The combined effects of lysozyme and ascorbic acid on microstructure and properties of zein-based films

Edible zein-based films containing lysozyme(LY) and ascorbic acid(AA) were developed in the presence of polyethylene glycol 400(PEG 400), the combined effects of LY and AA on the microstructure, mechanical properties and release properties of developed zein films were investigated in detail. The results of microstructure characterization indicated that zein-based films became compact and smooth, and LY aggregates were well distributed in the zein matrix because of the simultaneous addition of LY and AA. The results of mechanical tests showed that because of the synergistic effects of LY and AA on zein film, elongation at break of zein-based film could be up to 138%, which was 34.5 times higher than that of zein control film. LY release tests showed that when the concentration of AA was less than 3.1 mg·cm~(-2), the release rate of LY significantly decreased by 33.7%, and the total release increased by 80.6%. While the release profiles of AA showed that the release rate and total release of AA from the films containing LY increased by approximately 68.9% and 61.7% than the films without LY. Good antioxidant and sustained antimicrobial activities were found for the developed zein films.     

Formation of zein nanoparticles by electrohydrodynamic atomization: Effect of the main processing variables and suitability for encapsulating the food coloring and active ingredient curcumin

Nanoparticles with a compact spherical structure and a narrow size distribution were prepared from a zein protein polymer by electrohydrodynamic atomization. The effects of key parameters of the process (polymer concentration, flow rate and applied voltage) on the size and morphology of the particles was studied. Zein nanoparticles could be obtained from zein concentrations ranging from 2.5% to 15% (w/w). The sizes of these particles, ranging from 175 to 900 nm, increased with increasing polymer concentration. Compact nanostructures were obtained for 2.5% and 5% zein solutions whereas 10% and 15% solutions yielded collapsed and shrunken particles. Flow rate also exerted an effect, the lower the flow rate the smaller the nanoparticles. The morphology of the nanoparticles did not change after incorporating curcumin in proportions ranging from 1:500 to 1:10 (curcumin:zein), and the encapsulation efficiency was around 85–90%. Fluorescence microscopy images showed that the nanostuctures obtained took the form of matrix systems with the curcumin homogeneously distributed in the zein matrix. The curcumin remained in the amorphous state in the nanoparticle, as revealed by X-Ray diffractometry, evidencing intimate contact with the polymer. After three months of storage at 23 °C and 43% relative humidity in the dark, neither the size or the morphology of the nanoparticles had undergone significant changes, nor had the curcumin content altered. Thanks to encapsulation, the curcumin presented good dispersion in an aqueous food matrix: semi-skimmed milk.     

Viscoelastic properties of concentrated aqueous ethanol suspensions of α-zein

Viscoelastic properties of α-zein dispersed in aqueous ethanol were studied using oscillatory strain rheometry. In 55-80% v/v aqueous ethanol, zein was only partially soluble, forming a gel at a sufficiently high zein concentration. The strain dependence of the storage modulus and the loss modulus of gelled systems exhibited features characteristic to closely-packed swollen particles. Close-packing was found to occur at a lower zein concentration with increasing ethanol concentration as the threshold for gelation decreased from a zein concentration of ca. 29 to 20% w/v with increasing ethanol concentration from 55 to 80% v/v. A contrasting trend in the effect of the solvent quality was revealed at a constant zein concentration of 30% w/v, at which the storage modulus decreased from ca. 12,000-700 Pa with increasing ethanol concentration from 55 to 80% v/v. The two major factors determining viscoelastic properties of the partially solvated zein systems were identified to be: (1) the degree of dissolution of zein into the continuous phase that was negatively correlated with the volume fraction of the dispersed phase and positively correlated with the osmotic pressure of the continuous phase; and (2) the degree of swelling of partially solvated zein particles that was positively and negatively correlated with the volume fraction and the storage modulus of the dispersed phase, respectively.     

玉米醇溶蛋白在香蕉保鲜中的应用

探讨了玉米醇溶蛋白薄膜对香蕉的保鲜效果。研究表明：玉米醇溶蛋白良好的保湿性 性可使香蕉在贮存过程中的损失下降且存期延长。最佳涂膜液配比为：甘油０．８ｍｌ，油酸０．６ｍｌ，虫胶０．６ｍｌ。     

Encapsulation of food grade antioxidant in natural biopolymer by electrospinning technique: A physicochemical study based on zein–gallic acid system

Gallic acid was successfully incorporated into zein ultra-fine fibres at different loading amount (5%, 10% and 20%) in order to develop an encapsulating technology for functional ingredient delivery using electrospinning. The produced fibres exhibit diameters ranging from 327 to 387 nm. The physical and thermal properties of encapsulated gallic acid were determined by X-ray diffraction (XRD) and differential scanning calorimetry (DSC); and the interaction between gallic acid and zein was attested by attenuated total reflection-Fourier transform infrared (ATR-FTIR). Thermogravimetric analysis (TGA) demonstrated a different thermal stability of the fabricated complex before and after the gallic acid incorporation. Lastly, the 1,1′-diphenyl-2-picrylhydrazyl (DPPH) assay showed that the gallic acid had retained its antioxidant activity after incorporation in zein electrospun fibres. Overall, electrospinning technique had shown promising results as an efficient and effective method for the preparation of sub-micron structured encapsulated functional ingredient that may find uses in food industry.     

Tensile Properties of Extruded Zein Sheets and Extrusion Blown Films

Zein‐based plastic sheets and films were formed by extrusion through a slit‐die or blowing head. Zein was plasticized with oleic acid and formed into a wet moldable mass (resin) to feed the extruders. Both single‐ and twin‐screw extruded sheets showed higher elongation at break, lower tensile strength, and lower Young's Modulus than non‐extruded samples. Stress‐strain plots for extruded samples showed evidence of plastic behavior. Observed necking of samples under tensile stress was also taken as evidence of plastic behavior. Small differences in tensile strength and elongation at break between single‐ and twin‐screw extruded samples were attributed to the effect of small voids observed by SEM in single‐screw extruded samples. Blown film extrusion was affected by feed moisture content and barrel temperatures. Optimal moisture content was determined at 14–15% while temperature at the three extruder zones was maintained at 20–25, 20–25, and 35 °C, respectively. Temperature at the blowing head was 45 °C. Film samples blown after either single‐ or twin‐screw extrusion showed similar tensile properties to those of slit die extruded samples.

Blown extrusion of zein film with single‐screw extruder.     

海泡石增强壳聚糖/玉米醇溶蛋白复合膜的制备及性能

采用流延成膜法制备了不同海泡石(SP)质量分数的壳聚糖(CS)/玉米蛋白(ZN)复合膜。研究了SP质量分数对CS/ZN复合膜机械性能和断面形貌的影响,分析了SP对CS/ZN复合膜的增强机理。扫描电子显微镜结果表明,SP粒子在复合膜中分散较好,CS与ZN之间有较好的相容性。随着SP质量分数增加,SP/CS/ZN膜拉伸强度先增加后减小,当SP质量分数为2%时,其拉伸强度达到最大值21.1 MPa,比纯CS/ZN提高了8.1%;而断裂伸长率随着SP质量分数先增加后降低,从15.3%下降为7.5%;同时复合膜的耐水性能上升,复合膜的吸水率随着SP质量分数增加先减小后增加,在8%时达到最小值。SP的引入导致复合膜的透光性能下降,SP质量分数为6%时在波长800 nm处光透过率下降约20%。     

In vitro release kinetics of nisin as affected by Tween 20 and glycerol co-encapsulated in spray-dried zein capsules

Delivery systems with sustained release of antimicrobials have been proposed to improve long-term effectiveness of antimicrobials in foods. In this work, we studied the effect of Tween 20 and glycerol in spray-drying formulations on resultant microstructures of zein capsules and release profiles of encapsulated nisin. Tween 20 and glycerol changed capsules from a continuous matrix to shell-type structures. All samples showed complete release of nisin in 30 min at pH 2.0. Capsules with a higher amount of Tween 20 showed more complete release of nisin at pH 8.0, in contrast to no apparent impact by glycerol. Addition of 0.05% Tween 20 or glycerol in the feed both reduced the burst release of nisin at pH 6.0, but no conclusive trends were observed for the impact of their usage levels. Our work showed that an appropriate formulation is needed to obtain desirable delivery systems of antimicrobials such as nisin.     

玉米醇溶蛋白成膜工艺条件的探讨

对玉米醇溶蛋白的成膜条件进行了研究，结果表明，玉米醇溶蛋白在８０％乙醇中溶解效果良好，在４０℃恒温条件下可以在光滑的不锈钢板上形成具有的一定强度的可食性薄膜。     

高水稳定性的ZEIN/CA复合纳米纤维的制备及性能研究

采用静电纺制备了不同质量比的玉米醇溶蛋白(Zein)/醋酸纤维素(CA)复合纳米纤维。傅里叶变换红外光谱(FT-IR)曲线表明样品中两组分各自保持了其原有化学功能基团。利用扫描电镜(SEM)对样品的形貌和直径分布进行了分析。通过差示扫描量热仪(DSC)和热重分析(TGA)研究了样品的热学性能,结果证实了随着CA的加入,样品依然保持较高的热稳定性。表面张力仪(ST)测定结果表明,随着Zein组分的增加,样品的亲水性增加。同时样品具有一定的吸水能力。