Cellulose Acetate Nanofibres Containing Alizarin as a Halochromic Sensor for the Qualitative Assessment of Rainbow Trout Fish Spoilage

A halochromic sensor of cellulose acetate nanofibres and alizarin as a fish spoilage indicator in real time is described. The colour of this on-packaging sensor changes visually with an increase in the amount of total volatile basic nitrogen (TVB-N) and a rise in the pH value of product. Rainbow trout fillets were kept at refrigerator temperature (4 °C) for 12 days. TVB-N, pH, total viable count (TVC) and colourimetric tests were performed. Results showed that the pH, the TVB-N and the TVC increased with time. No colour changes were observed within 48 h, but after the fourth day, a very light brick colour on the nanosensor was observed. This colour became darker on the sixth day, representing actual pH changes. The colour of sensor tended towards violet on the 12th day; the colourimetric result proved the expected visual colour change in the electrospun nanosensor due to alizarin usage as a halochromic dye.     

聚乙烯醇-壳聚糖基抑菌指示膜的制备及在冷鲜肉中的应用

基于聚乙烯醇（polyvinyl alcohol,PVA）-壳聚糖（chitosan,CS）为成膜基材,蒙脱土（montmorillonite,MMT）负载茶多酚（tea polyphenols,TP）为抑菌剂,溴甲酚紫（bromocresol purple,BCP）、甲基红（methyl red,MR）及其复配物为指示剂制备多功能食品包装膜。研究BCP、MR及其复配和MMT负载TP对PVA-CS薄膜物理和功能特性的影响,并将其应用于冷鲜肉的保鲜指示。结果表明：各组分之间相容性较好;指示剂的添加增强了共混膜的结晶度,改善了薄膜的物理性能和光学性能;指示膜均能对氨气响应,其中BCP与MR质量比为1.5∶1时最为灵敏。抑菌剂的添加明显提高了薄膜的耐水性、水蒸气阻隔性、抗氧化性以及抑菌性。将抑菌指示膜应用于冷鲜肉的新鲜度监测及保鲜实验,发现BCP与MR质量比1.5∶1薄膜的颜色变化与冷鲜肉新鲜度之间存在明显正相关性,且实验组较空白组货架期延长1～2 d,表明抑菌指示膜能够实时监测冷鲜肉新鲜度并有效延长货架期。     

Development of films based on blends of gelatin and poly(vinyl alcohol) cross linked with glutaraldehyde

Both gelatin and poly(vinyl alcohol) (PVA) can be cross linked with glutaraldehyde (GLU). In the case of gelatin, the GLU reacts with each ε-NH2 functional group of adjacent lysine residues, while for PVA, the GLU reacts with two adjacent hydroxyl groups, forming acetal bridges. Thus it can be considered possible to cross link adjacent macromolecules of gelatin and PVA using GLU. In this context, the aims of this work were the development of biodegradable films based on blends of gelatin and poly(vinyl alcohol) cross linked with GLU, and the characterization of some of their main physical and functional properties. All the films were produced from film-forming solutions (FFS) containing 2 g macromolecules (PVA + gelatin)/100 g FFS, 25 g glycerol/100 g macromolecules, and 4 g GLU (25% solution)/100 g FFS. The FFS were prepared with two concentrations of PVA (20 or 50 g PVA/100 g macromolecules) and two reaction temperatures: 90 or 55 °C, applied for 30 min. The films were obtained after drying (30 °C/24 h) and conditioning at 25 °C and 58% of relative humidity for 7 days, and were then characterized. The results for the color parameters, mechanical properties, phase transitions and infrared spectra showed that some chemical modifications occurred, principally for the gelatin. However, in general, all the characteristics of the films were either typical of films based on blends of these macromolecules without cross linking, or slightly higher. A greater improvement in the properties of this material was probably not observed due to the crystallinity of the PVA, which has a melting point above 90 °C. The presence of microcrystals in the polymer chain probably reduced macromolecular mobility, hindering the reaction. Thus more research is necessary to produce biodegradable films with improved properties.     

Active chitosan–polyvinyl alcohol films with natural extracts

Active films were prepared from chitosan (Ch) and polyvinyl alcohol (PVA) containing aqueous mint extract (ME)/pomegranate peel extract (PE). The effect of these extracts on the physical, mechanical, antimicrobial and antioxidant properties of the films were studied. Increased protection against UV light was observed in the films containing the extracts. Addition of ME/PE improved the tensile strength of the films without affecting their puncture strength. Ch–PVA films incorporated with PE had the highest tensile strength (41.07 ± 0.88 MPa). Permeability characteristics of the films were not altered due to addition of extracts. ME/PE conferred antioxidant properties to Ch–PVA films as determined by DPPH radical scavenging activity. The films also exhibited antibacterial activity against Staphylococcus aureus and Bacillus cereus. PE containing films totally inhibited the growth of B. cereus and reduced the number of S. aureus by 2 log cycles. These results suggest that Ch–PVA film containing ME/PE can be used for development of active food packaging materials.     

Improving the oxygen barrier of microcapsules using cellulose nanofibres

In this study, the oxygen barrier and physical properties of two maltodextrin/gum Arabic (MD/GA) (3:1 w/w) microcapsules with dextrose equivalence (DE) 26 and 6 were assessed with or without the incorporation of cellulose nanofibres (CNF). The oxygen diffusion coefficient (D_eff) was between 10.6 × 10⁻¹⁵ m² s⁻¹ and 17.3 × 10⁻¹⁵ m² s⁻¹ for all microcapsules. The addition of CNF improved the oxygen barrier of MD/GA microcapsules. The incorporation of CNF did not significantly impact T_g due to the low quantity of CNF present in the microcapsules. Wettability was higher in CNF incorporated microcapsules, and dispersibility was lower only for microcapsules with maltodextrin of DE 26. Spray-dried microcapsules exhibited poor flowability and high cohesiveness due to the moisture content (2.0–2.5%) of the powders. The results suggest that incorporation of CNF can increase the oxygen barrier of MD/GA microcapsules which may lead to better oxidative stability of micronutrients incorporated in the microcapsules.     

亚麻分层纳米纤维素的制备及其增强热电复合材料性能

为从天然亚麻纤维中制备出分层纳米纤维素(即纤维素纳米纤维(CNF)与纤维素纳米晶(CNC)共存),并对其制备方法进行优化完善,提出将亚麻纤维在特定浓度的氢氧化钠溶液中碱化处理后,再进行四甲基哌啶氮氧化物(TEMPO)介导的三元氧化和机械处理的联合处理方法。然后将亚麻CNF与石墨烯复合制备CNF/石墨烯复合薄膜并研究亚麻CNF增强热电复合材料的性能。结果表明:碱化预处理使亚麻纤维直径变细,长度变短,半纤维素被脱除,是生成不同尺寸CNF的重要步骤;随着氢氧化钠用量在0~18%范围内的增加,所得CNF悬浮液的光透过率从3.7%增加到95.1%;CNF/石墨烯复合膜表现出最高功率因子,为8.0×10 ^-3 μW/(m·K ²),表明复合薄膜具有热电性能。     

Chitosan biobased and intelligent films: Monitoring pH variations

Many factors can influence the shelf-life product, such as pH, water activity, nutrient levels available oxygen, etc. Variations in food pH could occur due to microorganism growth and chemical reactions that may impact flavour, consistency and shelf-life. The objective of this paper was to obtain and characterize the fast pH-colourimetric indicator device, applying a simple manufacturing technique, using food grade and biodegradable materials. The intelligent film was based on natural compounds as chitosan and anthocyanin (pH-colourimetric indicator). Chitosan intelligent films (C-ATH, 2.0 g/100 g) were obtained incorporating anthocyanin (1.0 g/100 g) in matrix films. Initially, a dark violet colour was observed in chitosan films dried. When immersed in different pH buffers, the colour range of the films varied from pink (in acid pH) to bluish-green (in neutral pH) and to violet (in basic pH). The water solubility and water vapour transmission rate of C-ATH were decreased to 60% and 48%, respectively, as compared to control film (CF, without indicator). The mechanical properties such as tensile strength and rigidity were maintained, and the elongation at break was reduced to 47% compared to CF. The advantages of this system were the simple manufacturing process, biodegradability and usage of natural and safe compounds.     

Development of anti-insect food packaging film containing a polyvinyl alcohol and cinnamon oil emulsion at a pilot plant scale

Anti-insect packaging films containing cinnamon oil (CO) encapsulated by polyvinyl alcohol (PVA) for repelling Plodia interpunctella (Hübner) larvae were manufactured using pilot plant scale instruments. The microcapsule emulsion of CO and PVA was printed onto polypropylene (PP) film as an ink mixture using the gravure printing method. The printed PP film was then laminated with a low-density polyethylene (LDPE) film to protect the printed side. Four types of multilayer films were produced: control film, 2% CO film, encapsulated 1% CO film, and encapsulated 2% CO film. When mechanical properties were assessed, tensile strength and elongation-at-break were not significantly different among films, whereas the Young's modulus values were different between the control film and the three types of CO-containing films. In a repellent test, 2% CO film repelled P. interpunctella larvae most effectively. For sensory evaluation, which was performed using milk chocolate, caramel soft candy, and cookies packaged with the produced films, the produced films did not affect the sensory characteristics. Therefore, the films printed with emulsions of CO and PVA could be applied in the food industry to help protect foods from infestation by P. interpunctella.     

Effect of alkaline extraction on the structure of the protein of quinoa (Chenopodium quinoa Willd.) and its influence on film formation

It is important to produce hydrophobic edible protein films for use in foods. The aim of this study was to evaluate the effect of alkaline extraction of quinoa proteins (QP) on the structure and their film‐forming ability without plasticiser. QP were extracted between pH 8 to 12, and their structure was evaluated by PAGE‐SDS, size‐exclusion HPLC light scattering, fluorescence spectroscopy and SH and SS. Film was characterised by FTIR, SEM, tensile strength, barrier and colour. Structural changes of QP showing that alkalinisation over pH 10 produce significant denaturation/aggregation/dissociation structural changes in QP. pH 12 was the condition to form a film (film₁₂). FTIR showed hydrogen bonds and hydrophobic film interactions. Film₁₂ had 16.6 ± 3.8% elongation and 15.7 ± 1.1 MPa tensile strength, and water vapour permeability was 5.18 ± 0.38 g mm m^?2 day^?1 kPa^?1. Film₁₂ had a brownish colour. A high degree of denaturation/aggregation/dissociation of QP structure is required to form a film without plasticiser.     

基于甲基纤维素改性聚乙烯醇指示膜的制备、表征及对南美白对虾的鲜度指示

为实现水产品鲜度可视化实时监测,本研究以甲基纤维素（methyl cellulose,MC）共混改性聚乙烯醇（polyvinyl alcohol,PVA）为成膜基材,复配溴甲酚紫甲基红制备指示膜,比较基材配比对结构、物理及检测性能的影响,并应用于南美白对虾鲜度检测。结果表明：各组分相容性强,流变学结果表明m（MC）∶m（PVA）＝3∶1时分子间作用力最强烈。MC的引入可改善PVA性能,当PVA和MC质量比为1∶3时,指示膜具有最高的抗拉强度（（65.36±4.29）MPa）、疏水性能（水接触角（57.30±0.81）°）和阻隔性能。各指示膜均能对pH值响应,且具良好颜色稳定性。将性能最优的指示膜用于南美白对虾（4 ℃）鲜度检测,4 d时指示膜由红褐色转为紫褐色,对应次级鲜度;8 d时pH值和总挥发性盐基氮（total volatile basic nitrogen,TVB-N）含量分别达7.73±0.01和（60.90±7.00）mg/100 g,指示膜变为黑色,对应完全腐败。差异显著性分析表明指示膜颜色在不同鲜度区间具有明显差异,相关性分析表明指示膜色差值与pH值、TVB-N含量呈显著（P＜0.05）或极显著（P＜0.01）相关。鉴于伴随虾不同程度的腐败,指示膜可产生肉眼可辨的颜色变化,故可根据指示膜颜色对所保鲜虾类的鲜度等级进行划分,实现食品鲜度实时监控,具良好应用前景。     

Preparation and Characterization of Co3O4/Graphene/Cellulose Nanofiber Composite Films

Nanocellulose has served as an eye-catching nanomaterial for constructing advanced functional devices with renewability, light weight, flexibility, and environmental friendliness. In this study, Co₃O₄/graphene/cellulose nanofiber (CNF) flexible composite films, in which the CNF acted as a spacer for the graphene, were prepared via a facile and scalable vacuum filtration method. The effects of the CNF on the microstructure, hydrophilicity, thermal stability, tensile strength, surface resistance, and electrochemical performance of the Co₃O₄/graphene/CNF composite films were systematically investigated. The results showed that the synergistic interaction of the CNF and graphene substantially improved the overall properties of the Co₃O₄/graphene/CNF composite films, particularly their hydrophilicity and tensile strength. Meanwhile, Co₃O₄/graphene/CNF composite films with a CNF content of 4% appeared to have the optimal electrochemical performance, with an area specific capacitance of 56 mF/cm² and prominent capacitance retention of 95.6% at a current density of 1 A/g after 1000 cycles. This work demonstrated that the prepared Co₃O₄/graphene/CNF flexible composite films have great application potential in the field of flexible energy storage devices.     

A novel intelligent film with high stability based on chitosan/sodium alginate and coffee peel anthocyanin for monitoring minced beef freshness

This study aimed to develop a novel pH-sensitive intelligent film for monitoring minced beef freshness based on chitosan/sodium alginate (CS–SA) and coffee peel anthocyanin (CPA). The different CPA content effects on the internal structure, physical properties and pH sensitivity of the CS–SA films were investigated. The results showed low contents of CPA (≤2%) could be evenly distributed within the CS–SA matrix with good compatibility. The addition of CPA significantly improved the physical properties and pH sensitivity of the CS–SA films. The CS–SA film containing 2% CPA (CS–SA–CPA2) showed the best tensile strength, water vapour barrier performance and most noticeable colour change. Moreover, this film exhibited good colour stability after 120 days. The CS–SA–CPA2 film changed colour from light yellow to brown to dark brown during minced beef storage, successfully indicating freshness. Therefore, the CS–SA–CPA2 film has the potential to be a pH-sensitive material for monitoring minced beef freshness.     

Nanocellulose Reinforced Chitosan Composite Films as Affected by Nanofiller Loading and Plasticizer Content

ABSTRACT: Chitosan is a biopolymer obtained by N-deacetylation of chitin, produced from shellfish waste, which may be employed to elaborate edible films or coatings to enhance shelf life of food products. This study was conducted to evaluate the effect of different concentrations of nanofiller (cellulose nanofibers, CNF) and plasticizer (glycerol) on tensile properties (tensile strength—TS, elongation at break—EB, and Young's modulus—YM), water vapor permeability (WVP), and glass transition temperature (T_g) of chitosan edible films, and to establish a formulation to optimize their properties. The experiment was conducted according to a central composite design, with 2 variables: CNF (0 to 20 g/100 g) and glycerol (0 to 30 g/100 g) concentrations in the film (on a dry basis), which was produced by the so-called casting technique. Most responses (except by EB) were favored by high CNF concentrations and low glycerol contents. The optimization was based on maximizing TS, YM, and T_g, and decreasing WVP, while maintaining a minimum acceptable EB of 10%. The optimum conditions were defined as: glycerol concentration, 18 g/100 g; and CNF concentration, 15 g/100 g. AFM imaging of films suggested good dispersion of the CNF and good CNF-matrix interactions, which explains the good performance of the nanocomposite films. Practical Application: Chitosan is a biodegradable polymer which may be used to elaborate edible films or coatings to enhance shelf life of foods. This study demonstrates how cellulose nanofibers (CNF) can improve the mechanical and water vapor barrier properties of chitosan films. A nanocomposite film with 15% CNF and plasticized with 18% glycerol was comparable to some synthetic polymers in terms of strength and stiffness, but with poorer elongation and water vapor barrier, indicating that they can be used for applications that do not require high flexibility and/or water vapor barrier. The more important advantage of such films when compared to synthetic polymer films is their environmentally friendly properties.     

Thermomechanical properties of biodegradable films based on blends of gelatin and poly(vinyl alcohol)

The aim of this work was to study the effect of the poly(vinyl alcohol) (PVA) concentration on the thermal and viscoelastic properties of films based on blends of gelatin and PVA using differential scanning calorimetry (DSC) and dynamic-mechanical analysis (DMA). One glass transition was observed between 43 and 49 °C on the DSC curves obtained in the first scanning of the blended films, followed by fusion of the crystalline portion between 116 and 134 °C. However, the DMA results showed that only the films with 10% PVA had a single peak in the tan δ spectrum. However, when the PVA concentration was increased the dynamic mechanical spectra showed two peaks on the tan δ curves, indicating two T_gs. Despite this phase separation behavior the Gordon and Taylor model was successfully applied to correlate T_g as a function of film composition, thus determining k=7.47. In the DMA frequency tests, the DMA spectra showed that the storage modulus values decreased with increasing temperature. The master curves for the PVA–gelatin films were obtained applying the TTS principle (T_r=100 °C). The WLF model was thus applied allowing for the determination of the constants C₁ and C₂. The values of these constants increased with increasing PVA concentrations in the blend: C₁=49–66 and C₂=463–480. These values were used to calculate the fractional free volume of the films at the T_g and the thermal expansion coefficient of the films above the T_g.     

Nano-TiO2 particles and high hydrostatic pressure treatment for improving functionality of polyvinyl alcohol and chitosan composite films and nano-TiO2 migration from film matrix in food simulants

This study investigated the impact of nano-TiO₂ and high hydrostatic pressure (HHP) treatment on microstructure, water vapor and gas barrier, antibacterial and mechanical properties of polyvinyl alcohol (PVA)–chitosan (CHI) biodegradable films and determined the migration behavior of TiO₂ nanoparticles from the films to food simulants. Apart from the effect of filler, TiO₂ nanoparticles also could improve the antibacterial activity of the films and play a role as a plasticizer in the films. HHP treatment promoted the interaction between PVA and chitosan molecules, resulting in the formation of more compacted network structures in PVA–CHI films. The migration of TiO₂ from the films was investigated in food simulants including distilled water, acetic acid, ethanol and olive oil, in which the trace amount of TiO₂ (< 4.20 × 10^− 3‰) was only detected in olive oil. HHP treatment at 200–400 MPa significantly reduced migration of TiO₂ nanoparticles from the films.Industrial relevanceResults from this study provide a new application direction of high hydrostatic pressure (HHP) in the field of food packaging materials for improving the functionality of materials. Due to the non-thermal characteristic, HHP in combination with nano-TiO₂ not only improved the mechanical and barrier properties of the biodegradable PVA–CHI composite films (polyvinyl alcohol and chitosan based materials), but also enhanced the antibacterial activity of the films. The HHP treated PVA–CHI–TiO₂ films are very stable in food simulants, such as olive oils. Therefore, the utilization of HHP and nano-TiO₂ is promising in the preparation of food packaging materials with desirable functionalities.     

茶多酚改性对聚乙烯醇膜吸湿特性及抗氧化活性的影响

研究含不同质量分数茶多酚的聚乙烯醇膜的吸湿特性和抗氧化活性。通过等温吸湿实验研究了含不同质量分数茶多酚（0%、0.5%、1%、1.5%、2%）的聚乙烯醇膜的吸湿特性,并基于常用的等温吸湿模型对实验数据进行拟合表征;通过1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl,DPPH）自由基清除实验分析了薄膜的抗氧化活性。结果表明：含不同质量分数茶多酚的聚乙烯醇膜均具有吸湿性,其等温吸湿曲线整体变化趋势相似,属于Ⅱ型等温吸湿曲线;薄膜的平衡含水率随水分活度的增加而显著增加（P＜0.01）,当水分活度大于0.6时,其平衡含水率增加幅度增大;茶多酚对聚乙烯醇膜的改性增加了其疏水性,在相同水分活度条件下,薄膜的吸湿性能随薄膜中茶多酚质量分数的增加而下降,但5 种聚乙烯醇膜之间差异不显著（P＞0.05）;GAB等温吸湿模型对薄膜吸湿性能的拟合效果最好,R2≥0.996;茶多酚对聚乙烯醇膜的改性使其具有抗氧化活性,DPPH自由基清除率随着薄膜中茶多酚质量分数的增加而显著提高（P＜0.01）,表明经茶多酚改性后的聚乙烯醇膜的抗氧化性能随薄膜中茶多酚质量分数的增加而增强。经茶多酚改性的聚乙烯醇膜具有吸湿和抗氧化功能,预示其作为塑料复合薄膜内层或中间层应用于湿度敏感型、含高脂肪等干燥易氧化食品包装具有较好的前景。     

转谷氨酰胺酶改性明胶高强度薄膜的制备

在研究制备转谷氨酰胺酶（mTG）改性明胶可食性薄膜工作的基础上，通过在成型工艺中进一步采用室温干燥和湿态二次定向处理的方法，获得了抗张强度达18．3MPa，韧度达8．4J／cm^2的可食性明胶薄膜。在配料中添加质量分数2％的聚乙烯醇（PVA）并采用相同的成型工艺，所制备明胶薄膜的机械性能得到进一步提高。生物降解性实验表明，在被质量分数0．5％的Alcalase碱性蛋白酶作用4h后，不含PVA的可食性明胶薄膜的降解率可达99．2％，含PVA明胶薄膜的降解率也达到了97．5％。     

Development of moisture‐absorbing and antioxidant active packaging film based on poly(vinyl alcohol) incorporated with green tea extract and its effect on the quality of dried eel

Active packaging film with functions of moisture‐absorbing and antioxidant activity was developed based on poly(vinyl alcohol) (PVA) incorporated with green tea extract (GTE). The effects of GTE concentrations of 0, 0.5, 1, 1.5, and 2% on the physical, structural, and antioxidant properties of PVA films were investigated. The PVA film containing 2% GTE had lower moisture absorbing efficiency relatively and better antioxidant activity through DPPH radical‐scavenging ability experiment. A packaging system of GTE‐incorporated PVA films was applied to package dried eel and quality of dried eel was evaluated during storage. The result showed that dried eel packed with GTE‐incorporated PVA films showed lower weight change, peroxide value and TBARS value during storage than that packed without PVA films or with PVA films but no GTE. The PVA film containing 2% GTE showed the best quality protective effectiveness to prevent the dried eel from absorbing moisture and oxidizing of lipid.

Practical applications

Poly(vinyl alcohol) (PVA) is a synthetic polymer that is widely used in packaging applications because of its excellent film forming, biodegradability, good mechanical, and gas barrier properties. The present study evidenced that the PVA films incorporated with GTE showed good quality protective effectiveness to prevent the dried eel packed with these films from absorbing moisture and oxidizing of lipid. This active packaging film could be used as inner layer or intermediate layer in the composite packaging film system to improve the storage quality of moisture‐sensitive and high‐fat food. Based on this concept, the moisture‐absorbing agents and antioxidant can be incorporated into the packaging structures to develop an active multifunctional food packaging material potentially to remove or reduce moisture inside the food packaging system instead of desiccants and preservative added in the food.     

Nanocomposite Edible Films from Mango Puree Reinforced with Cellulose Nanofibers

ABSTRACT:  Cellulose nanoreinforcements have been used to improve mechanical and barrier properties of biopolymers, whose performance is usually poor when compared to those of synthetic polymers. Nanocomposite edible films have been developed by adding cellulose nanofibers (CNF) in different concentrations (up to 36 g/100 g) as nanoreinforcement to mango puree based edible films. The effect of CNF was studied in terms of tensile properties, water vapor permeability, and glass transition temperature ( T _g) of the nanocomposite films. CNF were effective in increasing tensile strength, and its effect on Young's modulus was even more noticeable, especially at higher concentrations, suggesting the formation of a fibrillar network within the matrix. The addition of CNF was also effective to improve water vapor barrier of the films. Its influence on T _g was small but significant. The study demonstrated that the properties of mango puree edible films can be significantly improved through CNF reinforcement.     

正交设计法优化大豆分离蛋白膜工艺参数

该文以大豆分离蛋白(SPI)为主要原料,添加甘油制成可食性膜,研究成膜介质和成膜方法对膜性能影响;并比较酸性和碱性条件下可食性膜性能,选择出最佳成膜工艺参数。酸性条件下为:蛋白质与甘油比例为2:1、pH为3、温度80℃、底物浓度8%;碱性条件下为:蛋白质与甘油比例为3:1、pH为10、温度90℃、底物浓度10%。