Properties of nisin‐incorporated polymer coatings as antimicrobial packaging materials

Nisin was incorporated into binder solutions of acrylic polymer and vinyl acetate‐ethylene co‐polymer, and then coated on to paper. Diffusive migration of incorporated nisin and the antimicrobial activity of the polymer coatings were investigated in order to understand the way of controlling nisin migration and the extent of microbial suppression by the coated paper. Vinyl acetate–ethylene co‐polymer exhibited a faster rate and higher degree of migration into aqueous food simulant solutions compared to acrylic polymer, and also exhibited a higher degree of suppression against Micrococcus flavus ATCC 10240 inoculated into the microbial medium. Addition of NaCl, sugar and citric acid to water significantly reduced the rate of diffusion of nisin in the case of acrylic polymer, while only slight change was observed due to the additive for vinyl acetate‐ethylene co‐polymer. The simulant type slightly affected the equilibrated migration level of nisin. When the nisin‐incorporated coatings were in contact with pasteurized milk and orange juice at 10°C, significant suppression of total aerobic bacteria and yeasts was observed without any noticeable difference between the two types of coatings. Copyright © 2002 John Wiley & Sons, Ltd.     

Multilayered antimicrobial polyethylene films applied to the packaging of ground beef

A natural antimicrobial agent, grapefruit seed extract (GFSE), was incorporated in a 0.5% or 1.0% concentration on the food‐contact surface of multilayered polyethylene (PE) film by a co‐extrusion or solution‐coating process. The fabricated films were tested in their antimicrobial activity against several food spoilage microorganisms, and then applied to the packaging of ground beef. During the storage of the packaged beef at 3°C, changes in microbial counts, pH, TBA value and meat colour were monitored in order to see the effect of the packaging film on meat quality changes. Coating the PE film with GFSE with the aid of a polyamide binder resulted in a more effective level of antimicrobial activity on the agar plate medium than did its incorporation by a co‐extrusion process. The film co‐extruded with a 1.0% GFSE layer showed antimicrobial activity only against Micrococcus flavus ATCC 10240, while the film coated with 1.0% GFSE showed activity against several microorganisms, such as Escherichia coli IFO 3301, Staphylococcus aureus IFO 3060 and Bacillus subtilis IFO 12113. Both types of GFSE‐incorporated multilayer PE films contributed to a reduction of the growth rates of aerobic and coliform bacteria on the ground beef, when compared to plain PE film. The film coated with a higher concentration (1.0%) of GFSE had a more pronounced effect than did the other films in inhibiting spoilage bacterial growth. They could also slow down chemical changes of the packaged beef. The GFSE‐coated film was more effective in preserving beef quality, but the level of GFSE addition did not affect the quality changes of the beef. Copyright © 2001 John Wiley & Sons, Ltd.     

Antimicrobial activity of chitosan attached to ethylene copolymer films

Ethylene copolymer film was coated with chitosan by attachment of the polymer to the corona‐treated surface of the film, and the composite film was analysed for antimicrobial activity. The film was active against bacteria in 0.625 mM phosphate buffer; it reduced colony counts of Escherichia coli 25922 and of Listeria monocytogenes Scott A by 5 and 2–3 log₁₀, respectively after 24 h exposure. The activity of the chitosan‐coated film against bacteria in buffer was increased when silver ions were incorporated into the films as demonstrated by complete killing of Escherichia coli O157:H7 DD3795 and the chicken exudate isolate Stenotrophomonas maltophilia within 2 h in buffer. The film was active against L. monocytogenes Scott A in 0.5% buffered peptone water up to a pH of about 7.0. Tests on beef and chicken meat exudates revealed antimicrobial activity of the film against Escherichia coli O157:H7 and L. monocytogenes Scott A of about 2 and 1–2 log₁₀ reductions in colony‐forming units, respectively. The antimicrobial activity of the film against L. monocytogenes Scott A was also tested on turkey breast, and a log₁₀ reduction of about 1.7 log₁₀ units after 10 days and 1.2 log₁₀ after 15 days at 4°C was achieved. Exposure to chitosan‐coated film and 350 MPa of pressure, 55°C or 1% sodium diacetate resulted in a synergistic effect. Copyright © 2008 John Wiley & Sons, Ltd     

Effectiveness of barrier film with a cellulose coating that carries nisin blends for the inhibition of listeria monocytogenes

The objective of this study was to determine the effectiveness of two nisin blend antimicrobial agents (Guardian NR 250, Novagard CBI) incorporated into a cellulose coating that was applied onto a barrier film against Listeria monocytogenes. The minimum inhibitory concentration (MIC) of the agents in solution against L. monocytogenes was found to be 2.74 mg/ml for the two nisin blends. The concentrations tested for both nisin blend treatments were 5.49, 10.9, 16.4 and 21.9 mg/ml. Guardian NR 250 resulted in wider zones of inhibition compared to the Novagard CBI at all levels tested. The MIC for Guardian NR 250 in the film was 5.49 mg/ml. Films containing Novagard CBI did not show any antimicrobial activity. A food challenge study was conducted using the film containing Guardian NR 250 at levels of 5.49 and 21.9 mg/ml. Inoculated fresh beef cubes were individually packaged with pre‐made barrier film pouches that had an interior cellulose coating containing the antimicrobial agent and stored at 4°C for 36 days. Bacterial colonies were enumerated every 6 days on modified Oxford agar. There was no significant difference in the L. monocytogenes population between two levels of Guardian NR 250 throughout the study. There was statistically significant inhibition of L. monocytogenes for both levels of Guardian NR 250 during 18–30 days of storage compared to a control film without the antimicrobial agent. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of chitosan coating and vacuum packaging on the quality of refrigerated grilled pork

The effects of chitosan coating and vacuum packaging on the quality and shelf‐life of retail packaged grilled pork in a PVDC/nylon pouch during refrigerated storage at 2 ± 1°C were investigated. Grilled pork without chitosan coating and packaged in 100% air was used as the control sample. Firmness, pH, colour, peroxide values, microbial population and shelf‐life (as determined by sensory characteristics) of the samples were determined during the storage. The results showed that colour, peroxide values and microbial population coincided with sensory characteristics. The delayed growth of microbes in vacuum packaging can be attributed to inhibition by low levels of O₂. Chitosan coating was shown to minimize oxidation, as reflected by the peroxide values, colour changes and microbial counts of the samples. Vacuum‐packaged chitosan‐coated grilled pork showed negligible microbial growth and was found to be organoleptically acceptable throughout the storage period. Chitosan coating along with vacuum packaging provided a type of active packaging to maintain quality and extend the shelf‐life of grilled pork. Copyright © 2006 John Wiley & Sons, Ltd.     

Properties of polysaccharide‐coated polypropylene films as affected by biopolymer and plasticizer types

Plasticized polysaccharide coatings on polypropylene (PP) film were prepared to evaluate the optical and tensile properties of the resulting coated films, as affected by biopolymer and plasticizer types, in order to develop a novel film structure of biopolymer coatings on common plastics intended for food packaging applications. Composite structures of PP film coated with several kinds of polysaccharides (MC, HPMC, chitosan, κ ‐carrageenan, dextrin) and plasticizers (PG, glycerol, PEG, sucrose, sorbitol) were obtained through a simple casting method. High glossy surfaces were observed on the coated films with chitosan and κ ‐carrageenan, with the sucrose‐plasticized chitosan coating giving the highest gloss of 142.7 GU. Biopolymers, but no plasticizers, exerted noticeable influence on the colour of the coated films. Chitosan‐ and κ ‐carrageenan‐coated PP films also showed greater transparency, tensile strength and elongation than the other coated films. Nisin‐incorporated κ ‐carrageenan coatings on PP film exhibited significant bacterial growth inhibition against Lactobacillus plantarum . The results suggest that coatings based on chitosan and κ ‐carrageenan with proper plasticizers possess excellent visual and mechanical characteristics and have great potential for acting efficiently as antimicrobial agent carriers in active packaging systems. Copyright © 2004 John Wiley & Sons, Ltd.     

Active wrapping paper against mango anthracnose fungi and its releasing profiles

Active wrapping papers varied in bio‐based coating materials (chitosan and carboxymethyl cellulose) and vanillin concentrations (0.5%, 1.0%, 2.0%, and 4.0% (w/v)) were prepared to study their antifungal effects and release properties. Chitosan‐coated paper with 1% (w/v) vanillin gave the best inhibition against mycelial growth of mango anthracnose fungi and could inhibit its conidiospores germination. The release of vanillin from a chitosan‐coated paper under different conditions of temperatures (13°C, 25°C, and 37°C), relative humidity (RH) (75%, 86%, and 96% RH), and pH values (pH 3.8, 5.2, and 6.2) was studied. Moreover, the vanillin release from the paper to mango fruit under an actual commercial storage condition (13°C, 90% RH) was also investigated. The predominant mechanism of vanillin release under low temperatures (13‐25°C) and all RH studied was a Fickian diffusion, whereas the high temperature (37°C) and in all buffers varying pH showed a non‐Fickian behaviour. Increasing temperature and RH enhanced in diffusion coefficient (D value) from 78.24 × 10^?10 to 162.10 × 10^?10 cm²/s and 42.87 × 10^?10 to 59.98 × 10^?10 cm²/s, respectively. Meanwhile, the increasing pH value reduced the D value from 233.87 × 10^?10 to 122.74 × 10^?10 cm²/s. The kinetic of vanillin release under an actual wrapping application exhibited a non‐Fickian behaviour, and the D value was considerably low (approximately 65.36 × 10^?12 cm²/s). The developed active wrapping paper can be great interest for food industry and is practically reasonable for postharvest mango fruits.     

Silicon Migration from High‐barrier Coated Multilayer Polymeric Films to Selected Food Simulants after Microwave Processing Treatments

The use of microwave (MW) technology for in‐package food sterilization and pasteurization has the potential for widespread use in the food industry. Because the use of MW technology requires that food be processed inside its packaging, the interaction between food and its packaging during processing must be studied to ensure package integrity as well as consumer safety. In this study, two commercially available multilayer films developed for retort sterilization were evaluated for their suitability to MW processing. Film A was composed of oriented nylon//coated polyethylene terephthalate//cast polypropylene (CPP); film B consisted of oriented nylon//coated nylon//CPP with overall oxygen transmission rates <0.2 cc/m². day. Silicon (Si) was a major component in the coated polyethylene terephthalate layer and food‐contact CPP layer. This study evaluated the influence of MW processing on Si migration from films into selected food‐simulating liquids (FSLs; water and 3% acetic acid) using inductively coupled plasma‐mass spectroscopy, as compared with conventional thermal processing. This study also assessed migration of Si into FSL in terms of process temperature (70–123 °C) and time (18–34 min). A Fourier transform infrared spectrometer was used to evaluate the stability of the silicon–oxygen (Si–O) bonds in the metal‐oxide coated and food‐contact layer of the packaging film. Overall, there were no significant differences (p > 0.05) between the level of Si migration from films to FSL and the stability of Si–O–Si bonds during MW processing as compared with the conventional thermal processing. However, we found that the final processing temperature and time had a significant (p < 0.05) impact on Si migration into the FSL. Copyright © 2013 John Wiley & Sons, Ltd.     

Tyrosinase‐catalysed grafting of food‐grade gallates to chitosan: surface properties of novel functional coatings

Plasma‐activated biaxially oriented polypropylene (BOPP) films and paper substrate have been coated with functional chitosan solutions. Plasma treatment increased the amount of surface peroxide groups and carboxyl groups on the BOPP films. As a result of plasma activation, the surface energy increased from 30 to 50 dynes/cm. The enzyme tyrosinase catalysed the grafting of octyl gallate and dodecyl gallate to amino groups of chitosan polysaccharide. Resulting coatings exhibited strong antimicrobial activity against Gram‐positive Staphylococcus aureus and Gram‐negative Listeria innocua. After 24 h of incubation, a total reduction in both bacteria cell numbers varied between >4.9 and 1.4 logarithmic units. Grafted dodecyl gallate and octyl gallate at pH 6 were found to have the lowest reduction values of <3 logarithmic units for S. aureus, while 1.4 logarithmic reduction value was obtained for grafted dodecyl gallate at pH 6 against L. innocua. Chitosan coatings were also effective barrier layers against oxygen transmission although the transmission rates clearly increased in high‐humidity conditions. In dry conditions, however, the transmission rate of 2 cm³/(m² · 24 h) was obtained with chitosan‐coated BOPP. Coatings did not have any effects on water vapour transmission. Both gallates were successfully grafted at pH 6. As increased flocculation and colour formation indicated, the tyrosinase‐catalysed grafting was more powerful with octyl gallate. Dodecyl gallate containing chitosan coatings was more hydrophobic as compared to octyl gallate. Total migration of substances into 95% ethanol was ≥5 mg/dm², thus materials may be exploitable in packaging purposes in direct contact with certain foodstuffs. Copyright © 2008 John Wiley & Sons, Ltd.     

Efficacy of chitosan‐coated paper incorporated with vanillin and ethylene adsorbents on the control of anthracnose and the quality of Nam Dok Mai mango fruit

Mango fruit is perishable and susceptible to anthracnose. Active‐coated paper is proposed as potential packaging for commercial application in wrapping mango fruit to control anthracnose and delay the ripening process of fruit. The surface of white standard bleached paper was coated using a vanillin‐chitosan coating solution containing varying amounts of zeolite or activated carbon at 0% (vanillin paper), 0.1%, 0.2%, and 0.4%, w/v of ethylene absorbers. The first objective was to study the effect of absorber types and their amounts on ethylene removal. After that, the coating formulation that provided the highest ethylene removal was selected to wrap commercial Nam Dok Mai mango fruit to study the quality changes. The efficacy of active‐coated paper on the severity index of anthracnose disease, change in physicochemical properties, and sensory acceptability during storage (13°C, 90% relative humidity (RH) for 30 days) were investigated. It was found that vanillin‐chitosan coated paper containing 0.2% (w/v) of zeolite (zeolite paper) exhibited the highest capacity of ethylene adsorption. Zeolite paper could delay the disease incidence of wrapped mango fruit and provided the lowest severity index of anthracnose disease throughout storage. Moreover, changes in physicochemical qualities (weight loss, firmness, titratable acidity, total soluble solid, and color) of mango fruits wrapped in zeolite paper was quite low, compared with those wrapped with vanillin and uncoated papers. In addition, mango wrapped by zeolite paper had the highest sensory acceptance score. The results suggest that zeolite paper can efficiently be applied as wrapping to extend the postharvest life of mango fruit.     

Packaging‐related properties of protein‐ and chitosan‐coated paper

The mechanical and gas‐barrier properties of paper and paperboard coated with chitosan–acetic acid salt (chitosan), whey protein isolate, whey protein concentrate and wheat gluten protein were studied. Paper sheets were solution‐coated using a hand applicator. In addition, bi‐layer composites of wheat gluten and paper or paperboard were produced by compression moulding, and the chitosan solution was also applied on paperboard using curtain coating. Young's modulus, fracture stress, fracture strain, tearing strength, air permeance and oxygen permeability were assessed. The mechanical and air permeance measurements of solution‐coated paper showed that chitosan was the most effective coating on a coat weight basis. This was due to its high viscosity, which limited the degree of penetration into the paper. The proteins, however, also enhanced the strength and toughness of the paper. Compression‐moulded wheat gluten/paper or paperboard, as well as curtain‐coated chitosan paperboard laminates, showed oxygen barrier properties comparable to those of paper and paperboard coated with commercial barrier materials. None of the composites could be delaminated without fibre rupture, indicating good adhesion between the coatings and the substrates. Copyright © 2005 John Wiley & Sons, Ltd.     

Properties of antimicrobial plastics containing traditional food preservatives

Traditional food preservatives, sodium benzoate, sodium nitrite, potassium sorbate and sodium lactate, were incorporated into synthetic plastics, low‐density polyethylene (LDPE), poly(maleic acid‐co‐olefine), polystyrene (PS) and polyethylene terephthalate (PET), aimed at producing antimicrobial packaging material for foodstuffs. The study was undertaken on plaques (thickness 2 mm) and films (thickness 70–120 µm), whose antimicrobial test results clearly differed. Plaques containing 15% sodium nitrite inhibited both Aspergillus niger and Bacillus subtilis, whereas the same concentration of sodium benzoate and potassium sorbate had activity only against B. subtilis. Sodium lactate‐containing samples did not have any antimicrobial activity and none of the samples inhibited Escherichia coli. Antimicrobial substances added into PS and PET produced the strongest activities; however, due to the brittle structure of these materials, they were not tested further. Thus, more thorough tests for antimicrobial activity, migration and oxygen and water vapour permeability were carried out using LDPE films with 2.5–15% sodium benzoate and sodium nitrite. The effects of both substances on permeability properties were negligible. Although the total migration into food simulants measured from the films in many cases exceeded the limit value of 10 mg/dm², no antimicrobial activity was observed. Copyright © 2003 John Wiley & Sons, Ltd.     

Effect of Antimicrobial Starch Edible Coating on Shelf‐Life of Fresh Strawberries

Strawberry is a very sensitive fruit and presents a short post‐harvest shelf‐life. Among the factors responsible for strawberries' quality loss are high metabolic activities and mold decay. To increase product shelf‐life, cassava starch–based edible coatings (3%), added or not with potassium sorbate (0.05%), were applied on minimally processed strawberries. Uncoated minimally processed strawberries were used as control samples. Physical and chemical properties, respiration rate and sensorial acceptance of uncoated and coated strawberries stored up to 15 days at 5°C were monitored. The results showed that coatings had no significant effect on soluble solids, titrable acidity, pH and colour of strawberries. Besides reducing the respiration rate of samples, cassava starch edible coatings were efficient in delaying weight and firmness loss of strawberries during storage. In the studied conditions, potassium sorbate was not efficient in controlling microbial growth. Strawberries coated with cassava starch without the antimicrobial agent showed good conditions for consumption and good sensorial acceptance up to 12 days of storage, whereas the control samples and the samples treated with the coating containing potassium sorbate achieved a shelf‐life of 9 days because of microbial spoilage. Copyright © 2011 John Wiley & Sons, Ltd.     

Migration of Tinuvin P,a UV stabilizer,from PET bottles into fatty‐food simulants

Tinuvin P migration from Polyethyleneterephthalate (PET) bottles was investigated using several fatty‐food simulants such as olive oil, soybean oil, n‐heptane and iso‐octane, at exposure conditions of 2–10 days at 40°C (total immersion). The stability of several UV stabilizers (BHT, Cyasorb UV 5411, Tinuvin P, Tinuvin 326 and Tinuvin 327) in n‐heptane and iso‐octane was also studied. After 10 days at 40°C, losses of 6% and 10% in iso‐octane and n‐heptane respectively, were verified for Tinuvin P. Other UV stabilizers at the same experimental conditions showed higher losses (up to 30% for Tinuvin 327). These results confirm that, when carrying out specific migration studies, the stability of the substance of interest should be established in the food simulant to avoid underestimating the real migration behaviour. In order to quantify UV stabilizer migration, n‐heptane and iso‐octane solutions were concentrated and directly analysed by SIM mode GC–MS. For olive and soybean oils, Tinuvin P was isolated using size‐exclusion chromatography and quantified by SIM mode GC–MS. Iso‐octane proved to be a more suitable fatty‐food simulant than n‐heptane for the migration study of Tinuvin P from PET. Higher levels of Tinuvin P migrated to olive and soybean oils rather than to n‐heptane. These results suggest that the MERCOSUL recommended official methods for specific migration studies should be revised, since the migration levels using n‐heptane as a fatty‐food simulant could be underestimated when compared to edible oils. Copyright © 1999 John Wiley & Sons, Ltd.     

Grease Penetration and Browning Resistance of Pulpboard and Paperboard Coated with Whey Protein

Whey protein concentrate (WPC) was explored alone and in combination with sucrose (Suc) plasticizer as a grease‐barrier coating for bulrush pulpboard and solid bleached sulfate paperboard used in food packaging. WPC‐coated and WPC : Suc‐coated pulpboards showed better oil‐barrier properties compared with untreated, water‐treated or Suc‐coated pulpboards. Coating formulations with 10% WPC, without and with Suc, resulted in oil barriers comparable with commercial fluorinated hydrocarbon for pulpboard. When pulpboard trays containing cheesy pasta were microwave‐heated, 10% WPC : 20% Suc solution‐coated trays showed grease barrier property comparable with fluorinated hydrocarbon‐treated trays. Caramelization and Maillard browning of WPC and WPC : Suc coatings were initiated at 300°F, but microwave‐heated foods do not normally reach this high temperature. Paperboard with 10% WPC : 20% Suc solution coating had oil barrier comparable with polyethylene‐coated paperboards. WPC : Suc solution mixture at 2.5% : 5% and 3.3% : 7% were determined as the solution concentration minima for 4 and 24 h tests, respectively. HunterLab colorimeter L and b values indicated slight colour change of the paperboard coated with the higher WPC concentration solutions. Coating resulted in thicker paperboards but not in a linear manner. The 10% WPC : 20% Suc solution‐coated solid bleached sulfate paperboards on which slabs of butter sat in a refrigerator did not show any butterfat penetration, comparable with polyethylene‐coated paperboards and unlike uncoated paperboards that showed poor butterfat‐barrier properties. WPC : Suc coating was shown in this study to have potential to replace synthetic materials as a grease barrier. Copyright © 2011 John Wiley & Sons, Ltd.     

Extruded Blends of Chitosan and Ethylene Copolymers for Antimicrobial Packaging

Chitosan was melt‐processed with an ethylene methyl acrylate copolymer ionomer and with an ethylene vinyl acetate copolymer to create antimicrobial extruded films. The key to obtaining a successful antimicrobial blend was the use of solid chitosonium acetate that remained after evaporation of water from the chitosan solution. When solid free‐flowing powders of chitosonium acetate were formed by spray drying chitosan solutions, blended in an extruder (at 2.5% and 4% chitosan) with Elvax® 3175 ethylene vinyl acetate copolymer, and extruded through a film die onto a chill roll to form films, the films exhibited antimicrobial activity against Escherichia coli 25922, Salmonella enterica serovar Enteritidis Nal^R, and Listeria monocytogenes Scott A. The log₁₀ reductions in CFU/ml after 24 h in a shake‐flask test were near 2 for films containing 4% chitosan. This melt‐blending/extrusion approach is expected to open applications for chitosan‐based antimicrobial packages and articles that were impossible or impractical with chitosan coatings. Copyright © 2011 John Wiley & Sons, Ltd.     

Understanding the effects of various edible coatings on the storability of fresh cherry

n this work, cherries, which have a very short shelf life, were packaged after being coated with various edible coatings [whey protein isolate (WPI), chitosan and shellac]. The changes in gas composition, weight loss, Brix, pH, electrical conductivity and firmness were measured periodically up to 11 days after harvest to compare the effects of the applied coatings. Fourier transform near‐infrared (FT‐NIR) spectroscopymeasurements were also taken individually. After storage, the gas composition within trays was about 1–10% O₂ and 14–47% CO₂. The lowest weight loss (25.56%) was observed in the shellac‐coated cherries, while the highest loss (48.58%) occurred in the control group. Coated cherries exhibited a significantly lower pH and electrical conductivity than the uncoated ones. The control group presented the highest total soluble solid (TSS) values (21.29) and shellac coating had (17.25) the lowest. At the end of storage, the highest ascorbic acid (AA) content was 0.64 mg/100 ml in the shellac‐coated cherries, and the lowest AA content of 0.40 mg/100 ml was measured in the control group. Firmness was maintained by coating, especially with shellac (3.734 N), whereas the control had the lowest firmness measured (2.138 N) at the end of storage. There were differences between the absorbance spectra for the coated and control cherries at the end of storage. This research concludes that shellac coating is more effective in reducing the respiration rate and maintaining the quality parameters of cherries than chitosan and WPI coatings. Major benefits of coatings were observed in lessening the weight‐loss process and in maintaining firmness, which were also supported by the FT‐NIR measurements. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel pineapple leaf fibre composites coating with antimicrobial compound as a potential food packaging

Biodegradable packaging coated with antimicrobial compounds has emerged as a new type of food packaging with potential to enhance food safety, extend shelf life and minimize plastic pollution. We have developed a polylactic acid (PLA) composite pineapple leaf fibre (PALF) biopolymer to fulfil the high demand of biodegradable materials for a potential use in food packaging. Our formulation with 10% pineapple fibre PLA/PALF composites exhibited enhanced melting temperatures and heat resistance, with a 44% reduction in the tensile strength and 2.7-fold reduction on the strain at the break when compared with neat PLA. To impart antimicrobial activity, the PLA/PALF was coated with crude supernatants isolated from Pediococcus pentosaceus PP04 containing 1.3% w/v of nisin. This material coated with the crude extract was shown to inhibit the growth of Bacillus cereus ATCC 11778, Salmonella enterica subsp. enterica serovar Typhimurium ATCC 13311, and Escherichia coli ATCC 8739 in culture conditions, as well as minimizing the number of the tested pathogens on coated material surfaces.     

Antimicrobial Activity of Natural Agents against Saccharomyces cerevisiae

The antimicrobial (AM) activity of starch‐based films coated with linalool, carvacrol or thymol against Saccharomyces cerevisiae in vitro and/or inoculated on the surface of Cheddar cheese was investigated. In solid medium using the agar diffusion method and in experiments involving the inoculation of the microorganism on the surface of Cheddar cheese, all the films containing these AM agents in coatings demonstrated an inhibitory effect against S. cerevisiae. The results suggest that the overall inhibitory effect of linalool, carvacrol or thymol increased significantly (p ≤ 0.05) with the concentration of each of the AM agents in the film coating and that the response is linear in the concentration range of 1 to 5% (w/w) of the AM agent. Thymol had the highest AM efficacy followed by carvacrol, whereas linalool had the lowest efficacy amongst the three systems. The zones of inhibition in the agar diffusion test method at 25°C for S. cerevisiae were found to be 7.6, 7.1 and 6.1 mm for thymol, carvacrol and linalool at 1% (w/w) loading and 13.2, 12.2 and 11.2 mm at 5% (w/w) loading of the AM agents, respectively. The death rates of S. cerevisiae on Cheddar cheese wrapped in films coated with thymol, carvacrol and linalool and stored for up to 28 days at 15°C were found to be 0.044, 0.043 and 0.038 per day at 1% (w/w) loading and 0.077, 0.073 and 0.063 per day at 5% (w/w) loading of the AM agents, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of chitosan‐propolis edible coatings on stability of refrigerated cachama (Piaractus brachypomus) vacuum‐packed fish fillets

The effect of chitosan‐based coatings containing ethanolic extracts of propolis (EEPs) on the quality of chill‐stored, vacuum‐packed fillets of cachama, an emerging aquaculture species of fish native to the Amazon basins, was evaluated. Coatings were prepared by adding propolis to chitosan following two different strategies: (1) incorporation of microencapsulated EEP and (2) direct incorporation of EEP. Fillets were dip‐coated, vacuum‐packed in medium‐oxygen barrier bags, stored at 4°C, and their quality was evaluated during 20 days, by monitoring lipid oxidation indexes, physicochemical parameters, microbiological quality indicators, texture profile, and sensory acceptance. Chitosan‐EEP coatings significantly increased the time stability of physicochemical, microbiological, and sensory quality indicators of the fish meat compared with control treatments (uncoated vacuum‐packed fillets). In particular, the secondary lipid oxidation of the coated muscles was 12% to 15% lower compared with uncoated samples after 12 days; pH and total volatile base nitrogen (TVB‐N) presented a slower increase in the coated samples; and a greater inhibition of coliforms was observed between days 8 and 16. The chitosan‐EEP coatings had a positive effect in both texture stability and sensory acceptance of the products during storage. Moreover, chitosan coatings with encapsulated EEP had better impact on the evaluated sensory quality parameters. The results indicate that the combination of the barrier properties of chitosan with the bioactive properties of propolis compounds against oxidative free radicals and microbiological deterioration allowed for the edible coatings to extend the shelf life of this aquaculture product with respect to conventionally vacuum‐packed fillets.