Effects of chitosan on the physicochemical and antimicrobial properties of PLA films

Films based on polylactic acid (PLA) and different amounts of chitosan powder (CH), were prepared by extrusion. The effects of CH particle size (715 and 180 μm) and the amount of chitosan incorporated in the PLA matrix (5% or 10% on PLA basis) were investigated in terms of physicochemical characteristics and antimicrobial activity of the films. The incorporation of CH particles led to less rigid and less stretchable films. Thermal properties of PLA were not affected by chitosan addition. Water vapor permeability of the composite films was higher than pure PLA films. PLA:CH composite showed significant antimicrobial activity against total aerobial and coliform microorganisms, especially when the particle size of CH was reduced.     

Development of PLA films containing oregano essential oil (Origanum vulgare L. virens) intended for use in food packaging

Consumers’ concerns about the environment and health have led to the development of new food packaging materials avoiding petroleum-based matrices and synthetic additives. The present study has developed polylactic acid (PLA) films containing different concentrations of essential oil from Origanum vulgare L. virens (OEO). The effectiveness of this new active packaging was checked for use in ready-to-eat salads. A plasticising effect was observed when OEO was incorporated in PLA films. The rest of the mechanical and physical properties of developed films did not show much change when OEO was included in the film. An antioxidant effect was recorded only for films containing the highest percentages of the active agent (5% and 10%). In addition, films exhibited in vitro antibacterial activity against Staphylococcus aureus, Yersinia enterocolitica, Listeria monocytogenes, Enterococcus faecalis and Staphylococcus carnosus. Moreover, in ready-to-eat salads, antimicrobial activity was only observed against yeast and moulds, where 5% and 10% of OEO was the most effective.     

Scalping of four aroma compounds by one common (LDPE) and one biosourced (PLA) packaging materials during high pressure treatments

The impact of high pressure thermal (HP/T) treatments on scalping of four aroma compounds (2-hexanone, ethyl butanoate, ethyl hexanoate, d-limonene) was assessed for low density polyethylene (LDPE) and polylactate (PLA). Two HP/T treatments intending to perform a pasteurization (800 MPa, 40 °C) and a sterilization (800 MPa, 115 °C) were carried out on film samples in contact with four food simulating liquids (water, acidic, alcoholic and fatty) enriched with aroma compounds.The aroma compounds tested were found rather stable after the HP/T pasteurization while significant losses were found after HP/T sterilization as expected. Regarding the scalping, both materials appeared as suitable for HP/T pasteurization. On the contrary LDPE melted during the conventional sterilization whereas it withstood the HP/T sterilization (and showed a significant increase of the uptake of aroma compounds). For scalping in PLA, temperature turned out to be a critical factor, especially if the temperature of the treatment goes over its glass transition temperature.     

Preparation and properties of poly (lactic acid) (PLA) suture loaded with PLA microspheres enclosed drugs (PM-Ds)

Drug loaded PLA suture has been one most potential surgery material to help wounds healing. The loaded drug amounts and sustained drug release effect were a vital part for PLA suture. In this research drug-loaded microspheres and finishing bath were prepared to ensure more drug particles loaded on PLA suture. Moreover, sustained drug release effect and mechanical properties of PLA suture were also observed. The results suggested that PLA concentration and emulsifier amounts had more effect on the size of PLA drug-loaded microspheres and the optimal technology was: 0.03 g/mL of PLA concentration, 0.3 g of amount of emulsifier and the total amount of drug and emulsifier was 3 g. Moreover, drug release test showed a significant sustained release effect of the drug-loaded PLA suture. Mechanical measurements indicated the flexibility and strength were not impaired by such drug-loaded method. This research is expected to benefit the surgery fields further.     

Effect of natural and synthetic antioxidants incorporation on the gas permeation properties of poly(lactic acid) films

Gas permeation properties (permeability, diffusivity and solubility coefficients) were determined for carbon dioxide and oxygen in poly(lactic acid) (PLA) films enriched with 0, 2, 4 and 10 wt.% of different antioxidants, at three temperatures, 284, 293 and 303 K, using a time-lag apparatus. Three antioxidants, a natural, α-tocopherol (AT), and two synthetic, butylated hydroxytoluene (BHT) and tert-butylhydroquinone (TBHQ), were tested. DSC results show that the polymer glass transition temperature slightly decreases with the increase of the antioxidant content. The crystallinity degree of PLA films decreases with the addition of BHT and TBHQ, whereas the incorporation of AT increases the crystallinity of PLA films. The permeability towards water vapour, at 299 K and 45% of relative humidity, and surface energy show a decreased in the wettability of the prepared materials with the increase of the antioxidants content. The incapacity to measure gas permeation in PLA films with 10 wt.% of AT and BHT incorporated was due to phase separation, proved by SEM images. The CO₂ and O₂ permeation results show that PLA barrier properties can be improved by the incorporation of antioxidants but are strongly dependent on the amount and structure of the antioxidant added.     

纺粘非织造用聚乳酸/聚(3-羟基丁酸-co-3-羟基戊酸共聚酯)的可纺性

为获得高质量的聚乳酸/聚(3-羟基丁酸-co-3-羟基戊酸共聚酯)(PLA/PHBV)双组分生物降解纺粘非织造材料,对PLA/PHBV母粒的相对分子质量及分布、熔体指数、热力学、结晶和流变性能进行了研究,并对PLA/PHBV纺粘纤维的热力学和结晶性能进行了探讨。结果表明:PLA/PHBV母粒重均分子质量约为120 000,分布指数为1.99;热失重起始热分解温度为285℃,适宜纺粘非织造挤出加工,合适的纺粘加工温度约为210℃。PLA/PHBV熔体在剪切速率小于1 000 rad/s时,表观黏度对剪切速率变化敏感;熔体对温度的敏感程度随着剪切速率的增大而降低。纺粘加工工艺对PLA/PHBV原料的热力学和结晶性能影响显著。与PLA/PHBV母粒相比,纺粘纤维结晶度下降明显,但非晶区取向程度提高。     

乳酸乙醇酸共聚物(PLGA)熔体的流变性能

采用直接法熔融缩聚制备了L-乳酸和乙醇酸共聚物PLGA ,并用锥板流变仪对PLGA的流变性能进行测试。结果表明 :PLGA熔体属于切力变稀流体 ,PLGA熔体的非牛顿指数值大于聚乳酸PLLA熔体的对应值 ,其表观粘度对剪切速率的依赖性小 ;PLGA熔体的表观粘流活化能较高 ,且在同样的切变速率下 ,PLGA熔体的表观粘流活化能大于PLLA熔体的对应值 ,其表观粘度对温度的敏感性大于PLLA熔体。     

聚苹果酸及其衍生物的研究与发展

综述了聚苹果酸及其衍生物的性能特点,总结了它们合成、制备方法研究的进展,以及相关的应用前景。     

Effects of gibberellic acid (GA3) on strawberry PAL (phenylalanine ammonia-lyase) and TAL (tyrosine ammonia-lyase) enzyme activities

Gibberellic acid (GA₃) treatments (30 and 60 μg litre⁻¹) were applied to young plants (Fragaria ananassa cv Chandler). Fruits were harvested at various developmental stages (14, 21, 28 and 35 days from fruit set). Weight and size, phenolic compounds (total polyphenols and anthocyanins) and enzyme activities, phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) were determined. Our aim was to obtain detailed information about PAL and TAL activities related to the strawberry colour during development and ripening processes and to determine the effects of exogenous treatments of GA₃ on PAL and TAL activities. Exogenous treatments of GA₃ improve weight, size and colour of strawberry fruits, and affect PAL and TAL activities. We found that the anthocyanin content and PAL activity are enhanced by the exogenous treatment of GA₃ in the range of 30 μg litre⁻¹. However, with the higher GA₃ treatment, only the anthocyanin content is affected in that way. These findings suggest that gibberellic acid effect on PAL, TAL and ultimately anthocyanin enhancement is dosage related and saturation of the response occurs at 30 μg litre⁻¹. © 1998 SCI.     

共轭亚油酸的抗氧化活性及其抗氧化剂筛选

目的:考查共轭亚油酸的抗氧化活性并筛选对其活性有保护作用的抗氧化剂。方法:采用连苯三酚体系考察共轭亚油酸及其乙酯的抗氧化性;运用气相色谱—质谱联用技术考察影响共轭亚油酸稳定性的因素,筛选保存共轭亚油酸适宜添加的抗氧化剂并考察合适的加入量。结果:共轭亚油酸及其乙酯在连苯三酚体系实验体系中均表现出良好的抗氧化作用,在筛选的抗氧化剂中,TBHQ、茶多酚、BHA、BHT效果理想。结论:共轭亚油酸具有明显的抗氧化性,建议使用抗氧化剂TBHQ与茶多酚保护其免于氧化分解。     

The Stability of Poly(lactic acid) Packaging Films as Influenced by Humidity and Temperature

The effect of moisture sorption on stability of poly(lactic acid) (PLA) films at food‐packaging conditions, obtained by different humidities (11% to 98% RH) and temperatures (5 °C and 25 °C), was investigated by decrease in number average molecular weight (M_n) and loss of tensile strength. Hydrolysis of the PLA ester linkages resulted in a 75% decrease over 130 d at 25 °C and 98% RH. At cooling conditions the decrease amounted to 35%. An equilibrium moisture sorption isotherm could not be determined as the irreversible hydrolysis of PLA induced an ongoing moisture uptake. The rate increased when the humidity and temperature increased from 5 °C to 25 °C. After 189 d at 98% RH, moisture sorption was 7 g/100 g and 86 g/100 g at 5 °C and 25 °C, respectively. Loss of tensile strength was minor and primarily due to reversible plastization by moisture. Only at 98% RH and 25 °C, loss of tensile strength became pronounced (45%). Consequently, the present PLA material is in general expected to be mechanically stable when packaging foods covering the region from dry to moist food and storage conditions from chill to ambient temperatures.     

熔喷非织造用聚(3-羟基丁酸-co-3-羟基戊酸共聚酯)/聚乳酸双组分生物降解材料的可纺性能

采用熔融共混法制备了质量比为100/0、75/25、50/50、25/75、0/100的熔喷非织造用PHBV/PLA共混材料,分别采用热重分析法（TG）、熔融指数法（MFI）、热台偏光镜法（POM）和毛细管流变法对共混材料的可纺性能进行了研究,并对其初生纤维的纺丝性能给予了初步评价。研究表明：PHBV的热稳定性差、加工窗口窄且熔体流动性差,PHBV/PLA共混材料的热稳定性和熔体流动性明显改善;PHBV结晶速率快, PLA对PHBV的结晶具有稀释作用;PHBV/PLA共混物为典型的切力变稀型流体,PHBV对温度和剪切速率变化敏感度高,PHBV/PLA共混材料的表观粘度随着PLA含量的提高而有所增大,但均小于纯PLA;PHBV纤维发粘现象严重,纺丝困难,随着共混材料中PLA含量的提高,纺丝性能提高,初生纤维表面变得光滑。     

Chemical characteristics,fatty acid composition and conjugated linoleic acid (CLA) content of traditional Greek yogurts

Many studies with conjugated linoleic acid (CLA) indicate that it has a protective effect against mammary cancer. Because dairy products are the most important dietary sources of CLA, we have investigated the CLA concentrations and additionally the fatty acid profiles and chemical composition of several commercial, traditional, Greek yogurts from different geographical origin. The fat content of yogurts was in the order of goat < cow < sheep. Cow, sheep and goat milk yogurts contain respectively 0.128–1.501, 0.405–1.250 and 0.433–0.976 g CLA/100 g fat. Low-fat milk yogurts showed lower values of c-9, t-11 CLA content on lipid basis compared to full-fat yogurts. Samples from mountain areas showed average c-9, t-11 CLA content higher than those from prairie districts. The highest amounts of saturated fatty acids (SFA) were found in low-fat yogurts, of monounsaturated fatty acids (MUFA) in sheep milk yogurts and of polyunsaturated fatty acid (PUFA) in low-fat cow milk yogurts.     

Influence of Citric Acid on the Properties of Glycerol‐plasticized dry Starch (DTPS) and DTPS/Poly(lactic acid) Blends

In the presence of citric acid (CA), one‐step extrusion processing is used to prepare poly(lactic acid)/thermoplastic dry starch (PLA/DTPS) blends (50/50, %, w/w) in a single‐screw extruder. The rheological study proves that CA decreases the viscosity of both DTPS and of DTPS/PLA blends. The low viscosity increases the dispersion and decreases the interfacial tension between DTPS and PLA, as shown by scanning electron microscopy (SEM). In the presence of CA, the tensile strength of DTPS/PLA reaches 41 MPa—similar to that of pure PLA—because of improved dispersion and compatibility. At the same time, CA increases not only the degradation of starch, but also the interaction between DTPS and PLA, as detected by Fourier transform infrared (FTIR) spectroscopy. The blend containing CA has a higher thermal stability. The water absorption of DTPS and DTPS/PLA blends is also studied.     

白酒丢糟酸水解制备木糖及其结构变化

采用混合酸水解法提取白酒丢糟中的木糖,并研究木糖提取过程中丢糟的结构变化。以木糖收率为指标,考查酸解温度、固液比、混合酸浓度和酸解时间4个因素对木糖提取效果的影响,利用正交试验优化工艺参数。结果表明,从丢糟中提取木糖的最优条件为温度110℃、固液比1∶12(g∶mL)、混合酸浓度1.5%和时间145min,该条件下的木糖收率为61.24%。经酸水解法提取木糖后,丢糟的木质纤维结构变化明显,孔隙率和比表面积增加,形貌结构改变,半纤维素和纤维素无定形区被降解,导致结晶度增加。     

转基因食品的检测方法及其应用与发展

随着转基因食品的迅速发展和普及,与其安全性相关的检测技术也日益受到人们的重视。针对目前国内外转基因食品的检测技术进行系统分类,简要介绍了各技术的原理、优缺点及应用情况,同时,对其面临的问题及未来发展方向做了初步探讨和展望。     

羟乙基纤维素接枝聚丙烯酸纳米颗粒的制备及药物缓释

羟乙基纤维素接枝聚丙烯酸共聚物(HEC g PAA)在选择性溶剂中进行自组装,制备了具有良好分散稳定性的纳米颗粒,用动态激光光散射和透射电子显微镜对纳米颗粒大小分布和形态进行了表征.以生物可降解的HEC g PAA接枝共聚物负载模型药物布洛芬(Ibuprofen),制备载药纳米颗粒(Ib HEC g PAA).在37℃于不同pH的缓冲溶液中进行了体外释放研究.药物释放速率的测定结果表明,以HEC g PAA作为布洛芬的载体,可以在选择性条件下实现药物可控释放的目的.     

竹红菌素-聚(甲基丙烯酸甲酯-co-甲基丙烯酸)纳米纤维的制备及其光敏抗菌性能

针对抗生素类药物在耐药性菌株处理中应用的局限性,在聚(甲基丙烯酸甲酯-co-甲基丙烯酸)纺丝液中添加光敏剂竹红菌素,采用静电纺丝法制备具有光动力广谱抗菌功能的纳米纤维膜。借助扫描电子显微镜、静态接触角测试、傅里叶变换红外光谱仪和热重分析仪等分析添加竹红菌素前后纳米纤维的形貌、润湿性能、化学结构和热稳定性,并研究了添加竹红菌素的纳米纤维膜对金黄色葡萄球菌和大肠杆菌的抗菌能力。结果表明:添加竹红菌素后纳米纤维直径变粗,静态接触角增加约20°,润湿性能下降,热稳定性略有降低;纤维膜在可见光下具有良好的光动力氧化性能,在光照下对金黄色葡萄球菌和大肠杆菌的抑菌率分别达99.97%和54.41%。