Antimicrobial and physicochemical properties of chitosan-HPMC-based films

To prepare composite films from biopolymers with anti-listerial activity and moisture barrier properties, the antimicrobial efficiency of chitosan-hydroxy propyl methyl cellulose (HPMC) films, chitosan-HPMC films associated with lipid, and chitosan-HPMC films chemically modified by cross-linking were evaluated. In addition, the physicochemical properties of composite films were evaluated to determine their potential for food applications. The incorporation of stearic acid into the composite chitosan-HPMC film formulation decreased water sensitivity such as initial solubility in water and water drop angle. Thus, cross-linking of composite chitosan-HPMC, using citric acid as the cross-linking agent, led to a 40% reduction in solubility in water. The water vapor transfer rate of HPMC film, approximately 270 g x m(-2) x day(-1) x atm(-1), was improved by incorporating chitosan and was further reduced 40% by the addition of stearic acid and/or cross-linking. Anti-listerial activity of films was determined on solid medium by a numeration technique. Chitosan-HPMC-based films, with and without stearic acid, inhibited the growth of Listeria monocytogenes completely. On the other hand, a loss of antimicrobial activity after chemical cross-linking modification was observed. FTIR and 13C NMR analyses were then conducted in order to study a potential chemical modification of biopolymers such as a chemical reaction with the amino group of chitosan. To complete the study, the mechanical properties of composite films were determined from tensile strength assays.     

Development of zein nanoparticles coated with carboxymethyl chitosan for encapsulation and controlled release of vitamin D3

In this study, zein nanoparticles coated with carboxymethyl chitosan (CMCS) were prepared to encapsulate vitamin D3 (VD3). VD3 was first encapsulated into zein nanoparticles using a low-energy phase separation method and coated with CMCS simultaneously. Then, calcium was added to cross-link CMCS to achieve thicker and denser coatings. The nanoparticles with CMCS coatings had a spherical structure with particle size from 86 to 200 nm. The encapsulation efficiency was greatly improved to 87.9% after CMCS coating, compared with 52.2% for that using zein as a single encapsulant. The physicochemical properties were characterized by differential scanning calorimetry and Fourier transform infrared spectroscopy. Nanoparticles with coatings provided better controlled release of VD3 in both PBS medium and simulated gastrointestinal tract. Photostability against UV light was significantly improved after encapsulation. Encapsulation of hydrophobic nutrients in zein nanoparticles with CMCS coatings is a promising approach to enhance chemical stability and controlled release property.     

Antimicrobial and antioxidant effects of milk protein-based film containing essential oils for the preservation of whole beef muscle

Milk protein-based edible films containing 1.0% (w/v) oregano, 1.0% (w/v) pimento, or 1.0% oregano-pimento (1:1) essential oils mix were applied on beef muscle slices to control the growth of pathogenic bacteria and increase the shelf life during storage at 4 degrees C. Meat and film were periodically tested during 7 days for microbial and biochemical analysis. The lipid oxidation potential of meat was evaluated by the determination of thiobarbituric reactive substances (TBARS). The availability of phenolic compounds from essential oils was evaluated by the determination of total phenolic compounds present in the films during storage. Antioxidant properties of films during storage were also evaluated following a modified procedure of the N,N-diethyl-p-phenylenediamine colorimetric method. Oregano-based films stabilized lipid oxidation in beef muscle samples, whereas pimento-based films presented the highest antioxidant activity. The application of bioactive films on meat surfaces containing 10(3) colony-forming units/cm2 of Escherichia coli O157:H7 or Pseudomonas spp. showed that film containing oregano was the most effective against both bacteria, whereas film containing pimento oils seems to be the least effective against these two bacteria. A 0.95 log reduction of Pseudomonas spp. level, as compared to samples without film, was observed at the end of storage in the presence of films containing oregano extracts. A 1.12 log reduction of E. coli O157:H7 level was noted in samples coated with oregano-based films.     

Storage stability and antibacterial activity against Escherichia coli O157:H7 of carvacrol in edible apple films made by two different casting methods

The antimicrobial activities against Escherichia coli O157:H7 as well as the stability of carvacrol, the main constituent of oregano oil, were evaluated during the preparation and storage of apple-based edible films made by two different casting methods, continuous casting and batch casting. Antimicrobial assays of films and high-performance liquid chromatography (HPLC) analysis of film extracts following storage up to 49 days at 5 and 25 degrees C revealed that (a) optimum antimicrobial effects were apparent with carvacrol levels of approximately 1.0% added to the purees prior to film preparation, (b) carvacrol in the films and film weights remained unchanged over the storage period of up to 7 weeks, and (c) casting methods affected carvacrol concentration, bactericidal activity, physicochemical properties, and colors of the apple films. Carvacrol addition to the purees used to prepare the films reduced water vapor and oxygen permeability of apple films. The results indicate that carvacrol has a dual benefit. It can be used to both impart antimicrobial activities and enhance barrier properties of edible films. The cited observations facilitate relating compositional and physicochemical properties of apple puree films containing volatile plant antimicrobials to their use in foods.     

Novel chitosan-derived nanomaterials and their micelle-forming properties

Six novel N-alkyl-N-dimethyl and N-alkyl-N-trimethyl chitosan derivatives were chemically synthesized and characterized using FT-IR, 1H NMR, 13C NMR, differential scanning calorimetry (DSC), and X-ray diffraction spectrometry (XRD). The alkyl groups included octyl (C8H17-), decanyl (C10H21-), and lauryl (C12H25-). These chitosan derivatives were also evaluated for their micelle-forming properties using dynamic light scattering (DLS) and transmission electron microscopy (TEM) techniques. All six chitosan derivatives were capable of forming polymeric micelles in water with an average particle diameter ranging from 36 to 218 nm. Both N-octyl-N-dimethyl and N-octyl-N-trimethyl chitosan derivatives formed nanomicelles under the experimental conditions, with an average particle diameter of 36.0 and 52.5, respectively. Both the length of alkyl group and the N-trimethylation degree of the chitosan derivatives altered the size of their polymeric micelles. To further understand the effect of N-alkyl substitution degree of chitosan derivatives on size of their micelles, additional five N-octyl-N-trimethyl chitosan derivatives with N-alkyl substitution degree ranging from 8 to 58% were prepared and their micelle sizes were determined. The results showed that the diameter of the nanomicelles was proportional to the degree of N-octyl substitution. These data suggest that novel N-alkyl-N-dimethyl and N-alkyl-N-trimethyl chitosan derivatives may form nanomicelles. Additional research is required to further investigate the potential value-added utilization of these chitosan derivatives in controlled release and targeted delivery of hydrophobic bioactive food factors.     

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.     

壳聚糖-胰蛋白酶抑制剂复合可食性膜的制备及抗黄曲霉活性

为探索新型生物膜材料的制备方法及抗黄曲霉活性,以壳聚糖和大豆胰蛋白酶抑制剂(TI)提取物为原料,甘油为增塑剂,利用溶液共混流延法制备壳聚糖-TI-甘油复合可食性膜,测试其厚度、表观结构、力学性质、透光率、水蒸气透过率及抗黄曲霉侵染活性。结果表明,当壳聚糖浓度为18mg/mL、TI浓度2mg/mL、甘油浓度12mg/mL和干燥温度45℃时,制备复合膜具有优良抗黄曲霉活性,且综合理化性能最佳。制备壳聚糖-TI-甘油复合膜液涂膜于花生上,接种黄曲霉培养后发现,复合膜对于黄曲霉侵染具有较强的抵抗和抑制作用。     

Structure elucidation and antifungal activity of an anthracycline antibiotic, daunomycin, isolated from Actinomadura roseola

The actinomycete strain Ao108 producing antifungal metabolites active against some plant pathogenic fungi was identified as Actinomadura roseola, based on the analyses of morphological and physiological characteristics. The antibiotic Da2B that showed a strong antifungal activity was isolated from the culture broth and mycelial mats of A. roseola strain Ao108 using various chromatographic procedures. On the basis of (1)H NMR, (13)C NMR, and 2-D NMR correlation data, the antibiotic Da2B was confirmed to have the structure of an anthracycline antibiotic, daunomycin. In vitro antimicrobial spectrum tests showed that the antibiotic Da2B had substantial inhibitory activity (10 microg mL(-)(1) of MICs) against mycelial growth of Phytophthora capsici and Rhizoctonia solani. The antibiotic also showed antiyeast activity against Saccharomyces cerevisiae, but the growth of Candida albicans was not affected. Antibacterial activity was found only against Gram-positive bacteria. In the further evaluation of in vivo efficacy, application of the antibiotic Da2B effectively inhibited the development of Phytophthora blight in pepper plants. However, the control efficacy of the antibiotic against Phytophthora infection was somewhat less than that of metalaxyl. The antibiotic Da2B did not show any phytotoxicity on pepper plants even at 500 microg mL(-)(1).     

Synthesis and biological activities of novel pyrazole oxime derivatives containing a 2-chloro-5-thiazolyl moiety

A series of novel pyrazole oxime derivatives containing a 2-chloro-5-thiazolyl moiety were synthesized. Their structures were confirmed by (1)H NMR, (13)C NMR, and elemental analysis. The preliminary bioassays showed that all of the title compounds had low acaricidal activity against Tetranychus cinnabarinus . However, most of them exhibited excellent insecticidal activity against Aphis medicagini at the dosage of 0.5 mg/mL, and some compounds still showed good insecticidal activity against A. medicagini even at the dosage of 0.2 mg/mL. Meanwhile, some title compounds displayed fungicidal and plant growth regulatory activities.     

入侵植物假臭草和胜红蓟提取物的抑菌活性研究

假臭草和胜红蓟是我国南方常见的入侵植物,为了防治和利用其开发植物源抑菌剂,本试验采用牛津杯法检测了不同溶剂(70%乙醇、95%乙醇、石油醚和乙酸乙酯)提取物对28种病原微生物的抑菌活性,并评估了不同器官部位提取物的抑菌活性。结果表明,不同溶剂提取物抑菌活性有差异,假臭草70%乙醇提取物对金黄色葡萄球菌(Staphylococcus aureus)抑制活性最强,抑菌圈直径为26.28±0.75mm;胜红蓟95%乙醇提取物对腐生葡萄球菌(Staphylococcus epidermidi)抑制活性最好,抑菌圈直径为17.31±0.46 mm。此外,假臭草和胜红蓟70%乙醇不同部位提取物对金黄色葡萄球菌(Staphylococcus aureus)的抑菌作用表现为叶部提取物(22.31±0.34 mm和19.52±0.28 mm)茎部提取物(22.25±0.65 mm和12.75±0.45 mm)根部提取物(11.78±0.69 mm和9.05±0.53 mm)。假臭草提取物对12种细菌和1种真菌黑曲霉菌(Aspergillus niger)具有抑制效果;胜红蓟提取物对9种细菌具有抑制效果。本研究结果为进一步研发具有潜力的植物源抑菌剂奠定了理论基础。     

Sensory evaluation of baked chicken wrapped with antimicrobial apple and tomato edible films formulated with cinnamaldehyde and carvacrol

The addition of plant essential oils to edible films and coatings has been shown to protect against bacterial pathogens and spoilage while also enhancing sensory properties of foods. This study evaluated the effect of adding 0.5 and 0.75% carvacrol (active ingredient of oregano oil) to apple- and tomato-based film-forming solutions and 0.5 and 0.75% cinnamaldehyde (active ingredient of cinnamon oil) to apple-based film-forming solutions on sensory properties of cooked chicken wrapped with these films. Paired preference tests indicated no difference between baked chicken wrapped with tomato and apple films containing 0.5% carvacrol and cinnamaldehyde compared to chicken wrapped with tomato or apple films without the plant antimicrobials. The taste panel indicated a higher preference for carvacrol-containing tomato-coated chicken over the corresponding apple coating. There was also a higher preference for cinnamaldehyde-containing apple films over corresponding carvacrol-containing wrapping. Films containing antibacterial active compounds derived from essential oils can be used to protect raw chicken pieces against bacterial contamination without adversely affecting preferences of wrapped chicken pieces after baking.     

Insecticidal activity of rhamnolipid isolated from pseudomonas sp. EP-3 against green peach aphid (Myzus persicae)

Microorganisms capable of growth on oils are potential sources of biopesticides, as they produce complex molecules such as biosurfactants and lipopeptides. These molecules have antimicrobial activity against plant pathogens, but few data are available on their insecticidal activity. The present study describes the insecticidal activity of a rhamnolipid isolated from diesel oil-degrading Pseudomonas sp. EP-3 (EP-3). The treatment of cell-free supernatants of EP-3 grown on glucose-mineral medium for 96 h led to > 80% mortality of aphids (Myzus persicae) within 24 h. Bioassay-guided chromatography coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MADLDI-TOF MS) and (1H, 13C) nuclear magnetic resonance (NMR) analyses was employed to isolate and identify the EP-3 insecticidal metabolites. Dirhamnolipid, with molecular formulas of C??H??O?? and C??H??O??, was identified as a main metabolite exhibiting insecticidal activity against aphids. Dirhamnolipid showed a dose-dependent mortality against aphids, producing about 50% mortality at 40 μg/mL and 100% mortality at 100 μg/mL. Microscopy analyses of aphids treated with dirhamnolipid revealed that dirhamnolipid caused insect death by affecting cuticle membranes. This is the first report of rhamnolipid as an insecticidal metabolite against M. persicae. Rhamnolipid shows potential for use as a pesticide to control agricultural pests.     

Physicochemical, antimicrobial, and cytotoxic characteristics of a chitosan film cross-linked by a naturally occurring cross-linking agent, aglycone geniposidic acid

The purpose of this study was to evaluate the characteristics of a chitosan film cross-linked by a naturally occurring compound, aglycone geniposidic acid (aGSA). This newly developed aGSA-cross-linked chitosan film may be used as an edible film. The chitosan film without cross-linking (fresh) and the glutaraldehyde-cross-linked chitosan film were used as controls. The characteristics of test chitosan films evaluated were their degree of cross-linking, swelling ratio, mechanical properties, water vapor permeability, antimicrobial capability, cytotoxicity, and enzymatic degradability. It was found that cross-linking of chitosan films by aGSA (at a concentration up to 0.8 mM) significantly increased its ultimate tensile strength but reduced its strain at fracture and swelling ratio. There was no significant difference in the antimicrobial capability between the cross-linked chitosan films and their fresh counterpart. However, the aGSA-cross-linked chitosan film had a lower cytotoxicity, a slower degradation rate, and a relatively lower water vapor permeability as compared to the glutaraldehyde-cross-linked film. These results suggested that the aGSA-cross-linked chitosan film may be a promising material as an edible film.     

Water and moisture susceptibility of chitosan and paper-based materials: structure-property relationships

Environmentally friendly and potentially bioactive food packaging based on chitosan-coated papers were elaborated. The morphology and the microstructure of these new materials were characterized by infrared spectroscopy and scanning electron microscopy. These observations suggested that the chitosan penetrated deeply into the paper, embedding the cellulose fibers, instead of forming a layer as expected. Through the barrier properties against moisture, the liquid water sensitivity, and NMR-relaxometry measurements, the water interactions were evaluated on the chitosan films and the chitosan-coated papers. They revealed that the coating by a chitosan film forming solution improved the paper moisture barrier properties but the surface hydrophilicity remained high. Relaxometry studies showed that, due to its hydrophilic character, chitosan controlled the interaction with water, despite the very low amount of deposit. On the other hand, the mechanical properties of papers were unmodified by the chitosan coating, which did not fundamentally affect the solid structure of the papers.     

酸溶剂对葛根淀粉/壳聚糖复合可食膜性能的影响

为了考察壳聚糖酸溶剂对葛根淀粉/壳聚糖复合可食膜抗菌、物理和机械性能的影响,该文选择质量分数为1%的乙酸、乳酸、苹果酸为溶剂,配制质量体积比2g/L的葛根淀粉-壳聚糖复合膜液,以0.5g/L的抗坏血酸为活性添加剂,0.6g/L的丙三醇为增塑剂,0.1g/L的吐温20为表面活性剂,采用流延法制备可食性复合膜。结果表明:复合膜液具有一定的表面活性;酸溶剂未对膜液表面张力产生显著影响。有机酸溶剂种类对复合膜性能影响显著,其中乙酸复合膜的机械强度最大,平均抗拉强度和穿透力分别为5.73MPa和8.63N,水溶性最小,约34%,对抗坏血酸缓释效果最明显;乳酸复合膜的延展性最优,平均断裂伸长率和穿透距离分别为71.5%和6.05mm;苹果酸复合膜的抑菌效果最佳,对大肠杆菌和金黄色葡萄球菌的抑制率分别达到98.9%和81.2%,阻水性最强,透湿系数为4.824.82×10-11g/(m·s·Pa),故可根据不同使用目的选择相应复合膜。研究结果为该类复合包装膜在实际食品上的应用提供理论依据。     

Water sensitivity, antimicrobial, and physicochemical analyses of edible films based on HPMC and/or chitosan

Several properties of chitosan films associated or not with hydroxypropylmethylcellulose polymer (HPMC) and HPMC films incorporating or not nisin and/or milk fat were studied. Nisin addition at a level of 250 microg mL-1 and likewise chitosan at 1% (w/v) concentration were efficient for total inhibiting Aspergillus niger and Kocuria rhizophila food deterioration microorganisms. HPMC and chitosan films were transparent, whereas nisin and/or fat incorporation induced a 2-fold lightness parameter increase and, consequently, involved more white films. Measurements of tensile strength, as well as ultimate elongation, showed that chitosan and HPMC initial films were elastic and flexible. High thermal treatments and additive incorporation induced less elastic and more plastic films. Water vapor transmission as far as total water desorption rates suggested that chitosan films were slightly sensitive to water. Water transfer was decreased by <60% as compared with other biopolymer films. Regarding its hydrophobic property, the capacity of fat to improve film water barrier was very limited.     

Properties of zein films coated with drying oils

Zein films prepared by resin were coated with either flax oil or tung oil and cured by UV- or gamma-radiation. Coated zein films were then evaluated for tensile and water barrier properties. Film microstructure was examined by transmitted light microscope. Tensile strength, elongation, and toughness of oil-coated samples increased substantially with respect to uncoated films. Flax oil coated samples showed an increase in elongation of 300%. It was suggested that oil coatings fill in pinholes and cracks existing in zein films, affecting their mechanical properties. Water vapor permeability also decreased statistically for coated film (except for tung oil coated-UV treated films), suggesting water vapor transfer was controlled by film hydrophobicity and microstructure. Moreover, the liquid water transmission rate of coated films was at least 10 times slower than for control films. Examination of film microstructure revealed that flax oil coatings had uniform coverage and smooth finish, which explained their high elongation, low water vapor permeability. Tung oil coatings cured under UV light showed patterns of intertwined dark and light regions, which may be caused by cross-linking and drying at different times. The oriented structures were found when tung oil coatings were cured by gamma-radiation.     

Design, synthesis, and quantitative structure-activity relationship study of herbicidal analogues of pyrazolo[5,1-d][1,2,3,5]tetrazin-4(3H)ones

A series of pyrazolo[5,1-d][1,2,3,5]tetrazin-4(3H)one derivatives were designed, synthesized, and evaluated for their herbicidal activities where some of these compounds provided >80% control of Brassica campestris at 10 microg/mL. Quantitative structure-activity relationship studies were performed on these compounds using physicochemical parameters (electronic, Verloop, or hydrophobic) as independent parameters and herbicidal activity as a dependent parameter, where herbicidal activity correlated best (r > 0.8) with physicochemical parameters in this set of molecules. The herbicidal activity against B. campestris was mainly affected by the molar refractivity (MR) for R1, Taft (Eso) for R2 or R6, Verloop (Lm) for R3 or R5, and electronic parameters (Hammett's constants) for R4. The optimal MR for herbicidal activity is 0.95. The herbicidal activity against Echinochloa crus-galli was mainly related with the substituents' hydrophobic parameter. The optimal pi parameters for R1 and R4 for herbicidal activity are 0.72 and 0.68, respectively. In general, these compounds showed greater herbicidal activity toward B. campestris than E. crus-galli.     

壳聚糖蜂蜡复合膜对冷冻黄桃片生理和品质的影响（英）

为了解决延长冷冻水果保质期问题,研究了壳聚糖和壳聚糖蜂蜡复合膜对冷冻黄桃片生理和品质的影响。分析了样品多酚氧化酶（PPO）、膜透性、pH值、硬度、色泽、汁液流失、维生素C和可溶性固形物含量在–20℃下60 d贮藏过程中的变化。结果表明：与对照相比,壳聚糖或壳聚糖蜂蜡复合膜抑制了PPO活性和膜透性的增加,降低了果肉褐变、汁液流失和维生素C损失。研究表明,壳聚糖-蜂蜡复合膜比单独壳聚糖更有助于减少冷冻黄桃片的汁液流失、硬度和维生素C损失,从而更好地保持了冷冻黄桃片的生理和品质。