Effect of re-crystallization on tensile, optical and water vapour barrier properties of corn starch films containing fatty acids

Starch films are very hygroscopic and undergo crystallization during processing and storage. In this work, fatty acids (SA, PA and OA) were incorporated into starch films containing glycerol as plasticizer, in order to reduce the hygroscopic character of the films and to improve water vapour permeability. Microstructural, mechanical, barrier and optical properties were studied in both non-stored films and those stored for 5 weeks. Fatty acid addition affected the main properties of films since mechanical resistance was decreased, water vapour permeability was reduced and gloss and transparency were reduced. The degree of starch and FA crystallinity increased with storage time and gave rise to changes in film properties: films became stiffer, less effective as water vapour barriers and less transparent and glossy. Saturated fatty acids were more efficient at reducing WVP as compared to oleic acid, but these differences decreased after storage due to the greater increase in crystallization of the former as it has been observed by X-ray diffraction.     

Influence of the homogenization conditions and lipid self-association on properties of sodium caseinate based films containing oleic and stearic acids

The effect of the homogenization conditions of the film-forming emulsions and lipid self-association on the physical properties of sodium caseinate films containing oleic and stearic acids was studied. For this purpose, different film-forming emulsions were prepared by using different homogenization methods and were characterized as to particle size distribution and rheological properties. Likewise, mechanical, structural and optical properties and water vapour permeability (WVP) of the obtained films were also determined. While films containing stearic acid showed a laminar-like structure, oleic acid was more homogeneously dispersed in the film matrix. These differences in structure make the stearic acid films less flexible, showing more surface roughness and less gloss and transparency than films containing oleic acid. The film microstructure also affects the WVP. In this sense, for oleic acid films, water barrier efficiency increased when homogenization conditions were more intense, whereas for films containing stearic acid, the opposite effect was observed. This different behavior was attributed to the different kind of lipid self-association in the aqueous media, protein interactions and their impact on the final film microstructure.     

Effect of ground corn steeping on starch properties

Pasting and thermal properties, and microstructure of starch from ground corn (GS) steeped at 52 °C in sulphurous acid solution (0.20%) at different steep times (8, 16, 24, 32 and 40 h) were investigated. The isolated starch obtained by wet milling was characterised by determining pasting properties in Rapid Visco Analyser (RVA), retrogradation enthalpy in differential scanning calorimetry (DSC), and microstructure of granules in light (LM) and scanning electron microscopy (SEM). Milling before steeping and long steep time caused reduction in peak, hot paste, cool paste, breakdown and setback viscosities. Steep time provoked an increase in the retrogradation temperatures (onset and peak), whereas no significant differences were found in retrogradation enthalpy. Microstructure characteristics analysed by SEM showed many cracks and cavities on surface in samples steeped 8 h, whereas samples steeped 40 h showed a great alteration and disruption of their inner layer. LM with polarised light confirmed that starches retained birefringence with several differences depending on the steep time. The use of ground kernels allowed a better steep solution–endosperm interaction, which caused changes in rheological, thermal and microstructural starch characteristics.     

Effect of flaxseed meal on the dynamic mechanical properties of starch-based films

Starch (S)–flaxseed meal (FM) biofilms were prepared from potato and maize starch by incorporating FM up to 15% (dry solid basis) and using glycerol as plasticizer. The dynamic mechanical properties, tensile properties and water vapor permeability (WVP) of these films were measured. The storage modulus of both the starch (control) and starch–FM films decreased as temperature increased. Tan δ increased initially in all the films with increase in temperature until a peak value was reached which allowed the determination of glass transition temperature (T_g). Both tensile strength and Young’s modulus of the starch–FM films increased with increase in the FM content. The WVP of the potato starch–FM films first increased to 2.261 (×10⁵ g m⁻² h⁻¹ Pa⁻¹) when FM content increased to 5% and decreased down to 1.832 (×10⁵ g m⁻² h⁻¹ Pa⁻¹) with further increase in the FM content to 15%. While the WVP values of the cornstarch and corn starch–FM films were not significantly (p > 0.05) different. The incorporation of FM increased the tensile strength, decreased the % elongation at break and increased the T_g.     

Phase transitions in starch based films containing fatty acids. Effect on water sorption and mechanical behaviour

The water sorption capacity (WSC) of starch films containing, or not, glycerol (1:0.25 starch:glycerol ratio) and fatty (palmitic, stearic and oleic) acids (1:0.15 starch:fatty acid ratio) was analysed at 10, 25 and 40 °C in the entire range of a_w. Starch re-crystallization during the equilibration time was also analysed by X-ray diffraction. Likewise, the glass transition and lipid melting properties as a function of the film water activity were determined. Mechanical behaviour was also analysed at 25 °C for film samples equilibrated at 0, 53, 68 and 75% RH. Crystallization was promoted at low temperature and high relative humidity which modifies the expected tendencies in WSC as a function of the temperature. In relationship with this, V-type structures were formed during time, mainly in fatty acids containing films. Glass transition of the starch matrix at low moisture contents was affected by the presence of saturated fatty acids. Microstructural observations seem to corroborate the complex formation between these and the polymer chains. The mechanical behaviour of the films, as a function of the moisture content, is coherent with the results of the phase transition analysis and microstructural observations. The plasticization effects and the structural discontinuities in the polymer matrices determine the value of the elastic modulus and the behaviour at break.     

Effect of surfactants on water barrier and physical properties of tapioca starch/decolorized hsian-tsao leaf gum films

The objective of this research is to enhance the water barrier properties of tapioca starch/dHG edible films by incorporating sucrose ester surfactants with different HLB values. The moisture sorption isotherms, mechanical properties, microstructure and optical character of the resulting films were examined as well. It was found that the water barrier property of starch/dHG films is promoted significantly by surfactants, alongside a decreasing tendency in tensile strength and tensile strain at break. Scanning electron micrographs of the starch/dHG/surfactant composite films revealed the folded (multi-layer) microstructure in contrast to the homogeneous matrix of the control films. Starch/dHG/surfactant composite films show low opacity values. With increasing HLB value of the surfactant, the water vapor permeability and tensile strength of starch/dHG/surfactant composite films decrease. Moreover, the water vapor permeability, tensile strength, strain at break, and equilibrium moisture content of starch/dHG/surfactant composite films decrease when the surfactant content is increased, accompanied by an increasing tendency in opacity value. On the other hand, starch/dHG composite film with an emulsion of surfactant and beeswax shows a lower mechanical strength and significantly higher opacity value with less improvement in water vapor permeability.     

Scale-up of the production of cassava starch based films using tape-casting

Most research on biodegradable and edible films uses the well-known casting technique, which allows the preparation of films of small dimensions. Besides, cassava starch films prepared by extrusion processes do not have good properties, because of the high shear rates applied. The tape-casting technique allows the spreading of a suspension on large supports, with the control of the thickness by an adjustable blade at the bottom of the spreading device. The drying of the film can be carried-out on the support itself, under controlled conditions. Film-forming suspensions with different formulations were prepared, varying the concentrations of starch (3 and 5 g/100 g of suspension), glycerol (0.20 and 0.25 g/g of starch) and cellulose fibers (0 and 0.30 g/g of starch) and used to produce films by tape-casting. The results showed that tape-casting is a suitable technology to scale-up the production of starch based films.     

两种分子量的海藻酸钠对高直链玉米淀粉物化性质的影响

为探讨海藻酸钠及其分子量(AGNa)对高直链玉米淀粉(HACS)物化性质的影响,采用快速黏度分析仪(RVA)、差示扫描量热仪(DSC)、动态流变仪、物性测定仪(TA)等,研究了不同分子量的海藻酸钠-高直链玉米淀粉复合体系(AGNa-HACS)的糊化、凝胶及老化性质。结果表明,随着AGNa分子量的增加,其本身的黏度与亲水的能力增加,导致AGNa-HACS的稠度增加。分子量较低的AGNa易与HACS发生相互作用,使HACS糊化能耗增加,抑制HACS的短期老化。分子量较高的AGNa对HACS的增稠作用更为显著,有利于维持HACS淀粉糊的均一稳定,提高HACS的热稳定性,抑制HACS的长期老化。     

Effects of storage conditions and acid solvent types on structural,mechanical and physical properties of kudzu starch (Pueraria lobata)‐chitosan composite films

Effects of acid solvents (acetic, lactic and malic acid) on properties of kudzu starch‐chitosan composite films were evaluated at −20 or 25°C during storage of 60 days. The yellowness of films enhanced, whereas water content and water vapour permeability of films declined with increasing storage time. Tensile strength of films choosing acetic and lactic acid as solvents, and solubility of all the films increased within 30 days thereafter decreased. Storage temperature had no impact on X‐ray diffraction, water content and solubility. Under the same storage conditions, the film using acetic acid as solvent presented the strongest mechanical property, the smallest solubility and the lightest colour. The film made from lactic acid solution was the most flexible and the yellowiest. The film with malic acid solvent showed the highest ordering degree, the lowest water content and the best water barrier property.     

Physical properties of polyol-plasticized edible films made from sodium caseinate and soluble starch blends

Aqueous blends of sodium caseinate and soluble starch, plasticized with polyols, were prepared by casting or by extrusion and hot pressing. The mechanical, thermal, gas and water permeation properties of these blends were studied after their conditioning at various relative humidities. With increasing plasticizer (water, polyols) content there was a progressive decrease of T_g of the blends. The plasticized blends also showed increased percentage elongation, whereas their flexural modulus and tensile strength exhibited a substantial drop. The gas permeability-temperature plots revealed Arrhenius-type relationships with an inflection in the glass transition temperature region.     

Structure and properties of nanocomposite films based on sodium caseinate and nanocellulose fibers

Films made from sodium caseinate and nanocellulose were prepared by dispersing the fibrils into film forming solutions, casting and drying. Composite films were less transparent and had a more hydrophilic surface than neat sodium caseinate ones. However, the global moisture uptake was almost not affected by filler concentration. Addition of nanocellulose to the neat sodium caseinate films produced an initial increase in the barrier properties to water vapor, and then, it decreases as filler content increased. This was explained in terms of additional detrimental changes (cracks and bubble formation) induced in the morphological structure of the film by the reinforcement.The tensile modulus and strength of composite films increased significantly with increasing cellulose concentrations, while the values of elongation decreased. In the same way it was found that the storage modulus increases considerably with filler addition in the low temperature range (<60 °C), though the effect of temperature on the films performance is even more dramatic, as expected in protein-based materials.     

酪蛋白酸钠流变特性的研究

研究了酪蛋白酸钠溶液的流变特性.酪蛋白酸钠属于假塑性流体,粘度与浓度成对数相关性,其流变特性受温度、pH、盐种类及盐浓度等因素的影响.     

羟丙基玉米淀粉的制备及特性研究

本文研究了用环氧丙烷制备羟丙基玉米淀粉的反应条件以及羟丙基化对玉米淀粉糊特性的影响,在反应条件中,着重研究了淀粉乳浓度、环氧丙烷用量、反应温度和时间对醚化程度以及反应效率的影响规律,试验表明：羟丙基化能大大提高玉米淀粉糊的抗剪切性能和抗盐性能,使淀粉糊的透明度和冻融稳定性都有所增加。     

Effects of plasticizers on thermal properties and heat sealability of sago starch films

Sago starch films were plasticized with sorbitol, glycerol, or a combination of sorbitol/glycerol (1:1, 1:3, and 3:1 ratios) and the effects on the thermal properties and heat sealability of the films were investigated. Films were sealed with an impulse heat sealer at a dwell time of 1 s and temperature of 110 ± 10 °C. Thermal properties of the films (determined using a differential scanning calorimeter) showed that onset temperatures (T_o) of sorbitol-plasticized films were significantly lower than those of glycerol-plasticized films. All films were heat sealable, but sorbitol-plasticized films exhibited better heat sealability than did the glycerol type. The highest seal strength was obtained with a 3:1 combination of sorbitol/glycerol. In summary, the type of plasticizer governed the heat sealability as well as the seal strength of starch films.     

玉米淀粉对麦醇溶蛋白凝胶特性的影响

将6％、9％、12％、15％、18％(质量分数)的玉米淀粉添加到麦醇溶蛋白溶液中形成复合物,复合物加热形成凝胶后,测定其化学作用力、保水率、白度、溶胀率、质构特性、流变特性等性质.结果表明,随着玉米淀粉添加量的增加,蛋白-淀粉复合凝胶中离子键、氢键、疏水相互作用和二硫键含量均呈先增加后减小趋势(P<0.05);凝胶保水...     

微波处理对普通玉米淀粉和蜡质玉米淀粉理化性质的影响

为探讨微波处理对普通玉米淀粉(CCS)和蜡质玉米淀粉(WCS)理化性质的影响,采用快速黏度分析法、差示扫描量热法、流变分析法,研究了不同时间或功率微波处理后CCS、WCS的理化性质。结果表明,微波处理时间和功率影响CCS、WCS的理化性质。60~90 s或462~700 W的微波处理增加CCS、WCS的糊化难度,使其起糊温度升高。微波处理导致CCS淀粉糊稠度、糊化焓降低,WCS的膨胀度降低。微波处理使WCS淀粉糊储能模量、损耗模量升高,增加其在外力作用下的稳定性,但只能形成弱凝胶。不同时间、不同功率的微波处理对CCS、WCS的短期老化和长期老化均有一定的抑制作用,使CCS、WCS的回生值、老化率均降低。     

Development and characterization of novel probiotic-residing pullulan/starch edible films

An innovative approach was performed to prepare novel pullulan/starch blended edible films by direct incorporation of multiple probiotic bacterial strains. Various starches different in origin were blended into the pullulan solutions with different ratios. The physical and mechanical properties of the films were investigated in the presence and absence of probiotic cells. An increase in the starch content of pullulan films resulted in a substantial decrease in relative cell viabilities and mechanical properties. Moreover, slight changes in the physical and mechanical properties of the films were observed with the addition of probiotic strains. Pullulan and pullulan/potato starch films were found to be the most suitable carrier matrices, with a maximum relative cell viability of 70–80% after 2 months of storage at 4 °C. The results suggest that pullulan and pullulan/starch films can be used as effective delivery and carrier systems for probiotics.     

干热处理对玉米淀粉性质的影响

研究了干热处理前后玉米淀粉的性质变化,对干热处理前后淀粉的溶解指数、糊化特性、热力学性质、颗粒形貌和结晶结构进行了测定及分析。结果表明,当干热处理温度低于150℃时,与原淀粉相比,干热淀粉的溶解指数、黏度均降低,糊化温度降低;当干热处理温度为150℃时,淀粉的溶解指数升高、黏度降低、糊化温度降低。干热处理后,淀粉表面出现凹坑,且颗粒间有黏结。