Biodegradable gelatin-chitosan films incorporated with essential oils as antimicrobial agents for fish preservation.

Essential oils of clove (Syzygium aromaticum L.), fennel (Foeniculum vulgare Miller), cypress (Cupressus sempervirens L.), lavender (Lavandula angustifolia), thyme (Thymus vulgaris L.), herb-of-the-cross (Verbena officinalis L.), pine (Pinus sylvestris) and rosemary (Rosmarinus officinalis) were tested for their antimicrobial activity on 18 genera of bacteria, which included some important food pathogen and spoilage bacteria. Clove essential oil showed the highest inhibitory effect, followed by rosemary and lavender. In an attempt to evaluate the usefulness of these essential oils as food preservatives, they were also tested on an extract made of fish, where clove and thyme essential oils were the most effective. Then, gelatin-chitosan-based edible films incorporated with clove essential oil were elaborated and their antimicrobial activity tested against six selected microorganisms: Pseudomonas fluorescens, Shewanella putrefaciens, Photobacterium phosphoreum, Listeria innocua, Escherichia coli and Lactobacillus acidophilus. The clove-containing films inhibited all these microorganisms irrespectively of the film matrix or type of microorganism. In a further experiment, when the complex gelatin-chitosan film incorporating clove essential oil was applied to fish during chilled storage, the growth of microorganisms was drastically reduced in gram-negative bacteria, especially enterobacteria, while lactic acid bacteria remained practically constant for much of the storage period. The effect on the microorganisms during this period was in accordance with biochemical indexes of quality, indicating the viability of these films for fish preservation.

Gómez-Estaca J ，López de Lacey A ，López-Caballero ME ，Gómez-Guillén MC ，Montero P ... -  《-》

Antimicrobial activity of whey protein isolate edible films with essential oils against food spoilers and foodborne pathogens.

The use of antimicrobial edible film is proposed as a means of improving food safety and extending the shelf-life of food systems by controlling the release of antimicrobials on food surfaces. In this work we first selected and studied 8 different essential oils (EOs) from plants, namely, oregano, clove, tea tree, coriander, mastic thyme, laurel, rosemary, and sage as natural antimicrobials against 2 gram-positive bacteria (Listeria innocua and Staphylococcus aureus) and 2 gram-negative bacteria (Salmonella enteritidis and Pseudomona fragi) by using the agar disk diffusion method. EOs from oregano, clove, and tea tree produced the largest surfaces of inhibition against the growth of the 4 bacterial strains tested. Second and following the assessment of compatibility, stable antimicrobial edible films based on whey protein isolate (WPI) with increasing concentrations (0.5% to 9%) of the 8 EOs were developed and tested for antimicrobial activity against the same gram-positive and gram-negative bacteria. WPI-edible films incorporating oregano or clove EO were found to have the most intense inhibitory effect of microbial growth. The bacterial strain gram-negative P. fragi presented the less susceptibility to the effect of those films. Moreover, only the edible films based on these 2 EOs were active against all 4 studied microorganisms. On the other hand, the edible films incorporating tea tree, coriander, mastic thyme, laurel, rosemary, or sage EOs even at high concentrations (7% to 9%) did not cause any antimicrobial effect against the pathogens S. aureus or S. enteritidis. Potential applications of this technology can introduce direct benefits to the food industry by improving safety and microbial product quality. The results of this research have direct application in the food industry with potential applications in various foodstuffs, including meat and poultry products where the control of spoilage bacteria such as P. fragi throughout their chilled storage or the improvement of food safety by controlling pathogens such as S. enteritidis are topics of particular interest for the industry.

Fernández-Pan I ，Royo M ，Ignacio Maté J 《-》

Effect of edible chitosan/clove oil films and high-pressure processing on the microbiological shelf life of trout fillets.

The inhibitory effect of chitosan films with clove oil (0-50 g kg(-1) ) was evaluated on a range of ten representative food spoilage and pathogenic bacteria. The most sensitive bacteria to the films was Shewanella putrefaciens and the most resistant was Aeromonas hydrophila (inhibition was apparent only at 50 g kg(-1) clove essential oil (CEO)). Films with 20 g kg(-1) CEO inhibited nine of ten of the bacteria tested. Chitosan films with 20 g kg(-1) CEO were combined with high-pressure (HPP) processing as treatments for trout fillets, and changes in physicochemical parameters and microbial load were evaluated at 4 °C over 22 days of storage. The films reduced weight loss and water activity compared to fresh and treated samples (HPP and cooking). Results showed that microbial load (total aerobic mesophilic, lactic acid bacteria and total coliform) of the trout fillets covered with chitosan films was lower than that for HPP-treated samples, and similar to cooked samples, except for coliform counts. The use of 20 g kg(-1) CEO-chitosan films showed a further improvement in the shelf-life of trout fillets when compared to that obtained with HPP and cooking treatment.

Albertos I ，Rico D ，Diez AM ，González-Arnáiz L ，García-Casas MJ ，Jaime I ... -  《-》

Antimicrobial activity of chitosan coatings and films against Listeria monocytogenes on black radish.

The antibacterial activity of chitosan coatings prepared with acetic or lactic acid, as well as of composite chitosan-gelatin films prepared with essential oils, was evaluated in fresh shredded black radish samples inoculated with Listeria monocytogenes ATCC 19115 and L. monocytogenes ATCC 19112 during seven days of storage at 4°C. The chitosan coating prepared with acetic acid showed the most effective antibacterial activity. All tested formulations of chitosan films exhibited strong antimicrobial activity on the growth of L. monocytogenes on black radish, although a higher inhibition of pathogens was achieved at higher concentrations of chitosan. The antimicrobial effect of chitosan films was even more pronounced with the addition of essential oils. Chitosan-gelatin films with thyme essential oils showed the most effective antimicrobial activity. A reduction of 2.4log10CFU/g for L. monocytogenes ATCC 19115 and 2.1log10CFU/g for L. monocytogenes ATCC 19112 was achieved in the presence of 1% chitosan film containing 0.2% of thyme essential oil after 24h of storage.

Jovanović GD ，Klaus AS ，Nikšić MP 《REVISTA ARGENTINA DE MICROBIOLOGIA》

Antimicrobial assays of natural extracts and their inhibitory effect against Listeria innocua and fish spoilage bacteria, after incorporation into biopolymer edible films.

The antimicrobial activity of twelve natural extracts was tested against two fish spoilage bacteria (Pseudomonas fluorescens and Aeromonas hydrophila/caviae) and Listeria innocua, in order to assess their potential utilization in the preservation and safety of minimally processed fish products. After a screening of the active extracts by agar diffusion and vapour diffusion methods, oregano and thyme essential oils and citrus extract were selected. The minimum inhibitory concentration (MIC) of the selected extracts was determined by disc diffusion method against target bacteria and at two temperatures: bacteria's optimal growth temperature (30 °C or 37 °C) and refrigeration temperature (4 °C). Due to its better solubility, lack of odour and greater inhibitory effect obtained against L. innocua at refrigerated temperature, citrus extract was selected and incorporated at 1% (v/v) into different biopolymer film forming solutions (gelatin, methyl cellulose and their blend 50:50 w/w). The antimicrobial activity of the developed films was then evaluated, just after preparation of the films and after one month of storage at 43±3% relative humidity and 24±3 °C. Regardless of the biopolymer matrix, all the developed films showed antimicrobial activity against the target bacteria. The most sensitive bacterium towards active films was L. innocua while P. fluorescens appeared as the most resistant one, in accordance with the previously performed antimicrobial tests for pure extracts. The differences in activity of the films between the tested two temperatures were not significant except for L. innocua, for which three times higher inhibition diameters were observed at refrigerated temperature. The inhibitory effectiveness of the films against the tested strains was maintained regardless of the biopolymer matrix for at least one month. Therefore, these edible films show potential for their future use in fresh fish fillets preservation.

Iturriaga L ，Olabarrieta I ，de Marañón IM 《-》