Effects of sub-lethal concentrations of hexanal and 2-(E)-hexenal on membrane fatty acid composition and volatile compounds of Listeria monocytogenes, Staphylococcus aureus, Salmonella enteritidis and Escherichia coli

In recent years, the interest in the possible use of natural alternatives to food additives to prevent bacterial and fungal growth has notably increased. Plants and plant products can represent a source of natural alternatives to improve the shelf-life and the safety of food. Some of these compounds, i.e. hexanal, hexanol, 2-(E)-hexenal and 3-(Z)-hexenol, produced throughout the lipoxygenase pathway have important roles in plant defence with a protective action towards microbial proliferation in wounded areas. Otherwise, hexanal and 2-(E)-hexenal have evidenced a marked antimicrobial activity against food spoilage and pathogenic microbial species both in model and real systems. The precise mechanisms of action of all these antimicrobial compounds are not yet clear. Because the usage of these compounds as antimicrobials in foods has to be supported by the comprehension of mechanisms of action of these compounds, the overall purpose of this work was to study the modifications of the cell membrane and volatile compounds of Listeria monocytogenes, Staphylococcus aureus, Salmonella enteritidis and Escherichia coli during the growth in the presence of sub-lethal doses of these two aldehydes. The results obtained evidenced that the tested molecules induced noticeable modifications of the composition of cell membrane and the volatile compounds produced during the growth. Although specific differences in relation to the species considered were identified, 2-(E)-hexenal and hexanal induced a marked increase of some membrane associated fatty acids, both linear and branched fatty acids as well as unsaturated fatty acids, and released free fatty acids.     

Effect of vacuum frying on main physicochemical and nutritional quality parameters of pineapple chips

BACKGROUND: Slices of MD‐2 pineapple hybrid were vacuum fried at 24 kPa according to a central composite experimental design that simultaneously varied frying time (6.3–7.7 min) and temperature (106.3–117.7 °C). Major physicochemical and nutritional quality factors were measured and modelled using a second‐order polynomial equation. RESULTS: Moisture content, water activity a_w, colour parameters L*, C* and H* and total vitamin C content decreased while total phenolic content and dehydroascorbic acid content increased with increasing frying time and temperature. Oil content, hardness and hydrophilic antioxidant capacity reached minimum values near the centre of the experimental field. By superimposing contour curves, it was determined that processing conditions of 6.9 min frying time and 112 °C frying temperature produced pineapple chips with a golden colour (L*≥ 60, C*≥ 50, H*≥ 80), an a_w of less than 0.29, a moisture content of about 4% and a hardness of less than 1.9 N, giving rise to a crispy texture. Oil content was about 20% (d.b) and residual total vitamin C content (～90 mg per 100 g wet basis (w.b.)) was high. Phenolic compound content was about 150 mg gallic acid equivalents per 100 g w.b. and antioxidant capacity was around 22 µmol Trolox equivalents g^?1 w.b. CONCLUSION: Vacuum frying is a dehydration process that produces healthy fruit snacks which partially preserve the fruit's original colour and nutritional compounds and have a high hydrophilic antioxidant capacity. Copyright © 2008 Society of Chemical Industry     

Antimicrobial Activity of Pd‐Doped ZnO Sol‐Gel‐Derived Films

Palladium doped ZnO was prepared by the sol‐gel and dip‐coating techniques, starting with zinc acetate and palladium chloride as precursors, followed by its hydrolysis in methanol. Acetic acid was incorporated to adjust pH, as well as acetylacetonate and monoehtylamine as stabilizers. The sol was later dipped 3 times in silica substrates. Structural, morphological, and antimicrobial properties of the films were investigated for three palladium contents (1.0, 2.5, and 5 mol %). X‐ray diffraction (XRD) showed that the films have a hexagonal structure after been annealed at 500°C. X‐ray photoelectron Spectroscope (XPS) showed that Pd is present in its oxidized form. Atomic force microscopy (AFM) from films showed a crack free and smooth surface (Ra= 18 nm), composed of cross‐linked particles. The synthesized films presented antibacterial activity against Escherichia coli and Pseudomona aeruginosa. It was observed that the higher Pd content (5 mol %) presents the higher antimicrobial ratio, 64.07%, for the E. coli, whereas for the P. aeruginosa, the lower Pd content (1 mol %), shows the higher antimicrobial ratio, 76.43%.     

Comparative study of initial stages of copper immersion deposition on bulk and porous silicon

Initial stages of Cu immersion deposition in the presence of hydrofluoric acid on bulk and porous silicon were studied. Cu was found to deposit both on bulk and porous silicon as a layer of nanoparticles which grew according to the Volmer-Weber mechanism. It was revealed that at the initial stages of immersion deposition, Cu nanoparticles consisted of crystals with a maximum size of 10 nm and inherited the orientation of the original silicon substrate. Deposited Cu nanoparticles were found to be partially oxidized to Cu₂O while CuO was not detected for all samples. In contrast to porous silicon, the crystal orientation of the original silicon substrate significantly affected the sizes, density, and oxidation level of Cu nanoparticles deposited on bulk silicon.     

Effects of novel modified atmosphere packaging on lipid quality and stability of sardine (Sardina pilchardus) fillets

Modified atmosphere packaging (MAP) is an efficient method to increase shelf-life of fishery products by inhibiting bacterial growth and oxidative reactions. Beside the traditional gases used for MAP, novel gases such as argon (Ar) and nitrous oxide (N₂O) were approved for food use in the European Union. The present research investigates the effect of MAP with unconventional gas mixtures, that previously positively affected microbial shelf-life, on colour, lipid oxidation and sensorial characteristics of sardine fillets during storage. Four atmosphere conditions were tested: Air (20.8% O₂/79.2% N₂), N₂ (30% CO₂/70% N₂), N₂O (30% CO₂/70% N₂O) and Ar (30% CO₂/70% Ar). Samples were stored for 12 days at 3 °C. Results showed that the removal of oxygen significantly inhibited the oxidation process; however, most of the investigated parameters related to fat oxidation did not show any improvement, except for a slight decrease in lipid hydrolysis and improvement in sensory properties in the packaging containing Ar.     

Supramolecular Self-Assembled Ligands in Asymmetric Transition Metal Catalysis

The design of novel chiral ligands is at the core of asymmetric catalysis. The catalytic characteristics of a transition metal catalyst such as activity, selectivity and stability can be fine-tuned by optimization of the steric and electronic properties of the coordinating ligands. In asymmetric transformations, catalyst optimization still relies to a large extent on trial-and-error and educated guesses. New strategies based on combinatorial screening and high-throughput experimentation have been introduced for the design and optimization of new ligands and catalytic systems. Supramolecular bidentate ligands that form by self-assembly of building blocks are particularly suited for this combinatorial approach as the potential number of catalysts grows exponentially with the number of building blocks synthesized. Catalytic systems based on supramolecular interactions have proven to be highly advantageous in creating large ligand libraries for high-throughput screening, which allows optimization of activity and selectivity for a variety of reactions. In this review we describe the progress in this field.     

Size-scaling in optical trapping of silicon nanowires

We investigate size-scaling in optical trapping of ultrathin silicon nanowires showing how length regulates their Brownian dynamics, optical forces, and torques. Force and torque constants are measured on nanowires of different lengths through correlation function analysis of their tracking signals. Results are compared with a full electromagnetic theory of optical trapping developed in the transition matrix framework, finding good agreement.     

Effect of wine addition on microbiological characteristics,volatile molecule profiles and biogenic amine contents in fermented sausages

The aim was to evaluate the effect of wine addition during manufacturing of dry fermented sausages, in terms of safety aspects (biogenic amine accumulation), aroma profile and sensory characteristics. Three batches of salami were produced: without wine addition and with 7.5% or 15% (v/w) of white wine. The fermented sausages showed characteristics that can increase product diversification. Some of the sensory features (i.e. increased salty perception) can represent an important strategy because of the trend to reduce salt intake for health reasons. The presence of wine immediately reduced the pH and is a source of ethanol, which can have an inhibitory effect against undesirable microflora. The microbiological results observed regarding Enterobacteriaceae and enterococci were encouraging. The addition of wine did not negatively affect the ripening time or increase the presence of biogenic amines. The samples containing wine showed reduced concentrations of putrescine.