, and temperature of 50°C. High yields (60% of the zein in corn) and high zein contents in the extracted solids (50%) were obtained at a solvent‐to‐solids ratio of 8 mL of 70% ethanol/g of corn. However, zein concentration in the extract was higher at lower ratios. Multiple extraction of the same corn with fresh ethanol resulted in a yield of 85% after four extractions, whereas multiple extractions of fresh corn with the same ethanol resulted in high (15 g/L) zein concentration in the extract. Optimum conditions for batch extraction of zein were 45°C, with 68% ethanol at a solvent‐to‐solids ratio of 7.8 mL/g for an extraction time of 55 min. Column extractions were also best at 50°C and 70% ethanol; a solvent ratio of 1 mL/g resulted in high zein concentrations in the extract (17 g/L) but yields were low (20%).  相似文献   

6.
The effect of moisture content and film composition on biodegradability is the focus of this study. Flexible films were first characterized for the effect on water sorption isotherms of relative humidity, temperature, zein content, and the addition of the plasticizers stearic acid, poly(ethylene glycol), or etoxylated ricine oil. Zein/ethylcellulose (EC) mixture films had a behavior between that for pure zein and EC films, which had the lowest water sorption. For films with plasticizer, the lowest water sorption at 25 degrees C was observed for those with stearic acid. Biodegradability of zein/EC films, evaluated using bacterial cultures selected for their zein proteolytic activity and isolated from a local solid waste landfill and a lagoon, showed no plasticizer effect even though its effect on moisture content was significant. Large differences were observed at different film zein concentration with the highest biodegradability for 100% zein. However, biodegradability did not mimic the water sorption behavior of zein/EC mixture films.  相似文献   

7.
We investigated the effects of a dual‐frequency frequency‐sweeping ultrasound (DFFSU) treatment on the functional properties and structure of zein. The solubility of ultrasound‐treated zein proteins increased slightly but significantly as the treatment time increased. The results showed that the DFFSU treatment had an obvious influence on the mean particle size and the size distribution. A significant (P < 0.05) increase in the size of the particles with respect to time was observed after a sonication time of more than 20 min in zein solutions. Differential scanning calorimetry results showed that sonication alters the thermal behavior of zein. Circular dichroism spectra showed a small increase in the percentage of ordered structure elements within the protein molecule. After 60 min of ultrasonication, the percentage of α‐helix structures increased by 0.9%, whereas the percentage of β‐sheets and β‐turns decreased by 0.5%. Microstructural analyses by scanning electron microscopy showed that several microholes appeared in the zein following ultrasonic pretreatment. Under the conditions investigated in this study, DFFSU treatment was found to affect the studied functional properties of the zein protein. This technology could be used to obtain improved functional properties in some protein samples.  相似文献   

8.
The hydrolysis of disodium p-nitrophenyl phosphate catalyzed by alkaline phosphatase was chosen as a model to study the kinetics of changes in frozen food products. The initial reaction rate was determined in concentrated sucrose solutions down to -24 degrees C, and the enzymatic characteristics K(M) and V(max) were calculated. The experimental data were compared to the kinetics predicted by assuming that the reaction was viscosity dependent. Indeed, an analysis of the enzymatic reaction demonstrated that both the diffusion of the substrate and the flexibility of the enzyme segments were controlled by the high viscosity of the media. When the temperature was too low for the viscosity to be measured simply, the Williams-Landel-Ferry equation was used to predict the viscosity, taking, as reference temperature, the glass transition temperature (T(g)) corresponding to the concentration of the freeze-concentrated phase at the test temperature. Predicted values of the reaction rate were very close to the experimental ones in the studied temperature range.  相似文献   

9.
The adsorption of a commercial zein sample on carboxylic (COOH) and alkyl (CH(3)) surfaces was monitored by high time resolution surface plasmon resonance. Zein showed higher affinity and higher mass adsorption on carboxylic than alkyl surfaces. A zein layer specific for each surface was obtained after flushing off loosely bound zein with 75% 2-propanol solutions. Zein deposits were examined under atomic force microscopy. Differences in layer thickness between carboxylic and alkyl surfaces were explained in terms of zein adsorption footprint.  相似文献   

10.
Addition of sorghum flour to wheat flour produces marked negative effects on rheological properties of dough and loaf volume. Although there are notable differences in the chemical composition of sorghum proteins (kafirins) compared with wheat gluten that might imply poor functionality in breadmaking systems, a larger constraint may be the unavailability of kafirins due to encapsulation in protein bodies. In this study, zein, the analogous maize prolamin to kafirin, was used to determine the potential effects of protein-body-free prolamins on dough rheology and baking quality of wheat-sorghum composite flour. Mixograms run at 35°C (above the glass transition temperature of zein) were significantly (P < 0.01) improved with addition of zein. Mixogram peak heights increased while mixing time decreased uniformly with addition of zein. Dough extensibility studies showed an increase in maximum tensile stress, while baking studies showed an increase in loaf volume with increasing amounts of added zein. These data are supported by a previous study showing that, in a model system, zein mixed with starch can form viscoelastic networks, and suggest that kafirin, if made available, could contribute to dough formation.  相似文献   

11.
Traditionally, zein is isolated and recovered from corn gluten meal (GCM) using aqueous alcohol as the solvent. Recovery of zein from this solvent is inconvenient and costly. Zein is insoluble in 100% ethanol at room temperature, but it is soluble at 120°C in ethanol. Absolute ethanol effectively extracted zein from CGM, distillers dried grains (DDG), and ground corn. Zein was extracted from CGM with absolute ethanol in a high‐pressure reactor at 130°C. After extracting at 130°C for 45 min, the solution was pumped out of the extractor and allowed to cool. Upon cooling, the zein precipitated from solution. The precipitate was removed from the solution and air‐dried, resulting in 14% recovery of the starting material. The recovered precipitate had an average protein content of >90% on a dry basis, accounting for ≈20% of the CGM protein and recovered ≈35% of its zein. No differences were seen in the amount of zein extracted from CGM samples that were hand‐collected off the dewatering screen and gently dried, versus commercial CGM samples. The commercial CGM did produce a greater amount of solubles. The extraction procedure also worked at temperatures as low as 90°C. The lower temperature did produce lower yields of extracted zein. The zein extracted at the lower temperatures was less brown, but zein extracted at either temperature was almost fully soluble in traditional zein solvents.  相似文献   

12.
Experiments on the adsorption of alpha-zein (characterized by SDS-PAGE) from aqueous ethanol and 2-propanol solutions onto hydrophilic and hydrophobic surfaces are reported. Zein adsorption onto self-assembled monolayers (SAMs) was detected by surface plasmon resonance (SPR). Gold substrates were prepared by thermal evaporation on glass slides. Gold-coated surfaces were modified by depositing SAMs of either a long-chain carboxylic acid terminated thiol [COOH(CH2)(10)SH] or a methyl-terminated alkanethiol [CH3(CH2)(7)SH]. Experimental measurements indicated that zein interacted with both hydrophilic and hydrophobic surfaces. Zein concentration affected the thickness of bound zein layers. The estimated thickness of the zein monolayer deposited on hydrophilic surfaces was 4.7 nm. Zein monolayer thickness on hydrophobic surfaces was estimated at 4.6 nm. The topography of zein layers was examined by atomic force microscopy (AFM) after solvent was evaporated. Surface features of zein deposits depended on the adsorbing surface. On hydrophilic surfaces, roughness values were high and distinct ring-shaped structures were observed. On hydrophobic surfaces, zein formed a uniform and featureless coverage.  相似文献   

13.
Corn is one of the most important food and industrial crops in the United States. Zein constitutes about half of the endosperm proteins in corn. Potential applications of zein include use in fibers, adhesives, inks, cosmetics, textiles, and chewing gum. Recently, attempts have been made to utilize zein for food coatings and biodegradable materials. The new applications of zein require it to be resistant to water. Thus, we are interested in new routes for chemical modification of zein (Biswas et al, unpublished). 2‐Octenyl succinic anhydride (OSA) is extensively used in modifying food starches. Our objective was to take advantage of OSA hydophobicity, flexibility, and compatibility with nonpolar groups and incorporate OSA onto zein. This OSA‐modified zein would possess the best of both OSA and zein. A zein solution in dimethyl formamide (DMF) was reacted with various levels of OSA to give modified zein. In a microwave reactor, the reactions proceeded tremendously fast and they were over in 5 min. The anhydride group of OSA reacted with the hydroxyl/amine group of zein to form ester/amide of zein. The reaction of OSA‐modified zein was confirmed by proton nuclear magnetic resonance (NMR) and IR spectroscopy. The preliminary evaluation showed that zein and OSA‐modified zein had comparable mechanical properties.  相似文献   

14.
The effect of processing conditions in an excess steam jet cooker on the degradation of waxy maize starch was studied. The temperature of the steam, the flow rate of the starch slurry, and the concentration of starch were determined to influence the extent of degradation. The viscosity of concentrated solutions of the jet‐cooked product and the intrinsic viscosity of dilute solutions were used as measures of the extent of molecular degradation. The viscosity decreased at higher reaction temperatures, and at higher team‐to‐starch ratios. Multiple passes through the jet cooker decreased the viscosity dramatically for the first two passes, but little additional change was observed for further passes. The results show that mechanical and thermal degradation effects are both important in the jet cooking of waxy maize starch, although the primary effect is due to mechanical degradation.  相似文献   

15.
Zein, the prolamin of corn, is attractive to the food and pharmaceutical industries because of its ability to form edible films. It has also been investigated for its application in encapsulation, as a drug delivery base, and in tissue scaffolding. Zein is actually a mixture of proteins, which can be separated by SDS-PAGE into α-, β-, γ-, and δ-zein. The two major fractions are α-zein, which accounts for 70-85% of the total zein, and γ-zein (10-20%). γ-Zein has a high cysteine content relative to α-zein and is believed to affect zein rheological properties. The aim of this study was to investigate the effect of γ-zein on the often observed phenomena of zein gelation. Gelation affects the structural stability of zein solutions, which affects process design for zein extraction operations and development of applications. The rheological parameters, storage modulus (G') and loss modulus (G″), were measured for zein solutions (27% w/w solids in 70% ethanol). β-Mercaptoethanol (BME) was added to the solvent to investigate the effect of sulfhydryl groups on zein rheology. Modulus data showed that zein samples containing γ-zein had measurable gelation times under experimental conditions, contrary to samples with no γ-zein, where gelation was not detected. Addition of BME decreased the gelation time of samples containing γ-zein. This was attributed to protein unfolding. SEM images of zein microstructure revealed the formation of microspheres for samples with relatively high content of α-zein, whereas γ-zein promoted the formation of networks. Results of this work may be useful to improve understanding of the rheological behavior of zein.  相似文献   

16.
Maize zein was hydrolyzed for 0.5-5 h by alcalase or papain. Protein solubility increased (P < 0.05) with the degree of hydrolysis (DH) and was higher for alcalase-hydrolyzed zein than for papain-hydrolyzed zein. The zein hydrolysates with both enzymes consisted mostly of small peptides or amino acids nondetectable by 15% acrylamide gel electrophoresis. Alcalase-hydrolyzed zein exhibited a stronger (P < 0.05) antioxidant activity than papain-hydrolyzed zein, as indicated by peroxide and thiobarbituric acid-reactive substance values in a liposome-oxidizing system. Zein hydrolysates possessed strong Cu(2+) chelation ability and marked reducing power, both of which were accentuated with hydrolysis time. The protein hydrolysates also showed strong radical-scavenging ability, which was not influenced by hydrolysis time. The antioxidant activity of alcalase-hydrolyzed zein at some specific low concentrations was close or comparable to those of butylated hydroxyanisole, alpha-tocopherol, and ascorbate. Although intact zein displayed an antioxidative effect, it was far less potent than hydrolyzed zein. The results demonstrated that enzyme-hydrolyzed zein can act as a metal ion chelator or a hydrogen donor, as well as a radical stabilizer to inhibit lipid oxidation. The effectiveness of the protein hydrolysates appeared to depend on both the concentration and the peptide/amino acid composition of the soluble protein fraction.  相似文献   

17.
Three essential oils, oregano, red thyme, and cassia (100% pure oil), were encapsulated by phase separation into zein nanospheres. Topographical images indicated that the powders were made up of irregularly shaped particles ( approximately 50 mum) containing close-packed nanospheres. Approximately 31% of the oregano encapsulated particles had mean diameters greater than 100 nm compared to 19% for the zein alone particles. In vitro digestion of zein particles with pepsin at a concentration ratio of 10:1 was complete after 52 h in phosphate-citrate buffer, pH 3.5, at 37 degrees C by spectroscopic analysis. Nonenzymatic, aqueous in vitro release of essential oils from encapsulated zein particles was carried out in phosphate buffered saline at pH 7.4 and 37 degrees C. Release occurred at varying rates over 20 h probably from different locations within the closely packed nanospheres of different sizes. Gel electrophoresis SDS-PAGE of zein incubated with freeze-dried swine manure solids at 37 degrees C indicated that preformed microbial enzymes capable of digesting zein within minutes were present in the manure. Except for differences in size of nanospheres, no structural differences were resolved by several microscopic methods, suggesting that the oil and proteins phases were blended during phase separation.  相似文献   

18.
A new method for preparation of zein films involving plasticization of zein with oleic acid to form an intermediate moldable resin was presented. The resin was stretched over rigid frames to form thin membranes that were set in flexible films. The objective of the study was to investigate the effect of film preparation method on film properties. Tensile properties, microstructure, and thermal behavior of zein films plasticized with oleic acid were investigated for films prepared by conventional casting from ethanol solutions and by stretching of plasticized resins. Cast films were stiff and brittle, whereas resin films showed more flexibility and toughness. Differential scanning calorimetry thermograms of cast films indicated phase separations were generated when heated that were not observed for resin films. Microstructure images showed a higher degree of structure development and orientation in resin than in cast films. Glass-transition temperatures of resin films were measured at -94 and 104.4° C, indicating the film remained flexible through a wide temperature range. Resin film flexibility and toughness were attributed to effective plasticization that led to fiber formation and orientation.  相似文献   

19.
Circular dichroism studies were performed on zein to determine how the secondary and tertiary structure changes with different solvents, temperatures, or pH. Alcoholic solvent type and common denaturants such as SDS and low amounts of urea had little effect on the secondary structure of zein. Utilization of dimethylformamide or acetic acid as solvent gave changes in tertiary structure. Solutions of zein in 8M urea produced solutions with large changes in tertiary structure. The dissolution of zein in 50 mM sodium hydroxide produces a zein with large changes in secondary and tertiary structure and little loss in primary structure. Increasing the temperature of zein to 70°C in 80% ethanol-water gave reversible changes in the primary structure (20% reduction in absolute magnitude of [θ]λ at 208 and 222 nm) and tertiary structure (40% reduction in absolute magnitude of [θ]λ at 268 nm).  相似文献   

20.
利用蛋白质和多糖构建纳米营养递送载体,是提高食品活性物质稳定性及利用率的重要手段。为了构建具有缓释特性的纳米营养递送体系,该研究以玉米醇溶蛋白（zein）为基材,构建玉米醇溶蛋白-壳聚糖纳米营养递送体系,以姜黄素（Cur）为营养模型,探究了壳聚糖分子量、zein与壳聚糖质量比对纳米粒子及其负载Cur性能的影响,通过扫描电子显微镜（Scanning Electron Microscope,SEM）、傅里叶红外光谱（Fourier Transform Infrared Spectroscopy,FTIR）等方法表征其结构,阐明复合纳米粒子形成机制,探讨其稳定性和缓释性能。结果表明：不同分子量的壳聚糖对纳米粒子的粒径、多分散性指数和zeta电位有影响。高分子量壳聚糖的加入可使纳米粒子粒径减小,且更加稳定。在zein与高分子量壳聚糖质量比为8∶1时,制备纳米粒子粒径较小（80.13 nm）,其zeta电位为46.18 mV;在此条件下,当姜黄素添加量为1.0%时,其包封率和负载量分别为82.93%和8.29%;通过SEM观察,纳米粒子呈球形,分布均匀;氢键及静电相互作用是组装该纳米粒子的作用力;壳聚糖的引入提高了纳米粒子的pH值、离子及储藏稳定性,扩展了其应用范围;与游离的姜黄素相比,纳米营养递送粒子呈现明显的缓释特性。研究结果为构建具有缓释特性的营养递送体系提供了理论基础。  相似文献   

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