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1.
Rice flour is a starchy material with low-cost, because it can be produced from rice that is broken during processing. The aim of this study was to develop biodegradable films based on rice starch and rice flour, and to characterize their physicochemical, microscopic and mechanical properties. Films from rice starch and rice flour were prepared by casting, with glycerol or sorbitol as plasticizer. SEM analysis of starch and flour films revealed compact structures. Rice flour films prepared in the present work have similar mechanical properties to those of starch based films. However, their water vapor permeabilities are two times higher than those of starch based films. Films with sorbitol were less permeable to water and more rigid, while films with glycerol are more plasticized and have poorer water vapor barrier properties. Therefore, preparing edible films from rice flour is a new alternative for using this raw material, which is sometimes much cheaper than commercial starches.  相似文献   

2.
In order to explore an alternative method instead of plasticization for improving the toughness, flexibility and processability of PLA based packaging films, two different kinds of modified polyethylene based elastomers, such as glycidyl methacrylate or maleic anhydride functionalized ethylene-acrylate based elastomers, were melt blended with PLA. Their properties were compared with conventional PEG plasticized PLA. The chemical interaction between end groups of PLA and epoxide or maleic anhydride functional groups of elastomers was shown by FTIR. Scanning electron microscopy showed that up to 20 % PEG loading, one phase morphology was achieved, however beyond this point, a phase separation was observed for plasticized PLA. For PLA/elastomer blends, a two-phase morphology was obtained as a result of immiscible nature of PLA and elastomers. Tensile and dynamic mechanical properties indicated that elastomer based blends were better than plasticized PLA independently from elastomer type. Differential scanning calorimeter (DSC) analysis exhibited that the T g value was remarkably lowered in the plasticized PLA; however, it did not change in the case of elastomers. In terms of oxygen permeability and biodegradability, plasticized PLA was found to be better than elastomer based blends.  相似文献   

3.
The effect of feed moisture content (10, 14 and 18%) and die temperature (110 and 160 °C) on functional properties, specific mechanical energy (SME), morphology, thermal properties, X-ray diffraction pattern (XRD), Fourier transform infrared spectroscopy (FTIR) and amylose-lipid complex formation of extruded sorghum flour was investigated. Results showed that the extrusion cooking significantly changed the functional properties of extruded sorghum flour. Increasing feed moisture increased the peak gelatinization temperature (Tp), the degree of gelatinization (%) and starch crystallinity (%) while it decreased the gelatinization temperature ranges (Tc - T0), starch gelatinization enthalpy (ΔHG) and amylose-lipid complex (%) formation. With increasing die temperature, the degree of gelatinization and amylose-lipid complex formation increased and the starch Tp, Tc-T0, ΔHG and crystallinity decreased. The FTIR spectra also showed that the extrusion cooking did not create new functional groups or eliminate them in sorghum protein, whereas the sorghum extrudate protein had random coil conformation.  相似文献   

4.
Cereal melts were produced via extrusion cooking using a twin-screw extruder at in-barrel moisture contents ranging from 25 to 42% (wb). Dynamic mechanical thermal analysis was performed to determine the plasticizing effect of water on the glass transition (Tg) for melts obtained from degermed corn meal, oat flour, pregelatinized corn starch and pregelatinized waxy maize. For degermed corn meal, Tgwas found to decrease with increasing water contents up to about 30% (wb). Above 30% moisture content, Tgwas found to be essentially constant and approximately equal to 270K. Thus, Wg′ was estimated to be 30% moisture content. For samples of moisture content less than Wg′, loss tangent vs. temperature plots in the glass transition region were observed to be broader and of smaller amplitude than those above Wg. Glass transitions ranged from 270 to 321K for sample moisture contents ranging from 36·3 to 22·2% (wb), respectively. For an oat flour, Tgvalues ranging from 270 to 303K were observed for moisture contents of 39·2 to 26·1% (wb), respectively. Melts formed from pregelatinized corn starch and pregelatinized waxy maize had glass transitions similar to corn meal at a similar moisture content of 27%. The significance of these results, in terms of extrusion cooking of cereals, is discussed in this work.  相似文献   

5.
The objective of this study was to investigate the influence of nanoclay incorporation procedure on the mechanical and water vapor barrier properties of starch/nanoclay composite films. Cassava starch films were prepared with (nanocomposite) and without nanoclay (control) in two steps: firstly the production of extruded pellets and secondly thermo-pressing. The nanocomposite films were prepared via two different methods: in D samples the nanoclay was dispersed in glycerol and subsequently incorporated into the starch; and in ND samples all ingredients were added in a single step before the extrusion. All the composite-films were prepared with cassava starch using 0.25 g of glycerol/g of starch and 0.03 g of nanoclay/g of starch. Control samples showed VA-type crystallinity induced by the manufacturing process and the nanocomposites presented a semicrystalline and intercalated structure. The nanoclay improved the water vapor barrier properties of the starch film and this effect was more pronounced in D samples, where the water vapor permeability (Kw) was 60% lower than that of the control samples. The Kw reduction was associated with decreases in the effective diffusion coefficient (approximately 61%) and in the coefficient of solubility (approximately 22-32%). On the other hand, the incorporation of nanoclay increased the tensile strength and the rigidity of the films and this effect was more significant when the nanoclay was dispersed in glycerol. Thus, the incorporation of nanoclay into starch-based films is a promising way to manufacture films with better mechanical and water vapor barrier properties.  相似文献   

6.
This research evaluates the miscibility and performance of polypropylene (PP)/polybutylene succinate (PBS) and PP/polylactic acid (PLA) blend and natural-flour-filled, PP/PLA and PP/PBS blend bio-composites. The melting temperature (T m ) and glass transition temperature (T g ) of pure PP, PBS and PLA showed a single peak but differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) presented two peaks for the T m and T g of the PP/PBS and PP/PLA blends. These results indicated that the PP/PBS and PP/PLA blend systems existed as immiscible blends. These results were also confirmed by the scanning electron microscopy (SEM) micrographs of the tensile fracture surface of the PP/PBS and PP/ PLA blends. At a PP/PBS and PP/PLA blend ratio of 70/30, the tensile and flexural strengths of bamboo flour (BF)- and wood flour (WF)-filled, PP/PBS and PP/PLA blend bio-composites were similar to those of BF- and WF-filled, PP and PBS bio-composites. In addition, these strengths of maleic anhydride-grafted PP (MAPP)- and acrylic acid-grafted PP (AAPP)-treated, BF- and WF-filled, PP/PBS and PP/PLA blend bio-composites were higher than those of non-treated bio-composites.  相似文献   

7.
Thermoplastic starch (TPS) was modified with ascorbic acid and citric acid by melt processing of native starch with glycerol as plasticizer in an intensive batch mixer at 160 °C. It was found that the molar mass decreases with acid content and processing time causing the reduction in melting temperature (Tm). As observed by the results of X-ray diffraction and DSC measurements, crystallinity was not changed by the reaction with organic acids. Tm depression with falling molar mass was interpreted on the basis of the effect of concentration of end-chain units, which act as diluents. FTIR did not show any appreciable change in starch chemical compositions, leading to the conclusion that the main changes observed were produced by the variation in molar mass of the material. We demonstrated that it is possible to decrease melt viscosity without the need for more plasticizer thus avoiding side-effects such as an increase in water affinity or relevant changes in the dynamic mechanical properties.  相似文献   

8.
In this study, new films based on triticale flour were prepared by using the casting technique. Colour, microstructure, mechanical, physicochemical and water vapour barrier properties were determined. Triticale flour films were aged up to 60 days at 52% relative humidity and 25 °C. The influence of storage time on functional properties was also studied. All films presented high (from 84.01 to 85.21) lightness values (L*). Results showed that during storage the values of permeability of the films did not change significantly. Tensile strength, elastic modulus of Young and puncture force values increased and the percent of elongation at break decreased towards the last days of storage. Analysis of SEM images of films showed the appearance of small cracks at 60 days of storage. After 45 days of storage, triticale flour films maintained acceptable functional properties. In conclusion, films based on triticale flour showed properties that make them a substantial potential to be incorporated in food packaging applications.  相似文献   

9.
Hydrophilic biopolymer systems reach a state of maximum plasticization at a concentration of water designated as Wg′. The thermomechanical behaviour of various extruded cereals were investigated at concentrations above and below Wg′ to determine the significance of Wg′ on the viscoelastic properties in the rubbery region above Tg. Cereal melts were produced via extrusion cooking using a twin-screw extruder at in-barrel moisture contents ranging from 25 to 42% (wb). Dynamic mechanical thermal analysis (DMTA) was used to determine the viscoelastic properties for melts obtained from degermed corn meal, oat flour, pregelatinized corn starch and pregelatinized waxy maize. All of the extruded melts displayed reductions in the storage modulus of about two orders of magnitude from the glassy to rubbery regimes. At temperatures greater than 320K, another transition is apparent for extruded oat flour. These losses may be attributed to a reduction in physical crosslinks and/or entanglements. With respect to the other melts investigated, differences in the oat flour melts at temperatures above Tgmay be due to the increased presence of protein and lipid. Given the apparent partly crystalline nature of these melts at moisture contents <Wg′, the most appropriate representation of the viscoelastic properties may be isotimic plots of the viscoelastic functions. These contour plots provide a more comprehensive guide to material behaviour than the ‘traditional’ state diagrams found throughout the literature. An important point is that prediction of viscoelastic properties above Tgfor polymers where the internal structure changes with temperature or moisture content, cannot be predicted using the same methods of reduced variables as for amorphous polymers. Thus rather than using these methods, experimental data, such as given here, may prove to be necessary to design or understand processes involving cereal melts based on their viscoelastic properties.  相似文献   

10.
Wheat flour was plasticized with glycerol and compounded with poly(lactic acid) in a one-step twin-screw extrusion process in the presence of citric acid with or without extra water. The influence of these additives on process parameters and thermal, mechanical and morphological properties of injected samples from the prepared blends, was then studied.Citric acid acted as a compatibilizer by promoting depolymerization of both starch and PLA. For an extrusion without extra water, the amount of citric acid (2 parts for 75 parts of flour, 25 parts of PLA and 15 parts of glycerol) has to be limited to avoid mechanical properties degradation. Water, added during the extrusion, improved the whole process, minimizing PLA depolymerization, favoring starch plasticization by citric acid and thus improving phases repartition.  相似文献   

11.
The effects of high pressure processing (HPP) at 500 and 800 MPa for 1 and 10 min, and the addition of glycerol (4% w/w) and salt (1% w/w) on the properties of water in corn tortillas were investigated. Moisture content and water activity were not affected by either HPP or addition of glycerol/salt. Thermal analysis techniques (such as differential scanning calorimetry and thermogravimetric analysis) and nuclear magnetic resonance spectroscopy (1H cross-relaxation and 1H T1 and T2 relaxation times) were used to characterize these samples at a structural and molecular level, respectively. Addition of glycerol and salt significantly decreased the ‘freezable’ water content of the tortillas while HPP had little effect on the measured structural properties. The proton mobility was significantly decreased by HPP but not affected by addition of glycerol and salt. These results show that both composition and HPP may alter the structural and molecular properties of water in corn tortillas.  相似文献   

12.
Textile industry generate significant amount of waste fibres in form of short lengths during mechanical processing. However these short fibres possess excellent properties suitable for many other applications. The objective of this work was to use them for the preparation of nanoparticles/nanofibres as fillers in biodegradable composite applications such as food packaging, agriculture mulch films, automotive plastics, etc. The present paper concerns with jute fibres as a source of nanocellulose for reinforcement of PVA mulch films. Jute fibres were first refined to micro/nanoscale particles in form of nanofibrillar cellulose (NFC) by high energy planetary ball milling process in dry and wet condition. Wet milling was observed more efficient than dry milling in terms of unimodality of size distribution with reduction in size below 500 nm after milling for 3 hours. Later the obtained particles were used as fillers in Poly vinyl alcohol (PVA) films and their reinforcement evaluated based on thermal properties. It was observed that glass transition temperature (Tg) of PVA films improved from 84.36 °C to 95.22 °C after addition of 5 % jute particles without affecting % crystallinity and melting temperature (T m) of PVA. Dynamic mechanical analysis of composite films with 5 % jute particles showed higher value of 14×108 Pa for storage modulus in comparison to 9×108 Pa of neat composite film. The percolation effect was observed more above glass transition temperature which consequently resulted in improved transfer of stiffness from jute particles to PVA matrix above 50 °C. The percolation phenomena also explained the improvement in thermal stability by 10 °C for every increased loading of jute particles due to formation of hydrogen bonds with PVA matrix.  相似文献   

13.
The aim of this study was to improve the baking quality of whole-wheat saltine cracker (WWSC) using endoxylanases, vital wheat gluten (VWG), and gum Arabic. SRC results showed both water-SRC and sucrose-SRC of soft white whole-wheat flour (SWWW) were significantly reduced by gum Arabic (r = 0.94, P < 0.05). Alveograph results indicated that the tenacity and extensibility of the whole-wheat dough (WWD) were increased by VWG. Rheometer G′ and G″ moduli increased with higher addition levels of endoxylanases, VWG, and gum Arabic. Low-field nuclear magnetic resonance (LF-NMR) detected three CPMG proton populations (T21, T22, and T23) in WWD. T21 peak area ratio (tightly bound water) reduced and T22 peak area ratio (less tightly bound water) increased with the levels of each additive. LF-NMR results revealed increased water mobility from T21 population to T22 population with addition of these additives, which was beneficial for gluten to form a continuous network. Both stack height and specific volume of WWSC were improved by the use of endoxylanases, VWG, and gum Arabic, but the breaking strength varied. The results of Orthogonal experimental design showed that the most-improved quality WWSC could be produced by combining 0.035% endoxylanases, 1.5% VWG, and 1.5% gum Arabic into SWWW flour.  相似文献   

14.
Cobaltous sulfate heptahydrate (CoSO4·7H2O) was incorporated as filler into diglycidyl ether of bisphenol A (DGEBA) based epoxy resin system, to prepare organic-inorganic polymer hybrid materials. Mechanical tensile studies and dynamic mechanical analysis (DMA) were carried out in order to study the static and dynamic mechanical properties of the prepared hybrid films. Mechanical tensile studies were carried out at room temperature, at a test speed of 30 mm/min. Highest tensile strength of 24.74±2.42 MPa was achieved for 4.44 wt% filler level (FL), along with an increase in the value of Young’s modulus. Storage modulus (E′), loss modulus (E″), damping factor (tan δ) were obtained by DMA studies. Glass transition temperature (Tg) was obtained for pure epoxy and filled epoxy, for various FLs varying from 0.28 wt% to 5.00 wt%. Pure epoxy showed highest Tg value compared to filled epoxy hybrids. Highest storage modulus of 9.5 GPa was obtained for 2.22 wt% FL, which also showed highest loss modulus peak. Parameters like effectiveness coefficient (C) and crosslink density were calculated from the storage modulus data. Loss modulus and tan δ curves were analyzed to study the energy dissipation properties of prepared hybrid films. Activation energy (Ea) value for glass transition was obtained from damping factor (tan δ), which showed highest Ea value of 630.5 kJmol-1, for 4.44 wt% FL. DMA studies for various FLs were carried out at different test frequencies in order to study the changes in dynamic mechanical properties of the prepared hybrid materials with respect to frequency  相似文献   

15.
The phase behavior of zein films has been investigated at nano-scale using atomic force microscopy (AFM) and compared to the phase behavior of the bulk using a thermal characterization technique. The local surface properties of the films were evaluated as a function of water activity using AFM. The glass transition temperature (Tg) of zein films decreased with increasing water activity. Adhesion forces measured by the AFM force curves increased with increasing water activity. Topography of zein and zein fractions were evaluated both qualitatively and quantitatively by the use of AFM and dedicated software to calculate the surface roughness. It has been found that processing technologies (solvent casting, drop deposition and spin casting) has influence on the surface structures of films. The films which were formed by the alpha zein rich fraction were found to have highest roughness values. Sectional surface profiles revealed that α-zein films have mean roughness (Ra) of 1.808 nm and root mean square roughness (RMS) of 2.239 nm while β-zein films have mean roughness (Ra) of 1.745 nm and root mean square roughness (RMS) of 3.623 nm. The discussions conducted on the differences/similarities in the observations were based on the hydrophobic/hydrophilic properties and interactions of these zein fractions.  相似文献   

16.
The quality of bread made from frozen dough is diminished, and staling rate is increased by changes that occur during freezing and storage. New cultivars of waxy wheat flour (WWF), containing higher levels of amylopectin, may help improve the quality of baked products. Bread quality and staling were investigated for bread containing 0–45% WWF and 55–65% water after freezing and 90-day frozen storage. The specific volume was highest with 15% WWF substitution and 60% water in bread made from both unfrozen and frozen dough. With higher levels of WWF and lower water content, bread staling rates decreased. Bread with higher levels of WWF were darker and had greater color variation. 1H NMR studies showed that bread with greater WWF and water had higher transverse relaxation (T2) times (9–11 ms), but less change in T2 during storage. This research demonstrated that specific combinations of WWF and water produced a better quality of bread after dough freezing.  相似文献   

17.
The quality of bread made from frozen dough is diminished, and staling rate is increased by changes that occur during freezing and storage. New cultivars of waxy wheat flour (WWF), containing higher levels of amylopectin, may help improve the quality of baked products. Bread quality and staling were investigated for bread containing 0–45% WWF and 55–65% water after freezing and 90-day frozen storage. The specific volume was highest with 15% WWF substitution and 60% water in bread made from both unfrozen and frozen dough. With higher levels of WWF and lower water content, bread staling rates decreased. Bread with higher levels of WWF were darker and had greater color variation. 1H NMR studies showed that bread with greater WWF and water had higher transverse relaxation (T2) times (9–11 ms), but less change in T2 during storage. This research demonstrated that specific combinations of WWF and water produced a better quality of bread after dough freezing.  相似文献   

18.
The study of food products is always a challenge due to the number of components involved and the interactions that may occur between them. Water is a particular ingredient which interacts with all hydrophilic compounds, although affinities may differ for limiting water amount. During this study, results obtained using 1H NMR on cake dough were compared in terms of the effects of flour type (soft or medium hard), the addition of gluten (5%–20%) and the use of soft flour fractions (flour particle fractions smaller or larger than 50 μm). T2 values and the signal intensities of different proton populations were studied as a function of the wheat protein contents of dough samples. Physicochemical characterization methods were used to better understand how the origin and particle size of flour might impact the hydration properties and mobility of a model system. Increasing the protein content in dough samples was related to an increase of the mobility of fat protons and of the least mobile proton population (relaxation times ranging from 175 to 180 ms and from 5 to 7 ms, respectively).  相似文献   

19.
Starch is a major component of rice grain and thus plays an important role in grain quality. For breeding rice with improved quality, the thermal and retrogradation properties of starch may be routinely measured. Since direct measurement is time-consuming and expensive, rapid predictive methods based on near-infrared spectroscopy (NIRS) can be applied to measure these quality parameters. In this study, calibration models for measurement of thermal and retrogradation properties were built from the spectra of grain and flour samples. The results indicated that both grain and flour spectra could give similar accuracy (r2=∼0.78) in determining the peak temperature (Tp) and conclusion temperature (Tc) of gelatinization. However, flour spectra (r2=0.80) were superior to the grain spectra (r2=0.73) in measuring onset temperature (To). Furthermore, the thermal properties of width at half peak height (ΔT1/2) and enthalpy of gelatinization (ΔHg), and retrogradation properties of enthalpy of retrogradation (ΔHr) and retrogradation percentage (R%) could only be successfully modeled with the flour spectra. The models reported in the present study are usable for routine screening of a large number of samples in early generation of selection in breeding programs. For accurate assay of the thermal and retrogradation properties, however, direct instrumental measurement should be employed in later generations.  相似文献   

20.
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 (Tg) 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 Tg softer (i.e. |G*| was significantly lower). LSCM revealed that cooling below Tg alone did not destroy the zein strands; however, upon mechanical impact below Tg, they shattered into small pieces. When such dough was heated above Tg 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 Tg and subsequently reheated, breads had large void spaces under the crust. Likely, expanding gas bubbles broke zein strands below Tg resulting in structural weakness.  相似文献   

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