M.E. López-Caballero

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.

Oyster Preservation by High-Pressure Treatment

The purpose of this study was to analyze the effect of 10-min continuous pressure and pulsed pressure in two 5-min steps (400 MPa at 7 degrees C) on the microbial flora, total volatile bases, pH, and texture of purified and unpurified oysters. High-pressure treatment reduced the number of all the target microorganisms (total viable count, H2S-producing microorganisms, lactic acid bacteria, Brochothrix thermosphacta, and coliforms), in some cases by around 5-log units. The difference between the counts in the control and the pressurized oysters remained stable throughout 41 days of storage at 2 degrees C. No Salmonella spp. were detected in either the control batch or the pressurized batches during this storage period. Deterioration of the oyster was accompanied by increased total volatile bases, mainly in the nonpressurized samples. The pH was practically constant in the pressurized oysters and fell slightly in unpressurized samples. As for mechanical properties, shear strength values were higher in pressurized than in unpressurized oysters. Step-pulse pressurizing (400 MPa at 7 degrees C in two 5-min pulses) produced no apparent advantages over continuous pressurizing based on any of the indices used.

Extension of the Shelf Life of Prawns (Penaeus japonicus) by Vacuum Packaging and High-Pressure Treatment

The present study has investigated the application of high pressures (200 and 400 MPa) in chilled prawn tails, both conventionally stored (air) and vacuum packaged. Vacuum packaging and high-pressure treatment did extend the shelf life of the prawn samples, although it did affect muscle color very slightly, giving it a whiter appearance. The viable shelf life of 1 week for the air-stored samples was extended to 21 days in the vacuum-packed samples, 28 days in the samples treated at 200 MPa, and 35 days in the samples pressurized at 400 MPa. Vacuum packaging checked the onset of blackening, whereas high-pressure treatment aggravated the problem. From a microbiological point of view, batches conventionally stored reached about 6 log CFU/g or even higher at 14 days. Similar figures were reached in total number of bacteria in vacuum-packed samples and in pressurized at 200-MPa samples at 21 days. When samples were pressurized at 400 MPa, total numbers of bacteria were below 5.5 log CFU/g at 35 days of storage. Consequently, a combination of vacuum packaging and high-pressure treatment would appear to be beneficial in prolonging freshness and preventing spotting.

Antimicrobial Activity of Composite Edible Films Based on Fish Gelatin and Chitosan Incorporated with Clove Essential Oil

Edible films based on fish-skin gelatin incorporated with chitosan and/or clove essential oil were elaborated and their antimicrobial activity was tested on Lactobacillus acidophilus, Pseudomonas fluorescens, Listeria innocua, and Escherichia coli. The films incorporated with the clove essential oil were the most effective although differences were observed depending on the biopolymeric matrix in which it was included. When a clove added film was applied to the preservation of raw sliced salmon, a reduction of the growth of total bacteria was observed after 11 days of storage at 2°C. So, edible films based on fish gelatin can be used as an active packaging applied to fish products.

Microbiological changes in pressurized, prepackaged sliced cooked ham

This was a study of the influence of high-pressure conditions (200 and 400 MPa, 5 and 20 min, 7 degrees C) on microbiological quality and water-binding properties of vacuum-prepackaged sliced cooked ham and how this affects microbiological changes during chilled storage (2 degrees C). Pressurization caused a degree of microbiological inactivation, which increased with pressure level and processing time. Pressurization at 400 MPa significantly reduced the total viable count and lactic acid bacteria to the extent that after 20 min no Enterobacteriaceae, Baird Parker flora, or Brochothrix thermosphacta were detected throughout any of the chilled storage periods studied. In general, gram-positive flora was more resistant to pressure than gram-negative flora. The fact that high pressure (400 MPa) causes considerable inactivation of microorganisms could be used to prolong the shelf life of vacuum-prepackaged sliced cooked ham.

Characterization and identification of microflora from soaked cod and respective salted raw materials

The microflora of soaked cod products from salted and dried salted cod were identified to the species level by the Vitek® automated identification system using the Gram-positive identification (GPI) and Gram-negative identification plus (GNI+) cards, and a cluster analysis was performed to determine the similarity among the strains. Within the Gram-positive bacteria, Staphylococcus epidermidis, S. hominis, S. warneri, S. haemolyticus, S. simulans and S. saprophyticus were found. Regarding Gram-negative, Stenotrophomonas maltophilia, Vibrio alginolyticus, Pasteurella haemolytica, Enterobacter agglomerans, E. asburiae, E. cloacae, Pseudomonas putida, P. fluorescens, Shewanella putrefaciens, Morganella morganii, Actinobacillus urea, Acinetobacter lwoffi/junii and non-fermentative bacilli were identified. Several species found in the soaked products were also isolated from the salted and dried salted cod. Thus, despite of the low water activity of these products, the mentioned strains were able to survive. Some of these, had the ability to produce H2S and/or presented decarboxylase activity, therefore it is probable that the growth of these bacteria during soaking might contribute to the spoilage of soaked cod. Aeromonas hydrophila and A. caviae were not isolated from the soaked food, but from the raw material (dried salted cod). Their presence might constitute a potential hazard, especially considering that these foods may be eaten raw.

Growth and metabolic activity of Shewanella putrefaciens maintained under different CO2 and O2 concentrations

Growth, trimethylamine (TMA), off-odour and biogenic amine production by a strain of Shewanella putrefaciens isolated from spoiled hake (Merlucius merluccius L.) and cultured in a model system, were tested under four different gas compositions (60% CO2/40% O2, 60% CO2/15% O2/25% N2, 40% CO2/60% O2, 40% CO2/40% O2/20% N2) and under air. After 3 weeks of incubation, the control (air) batch showed the highest microbial counts (> 9 log cfu/ml) and TMA concentrations (45 mg N-TMA/100 ml), and strong putrid off-odours were detected from day 15. High amounts of putrescine and cadaverine were produced in this batch, but histamine increased only slightly. Batches under controlled atmospheres showed reduced growth, TMA, off-odour and biogenic amine production. The 40% CO2/60% O2 mixture had the strongest inhibitory effect on bacterial growth, while the 60% CO2/15% O2/25% N2 mixture was less effective. Putrescine and histamine production was lowest in S. putrefaciens under the 40% CO2/60% O2 mixture. However, the level of histamine in S. putrefaciens was higher under 40% CO2/40% O2/20% N2 than when the bacteria was incubated in air. Under the gas mixtures, there was a similar decrease in the production of cadaverine and agmatine by S. putrefaciens, irrespective of the gas concentrations. The production of 2-phenylethylamine appeared to be inhibited under any atmospheric condition.

Active nanocomposite films based on soy proteins-montmorillonite- clove essential oil for the preservation of refrigerated bluefin tuna (Thunnus thynnus) fillets

This manuscript evaluates the potential application of active nanocomposite films based on soy protein isolate (SPI)-montmorillonite (MMT)-clove essential oil (CEO) to the preservation of muscle fillets of bluefin tuna (Thunnus thynnus) during refrigerated storage, and furthermore analyzes whether the clay diffuses from the package to food. SPI films with: CEO (SPI-CEO), MMT (SPI-MMT), or both CEO and MMT (SPI-MMT-CEO), were prepared and used to cover tuna fillets during 17days of storage at 2°C. Polyethylene films were also used as control. Protein films nanoreinforced with 10g MMT/100g SPI and activated with CEO were able to decrease microbial growth (evaluated by TVBN and microorganism counts) and lipid autooxidation (evaluated according to the TBA index, FTIR and color parameters) of tuna fillets during the storage period studied. The presence of clay seemed to favor the release of the active principles of clove oil by prolonging its antimicrobial (especially effective to inhibit Pseudomonas spp.) and antioxidant activity over time without observing the diffusion of the clays own metals (Si and Al) from the nanocomposite materials to the muscle of fish. These results are encouraging for the use of nanocomposite films in food packaging.

Antioxidant, ACE-Inhibitory, and Antimicrobial Activities of Peptide Fractions Obtained From Dried Giant Squid Tunics

ABSTRACT Squid tunics were divided in two batches: freeze-dried and air-dried. Dried squid tunics were directly hydrolyzed with pepsin, Alcalase, and Esperase. Freeze-dried tunics showed better aptitude for hydrolysis than air-dried tunics. Pepsin showed the lowest efficiency in protein breakdown and gave hydrolysates with low antioxidant activity, whereas Alcalase and Esperase peptide fractions showed strong radical scavenging ability, ACE-inhibitory activity, and noticeable antimicrobial properties. B. cereus, B. coagulans, and D. hansenii were found to be the most sensitive bacteria. Dried squid tunics proved to be an alternative to a previously extracted gelatin for obtaining bioactive peptides.

The effect of the combined use of high pressure treatment and antimicrobial edible film on the quality of salmon carpaccio

Fish carpaccio is a ready-to-eat product with a very limited shelf life. In the present work, the use of high pressure treatment (HP) and/or antimicrobial edible film was studied in order to improve quality and stability of salmon carpaccio. In a preliminary part of the work, a film composed of gelatin plus chitosan incorporating clove essential oil was selected, based on its physicochemical and antimicrobial properties. Eugenol and β-caryophyllene, the main volatile components of the film, migrated to salmon muscle, the release being favored by HP and storage time. Concurrently, reducing power of the muscle increased, resulting in prevention of lipid oxidation derived from either HP or refrigerated storage. HP treatment reduced total microbial counts by 1.5 log cycles from the onset of storage, whereas the film reduced it by 2 log cycles after 3 days. The combination of HP and edible film exerted the most intense antimicrobial effect, total bacterial counts, luminescent bacteria, H2S-producing organisms, pseudomonads, enterobacteria, and lactic acid bacteria remaining constant or under detection limit over the whole storage period (11 days). The combined use of HP treatment and gelatin-chitosan-clove essential oil film is an effective way of improving quality and stability of salmon carpaccio.