Self-assembled pullulan-silica oxygen barrier hybrid coatings for food packaging applications

The scope of this study encompassed the evaluation of pullulan as a suitable biopolymer for the development of oxygen barrier coatings to be applied on poly(ethylene terephthalate) (PET), especially for food packaging applications. To enhance the oxygen barrier properties of the organic phase (pullulan) even at high relative humidity values, an inorganic phase (silica), obtained through in situ polymerization, was also utilized to obtain hybrid coatings via the sol-gel technique. Transmission electron microscopy (TEM) images and Fourier transform infrared (FT-IR) spectra showed that mixing the two phases yielded a three-dimensional hybrid network formed by self-assembly and mediated by the occurrence of new hydrogen-bond interactions at the intermolecular level, although the formation of new covalent bonds could not be excluded. The deposition of the hybrid coatings decreased the oxygen transmission rate (OTR) of the plastic substrate by up to 2 orders of magnitude under dry conditions. The best performance throughout the scanned humidity range (0%-80% relative humidity) was obtained for the formulation with the lowest amount of silica (that is, an organic/inorganic ratio equal to 3).     

Preparation of antimicrobial reduced lysozyme compatible in food applications

The structural and antimicrobial functions of lysozyme reduced with food-compatible reducing agents-cysteine (Cys) and glutathione (GSH)-were investigated. The disulfide bonds were partially reduced by thiol-disulfide exchange reactions under heat-induced denaturing conditions from 55 to 90 degrees C. The results showed that treatment of lysozyme with Cys and GSH resulted in the introduction of new half-cystine residues (2-3 residues/mol of protein). The released SH groups, in turn, rendered the lysozyme molecule more flexible, being accompanied by a dramatic increase in the surface hydrophobicity and exposure of tryptophan residues. As a consequence, the resulting reduced lysozymes were more capable of binding to lipopolysaccharides (LPS) and permeabilizing the bacterial outer membrane, as evidenced by the liposome leakage experiment, than were native or heated lysozyme. Both reduced lysozymes displayed significantly higher antimicrobial activity than native or heated lysozyme against Salmonella enteritidis (SE) in sodium phosphate buffer (10 mM, pH 7.2) at 30 degrees C for 1 h. Their minimal inhibitory concentrations (MICs) against the tested bacteria were about 150- and 25-fold lower than their respective MICs of native or heated lysozyme. The results suggest that partially reduced lysozyme could be used as a potential antimicrobial agent for prevention of SE attack.     

食品智能包装体系的研究进展

随着消费者对食品品质和安全性要求的不断提高,消费者对食品包装性能的要求也随之提高,并希望食品包装能够保证食品的质量、新鲜性和安全性。为了满足消费者的要求,智能包装技术便应运而生。它通过监视包装食品的环境,为消费者提供包装食品品质和安全性等信息。本文对食品智能包装体系的主要技术及其发展趋势进行了较全面的分析归纳。     

Using ATR-FTIR spectroscopy to design active antimicrobial food packaging structures based on high molecular weight chitosan polysaccharide

ATR-FTIR spectroscopy has been used in this study to characterize the molecular mechanisms and kinetic processes that take place when a chitosonium acetate thin coating is put in contact with water solutions, Staphylococcus aureus solutions, microbial nutrient solutions, and with a high water activity TSA hydrogel medium to simulate the effect of direct contact with high moisture foods such as fresh meats, fish, and seafood products or beverages. The results of this work suggest that the biocide carboxylate groups that form when chitosan is cast from acetic acid solutions are being continuously evaporated from the formed film in the form of acetic acid (mechanism I) in the presence of environmental humidity, rendering weak biocide film systems. On the other hand, upon direct contact of the cast chitosonium acetate film with liquid water, water solutions, or the high moisture TSA hydrogel, a positive rapid migration, with a diffusion coefficient faster than 3.7 x 10(-12) m2/s, of protonated glucosamine water soluble molecular fractions (mechanism II) takes place from the film into the liquid phase, yielding strong antimicrobial performance and leaving in the remaining cast film only the non-water soluble chitosan fractions. Finally, this study describes a refined spectroscopic methodology to predict the antimicrobial properties of chitosan and gives insight into the capacity of chitosan as a natural biocide agent.     

Development of an iron chelating polyethylene film for active packaging applications

Metal-promoted oxidation reactions are a major cause of food quality deterioration. Active packaging offers novel approaches to controlling such oxidation for the purpose of extending shelf life. Herein, we report modification of the surface of polyethylene (PE) films to possess metal chelating activity. Metal chelating carboxylic acids were introduced to the film surface using cross-linking agents [polyethylenimine (PEI) or ethylenediamine (ED)] to increase the number of available carboxylic acids. ATR-FTIR, contact angle, dye assay, and iron chelating assay were used to characterize changes in surface chemistry after each functionalization step. The chelator poly(acrylic acid) (PAA) was attached to the surface at a density of 9.12 ± 0.71 nmol carboxyl groups/cm2, and exhibited an iron chelating activity. The results indicate that PAA-modified PE films might have a higher affinity to Fe3? than Fe2? with the optimum binding pH at 5.0. Such inexpensive active packaging materials are promising in food industry for the preservation of liquid and semiliquid food products and have application in heavy metal chelation therapy for biomedical materials as well.     

Effect of sorbed oil on food aroma loss through packaging materials.

Mass transport of six food aroma components, D-limonene, n-decane, ethyl caproate, phenylethanol, 1-hexanol, and hexanal, through three sealable polymer films suitable for direct food contact, ultra-low-density polyethylene (ULDPE), ionomer (ION), and modified polyester (mPET), was analyzed by permeation experiments. Transport was characterized by the permeability coefficient and its two contributing factors, the diffusion coefficient (related to kinetics) and the solubility coefficient (related to equilibrium). The results show that ULDPE is more permeable to aromas that ION, which is more so than mPET. Differences in diffusivity are mainly responsible for barrier improvement. With aromas, nonpolar compounds permeate faster than polar ones through ULDPE. The effect of sorbed oil on the behavior of these materials as food aroma barriers was investigated. The sorption of oil apparently resulted in polymer swelling, increasing the solubility of aromas into the polymer matrixes. Little or no effect was found on the values of the diffusion coefficient. The permeability coefficient was affected as a consequence of changes in solubility. When aromas were compared, the transport of nonpolar penetrants showed a considerable increase while permeability values for the polar ones were either unaffected or even reduced. This behavior has been discussed in terms of polymer/oil/aroma compatibility.     

Antimicrobial properties of basil and its possible application in food packaging

Basil (Ocimum basilicum L.) is a popular culinary herb, and its essential oils have been used extensively for many years in food products, perfumery, and dental and oral products. Basil essential oils and their principal constituents were found to exhibit antimicrobial activity against a wide range of Gram-negative and Gram-positive bacteria, yeast, and mold. The present paper reviews primarily the topic of basil essential oils with regards to their chemical composition, their effect on microorganisms, the test methods for antimicrobial activity determination, and their possible future use in food preservation or as the active (antimicrobial), slow release, component of an active package.     

纳米氧化锌改性LDPE食品包装薄膜中锌粒子的迁移规律

为探究纳米氧化锌改性(low-density polyethylene,LDPE)薄膜中纳米锌粒子的迁移规律,依照欧盟法规(EU)No.10/2011,分别采用蒸馏水、30 g/L乙酸溶液、体积分数10%的乙醇溶液、体积分数95%的乙醇溶液作为中性、酸性、脂肪性和酒精性食品模拟物,研究在不同温度条件下(40、70℃)纳米锌粒子的迁移情况,同时探究微波和紫外处理对迁移结果的影响。研究发现,纳米锌粒子在4种食品模拟物中的迁移量从高到低依次为:酸性食品模拟物、中性食品模拟物、酒精性食品模拟物和脂肪性食品模拟物,并且随温度的升高,纳米锌粒子的迁移量增大。此外,微波处理能促进纳米锌粒子的迁移,而紫外处理则没有促进效果。纳米锌粒子的迁移量范围为0.52~14.17 mg/kg。根据欧盟规定所允许的最大迁移量5 mg/kg,迁移试验表明纳米氧化锌改性LDPE薄膜还需要进一步开展减少纳米粒子迁移的研究工作,以确保其在食品包装中的安全使用。     

胍盐聚合物添加量对抗菌食品包装膜抗菌性及物理性能的影响

为了开发出一种安全高效的抗菌食品包装材料,添加不同质量分数(0～7%)的聚六亚甲基双胍盐酸盐(polyhexamethylene biguanidine hydrochloride,PHMB)抗菌母粒到聚乙烯基材中,制成PHMB抗菌膜,比较PHMB母粒添加量对抗菌食品包装薄膜的抗菌性和性能的影响。结果表明,随着PHMB母粒添加量的增大,薄膜抗菌性增强。PHMB母粒添加量为4%时,薄膜对大肠杆菌、金黄色葡萄球菌和杂菌样品的抗菌率分别为99.1%、99.2%和83.4%,且存放6个月后薄膜仍保持较强的抗菌作用;添加PHMB母粒后,薄膜的透光率、水蒸气透过率影响较小;薄膜的力学性能在PHMB母粒添加量为4%时最优;PHMB(4%)抗菌膜对实际试样(鳕鱼干)表现出良好的微生物抑制作用。因此,确定抗菌薄膜中PHMB母粒最佳添加量为4%,薄膜具备强抗菌作用和良好的性能。该研究为抗菌材料的研制提供了参考。     

薰衣草精油改善壳聚糖基食品包装膜的应用品质

为改善现有壳聚糖基食品包装膜的机械性能和防水性能,该文使用浇铸-蒸发-碱浸法制备了添加薰衣草精油的壳聚糖基复合膜。采用红外光谱、X射线衍射对膜进行了表征,并分析了薰衣草精油添加量对膜的厚度、机械性质、可挥发物质量分数、接触角、水溶性、溶胀性等性质的影响。结果表明:薰衣草精油成分占据了壳聚糖骨架中的部分官能团的位置,降低了壳聚糖分子中共价键的振动强度,同时膜中可以与水形成亲水键的自由H基团减少,膜的含水量降低。薰衣草精油的添加,增大了膜中壳聚糖乙酸盐的含量。膜的厚度和薰衣草精油添加量并不成线性关系,所得膜的厚度范围为(20.60±0.34)~(23.35±0.65)μm。随着薰衣草精油添加量的增加,膜的拉伸强度和断裂伸长率的变化趋势基本相同。当薰衣草精油添加量为8%时,拉伸强度和断裂伸长率都达到最大值,分别为(123.44±0.33)MPa和3.74%±0.02%。与壳聚糖膜相比,薰衣草精油/壳聚糖复合膜的的可挥发物质量分数较低,薰衣草精油添加量为2%时,可挥发物质量分数最低,为8.98%±0.05%。薰衣草精油的添加,增大了膜的溶解性,但膜在水中的溶解度均不大于(1.21±0.04)mg/100 g,属于难溶物质范畴。膜的接触角和溶胀指数都随薰衣草精油添加量的增加而减小,即当薰衣草精油添加量为10%时,膜的接触角和溶胀指数都达到最大值,分别为80.73°±0.32°和0.62±0.01。薰衣草精油的加入改善了由浇铸-蒸发-碱浸法制备的CS基复合膜的机械性质和物理性质。研究结果为薰衣草精油/壳聚糖复合膜的生产和应用提供了技术依据。     

Analytical procedure for quantifying five compounds suspected as possible contaminants in recycled paper/paperboard for food packaging

Because contaminants in recycled paper intended for food packaging could be a risk to public health, analytical methods are needed to identify and quantify residues of concern in paper/paperboard. The U. S. Food and Drug Administration is considering development of a guidance document for testing levels of contaminants that might be retained through paper recycling processes. An analytical procedure was developed using paper spiked with suspected contaminants at concentrations of 1-50 ppm in the paper. Benzophenone, dimethyl phthalate, anthracene, methyl stearate, and pentachlorophenol were introduced by soaking the paper in a solution in acetone at 25 degrees C for 24 h; the paper was removed and dried by evaporating the solvent with nitrogen. The model contaminant residues were extracted from the paper using ultrasonication and quantified by GC with flame ionization and electron capture detectors. Recoveries from the spiked paper were 80-109% with a repeatability of +/-4%. The method was also used to analyze commercial recycled paperboard to validate its applicability.     

Development and characterization of silver-based antimicrobial ethylene-vinyl alcohol copolymer (EVOH) films for food-packaging applications

The use of silver as an antimicrobial in the food area has raised wide interest in recent years. In the present work, 0.001-10 wt % silver ions was satisfactorily incorporated into an ethylene-vinyl alcohol (EVOH) copolymer matrix by a solvent casting technique. The antibacterial efficacy of the composite was evaluated under laboratory conditions and in contact with some foods. The ionic compound did not affect the crystallinity or the water-induced plasticization of the materials and was homogeneously distributed across the surface and thickness of the films. When immersed in water, sorption-induced release of 50-100% of the silver ions took place in <30 min. In the bacterial minimal growth medium M9, the minimal inhibitory concentration (MIC) of the film was in the range of 0.01-0.1 ppm. High protein content food samples displayed low susceptibility to the films (<1 log reduction in any case), whereas low protein content food samples exhibited no detectable bacterial counts for films with 1 and 10 wt % silver and about 2 log reduction for films with 0.1 wt % silver. These results represent a step forward in the understanding of silver antimicrobial efficacy and its possible application in the food-packaging industry, most likely as food coatings.     

Development of flexible antimicrobial packaging materials against Campylobacter jejuni by incorporation of gallic acid into zein-based films

In this study, antimicrobial films were developed against Campylobacter jejuni by incorporation of gallic acid (GA) into zein-based films. The zein and zein-wax composite films containing GA between 2.5 and 10 mg/cm(2) were effective on different C. jejuni strains in a concentration-dependent manner. Zein and zein-wax composite films showed different release profiles in distilled water but quite similar release profiles at solid agar medium. Depending on incorporated GA concentration, 60-80% of GA released from the films, while the remaining GA was bound or trapped by film matrix. The GA at 2.5 and 5 mg/cm(2) caused a considerable increase in elongation (57-280%) of all zein films and eliminated their classical flexibility problems. The zein-wax composite films were less flexible than zein films, but the films showed similar tensile strengths and Young's modulus. Scanning electron microscopy indicated different morphologies of zein and zein-wax composite films. This study clearly showed the good potential of zein and GA to develop flexible antimicrobial films against C. jejuni.     

基于层次分析法的面制主食杀菌及包装生产线设计与试验

为适应面制主食工业化生产,保证主食流通过程中的质量,研制可集成于面制主食工业化生产线末端的复合杀菌包装生产线。依据面制主食贮藏特性及流通过程中变质的影响因素,结合食品保鲜包装的技术与方法,确定面制主食杀菌包装生产线由主食干燥、复合杀菌和包装三大功能装置组成。在设计方案时采用层次分析法,选择主食杀菌包装生产线上所用食品干燥、杀菌保鲜技术方案,并设计生产线的物料流程。优选的结果为,干燥采用红外线干燥,复合杀菌方式为低温、紫外线和臭氧相结合,包装采用接缝式裹包,且整条生产线可程序化控制,实现杀菌时间、紫外线照度、臭氧浓度和温度的实时调节,为主食品工业化生产提供杀菌包装装备。利用该设备对馒头进行复合杀菌试验,结果表明馒头的色泽和质构均优于自然放置的馒头,经杀菌包装后的馒头在温度4℃,相对湿度为50%~70%的环境中贮存20 d其菌落总数为3.5 lg(CFU/g),达到预定20 d的保质期。研究结果为面制主食工业化生产及复合杀菌包装装备设计提供参考。     

Immobilization of angiotensin-converting enzyme on glyoxyl-agarose

The assay of angiotensin-converting enzyme (ACE) inhibition by food-derived peptides is usually carried out by using soluble ACE in a batch process. The purification of this enzyme from tissues is not an easy task, and the resulting preparation loses activity very fast. In addition, ACE commercial preparations are very expensive. In this work the immobilization of ACE, through lysine amino groups, to 4% beads cross-linked (4 BCL) glyoxyl-agarose is described. The amount of immobilized enzyme increased with increasing concentrations of enzyme and with incubation time until a saturation point was reached at 50 mg protein/mL gel and 3.5 hours, respectively. The IC50 values for a noncompetitive sunflower peptide inhibitor were similar for the soluble (30.56 microM) and immobilized (32.7 microM) enzymes. An immobilized derivative was obtained that was 60 times more stable than the soluble enzyme at 60 degrees C. This procedure yields a derivative that can be reused and has increased thermal stability compared to that of the soluble enzyme. Thus, ACE immobilization is a good alternative to using soluble freshly prepared or commercial preparations because of economical and practical reasons.     

Investigation of packaging systems for shelled walnuts based on oxygen absorbers

Storage of nuts at a high oxygen concentration results in rancid nuts whereas storage at a low oxygen concentration results in fine-tasting nuts. During a 13 month experiment, packaging of walnuts with an oxygen absorber was compared to packaging in nitrogen or atmospheric air. At the same time, the effects of oxygen permeability of the packaging material and storage temperature (11 and 21 degrees C) were investigated by determination of hexanal and rancid taste of the walnuts. The optimal storage condition for walnuts is at 11 degrees C or lower, eventually combined with an oxygen absorber. However, without chilled storage and use of an oxygen absorber, it is possible to obtain an acceptable quality of walnuts with a packaging material having a very low oxygen permeability (e.g., laminate with EVOH) combined with nitrogen flushing. The results also revealed that the development of hexanal during time can be described by a second-order polynomial regression model.     

Some characteristics of sugar ester nonionic microemulsions in view of possible food applications

This study explores some characteristics of microemulsions composed of sucrose monostearate (SMS), medium-chain triglycerides (MCT), or R-(+)-limonene, alcohols, and water. The systems are homogeneous, soft, and waxy solids at room temperature but liquefy and structure into homogeneous microemulsions when heated to >40 degrees C. The amount of solubilized water is enhanced as a function of the alcohol/oil ratio and is inversely proportional to the alcohol chain length. Over 60 wt % water can be solubilized in systems consisting of propanol/MCT/SMS at a weight ratio of 3:1:4 (initial weight ratio). These microemulsions are unique and differ from nonionic ethoxylated-based microemulsions in that their viscosity is very low and is reduced with increasing amounts of solubilized water. The electrical conductivity increases only slightly as a function of the water content and does not show typical bicontinuous or percolated behavior. The water in the core of the microemulsion strongly binds to the headgroups of the surfactant. Only at >15 wt % solubilization of water was free or bulk water detected in the core of the microemulsions. Such unique behavior of the core water might have a possible application in systems requiring monitoring of enzymatic (lipase) reactions carried out in the microemulsions as microreactors.