Physical and antioxidant properties of chitosan and methylcellulose based films containing resveratrol

New trends in edible films focus on the improvement of their functionality through the incorporation of active compounds, such as antimicrobial or antioxidant agents. Resveratrol is a natural antioxidant found in a variety of plant species, such as grapes, and could be used for minimizing or preventing lipid oxidation in food products, retarding the formation of oxidation products, maintaining nutritional quality and prolonging the food shelf life. The aim of this work was to develop and characterize two different polymeric composite films (made with chitosan (CH) and methylcellulose (MC)) containing different amounts of resveratrol. This compound could be incorporated efficiently into both films, but provoke structural changes in the matrices, which became less stretchable (65–70% reduction of deformation at break at the greatest resveratrol content) and resistant to fracture (26 and 54% reduction of tensile at break for MC and CH, respectively, at the greatest resveratrol content) more opaque (significant reduction of the internal transmittance) and less glossy (about 60–65% reduction of gloss at the greatest resveratrol content). Film barrier properties were hardly improved by the presence of resveratrol; water vapour and oxygen permeability tend to slightly decrease when resveratrol was incorporated into both polymers. Composite films showed antioxidant activity, which was proportional to the resveratrol concentration in the film. None of the films showed antimicrobial activity against Penicillium italicum and Botrytis cinerea. Thus, these films could be applied to food products which are sensitive to oxidative processes to prolong their shelf life.     

高直链玉米淀粉/羟丙基甲基纤维素可食性膜的制备及性能研究

以高直链玉米淀粉(HACS)和羟丙基甲基纤维素(HPMC)为主要成膜基材,采用溶液流延法制备了HACS/HPMC可食性膜。研究了不同配比的HACS与HPMC对可食性膜的结晶性能、力学性能、亲水性能和水蒸气阻隔性能等的影响。结果表明,随着HPMC比例的增大,HACS与HPMC之间的氢键作用减弱,复合膜的水溶性增大,连续相由HACS转变为HPMC,但HACS与HPMC的相容性变差。HPMC可有效降低可食性膜的结晶程度并抑制其在储藏过程中的老化。在复合膜中,当HACS与HPMC比例为8∶2时,可食性膜具有最大抗拉强度(7.5 MPa)、断裂伸长率(14.7%)、水接触角(84.33°)和最低水蒸气透过系数(2.17×10~(-10 )g·m·m~(-2)·s~(-1)·Pa~(-1))。纯HACS膜和纯HPMC膜的透光性能均优于HACS/HPMC复合膜。     

Effect of surfactants and drying rate on barrier properties of emulsified edible films

The effects of globule size, nature and concentration of surfactant, and drying duration of water vapour transmission rate and tensile strength of emulsified edible barriers containing methylcellulose and paraffin wax, were measured. of the six surfactants tested, 0.6% purified glycerol monostearate (GMS) produced films with the lowest water vapour transmission rates and the highest mechanical resistance. Longer drying times of film-forming emulsions produced better barrier and mechanical properties. Control of the film forming emulsion stability allowed the reduction of the water vapour transfer rate by an order of magnitude.     

Using polysaccharide-based edible coatings to enhance quality and antioxidant properties of fresh-cut melon

The effect of alginate, pectin and gellan-based edible coatings on the shelf-life of fresh-cut ‘Piel de Sapo’ melon was investigated. Gas exchange, antioxidant properties, color, firmness, sensory quality and microbial growth of fresh-cut melon were studied during 15 days at 4 °C. Gellan, pectin and alginate coatings increased the water vapor resistance of fresh-cut melon, thus preventing dehydration. They also had an inhibitory effect on ethylene production although O₂ and CO₂ diffusion through coated melon tissue was not avoided. Calcium chloride used as a crosslinking agent helped to maintain fruit firmness. Edible coatings themselves did not improve microbiological stability of fresh-cut ‘Piel de Sapo’ melon packaged under passive modified atmosphere. Pectin or alginate could reduce the wounding stress induced in fresh-cut melon, which triggered an accumulation of total phenolic compounds and other compounds with antioxidant properties. In addition, pectin-based coating seemed to best maintain sensory attributes.     

Effectiveness of chitosan edible coatings to improve microbiological and sensory quality of fresh cut broccoli

The effects of chitosan edible coating on microbiological and sensory quality of refrigerated broccoli were studied. The antimicrobial effects of chitosan on the native microflora (mesophilic, psychrotrophic, yeast and molds, lactic acid bacteria and coliforms) and on the survival of E. coli O157:H7 inoculated in broccoli were evaluated.Chitosan treatments resulted in a significant reduction in total mesophilic and psychrotrophic bacteria counts with respect to the control samples during the entire storage period. There was an immediate decontaminating activity of chitosan. At the end of the storage, yeast and molds was the most dominant flora representing the largest part of the total aerobic counts. Lactic acid bacteria (LAB) numbers remained relatively low during the whole storage in all samples. Chitosan coating inhibited the growth of total coliform throughout the storage time. Also, chitosan treatments resulted in a bactericidal effect on E. coli endogenous and a significant decreased in total E. coli counts (endogenous and O157:H7). The application of chitosan coating on fresh cut broccoli inhibited the yellowing and opening florets. The results of this experiment showed that the use of chitosan coating is a viable alternative in controlling the microorganisms present in minimally processed broccoli, improving its sensory quality.     

Influence of calcium on tensile, optical and water vapour permeability properties of sodium caseinate edible films

The influence of calcium on sodium caseinate edible films with and without lipid addition (oleic acid (OA)–beeswax (BW) mixtures) was investigated through the analysis of tensile, optical and water vapour barrier properties. Calcium was added by substitution of sodium caseinate by calcium caseinate. Calcium caseinate films have less transparency and more rigidity but they have lower water vapour permeability values than sodium caseinate films. The effect of substitution was different for films with and without lipids. Calcium caseinate increased tensile strength and decreased elongation of films, depending on the level of substitution and lipid presence. Among control films (without lipid), water vapour permeability was reduced when calcium caseinate was present, reaching values of 3.9 (±0.2) g mm kPa⁻¹ h⁻¹ m⁻². Nevertheless, in the films containing lipids, this reduction was inhibited when the level of sodium caseinate substitution exceeded 50%. Film transparency and gloss was reduced by calcium caseinate and lipid presence, although pure calcium caseinate films were glossier. When taking all the studied variables into account, the films prepared with 2:1 NaCas:CaCas ratio and 70:30 OA:BW ratio showed the most adequate properties.     

Physical properties of edible coatings and films made with a polysaccharide from Anacardium occidentale L.

The effect of the concentrations of the polysaccharide from Anacardium occidentale L. (Policaju) and a surfactant (Tween 80) on relevant properties of edible coatings/films, in view of their application on apples (cv. Golden) was evaluated. The influence of the interactions between those two constituents on apples’ surface properties and on the coating/film’s wettability, water vapor permeability, opacity and mechanical properties was evaluated. The effects of the studied variables (polysaccharide and surfactant concentrations) were analyzed according to a 2² factorial design. Pareto bar charts were used to understand the most significant factors on the studied properties. The addition of surfactant reduced the cohesion forces, therefore reducing the surface tension and increasing the wettability; this resulted in an improved compatibility between the solution and the fruit skin surface. The opacity was also reduced. The results of each of the analyzed properties were adjusted to a polynomial, multifactor model, which provided a good fitting accuracy. This model is important once it will reduce the characterization work needed in subsequent applications of these coatings/films on foods.     

Effect of beeswax content on hydroxypropyl methylcellulose-based edible film properties and postharvest quality of coated plums (Cv. Angeleno)

The effect of beeswax (BW) content of hydroxypropyl methylcellulose (HPMC)–BW edible coatings on stand-alone film properties and on postharvest quality of coated ‘Angeleno’ plums was studied. The coatings contained BW at 4 lipid content levels (0, 20, 40 and 60 g/100 g, dry basis). Coated and uncoated plums were stored 4 weeks at 1 °C and transferred to 20 °C for 1–3 weeks. Addition of BW to the HPMC film matrix reduced film mechanical resistance and oxygen barrier, and improved film moisture barrier. Film mechanical properties showed a good fit with an exponential and/or linear model that could provide a useful tool to predict mechanical properties with others HPMC–BW composition mixtures. Coatings with BW reduced plum weight loss compared to HPMC-based coatings with no BW. Plum weight loss decreased as BW content increased from 20 to 40 g/100 g, but above 40 g/100 g BW content, weight loss was not further reduced. Whereas, water vapor permeability of stand-alone films decreased significantly as BW content increased to 60 g/100 g. Coatings reduced plum softening and bleeding, with those with lower BW content being more effective, which could be related to the ability of coatings to create a modified atmosphere in the fruit. Flavor was not affected by coating application. Results indicate that HPMC–BW coatings with 20 g/100 g BW would provide the best compromise to extend shelf life of ‘Angeleno’ plums.     

Stability, solubility, mechanical and barrier properties of cassava starch - Carnauba wax edible coatings to preserve fresh-cut apples

This work aimed at evaluating edible coatings/films formulated with cassava starch, glycerol, carnauba wax and stearic acid, analyzing the stability of emulsion (creaming index and lipid particle size), the barrier properties of coatings applied in fresh-cut apples (respiration rate and water vapor resistance), the solubility and mechanical properties of films prepared with coating solutions. A central composite rotatable design 2³ was used to select optimized formulation. Independent variables used were: cassava starch concentration (2-4% w/w), glycerol content (1-3% w/w) and carnauba wax: stearic acid ratio (0.0:0.0-0.4:0.6% w/w). The creaming index and the lipid particle size of emulsified coatings were strongly affected by the carnauba wax: fatty acid ratio. Glycerol content was the variable that most influenced the respiration rate of coated apple slices, water vapor resistance of coatings and the elastic modulus of films. The water solubility was positively affected by the cassava starch and glycerol contents. Models and response surfaces were obtained for the respiration rate, water vapor resistance of coatings, elastic modulus and solubility of films. According to statistical analysis results, the optimized conditions corresponded to 3.0 g of cassava starch/100 g of coating solution, 1.5 g of glycerol/100 g of coating solution, 0.2:0.8 g of carnauba wax: stearic acid ratio/100 g of coating solution. The models obtained in the experimental design were predictive, which was evidenced by the relative deviations below 10% in validation procedure.     

Evaluation of antimicrobial and physical properties of edible film based on carboxymethyl cellulose containing potassium sorbate on some mycotoxigenic Aspergillus species in fresh pistachios

Active packaging is a relatively novel concept of packaging that changes the conditions of the packaged food to extend its shelf-life and improve its safety. In this study, antimicrobial effects of carboxymethyl cellulose based-edible film containing potassium sorbate as an antimicrobial agent were studied against Aspergillus flavus (PTCC-5004), Aspergillus parasiticus (PTCC-5286) and A. parasiticus (PTCC-5018) by using agar diffusion assay. Results showed suitable inhibition effects against A. parasiticus (PTCC-5286) and A. flavus (PTCC-5004) in comparison with A. parasiticus (PTCC-5018). Pistachios were coated with this edible antimicrobial film containing three concentrations of sorbate (1, 0.5 and 0.25 g/100 mL film solution); all concentrations showed no growth of molds. Tensile strength values of films with potassium sorbate, decreased when compared to control, and film’s flexibility, was 28.82 percent for 3 g/100 mL sorbate, while higher concentration of sorbate, decreased the flexibility. The water vapor permeability values (WVP) of films were determined to be 1.18 (g mm/m² day kPa) for films plasticized with glycerol, without sorbate while WVP values for the films containing 1 and 2 g/100 mL sorbate increased to 3.77 and 15.5 (g mm/m² day kPa), respectively. The observed glass transition temperature (T_G) depression for these polymer blends was related to the plasticizer content (water, polyethylene, and glycerol), especially water.